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Potential observations of an electron-emitting rocket payload and other related plasma measurements
Planer. Space Sci., Vol. 36, No. 4, pp. 39-10, Printed in Great Britain.
0032-0633/88 $3.00+0.00 Pergamon Press plc
1988
POTENTIAL OBSERVATIONS OF AN ELECTRONEMITTING ROCKET PAYLOAD AND OTHER RELATED PLASMA MEASUREMENTS* G. G. MANAGADZE,V. M. BALEBANOV.A. A. BURCHUDLADZE,T. I. GAGUA, N. A. LEONOV, S. B. LYAKHOV, A. A. MARTINSON snd A. D. MAYOROV Space Research Institute of the Soviet Academy of Sciences (IKI), Profsoyusnaya 84, 117810 Moscow, U.S.S.R. W. K. RIEDLERt aad M. F. FRIEDRICHS Department of Communications and Wave Propagation, Technical University Graz, Inffeldgasse 12, A-8010 Gnu, Austria K. M. TORKAR Space Research Institute of the Austrian Academy of Sciences, Inffeldgasse 12, A-8010 Grax, Austria A. N. LALL4SHVILI Georgian Academy of Sciences, Tbilisi, U.S.S.R.
Z. KLOS aad Z. ZBYSZYNSKI Space Research Centre of the Polish Academy of Sciences, Ordona 21, PL-01237 Warsaw, Poland (Received 26 October 1987)
Ahstraet-Gbservations of plasma effects due to an energetic electron beam near a rocket payload are summarized and an attempt is made to outline the basic processes in the plasma such as beam plasma discharge (BPD). The experiment had some unique features such as a high apogee and low background plasma density. The measurements covered most parameters relevant for the study of plasma effects, as well as payload potential, optical and radio emissions, energetic charged particles and plasma densities. Among the noteworthy observations are radio emissions up to VHF frequencies and very high payload potentials which even exceeded the gun voltage. The observed features are interpreted as BPD at low altitudes and as discharges in the E x B field at other heights.
1. INTRODUCTION
the experiments quoted therein) are in particular the
The rocket experiment Gruziya-60-Spurt (G-60-S) was aimed at studying processes in the vicinity of the vehicle caused by the injection of electrons. One aspect was the neutralization process during and after the payload charging due to the emission of electrons, the other to study optical and radio emissions as a consequence on non-linear processes such as beam plasma discharge (BPD). The main features which distinguish the present experiment from most previous ones (see the review by Szuszczewicz, 1985, and
following.
* Dedicated to the memory of our colleagues and friends Sergej Lyakhov who tragicauy died at the age of 38, on 19 August 1986, in a mountaineering accident and Andrej Martinson who unexpectedly passed away on 13 August 1987. tAIso at the Space Research Institute of the Austrian Academy of sciences, IntTeldgasse12, A-8010 Graz, Austria. $ Author to whom alI correspondence should be addressed.
-High apogee of over 1500 km. On the one hand this obviously provided a long observation time, but on the other also a sufficiently long time for outgassing of the payload. -Cleanliness of the payload. The surface consisted almost exclusively of aluminium. Furthermore, the motor separation at 170 km on the upleg contributed to a reduction of unpredictable gas concentrations in the region of the measurements. -Near-spherical shape of the payload. The equivalent sphere of 75 cm radius facilitates calculations using theoretical considerations. -Attitude stabilization by an internal gyro. Although, in contrast to other active rocket experiments (e.g. Maehlum, 1983), variations with the pitch angle cannot be deduced, the present configuration allows a comparison from pulse to pulse
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without having to disentangle pitch angle from altitude effects. Preliminary results dealing with certain aspects have been published earlier in the form of internal reports (Balebanov et al., 1981; Gagua et al., 1983 ; Klos and Zbyszynski, 1984 ; Lyakhov et al., 1984 ; Managadze et al., 1983a, b; Torkar et al., 1985; Managadze et al., 1986), as conference proceedings (Managadze et al., 1983~; Friedrich et al., 1988; Klos et al., 1988) and as some laboratory results with the flight instrumentation by Lyakhov et al. (1982). The present paper is based on all information given previously in the above papers and hence supersedes them in all aspects ; it aims to present a consistent picture
of the complex physical phenomena observed during and after electron injections in the region near the payload. 2. INSTRUMENTATION
The rocket payload carried a large number of diagnostic instruments whereof only those relevant in the present context will be listed below (Fig. 1). The analogue telemetry had a basic sampling rate of 100 s-l and the frequency of the 20 W transmitter was about 80 MHz. During earlier flights with this telemetry system, but also with much higher frequencies and lower power (Maehlum, 1986, private communication), drop-outs were observed during intense (0.8 A)
FIG. 1. GENERALmw OFTHEPAYLOAD. (1) Electron gun, (2) gas injector, (3) particle spectrometer USHBA-MOS, (4) electron spectrometer ANTEIMETR, (5) upward-looking photometer, (6) sideward-looking photometers, (7) capacitance probe, (8), (9) aerials for the HF and VHF spectrometers, respectively, (10) Geiger-Miiller tubes, (11) potential probe No. 1, (12) double probe, (13) electric field probe, (14) ion and plasma probes, (15) potential probes Nos 2,3 and 4.
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gun pulses. In order to overcome these data gaps, the eight channels considered most relevant for the overall success of the experiment were delayed by 1 s (i.e. longer than the duration of a gun pulse) and transmitted in addition to the direct signals. The forward (upward)-directed electron gun alternatingly emitted rectangular and triangular pulses with a duration of 0.6 s and a repetition rate of 5 s. The maximum peak energy of rectangular pulses was 6.7 keV associated with a current of 0.55 A; most pulses, however, typically had peak values of 6.3 keV at 0.5 A. In order to study controlled BPD a gas injector was included in order to release gas during certain pulses. Three potential probes were mounted on a boom at distances of 1, 2.2 and 3.2 m from the payload in order to establish the spatial variation of the potential (input impedance > 1 GQ). The nearest probe at 60 cm was mounted on another boom. A capacitance probe oscillating near 900 kHz was used to establish the electron density. This kind of probe is primarily sensitive to the sheath thickness or the ratio of electron density to electron tem~rature (Jacobsen, 1972; Friedrich, 1979). The probe (ungridded sphere of 4.2 cm diameter) itself was dc-connected to the payload body via 100 ksz. Photometers along and across the main payload axis (same as the gun axis) were employed at 427& 2 nm with a dynamic range of 100. The radio spectrometer consisted of two instruments (PRS and ISKRA), whose frequency ranges did unfortunately not overlap. The instrument PRS covered 0.1-10 MHz at 20 discrete, linearly spaced frequency slots of 36 kHz bandwidth. The sweep (50 ms) was synchronized to the gun operation. The instrument included a built-in bufIer to read out the spectra measured during gun operation, delayed between the pulses at a slower rate suitable for the telemetry. Thus here no problems occurred due to the drop-outs in the telemetry. The frequency range 2% 320 MHz was covered by the instrument ISKRA in five segments which were swept sim~taneously. The bandwidth was 1 MHz and the sweep time 0.3 s; only the first segment from 20 to 80 MHz worked properly. Fluxes of energetic charged particles were detected by three instruments, namely ANTEIMETR (40 eV7.4 kev), USHBA-MOS (120 eV-16 keV) and three orthogonal Niger-Mailer tubes (>40 keV). The latter were mounted on a collapsable boom of 63 cm. They were oriented looking upward, downward and to the North in the horizontal plane and were collimated to an effective opening angle of Ifr2.5”. This configuration covers pitch angles of 24,156 and 114”, respectively.
3. MEASUREMENTS
Some of the instruments flown aboard the present payload failed or showed irregular behaviour and are therefore not used in the following. In particular, the injector for neutral gas did apparently not work, except perhaps on the downleg around 1450 km (cf. Fig. 5). At this altitude there are some observations which are similar to those at much lower altitudes on the downieg; since no corresponding behaviour is observed at that altitude on the upleg, it is assumed that some gas may have escaped in an uncontrolled manner. The other malfunction relevant to the present study is an irregular behaviour of one telemetry commutator which in particular affected the nearer probes of the potential instrument. 3.1. Background The payload was launched on 18 September 1981, with a rocket of the type “Vertikal” from the Soviet mid-latitude range Kapustin Yar. The launch time was 17:59:58.3 U.T. (21:59:58.3 Moscow time), the solar zenith angle was 117”, the rocket elevation 88” and the apogee 15 14 km. The geophysical conditions were A, = 18, F(10.7) = 216 and R, = 145. The payload was switched on after motor separation and became fully operational at an altitude of 270 km. The Lvalue varied between 2.0 and 2.4 during the flight. Generally the capacitance probe behaved regularly between gun pulses, whereas the oscillation apparently ceased during the accelerator operation. Laboratory investigations in a small plasma chamber with a similar probe showed that with only small positive potentials (ca IV) in the presence of only moderate electron densities the oscillation stopped. This is probably due to an ohmic loading of the LC circuit whereupon the feedback condition is no longer fulfilled. Figure 2 shows the background electron density established from the capacitance probe readings just before the beginning of the gun pulses. A sheath thickness of 5 Debye lengths was assumed, the electron temperature was taken from IRI (Rawer et uf., 1981) for the appropriate conditions, and the whole profile was normalized to the reading of the range ionosonde. 3.2. Potential The main source of information about the payload potential is obviously the potential probes. Due to problems of the telemetry as mentioned above, data from the nearer spheres are only available for the first pulse. However, the spatial distribution of the potential during that first pulse suggests that the readings of the farthest probe represent the true payload potential (Fig. 3). In the following, “potential” means
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potential of the payload relative to the plasma or voltage between probe 4 and the payload. Figure 4 shows an example of the voltagecurrent characteristics of the payload and the gun. One can see that above a certain threshold the payload potential exceeds the gun voltage. The higher potentials during the falling edge of the gun pulse, compared to corresponding values during the rising edge, are not due to a mere hysteresis of the payload potential or indeed the electronics; at the end of rectangular pulses we do not observe a slow recovery from high positive potentials. Figure 5 shows the payload potential vs altitude for injection voltages of 1, 2, 3, 4 and 5 kV. The values were taken during the leading edges of triangular pulses on the downleg of the trajectory, because upleg data do not cover altitudes below 270 km. Features not presented by Fig. 5 include the fact that potentials are higher during the falling edge (see Fig. 4) and that the potentials are somewhat lower on the downleg than on the upleg. At lower altitudes (near the F-region peak in the electron density) the potential is significantly below the injection voltage. At higher altitudes (lower electron densities) it approaches the gun voltage and even exceeds it at higher gun voltages. Alternatively a dependence of these “superpotentials” on the injection current was sought. For this purpose the ratio between payload potential and gun voltage vs gun current was established. Figure 6 shows three examples, one near the F-region peak and the other two at low electron densities, i.e. one close to apogee and the other below the F-region peak. At larger electron densities the potential remains small and only exceeds the value of the gun voltage at currents beyond 200 mA. At electron densities below ca 1.5 x IO” mP3 the rise to a “superpotentia~ is not resolved (below 10 ms). With increasing current the potential falls from ca 3 VBunto about 1.5 Vgun.An inverse dependence of the vehicle charging on ambient plasma density was also observed by Bush et al. (1984). The low potential is a feature observed in most other active experiments and explicable by efficient neutralization due to small contact impedance between the payload and the ambient plasma. Excess potentials have hitherto not been reported in the literature, but values close to the injection voltage and slightly exceeding it have been observed in the tethered mother-daughter experiment MAIMIK (Maehlum, 1987). A notable feature common to both experiments is the low background electron density (lOlo m -3 in the case of MAIMIK, a value even lower than in the present experiment), whereas the reported background electron densities in other experiments
Potential of an electron emitting payload
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were condsiderably larger. Also the pitch angle of 156 (i.e. far from 90”) may be responsible for the insufficient neutralization ; both Kawashima (1983) and Maehlum (1986, private communication) find that the payload charging is smallest (neutralization most efficient) for injection angles nearest to 90”. Since in the present experiment both the current and the gun voltage vary simultaneously, we are unfortunately not in the position to attribute the “super-potentials” uniquely to a threshold of current or voltage. Another interesting feature is the reading of the capacitance probe, which shows an apparent electron density decrease after the pulse recovering to normal values with time-constants of the order of seconds (Fig. 7). A decrease of the sphere’s capacitance can be caused by (a) a decrease of the electron density, (b) an increase of the electron temperature, and (c) a decrease of the probe potential. With the velocity of the vehicle being ca 3 km SC’ and the angle of the velocity vector to the magnetic field being 157”, the probe leaves the flux tube (diameter 2 m for 6 keV) after fractions of a second. The observations by mother-daughter payloads have established the diameter of disturbances caused by an electron beam as slightly under 2 gyro radii across the magnetic field (Jacobsen et al., 1981). Another argument against a real plasma density disturbance (electron depletion) is the fact that the magnitude of the capacitance decreases, whereas the time constant of the recovery does not noticeably depend on the type of gun pulse (triangular or rectangular). With similar arguments an electron temperature increase in a disturbed region
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can be ruled out. Based on laboratory measurements we interpret the capacitance probe readings after the gun pulses as negative payload potentials of l-2 V. 3.3. Emissions 3.3.1. Radiowaves. The measurements of the PRS instrument (0.1-9 MHz) were satisfactory, whereas the ISKRA instrument showed poor data quality for four of the five segments, and only the segment 20-80 MHz can be used. Furthermore, the data from ISKRA were transmitted directly and hence telemetry drop-outs occurred during intense pulses at higher altitudes. Suitable corrections for the different efficiencies of the two aerials as well as for a change
in impedance due to the ambient plasma were applied. Figure 8 shows the background emissions between 1 and 80 MHz vs altitude on the downleg. The shading is in steps of 10 dB above a reference of 10 PV m-i MHz-‘. The left side shows a clear maximum of the emissions which roughly coincides with the local plasma frequency (dotted line) as derived from the measurement with the capacitance probe. The fact that the electron density measurement was made on the upleg-in contrast to the emission observationsmay explain the small discrepancies. Data below the electron density peak (250 km) and above the critical frequency (4.02 MHz) probably do not originate in the plasma, but are rather man-made. In particular,
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ELECTRON DENSITY, m.3 FIG. 8. CONTOURSOF CONSTANT RADIO EMISSIONPOWER MEWRED BETWEENPULSESvs ALTITUDE OF THE DOWNLEG.
Units are dB above a reference field strength of 10 PV per metre and a bandwidth of 1 MHz. The dotted line is the local plasma frequency as measured by the capacitance probe.
the signals observed near 70 MHz are most likely due to stations in the FM broadcast band, which in the Soviet Union ranges from 66 to 72 MHz. Figure 9 shows the increase of the emissions during rectangular pulses over the values in Fig. 8 in contours of 5 dB. Note that in some areas (at low frequencies) the emissions decreased during the gun operations. Significant emissions occur at most HF frequencies, particularly below 9 MHz and at altitudes below 270 km. Emission in the 2&80 MHz range can not be resolved at all altitudes because of telemetry problems during the gun injection.
3.3.2.0ptical. Glow was observed both in the longitudinal and transverse directions (relative to the payload/gun axis). Figure 10 shows the altitude dependence of the glow measured by the photometer in the direction along the beam. Note that the Earth’s shadow has risen from 900 to over 1000 km in the time interval between up- and downleg and that on the upleg the scattered fluxes are consistently larger than in the downleg; we consider this as supporting the hypothesis that outgassing led to a different environment between up- and downleg. Figure 11 shows the optical flux in the beam direction as a func-
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Contours are every 5 dB relative to the values of Fig. 8. Note that in some areas the observed emissions were below the natural background.
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tion of the gun current; the data are taken from all heights below the shadow line. One can clearly see a threshold of about 200 mA and a dependence of the optical flux on the current to the power of 7-8. The last part of the downleg, i.e. below 135 km, was also interesting. At this time glow was only measured in the transverse direction and the intensity increased rapidly in the beam region. Between 109 and 88 km the glow intensity increased by more than a factor of 60, whereas the ambient pressure-according to atmospheric models-increased only by a factor of 20. 3.4. Particle measurements All of the particle detectors worked well. Despite the high threshold energy of 40 keV the Geiger-Miiller counters are best suited for the purpose of studying
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the gun response because of their high time resolution. Fluxes of the northward-looking detector indicate that the gun operation stimulated the precipitation of trapped particles ; these data, and those of the other particle detectors, will be published elsewhere. Figure 12 shows an example of the particle fluxes observed by the upward- and downward-looking Geiger-Mtiller tubes at 436 s (1179 km) on the upleg during a rectangular pulse. The most noteworthy features observed by these particle counters during the pulses are the following. -Sudden enhancements of both particle count rates within the duration of the pulse. In the height range 960-1410 km (upleg), 14 of the 23 rectangular pulses show this feature. These enhancements occur between 200 and 400 ms after the beginning of the electron injection. The observed delays in the sudden onset of the count rates may for example be due to pitch angle scattering at some distance along the field line. Xlear anticorrelation of these enhanced count rates with the payload potential. It is therefore reasonable to associate these fluxes (> 40 keV) with fluxes of lower energies providing the neutralization current.
Potential of an electron emitting payload
-Anisotropy of the fluxes, i.e. fluxes from below on average exceed those from above by a factor of two. This may be explained by precipitating particles with pitch angles near 90”, which are only poorly detected by the upward-directed, collimated Geiger-Miiller tubes. The downward-directed tubes, in contrast, will observe fluxes which are scattered in the atmosphere and are hence fairly isotropic.
4. DISCUSSION AND CONCLUSIONS
An attempt to describe theoretically the picture of the spatial distribution of the potential (Fig. 3) and the dynamics of the potential formation is given e.g. by Alpert et al. (1964). At larger plasma densities, as e.g. observed by Sagdeev et al. (1981) aboard a small rocket, the potential dropped within a shorter distance from the vehicle. Furthermore the total potential will be close to, but below, the gun voltage. In the following we try to find a mechanism capable of providing a payload potential above the gun voltage and to discuss an explanation for the potential jump in the voltage-current characteristics of the payload. The plasma processes which occur during beam injection have been analysed to some extent in theoretical papers (Beard and Johnson, 1961; Parker and Murphy, 1967; Galeev et al., 1976; Linson, 1969) where neutralization processes were discussed. The payload neutralization current of the ionospheric electrons strongly depends on the potential value and its spatial distribution. A small positive potential between 500 and 1500 km is observed between pulses. The neutralization current is approximately I, = eNCv,,,S= 5 mA (N. = lo5 cnm3, T, = 3300 K, effective payload cross section S = 1 m’). If the vehicle has a potential of 6 kV-according to calculations made for a drift approximation (Parker and Murphy, 1967Fthe neutralization current of the ionospheric electrons increases approximately by an order of magnitude and will amount to Znemt, = 10 x Z,, = 50 mA, i.e. 10% of the maximum injection current. Our calculation, based on the experimentally determined potential distribution as well as the full equation of electron motion in the magnetic and time-varying electric field, gives 180 mA for 6 kV (Klos et al., 1988). A simpler explanation of these “superpotentials” may be through the movement of the beam electrons in the space charge region. When the payload potential approaches the gun voltage, the current through the surface which encloses the space charge region of the payload becomes zero. At this moment, the injection which still continues charges the payload further, until the beam electrons lose their energy and
407
are reflected at the boundary of the space charge region. The additional charge required for increasing the potential from 6 kV to the observed 8-9 kV, with the payload capacitance of about 100 pF, is very small (4 x 10e7 As). It is straightforward to show that this charge is sufficient to attract the beam electrons (0.5 A, 6 keV) into the space charge region of typically 5 m. Beam or ionosopheric electrons can be trapped in the E x B field (Linson, 1982) and lead to a deficit of the neutralization current. This process depends on the high potential and the characteristic size and is initiated at a certain moment at a threshold in size and gun voltage. In other words, the trapping process increases the effective source impedance of the neutralization current and causes the higher payload potential in order to provide the required current. Another, more complicated mechanism may be the following. If part of the beam is diverted outside the space charge region, with the initial condition that the payload potential is of the same order as the gun voltage, a higher value of Qp than VBYncan result. Preaccelerated particles can appear during the beam motion inside the space charge region due to beamplasma interaction. The motion away from the space charge region of these electrons with energies larger than those of the electrons leaving the gun, results in mp > VW,. Preaccelerated electrons with energies 1.5 x cl/gun were observed in a laboratory experiment on BPD (Berezin et al., 1963 ; Kochmarev et al., 1985) and their contribution reached up to 5% of the total number of charged particles leaving the gun. These energy values and the fraction of preaccelerated electrons can give rise to Dp > VW if I,, is of the order of Zncutr.Applying the laboratory results to our data, the maximum preacceleration current amounts to 25 rn4 at the maximum gun current of 500 rn4. If we include the phenomenon of a virtual cathode and wake effects (see e.g. Miller, 1982), I,,, is even smaller by a factor of two or more compared to the value derived above, and must be 25 mA. In this case we can expect the potential to rise to 1.5 x V,, , i .e. here 7.5 kV for V,, = 5 kV which is indeed seen on the upleg of the experiment. A detailed inspection of the current-voltage characteristics (Fig. 4) shows a maximum threshold at about 200 mA which apparently depends on the background electron density, and a pronounced hysteresis between the leading and trailing edges in triangular pulses. These “superpotentials” appear rather suddenly and may be related either to the characteristic size of the space charge region, or to the voltage required for particle trapping or acceleration. At the moment when the potential deviates from the gun voltage all three parameters (gun voltage, gun current and the size of
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the space charge region, i.e. neutralization current) change and we are not in the position to judge which of the parameters is primarily responsible. It is interesting to note that according to our calculation (Klos et al., 1988) this threshold appears when the gun current begins to increase faster than the associated neutralization current. An alternative, hypothetical explanation could be secondary electrons emitted from the payload by returning beam electrons ; in the present case, the injection angle being far away from 90”, however, excludes the possibility of energetic (beam) electrons hitting the payload. In the present experiment we observe two kinds of discharge, induced by the natural ambient atmosphere and by outgassing. Both kinds were studied in the laboratory (Lyakhov et al., 1982; Managadze, 1979) and can be distinguished by the effect of the emissions on plasma density. BPD, the first kind of discharge to be discussed, is observed on the downleg below 160 km as an interaction with the natural atmosphere. Due to the payload geometry (pitch angle), the vehicle is always near to or on the same field line as the beam. This explains that BPD, which is generated farther away, occurs on the same magnetic field line as the main payload body and hence results in full neutralization. In the following we describe some characteristics which provide evidence for BPD. The threshold altitude for BPD ignition in the case of the undisturbed atmosphere (downleg) was between 160 and 136 km, i.e. the adequate number density of neutral molecules was 2 x 10’“-lO1i cmm3. The BPD development time could not be resolved properly, but-based on the observation of the onset of photoemissions-was below 3 ms. The plasma number density in the discharge region is estimated to be in excess of lOI m-3 because the telemetry signal at 80 MHz, which was normally observed in the radio spectrometer, was attenuated. Since during this last pulse the payload potential reached even a slight negative value, the thermal velocity of the ambient electrons must have provided a current equal to the gun current. The empirical relation by Bernstein et al. (1978) for the BPD threshold current for pressures below 2 x 1O-5 Torr is : z _ 2 x 103v;,; gunPB”~L P B V wn Zgun L
(1)
ambient pressure in Torr Earth’s magnetic field in Gauss in kilovolts in milliamps characteristic size of the BPD region in metres.
At 140 km, a gun voltage of 1 kV and a corresponding current of 100 mA (at the beginning of BPD) yields a length L of the disturbed region of between 20 and 30 m. Such a large-scale BPD has been studied in the laboratory by Bernstein et al. (1983). Its formation led to total neutralization of the payload discharge which occurred at the beginning of the injection. When the payload descended to 88 km the size of BPD decreased and the plasma density in the discharge increased to 1O’j m-3. The experimentally observed phenomena satisfy the criteria for beam plasma discharge, namely : occurrence of optical and radio emissions, -production of plasma with high density and temperature capable of providing total payload neutralization, -non-linear (threshold) characteristics of the above phenomena. The perveance of the present gun (2 x 10m6A V-‘/‘) was two orders of magnitude above the minimum value for BPD quoted by Winkler (1982). The interpretation of the upleg data between 272 and 6.50 km is less straightforward. In previous preliminary presentations, we described the phenomena as “local” BPD made possible by the payload’s outgassing (Managadze et al., 1983~). This explanation has, however, shortcomings because we observe a number of characteristics typical for BPD, although total neutralization does not occur. Data which have become available since then suggest another interpretation. According to the new data, it is reasonable to assume that in this altitude region the observed discharge occurred in the E x B field. Some observations very distinctly support such a type of discharge : -optical emissions which are only observed transverse to the gun by the photometer looking into the discharge region ; -hysteresis between leading and trailing edges in triangular pulses and threshold effects of optical and radio emissions associated with characteristic payload potential drops during leading and trailing edges of triangular pulses at l-2 kV ; -very strong dependence between the intensity of optical em&ions and I,,, x V,,, to the power of ca 3.54, which in the case of BPD is not typical (usually in BPD light intensity and current are linearly related). These arguments make our assumptions about the because some phenomena can for the first time be explained and estimates made according to the paper by Galeev E x B field in this altitude region plausible,
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et af. (19’76),in which it is su~est~ that the Townsend condition can be met for the ignition of a stationary discharge of this type. Such potential jumps in the slopes of the gun current are seen with a hysteresis in all pulses which support the E x 3 hypothesis, except during BPD (i.e. below 160 km). The observed particle data show, for example, that the integral flux over the energy covered (i.e. 40 eV7.4 keV) yields a current of 0.44 A, which is very near to that injected by the gun and we can clearly see two populations of particles (characteristic for E x B discharge), whereas during BPD the spectrum is flat. The effect of the asymmetry of the payload potential between up- and downleg follows the explanation outlined by Managadze et al. (1986) : in the altitude region 450-1200 km on the upleg the payload potential was some 1.5 kV above the corresponding values on the downleg. This effect was seen here for the first time ; earlier similar flights showed the reverse behaviour, i.e. higher potentials on the downleg (Managadze, 1979; Managadze and Lyakhov, 1979). We tentatively explain this observed asymmetry by the formation of a virtual cathode, i.e. local formation of negative charges in front of the gun when firing in the ram direction (upleg). The space charge of this virtual cathode ~hibits the returning electrons from reaching the payload body. According to the calculations for the formation of a virtual cathode by Alyekhin et af. (1971), the beam current has to exceed the critical value of &i, = (w”‘Y(eJ2m.)
(2)
Win electronvolts which in the present case amounts to 0.45 A when the ejected electrons have lost more than W = 250 eV in the surrounding potential; thus a virtual cathode is formed 4-5 m from the payload. The typical crosssection of the virtual cathode is limited by the electron gyro radius (ca 1.5 m) and forms an efficient screen for the neutralizing ionospheric electrons. In the present case the vertical velocity of the vehicle exceeds the thermal velocity of ions up to 1200 km. In the upleg case, the wake is devoid of plasma and hence cannot efficiently collect neutralizing ionospheric electrons. On the downleg, however, they are in the wake of the virtual cathode and the collection of neutralizing electrons is more effective, A similar asymmetry was also seen in the particle data from up- and do~ward-looking Geiger-Miiller tubes. The remaining explanation is that i~e~ately after the end of the gun action the payload acquires a slight negative potential. The low background electron density and surface of the payload consisting of untreated
409
gurney suggest that the observed slow recovery is due to slow neutmli~tion from a negative potential. One can qualitatively understand the negative charging by ions being repelled during the pulse due to the large positive potential and hot electrons “overneutralizing” the payload at the end of the gun operation. Similar effects have been observed by Amoldy and Winckler (1981) and in the Spacelab- flight (Beghin et al., 1984), although with much shorter recovery times which may be explained by larger and better conducting surfaces and/or larger electron densities. A theoretical estimate which yields comparably long recovery times is presented by Garrett (1981). ~Cknowle~e~en~~The discussions with A. A. Galeev, V. D. Shapiro, V. I. Shevchenko, S. G. Shustin and B. N. Maehlum are deeply appreciated. The Austrian participation was financially covered by a direct grant from the Federal Austrian Ministry for Research.
REFERENCES Alpert,
Ya. L., Gurevich, A. V. and Pitayevski, L. P. (1964), in Iskusstvennye Sputniki v Razrezhennoi P&me. Nauka, Moscow. ~yekhin, Yu. K., Karpman, V. I., Ryutov, D. D. and Sagdeev, R. Z. (1971) Gn the stability of electron beams injected along the geomagnetic field line. Cosmic Electradyn~ics
2,280.
Arnoldy, R. L. and Winckler, J. R. (1981) The hot plasma environment and floating potentials of an electron-beamemitting rocket in the ionosphere. J. geophys. Rex 86,575. Balebanov, V. M., Gagua, T. I., Klos, Z., Laliashvili, A. N., Leonov. N. A.. Lvakhov. S. B., Mavorov, A. D., Managadze, G. G., Martins&, A. A., Riedler, W. K. and Friedrich, M. F. (1981) Osobennosti plazmennykh protsessov, voznikayushcbikh v zone inzhektsii puchka elektronov s vysotnoio zonda, Issledovanie puchkoioplazmennoio ra&ada. Preprint IKI, Pr-781. _ Beard. B. D. and Johnson. F. S. (19611 Ionosuheric limitations on attainable satellite potent&l. J. geophys. Res. C&,4113.
Beghin, C., Lebreton, J.-P., Mae~um, B. N., Treim, J., Ingsay, - _. P. and Michau, J. L. (1984) Phenomena induced by charged particle beams. Science 225,188 1. Berezin. A. K.. Berezina. G. K.. Bolotin. I. L. and Fait&era. Ya. i. (1963) On the inter&on high current beam pulses with plasma in a magnetic field. Atomnaya Energiya 14,249 (in Russian). Bernstein, W., Leinbach, H., Kellogg, P., Monson, S., Hallinan, T., Garriott, 0. K., Konradi, A., McCoy, J., Daly, P., Baker, B. and Anderson, H. R. (1978) Electron beam experiments : the beam plasma discharge at low pressures and magnetic field stre&ths. Geophys.>es. Left.-5, 127. Bernstein. W.. Mantioukis. G.. Leinbach. F. H. and Hallinan, T.~(1983) Op&aI &eas&ements of a large scale Iaboratory BPD. ESA SP-195, 177. Bush, R. I., Hawkins, J. G., Williams, P. R., Banks, P. M. and Raitt, W. J. (1984) Charging of the Shuttle Orbiter as a result of electron beam emission (Abstract). EOS, 1053. Friedrich, M. (1979) A fast high resolution capacitance
of
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probe. Internal Report INW 7911, Technical University Graz. Friedrich, M., Riedler, W., Torkar, K. M., Managadze, G. G., Leonov, N., Lyakhov, S. B. and Martinson, A. A. (1988) Potential observations of an electron emitting rocket payload. Adv. Space Res., in press. Gagua, T. I., Klos, Z., Laliashvili, A: N., Leonov, N. A., Lvakhov. S. B.. Mavorov. A. D.. Manaaadze. G. G.. Martinson, A. A., sedler,’ W. K.‘and Frildrich, M. F: (1983) Osobennosti plazmennykh protsessov, voznikayushchikh v zone inzhektsii puchka elektronov s wsotnoio zonda, Protzessv neitralizatsii. Preprint IKI, Pi-617. Galeev, A. A., Mishin, E. V., Sagdeev, R. Z., Shapiro, V. D. and Shevchenko, V. I. (1976) Discharge in the region around a rocket following injection of electron beams&to the ionosphere. Doklady Akad. Nauk SSSR 231, 71 (in Russian). Garrett, H. B. (1981) The charging of spacecraft surfaces. Rev. Geophys.. Space Phys. 19, 577.
Jacobsen. T. A. (1972) Hieh-latitude ionospheric studies bv \ rocket measurements w:th emphasis on-RF capacitance probes. Internal Report E-204, Norwegian Defence Research Establishment, Kjeller. Jacobsen, T. A., Trsim, J., Maehlum, B. N. and Friedrich, M. (1981) Ionospheric electron heating by a rocket borne electron accelerator. Adv. Space. Res. 1, 123. Kawashima, N. (1983) Highlights of the electron beam experiments in space in Japan. ESA SP-195, 141. Klos, Z. and Zbyszinski, Z. (1984) Plasma processes caused by an electron beam injected from a high-altitude rocket probe, III. Generation of HF-emissions. Internal Report, Space Research Institute of the Polish Academy of Sciences. Klos, Z., Zbyszynski, Z., Managadze, G. G., Lyakhov, S. B., Gagua, T. I., Torkar, K. M., Friedrich, M. and Riedler, W. (1988) Some features of RF emissions observed by an electron emitting rocket payload. Adv. Space Res., in press. Kochmarev, L. Yu., Lyakhov, S. B., Mayorov, A. D., Managadze, G. G., Chmil, A. I. and Shustin, E. G. (1985) Uskorenie elektronov v puchkov-plazmennom razradye. Fizika Plasmy 11, 622. Linson, L. M. (1969) Current-voltage characteristic of an electron emitting satellite in the ionosphere. J. geophys. Res. 14, 2368 Linson, L. M. (1982) Charge neutralisation as studied experimentally and theoretically, in Artificial Space Plasma Studies (Edited by Grandal, B.), pp. 573-595. Plenum Press, London/New York. _ Lvakhov. S. B.. Friedrich. M. F.. Klos. Z.. Manazadze. G. -G., Rikdler, W. K., Tdrkar, K. M.‘and Zbyszynski; Z. (1984) Radio observations by the high altitude rocket experiment G60S during electron injection. Internal Report IWF 8405, Austrian Academy of Sciences. Lyakhov, S. B., Mayorov, A. D., Managadze, G. G., Povalyaev, 0. A., Chmil, A. I., Kochmarev, L. Yu., Shustin, E. G., Friedrich, M. F., Riedler, W. K., Laliashvili, A. N., Kiraza. A.. Klos. Z.. Kravchic. Z. and Leonov, N. A. (1985) ‘Laboratory studies for beam plasma experiments with rockets. Planet. Space Sci. 30, 347. Maehlum, B. N. (1983) Ionospheric modification by electron beams. ESA SP-195, 121. I
Maehlum, B. N. (1987) Beam-plasma experiments, in Computer Physics Communications. North Holland, Amsterdam (in press). Managadze, G. G. (1979) Neutralisation process and determination of payload potential during the injection of a powerful electron beam in the experiment ARAKS. Fizika Ptasmy 5, 1100 (in Russian). Managadze, G. G., Gagua, T. I., Lyakhov, S. B., Mayorov, A. D., Martinson, A. A., Riedldr, W. K., Friedrich, M. F.. Leonov. N. A.. Klos. Z. and Laliashvili. A. N. (1983a) Plasma processes caused’by an electron beam injected from a high altitude rocket probe, I. Neutralisation processes. Internal Report IWF 8302, Austrian Academy of Sciences. Managadze, G. G., Gagua, T. I., Nokel, V. P., Burchuladze, A. A. and Shutyayev, I. Yu. (1986) Zavisimost belichini potentziala injektiruyuchego elektroni zonda ot visoti i napravleniya yego poleta (eksperiment “Gruziya-60Spurt”). Preprint IKI, Pr-1148, Moscow. Managadze, G. G. and Lyakhov, S. B. (1979) The effect of altitude, artificial plasma and injection pitch-angle of electrons on the process of neutralisation of payload charge in the ARAKS experiment. Preprint IKI, Pr-471, Moscow (in Russian). Managadze, G. G., Lyakhov, S. B., Balebanov, B. M., Gaba, T. I., Ma&son, A. A., Mayorov, A. D., Friedrich. M. F.. Riedler. W. K.. Klos. Z.. Laliashvili. A. N. and Leonov,‘N. A. (1983b) Plasma processes caused by an electron beam injected from a high altitude rocket probe, II. Studies of beam plasma discharge. Internal Report IWF 8303, Austrian Academy of Sciences. Managadze, G. G., Riedler, W., Balebanov, B. M., Friedrich, M., Gagua, T. I., Klos, Z., Laliashvili, N. A., Leonov, N. A., Lyakhov, S. B., Martinson, A. A. and Mayorov, N. A. (1983~) Plasma processes in the region of electron beam injection from a high-altitude payload. ESA SP-195, 161. Miller, R. B. (1982) An Introduction to the Physics of Intense Charged Particle Beams. Plenum Press, New York. Parker, L. W. and Murphy, B. L. (1967) Potential build-up of an electron emitting ionospheric satellite. J. geophys. Res. 72, 1631. Rawer, K., Ramanakrishnan, S. and Bilitza, D. (1981) International reference ionosphere. World Data Center-A (STP), UAG-81. Sagdeev, R. Z., Managadze, G. G., Mayorov, A. D., Lyakhov. S. B.. Martinson. A. A.. Romanovskv. Yu. A.. Adeishvili, T. ‘G., Leonov, N. A. and Gagua, T. I. ‘(1981) Peculiarities of the environment disturbance during the electron beam injection from the rocket. Adv. Space. Res. 1, 77. Szuszczewicz, E. P. (1985) Controlled electron beam experiments in space and supporting laboratory experiments : a review. J. atmos. terr. Phys. 47, 1189. Torkar, K. M., Friedrich, M., Riedler, W., Lyakhov, S. B., Manaaadze. G. G.. Klos. Z. and Zbvszvnski, Z. (1985) Collection of data obtained from the rocket flight G-60-S. Internal Report IWF 8501, Austrian Academy of Sciences. Winckler, J. R. (1982) The use of artificial electron beams as probes of the distant magnetosphere, in Arttficial Particle Beams in Space Plasma Studies (Edited by Grandal, B.). Plenum Press, New York/London.
0032-0633/88 $3.00+0.00 Pergamon Press plc
1988
POTENTIAL OBSERVATIONS OF AN ELECTRONEMITTING ROCKET PAYLOAD AND OTHER RELATED PLASMA MEASUREMENTS* G. G. MANAGADZE,V. M. BALEBANOV.A. A. BURCHUDLADZE,T. I. GAGUA, N. A. LEONOV, S. B. LYAKHOV, A. A. MARTINSON snd A. D. MAYOROV Space Research Institute of the Soviet Academy of Sciences (IKI), Profsoyusnaya 84, 117810 Moscow, U.S.S.R. W. K. RIEDLERt aad M. F. FRIEDRICHS Department of Communications and Wave Propagation, Technical University Graz, Inffeldgasse 12, A-8010 Gnu, Austria K. M. TORKAR Space Research Institute of the Austrian Academy of Sciences, Inffeldgasse 12, A-8010 Grax, Austria A. N. LALL4SHVILI Georgian Academy of Sciences, Tbilisi, U.S.S.R.
Z. KLOS aad Z. ZBYSZYNSKI Space Research Centre of the Polish Academy of Sciences, Ordona 21, PL-01237 Warsaw, Poland (Received 26 October 1987)
Ahstraet-Gbservations of plasma effects due to an energetic electron beam near a rocket payload are summarized and an attempt is made to outline the basic processes in the plasma such as beam plasma discharge (BPD). The experiment had some unique features such as a high apogee and low background plasma density. The measurements covered most parameters relevant for the study of plasma effects, as well as payload potential, optical and radio emissions, energetic charged particles and plasma densities. Among the noteworthy observations are radio emissions up to VHF frequencies and very high payload potentials which even exceeded the gun voltage. The observed features are interpreted as BPD at low altitudes and as discharges in the E x B field at other heights.
1. INTRODUCTION
the experiments quoted therein) are in particular the
The rocket experiment Gruziya-60-Spurt (G-60-S) was aimed at studying processes in the vicinity of the vehicle caused by the injection of electrons. One aspect was the neutralization process during and after the payload charging due to the emission of electrons, the other to study optical and radio emissions as a consequence on non-linear processes such as beam plasma discharge (BPD). The main features which distinguish the present experiment from most previous ones (see the review by Szuszczewicz, 1985, and
following.
* Dedicated to the memory of our colleagues and friends Sergej Lyakhov who tragicauy died at the age of 38, on 19 August 1986, in a mountaineering accident and Andrej Martinson who unexpectedly passed away on 13 August 1987. tAIso at the Space Research Institute of the Austrian Academy of sciences, IntTeldgasse12, A-8010 Graz, Austria. $ Author to whom alI correspondence should be addressed.
-High apogee of over 1500 km. On the one hand this obviously provided a long observation time, but on the other also a sufficiently long time for outgassing of the payload. -Cleanliness of the payload. The surface consisted almost exclusively of aluminium. Furthermore, the motor separation at 170 km on the upleg contributed to a reduction of unpredictable gas concentrations in the region of the measurements. -Near-spherical shape of the payload. The equivalent sphere of 75 cm radius facilitates calculations using theoretical considerations. -Attitude stabilization by an internal gyro. Although, in contrast to other active rocket experiments (e.g. Maehlum, 1983), variations with the pitch angle cannot be deduced, the present configuration allows a comparison from pulse to pulse
399
400
G. G. MANAGADZEet al.
without having to disentangle pitch angle from altitude effects. Preliminary results dealing with certain aspects have been published earlier in the form of internal reports (Balebanov et al., 1981; Gagua et al., 1983 ; Klos and Zbyszynski, 1984 ; Lyakhov et al., 1984 ; Managadze et al., 1983a, b; Torkar et al., 1985; Managadze et al., 1986), as conference proceedings (Managadze et al., 1983~; Friedrich et al., 1988; Klos et al., 1988) and as some laboratory results with the flight instrumentation by Lyakhov et al. (1982). The present paper is based on all information given previously in the above papers and hence supersedes them in all aspects ; it aims to present a consistent picture
of the complex physical phenomena observed during and after electron injections in the region near the payload. 2. INSTRUMENTATION
The rocket payload carried a large number of diagnostic instruments whereof only those relevant in the present context will be listed below (Fig. 1). The analogue telemetry had a basic sampling rate of 100 s-l and the frequency of the 20 W transmitter was about 80 MHz. During earlier flights with this telemetry system, but also with much higher frequencies and lower power (Maehlum, 1986, private communication), drop-outs were observed during intense (0.8 A)
FIG. 1. GENERALmw OFTHEPAYLOAD. (1) Electron gun, (2) gas injector, (3) particle spectrometer USHBA-MOS, (4) electron spectrometer ANTEIMETR, (5) upward-looking photometer, (6) sideward-looking photometers, (7) capacitance probe, (8), (9) aerials for the HF and VHF spectrometers, respectively, (10) Geiger-Miiller tubes, (11) potential probe No. 1, (12) double probe, (13) electric field probe, (14) ion and plasma probes, (15) potential probes Nos 2,3 and 4.
401
Potential of an electron emitting payload
gun pulses. In order to overcome these data gaps, the eight channels considered most relevant for the overall success of the experiment were delayed by 1 s (i.e. longer than the duration of a gun pulse) and transmitted in addition to the direct signals. The forward (upward)-directed electron gun alternatingly emitted rectangular and triangular pulses with a duration of 0.6 s and a repetition rate of 5 s. The maximum peak energy of rectangular pulses was 6.7 keV associated with a current of 0.55 A; most pulses, however, typically had peak values of 6.3 keV at 0.5 A. In order to study controlled BPD a gas injector was included in order to release gas during certain pulses. Three potential probes were mounted on a boom at distances of 1, 2.2 and 3.2 m from the payload in order to establish the spatial variation of the potential (input impedance > 1 GQ). The nearest probe at 60 cm was mounted on another boom. A capacitance probe oscillating near 900 kHz was used to establish the electron density. This kind of probe is primarily sensitive to the sheath thickness or the ratio of electron density to electron tem~rature (Jacobsen, 1972; Friedrich, 1979). The probe (ungridded sphere of 4.2 cm diameter) itself was dc-connected to the payload body via 100 ksz. Photometers along and across the main payload axis (same as the gun axis) were employed at 427& 2 nm with a dynamic range of 100. The radio spectrometer consisted of two instruments (PRS and ISKRA), whose frequency ranges did unfortunately not overlap. The instrument PRS covered 0.1-10 MHz at 20 discrete, linearly spaced frequency slots of 36 kHz bandwidth. The sweep (50 ms) was synchronized to the gun operation. The instrument included a built-in bufIer to read out the spectra measured during gun operation, delayed between the pulses at a slower rate suitable for the telemetry. Thus here no problems occurred due to the drop-outs in the telemetry. The frequency range 2% 320 MHz was covered by the instrument ISKRA in five segments which were swept sim~taneously. The bandwidth was 1 MHz and the sweep time 0.3 s; only the first segment from 20 to 80 MHz worked properly. Fluxes of energetic charged particles were detected by three instruments, namely ANTEIMETR (40 eV7.4 kev), USHBA-MOS (120 eV-16 keV) and three orthogonal Niger-Mailer tubes (>40 keV). The latter were mounted on a collapsable boom of 63 cm. They were oriented looking upward, downward and to the North in the horizontal plane and were collimated to an effective opening angle of Ifr2.5”. This configuration covers pitch angles of 24,156 and 114”, respectively.
3. MEASUREMENTS
Some of the instruments flown aboard the present payload failed or showed irregular behaviour and are therefore not used in the following. In particular, the injector for neutral gas did apparently not work, except perhaps on the downleg around 1450 km (cf. Fig. 5). At this altitude there are some observations which are similar to those at much lower altitudes on the downieg; since no corresponding behaviour is observed at that altitude on the upleg, it is assumed that some gas may have escaped in an uncontrolled manner. The other malfunction relevant to the present study is an irregular behaviour of one telemetry commutator which in particular affected the nearer probes of the potential instrument. 3.1. Background The payload was launched on 18 September 1981, with a rocket of the type “Vertikal” from the Soviet mid-latitude range Kapustin Yar. The launch time was 17:59:58.3 U.T. (21:59:58.3 Moscow time), the solar zenith angle was 117”, the rocket elevation 88” and the apogee 15 14 km. The geophysical conditions were A, = 18, F(10.7) = 216 and R, = 145. The payload was switched on after motor separation and became fully operational at an altitude of 270 km. The Lvalue varied between 2.0 and 2.4 during the flight. Generally the capacitance probe behaved regularly between gun pulses, whereas the oscillation apparently ceased during the accelerator operation. Laboratory investigations in a small plasma chamber with a similar probe showed that with only small positive potentials (ca IV) in the presence of only moderate electron densities the oscillation stopped. This is probably due to an ohmic loading of the LC circuit whereupon the feedback condition is no longer fulfilled. Figure 2 shows the background electron density established from the capacitance probe readings just before the beginning of the gun pulses. A sheath thickness of 5 Debye lengths was assumed, the electron temperature was taken from IRI (Rawer et uf., 1981) for the appropriate conditions, and the whole profile was normalized to the reading of the range ionosonde. 3.2. Potential The main source of information about the payload potential is obviously the potential probes. Due to problems of the telemetry as mentioned above, data from the nearer spheres are only available for the first pulse. However, the spatial distribution of the potential during that first pulse suggests that the readings of the farthest probe represent the true payload potential (Fig. 3). In the following, “potential” means
402
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MANAGADZE
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potential of the payload relative to the plasma or voltage between probe 4 and the payload. Figure 4 shows an example of the voltagecurrent characteristics of the payload and the gun. One can see that above a certain threshold the payload potential exceeds the gun voltage. The higher potentials during the falling edge of the gun pulse, compared to corresponding values during the rising edge, are not due to a mere hysteresis of the payload potential or indeed the electronics; at the end of rectangular pulses we do not observe a slow recovery from high positive potentials. Figure 5 shows the payload potential vs altitude for injection voltages of 1, 2, 3, 4 and 5 kV. The values were taken during the leading edges of triangular pulses on the downleg of the trajectory, because upleg data do not cover altitudes below 270 km. Features not presented by Fig. 5 include the fact that potentials are higher during the falling edge (see Fig. 4) and that the potentials are somewhat lower on the downleg than on the upleg. At lower altitudes (near the F-region peak in the electron density) the potential is significantly below the injection voltage. At higher altitudes (lower electron densities) it approaches the gun voltage and even exceeds it at higher gun voltages. Alternatively a dependence of these “superpotentials” on the injection current was sought. For this purpose the ratio between payload potential and gun voltage vs gun current was established. Figure 6 shows three examples, one near the F-region peak and the other two at low electron densities, i.e. one close to apogee and the other below the F-region peak. At larger electron densities the potential remains small and only exceeds the value of the gun voltage at currents beyond 200 mA. At electron densities below ca 1.5 x IO” mP3 the rise to a “superpotentia~ is not resolved (below 10 ms). With increasing current the potential falls from ca 3 VBunto about 1.5 Vgun.An inverse dependence of the vehicle charging on ambient plasma density was also observed by Bush et al. (1984). The low potential is a feature observed in most other active experiments and explicable by efficient neutralization due to small contact impedance between the payload and the ambient plasma. Excess potentials have hitherto not been reported in the literature, but values close to the injection voltage and slightly exceeding it have been observed in the tethered mother-daughter experiment MAIMIK (Maehlum, 1987). A notable feature common to both experiments is the low background electron density (lOlo m -3 in the case of MAIMIK, a value even lower than in the present experiment), whereas the reported background electron densities in other experiments
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were condsiderably larger. Also the pitch angle of 156 (i.e. far from 90”) may be responsible for the insufficient neutralization ; both Kawashima (1983) and Maehlum (1986, private communication) find that the payload charging is smallest (neutralization most efficient) for injection angles nearest to 90”. Since in the present experiment both the current and the gun voltage vary simultaneously, we are unfortunately not in the position to attribute the “super-potentials” uniquely to a threshold of current or voltage. Another interesting feature is the reading of the capacitance probe, which shows an apparent electron density decrease after the pulse recovering to normal values with time-constants of the order of seconds (Fig. 7). A decrease of the sphere’s capacitance can be caused by (a) a decrease of the electron density, (b) an increase of the electron temperature, and (c) a decrease of the probe potential. With the velocity of the vehicle being ca 3 km SC’ and the angle of the velocity vector to the magnetic field being 157”, the probe leaves the flux tube (diameter 2 m for 6 keV) after fractions of a second. The observations by mother-daughter payloads have established the diameter of disturbances caused by an electron beam as slightly under 2 gyro radii across the magnetic field (Jacobsen et al., 1981). Another argument against a real plasma density disturbance (electron depletion) is the fact that the magnitude of the capacitance decreases, whereas the time constant of the recovery does not noticeably depend on the type of gun pulse (triangular or rectangular). With similar arguments an electron temperature increase in a disturbed region
404
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can be ruled out. Based on laboratory measurements we interpret the capacitance probe readings after the gun pulses as negative payload potentials of l-2 V. 3.3. Emissions 3.3.1. Radiowaves. The measurements of the PRS instrument (0.1-9 MHz) were satisfactory, whereas the ISKRA instrument showed poor data quality for four of the five segments, and only the segment 20-80 MHz can be used. Furthermore, the data from ISKRA were transmitted directly and hence telemetry drop-outs occurred during intense pulses at higher altitudes. Suitable corrections for the different efficiencies of the two aerials as well as for a change
in impedance due to the ambient plasma were applied. Figure 8 shows the background emissions between 1 and 80 MHz vs altitude on the downleg. The shading is in steps of 10 dB above a reference of 10 PV m-i MHz-‘. The left side shows a clear maximum of the emissions which roughly coincides with the local plasma frequency (dotted line) as derived from the measurement with the capacitance probe. The fact that the electron density measurement was made on the upleg-in contrast to the emission observationsmay explain the small discrepancies. Data below the electron density peak (250 km) and above the critical frequency (4.02 MHz) probably do not originate in the plasma, but are rather man-made. In particular,
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405
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Units are dB above a reference field strength of 10 PV per metre and a bandwidth of 1 MHz. The dotted line is the local plasma frequency as measured by the capacitance probe.
the signals observed near 70 MHz are most likely due to stations in the FM broadcast band, which in the Soviet Union ranges from 66 to 72 MHz. Figure 9 shows the increase of the emissions during rectangular pulses over the values in Fig. 8 in contours of 5 dB. Note that in some areas (at low frequencies) the emissions decreased during the gun operations. Significant emissions occur at most HF frequencies, particularly below 9 MHz and at altitudes below 270 km. Emission in the 2&80 MHz range can not be resolved at all altitudes because of telemetry problems during the gun injection.
3.3.2.0ptical. Glow was observed both in the longitudinal and transverse directions (relative to the payload/gun axis). Figure 10 shows the altitude dependence of the glow measured by the photometer in the direction along the beam. Note that the Earth’s shadow has risen from 900 to over 1000 km in the time interval between up- and downleg and that on the upleg the scattered fluxes are consistently larger than in the downleg; we consider this as supporting the hypothesis that outgassing led to a different environment between up- and downleg. Figure 11 shows the optical flux in the beam direction as a func-
oh 3
I
4
6
6
7
88x)
20
30
40
50
60mBo.
FREQUENCY, *MHz FIG. 9. INCRERA~EOF THE RADIO EMLSION POWER STMJLATELI BY RECTANGULAR PULSESOF THE ELECTRON GUN.
Contours are every 5 dB relative to the values of Fig. 8. Note that in some areas the observed emissions were below the natural background.
406
et al.
G. G. MANAGADZE
r
E.5
34 23 2
+-----i FLlJX,arb.units
1
FIG. 10. OPTICAL GLOW MEASURED BETWEEN PULSES WITH THEUPWARD-LOOKINGPHOTOMETER.
tion of the gun current; the data are taken from all heights below the shadow line. One can clearly see a threshold of about 200 mA and a dependence of the optical flux on the current to the power of 7-8. The last part of the downleg, i.e. below 135 km, was also interesting. At this time glow was only measured in the transverse direction and the intensity increased rapidly in the beam region. Between 109 and 88 km the glow intensity increased by more than a factor of 60, whereas the ambient pressure-according to atmospheric models-increased only by a factor of 20. 3.4. Particle measurements All of the particle detectors worked well. Despite the high threshold energy of 40 keV the Geiger-Miiller counters are best suited for the purpose of studying
0
0
ltl0
OS
upward
0.2
0.3
0.4
GUN CURRENT A FIG. 11.DEPENDENCE OF THE OPTICAL EMISSIONACROSS THE BEAMDlRECTIONONTHEGUNCURRENT. Data weretaken from 270to 760 km (i.e. fromthepart of the trajectory in darkness).
-i O-
h
I
0
f
1
I
1
I
I
I
,
0.5 RELATNE TIME, s
FIG. 12. FLUXFS OF RETURNING CHARGED PARTICLES AS MEASURED WITH THE GEIGER-MUELLER INSTRUMENT AT 1179 km TOGETHER WITH THE PAYLOAD POTENTIAL.
the gun response because of their high time resolution. Fluxes of the northward-looking detector indicate that the gun operation stimulated the precipitation of trapped particles ; these data, and those of the other particle detectors, will be published elsewhere. Figure 12 shows an example of the particle fluxes observed by the upward- and downward-looking Geiger-Mtiller tubes at 436 s (1179 km) on the upleg during a rectangular pulse. The most noteworthy features observed by these particle counters during the pulses are the following. -Sudden enhancements of both particle count rates within the duration of the pulse. In the height range 960-1410 km (upleg), 14 of the 23 rectangular pulses show this feature. These enhancements occur between 200 and 400 ms after the beginning of the electron injection. The observed delays in the sudden onset of the count rates may for example be due to pitch angle scattering at some distance along the field line. Xlear anticorrelation of these enhanced count rates with the payload potential. It is therefore reasonable to associate these fluxes (> 40 keV) with fluxes of lower energies providing the neutralization current.
Potential of an electron emitting payload
-Anisotropy of the fluxes, i.e. fluxes from below on average exceed those from above by a factor of two. This may be explained by precipitating particles with pitch angles near 90”, which are only poorly detected by the upward-directed, collimated Geiger-Miiller tubes. The downward-directed tubes, in contrast, will observe fluxes which are scattered in the atmosphere and are hence fairly isotropic.
4. DISCUSSION AND CONCLUSIONS
An attempt to describe theoretically the picture of the spatial distribution of the potential (Fig. 3) and the dynamics of the potential formation is given e.g. by Alpert et al. (1964). At larger plasma densities, as e.g. observed by Sagdeev et al. (1981) aboard a small rocket, the potential dropped within a shorter distance from the vehicle. Furthermore the total potential will be close to, but below, the gun voltage. In the following we try to find a mechanism capable of providing a payload potential above the gun voltage and to discuss an explanation for the potential jump in the voltage-current characteristics of the payload. The plasma processes which occur during beam injection have been analysed to some extent in theoretical papers (Beard and Johnson, 1961; Parker and Murphy, 1967; Galeev et al., 1976; Linson, 1969) where neutralization processes were discussed. The payload neutralization current of the ionospheric electrons strongly depends on the potential value and its spatial distribution. A small positive potential between 500 and 1500 km is observed between pulses. The neutralization current is approximately I, = eNCv,,,S= 5 mA (N. = lo5 cnm3, T, = 3300 K, effective payload cross section S = 1 m’). If the vehicle has a potential of 6 kV-according to calculations made for a drift approximation (Parker and Murphy, 1967Fthe neutralization current of the ionospheric electrons increases approximately by an order of magnitude and will amount to Znemt, = 10 x Z,, = 50 mA, i.e. 10% of the maximum injection current. Our calculation, based on the experimentally determined potential distribution as well as the full equation of electron motion in the magnetic and time-varying electric field, gives 180 mA for 6 kV (Klos et al., 1988). A simpler explanation of these “superpotentials” may be through the movement of the beam electrons in the space charge region. When the payload potential approaches the gun voltage, the current through the surface which encloses the space charge region of the payload becomes zero. At this moment, the injection which still continues charges the payload further, until the beam electrons lose their energy and
407
are reflected at the boundary of the space charge region. The additional charge required for increasing the potential from 6 kV to the observed 8-9 kV, with the payload capacitance of about 100 pF, is very small (4 x 10e7 As). It is straightforward to show that this charge is sufficient to attract the beam electrons (0.5 A, 6 keV) into the space charge region of typically 5 m. Beam or ionosopheric electrons can be trapped in the E x B field (Linson, 1982) and lead to a deficit of the neutralization current. This process depends on the high potential and the characteristic size and is initiated at a certain moment at a threshold in size and gun voltage. In other words, the trapping process increases the effective source impedance of the neutralization current and causes the higher payload potential in order to provide the required current. Another, more complicated mechanism may be the following. If part of the beam is diverted outside the space charge region, with the initial condition that the payload potential is of the same order as the gun voltage, a higher value of Qp than VBYncan result. Preaccelerated particles can appear during the beam motion inside the space charge region due to beamplasma interaction. The motion away from the space charge region of these electrons with energies larger than those of the electrons leaving the gun, results in mp > VW,. Preaccelerated electrons with energies 1.5 x cl/gun were observed in a laboratory experiment on BPD (Berezin et al., 1963 ; Kochmarev et al., 1985) and their contribution reached up to 5% of the total number of charged particles leaving the gun. These energy values and the fraction of preaccelerated electrons can give rise to Dp > VW if I,, is of the order of Zncutr.Applying the laboratory results to our data, the maximum preacceleration current amounts to 25 rn4 at the maximum gun current of 500 rn4. If we include the phenomenon of a virtual cathode and wake effects (see e.g. Miller, 1982), I,,, is even smaller by a factor of two or more compared to the value derived above, and must be 25 mA. In this case we can expect the potential to rise to 1.5 x V,, , i .e. here 7.5 kV for V,, = 5 kV which is indeed seen on the upleg of the experiment. A detailed inspection of the current-voltage characteristics (Fig. 4) shows a maximum threshold at about 200 mA which apparently depends on the background electron density, and a pronounced hysteresis between the leading and trailing edges in triangular pulses. These “superpotentials” appear rather suddenly and may be related either to the characteristic size of the space charge region, or to the voltage required for particle trapping or acceleration. At the moment when the potential deviates from the gun voltage all three parameters (gun voltage, gun current and the size of
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MAN AGADZE et al.
the space charge region, i.e. neutralization current) change and we are not in the position to judge which of the parameters is primarily responsible. It is interesting to note that according to our calculation (Klos et al., 1988) this threshold appears when the gun current begins to increase faster than the associated neutralization current. An alternative, hypothetical explanation could be secondary electrons emitted from the payload by returning beam electrons ; in the present case, the injection angle being far away from 90”, however, excludes the possibility of energetic (beam) electrons hitting the payload. In the present experiment we observe two kinds of discharge, induced by the natural ambient atmosphere and by outgassing. Both kinds were studied in the laboratory (Lyakhov et al., 1982; Managadze, 1979) and can be distinguished by the effect of the emissions on plasma density. BPD, the first kind of discharge to be discussed, is observed on the downleg below 160 km as an interaction with the natural atmosphere. Due to the payload geometry (pitch angle), the vehicle is always near to or on the same field line as the beam. This explains that BPD, which is generated farther away, occurs on the same magnetic field line as the main payload body and hence results in full neutralization. In the following we describe some characteristics which provide evidence for BPD. The threshold altitude for BPD ignition in the case of the undisturbed atmosphere (downleg) was between 160 and 136 km, i.e. the adequate number density of neutral molecules was 2 x 10’“-lO1i cmm3. The BPD development time could not be resolved properly, but-based on the observation of the onset of photoemissions-was below 3 ms. The plasma number density in the discharge region is estimated to be in excess of lOI m-3 because the telemetry signal at 80 MHz, which was normally observed in the radio spectrometer, was attenuated. Since during this last pulse the payload potential reached even a slight negative value, the thermal velocity of the ambient electrons must have provided a current equal to the gun current. The empirical relation by Bernstein et al. (1978) for the BPD threshold current for pressures below 2 x 1O-5 Torr is : z _ 2 x 103v;,; gunPB”~L P B V wn Zgun L
(1)
ambient pressure in Torr Earth’s magnetic field in Gauss in kilovolts in milliamps characteristic size of the BPD region in metres.
At 140 km, a gun voltage of 1 kV and a corresponding current of 100 mA (at the beginning of BPD) yields a length L of the disturbed region of between 20 and 30 m. Such a large-scale BPD has been studied in the laboratory by Bernstein et al. (1983). Its formation led to total neutralization of the payload discharge which occurred at the beginning of the injection. When the payload descended to 88 km the size of BPD decreased and the plasma density in the discharge increased to 1O’j m-3. The experimentally observed phenomena satisfy the criteria for beam plasma discharge, namely : occurrence of optical and radio emissions, -production of plasma with high density and temperature capable of providing total payload neutralization, -non-linear (threshold) characteristics of the above phenomena. The perveance of the present gun (2 x 10m6A V-‘/‘) was two orders of magnitude above the minimum value for BPD quoted by Winkler (1982). The interpretation of the upleg data between 272 and 6.50 km is less straightforward. In previous preliminary presentations, we described the phenomena as “local” BPD made possible by the payload’s outgassing (Managadze et al., 1983~). This explanation has, however, shortcomings because we observe a number of characteristics typical for BPD, although total neutralization does not occur. Data which have become available since then suggest another interpretation. According to the new data, it is reasonable to assume that in this altitude region the observed discharge occurred in the E x B field. Some observations very distinctly support such a type of discharge : -optical emissions which are only observed transverse to the gun by the photometer looking into the discharge region ; -hysteresis between leading and trailing edges in triangular pulses and threshold effects of optical and radio emissions associated with characteristic payload potential drops during leading and trailing edges of triangular pulses at l-2 kV ; -very strong dependence between the intensity of optical em&ions and I,,, x V,,, to the power of ca 3.54, which in the case of BPD is not typical (usually in BPD light intensity and current are linearly related). These arguments make our assumptions about the because some phenomena can for the first time be explained and estimates made according to the paper by Galeev E x B field in this altitude region plausible,
Potential of an electron emitting payload
et af. (19’76),in which it is su~est~ that the Townsend condition can be met for the ignition of a stationary discharge of this type. Such potential jumps in the slopes of the gun current are seen with a hysteresis in all pulses which support the E x 3 hypothesis, except during BPD (i.e. below 160 km). The observed particle data show, for example, that the integral flux over the energy covered (i.e. 40 eV7.4 keV) yields a current of 0.44 A, which is very near to that injected by the gun and we can clearly see two populations of particles (characteristic for E x B discharge), whereas during BPD the spectrum is flat. The effect of the asymmetry of the payload potential between up- and downleg follows the explanation outlined by Managadze et al. (1986) : in the altitude region 450-1200 km on the upleg the payload potential was some 1.5 kV above the corresponding values on the downleg. This effect was seen here for the first time ; earlier similar flights showed the reverse behaviour, i.e. higher potentials on the downleg (Managadze, 1979; Managadze and Lyakhov, 1979). We tentatively explain this observed asymmetry by the formation of a virtual cathode, i.e. local formation of negative charges in front of the gun when firing in the ram direction (upleg). The space charge of this virtual cathode ~hibits the returning electrons from reaching the payload body. According to the calculations for the formation of a virtual cathode by Alyekhin et af. (1971), the beam current has to exceed the critical value of &i, = (w”‘Y(eJ2m.)
(2)
Win electronvolts which in the present case amounts to 0.45 A when the ejected electrons have lost more than W = 250 eV in the surrounding potential; thus a virtual cathode is formed 4-5 m from the payload. The typical crosssection of the virtual cathode is limited by the electron gyro radius (ca 1.5 m) and forms an efficient screen for the neutralizing ionospheric electrons. In the present case the vertical velocity of the vehicle exceeds the thermal velocity of ions up to 1200 km. In the upleg case, the wake is devoid of plasma and hence cannot efficiently collect neutralizing ionospheric electrons. On the downleg, however, they are in the wake of the virtual cathode and the collection of neutralizing electrons is more effective, A similar asymmetry was also seen in the particle data from up- and do~ward-looking Geiger-Miiller tubes. The remaining explanation is that i~e~ately after the end of the gun action the payload acquires a slight negative potential. The low background electron density and surface of the payload consisting of untreated
409
gurney suggest that the observed slow recovery is due to slow neutmli~tion from a negative potential. One can qualitatively understand the negative charging by ions being repelled during the pulse due to the large positive potential and hot electrons “overneutralizing” the payload at the end of the gun operation. Similar effects have been observed by Amoldy and Winckler (1981) and in the Spacelab- flight (Beghin et al., 1984), although with much shorter recovery times which may be explained by larger and better conducting surfaces and/or larger electron densities. A theoretical estimate which yields comparably long recovery times is presented by Garrett (1981). ~Cknowle~e~en~~The discussions with A. A. Galeev, V. D. Shapiro, V. I. Shevchenko, S. G. Shustin and B. N. Maehlum are deeply appreciated. The Austrian participation was financially covered by a direct grant from the Federal Austrian Ministry for Research.
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Ya. L., Gurevich, A. V. and Pitayevski, L. P. (1964), in Iskusstvennye Sputniki v Razrezhennoi P&me. Nauka, Moscow. ~yekhin, Yu. K., Karpman, V. I., Ryutov, D. D. and Sagdeev, R. Z. (1971) Gn the stability of electron beams injected along the geomagnetic field line. Cosmic Electradyn~ics
2,280.
Arnoldy, R. L. and Winckler, J. R. (1981) The hot plasma environment and floating potentials of an electron-beamemitting rocket in the ionosphere. J. geophys. Rex 86,575. Balebanov, V. M., Gagua, T. I., Klos, Z., Laliashvili, A. N., Leonov. N. A.. Lvakhov. S. B., Mavorov, A. D., Managadze, G. G., Martins&, A. A., Riedler, W. K. and Friedrich, M. F. (1981) Osobennosti plazmennykh protsessov, voznikayushcbikh v zone inzhektsii puchka elektronov s vysotnoio zonda, Issledovanie puchkoioplazmennoio ra&ada. Preprint IKI, Pr-781. _ Beard. B. D. and Johnson. F. S. (19611 Ionosuheric limitations on attainable satellite potent&l. J. geophys. Res. C&,4113.
Beghin, C., Lebreton, J.-P., Mae~um, B. N., Treim, J., Ingsay, - _. P. and Michau, J. L. (1984) Phenomena induced by charged particle beams. Science 225,188 1. Berezin. A. K.. Berezina. G. K.. Bolotin. I. L. and Fait&era. Ya. i. (1963) On the inter&on high current beam pulses with plasma in a magnetic field. Atomnaya Energiya 14,249 (in Russian). Bernstein, W., Leinbach, H., Kellogg, P., Monson, S., Hallinan, T., Garriott, 0. K., Konradi, A., McCoy, J., Daly, P., Baker, B. and Anderson, H. R. (1978) Electron beam experiments : the beam plasma discharge at low pressures and magnetic field stre&ths. Geophys.>es. Left.-5, 127. Bernstein. W.. Mantioukis. G.. Leinbach. F. H. and Hallinan, T.~(1983) Op&aI &eas&ements of a large scale Iaboratory BPD. ESA SP-195, 177. Bush, R. I., Hawkins, J. G., Williams, P. R., Banks, P. M. and Raitt, W. J. (1984) Charging of the Shuttle Orbiter as a result of electron beam emission (Abstract). EOS, 1053. Friedrich, M. (1979) A fast high resolution capacitance
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probe. Internal Report INW 7911, Technical University Graz. Friedrich, M., Riedler, W., Torkar, K. M., Managadze, G. G., Leonov, N., Lyakhov, S. B. and Martinson, A. A. (1988) Potential observations of an electron emitting rocket payload. Adv. Space Res., in press. Gagua, T. I., Klos, Z., Laliashvili, A: N., Leonov, N. A., Lvakhov. S. B.. Mavorov. A. D.. Manaaadze. G. G.. Martinson, A. A., sedler,’ W. K.‘and Frildrich, M. F: (1983) Osobennosti plazmennykh protsessov, voznikayushchikh v zone inzhektsii puchka elektronov s wsotnoio zonda, Protzessv neitralizatsii. Preprint IKI, Pi-617. Galeev, A. A., Mishin, E. V., Sagdeev, R. Z., Shapiro, V. D. and Shevchenko, V. I. (1976) Discharge in the region around a rocket following injection of electron beams&to the ionosphere. Doklady Akad. Nauk SSSR 231, 71 (in Russian). Garrett, H. B. (1981) The charging of spacecraft surfaces. Rev. Geophys.. Space Phys. 19, 577.
Jacobsen. T. A. (1972) Hieh-latitude ionospheric studies bv \ rocket measurements w:th emphasis on-RF capacitance probes. Internal Report E-204, Norwegian Defence Research Establishment, Kjeller. Jacobsen, T. A., Trsim, J., Maehlum, B. N. and Friedrich, M. (1981) Ionospheric electron heating by a rocket borne electron accelerator. Adv. Space. Res. 1, 123. Kawashima, N. (1983) Highlights of the electron beam experiments in space in Japan. ESA SP-195, 141. Klos, Z. and Zbyszinski, Z. (1984) Plasma processes caused by an electron beam injected from a high-altitude rocket probe, III. Generation of HF-emissions. Internal Report, Space Research Institute of the Polish Academy of Sciences. Klos, Z., Zbyszynski, Z., Managadze, G. G., Lyakhov, S. B., Gagua, T. I., Torkar, K. M., Friedrich, M. and Riedler, W. (1988) Some features of RF emissions observed by an electron emitting rocket payload. Adv. Space Res., in press. Kochmarev, L. Yu., Lyakhov, S. B., Mayorov, A. D., Managadze, G. G., Chmil, A. I. and Shustin, E. G. (1985) Uskorenie elektronov v puchkov-plazmennom razradye. Fizika Plasmy 11, 622. Linson, L. M. (1969) Current-voltage characteristic of an electron emitting satellite in the ionosphere. J. geophys. Res. 14, 2368 Linson, L. M. (1982) Charge neutralisation as studied experimentally and theoretically, in Artificial Space Plasma Studies (Edited by Grandal, B.), pp. 573-595. Plenum Press, London/New York. _ Lvakhov. S. B.. Friedrich. M. F.. Klos. Z.. Manazadze. G. -G., Rikdler, W. K., Tdrkar, K. M.‘and Zbyszynski; Z. (1984) Radio observations by the high altitude rocket experiment G60S during electron injection. Internal Report IWF 8405, Austrian Academy of Sciences. Lyakhov, S. B., Mayorov, A. D., Managadze, G. G., Povalyaev, 0. A., Chmil, A. I., Kochmarev, L. Yu., Shustin, E. G., Friedrich, M. F., Riedler, W. K., Laliashvili, A. N., Kiraza. A.. Klos. Z.. Kravchic. Z. and Leonov, N. A. (1985) ‘Laboratory studies for beam plasma experiments with rockets. Planet. Space Sci. 30, 347. Maehlum, B. N. (1983) Ionospheric modification by electron beams. ESA SP-195, 121. I
Maehlum, B. N. (1987) Beam-plasma experiments, in Computer Physics Communications. North Holland, Amsterdam (in press). Managadze, G. G. (1979) Neutralisation process and determination of payload potential during the injection of a powerful electron beam in the experiment ARAKS. Fizika Ptasmy 5, 1100 (in Russian). Managadze, G. G., Gagua, T. I., Lyakhov, S. B., Mayorov, A. D., Martinson, A. A., Riedldr, W. K., Friedrich, M. F.. Leonov. N. A.. Klos. Z. and Laliashvili. A. N. (1983a) Plasma processes caused’by an electron beam injected from a high altitude rocket probe, I. Neutralisation processes. Internal Report IWF 8302, Austrian Academy of Sciences. Managadze, G. G., Gagua, T. I., Nokel, V. P., Burchuladze, A. A. and Shutyayev, I. Yu. (1986) Zavisimost belichini potentziala injektiruyuchego elektroni zonda ot visoti i napravleniya yego poleta (eksperiment “Gruziya-60Spurt”). Preprint IKI, Pr-1148, Moscow. Managadze, G. G. and Lyakhov, S. B. (1979) The effect of altitude, artificial plasma and injection pitch-angle of electrons on the process of neutralisation of payload charge in the ARAKS experiment. Preprint IKI, Pr-471, Moscow (in Russian). Managadze, G. G., Lyakhov, S. B., Balebanov, B. M., Gaba, T. I., Ma&son, A. A., Mayorov, A. D., Friedrich. M. F.. Riedler. W. K.. Klos. Z.. Laliashvili. A. N. and Leonov,‘N. A. (1983b) Plasma processes caused by an electron beam injected from a high altitude rocket probe, II. Studies of beam plasma discharge. Internal Report IWF 8303, Austrian Academy of Sciences. Managadze, G. G., Riedler, W., Balebanov, B. M., Friedrich, M., Gagua, T. I., Klos, Z., Laliashvili, N. A., Leonov, N. A., Lyakhov, S. B., Martinson, A. A. and Mayorov, N. A. (1983~) Plasma processes in the region of electron beam injection from a high-altitude payload. ESA SP-195, 161. Miller, R. B. (1982) An Introduction to the Physics of Intense Charged Particle Beams. Plenum Press, New York. Parker, L. W. and Murphy, B. L. (1967) Potential build-up of an electron emitting ionospheric satellite. J. geophys. Res. 72, 1631. Rawer, K., Ramanakrishnan, S. and Bilitza, D. (1981) International reference ionosphere. World Data Center-A (STP), UAG-81. Sagdeev, R. Z., Managadze, G. G., Mayorov, A. D., Lyakhov. S. B.. Martinson. A. A.. Romanovskv. Yu. A.. Adeishvili, T. ‘G., Leonov, N. A. and Gagua, T. I. ‘(1981) Peculiarities of the environment disturbance during the electron beam injection from the rocket. Adv. Space. Res. 1, 77. Szuszczewicz, E. P. (1985) Controlled electron beam experiments in space and supporting laboratory experiments : a review. J. atmos. terr. Phys. 47, 1189. Torkar, K. M., Friedrich, M., Riedler, W., Lyakhov, S. B., Manaaadze. G. G.. Klos. Z. and Zbvszvnski, Z. (1985) Collection of data obtained from the rocket flight G-60-S. Internal Report IWF 8501, Austrian Academy of Sciences. Winckler, J. R. (1982) The use of artificial electron beams as probes of the distant magnetosphere, in Arttficial Particle Beams in Space Plasma Studies (Edited by Grandal, B.). Plenum Press, New York/London.