Experiment VARIANT – first results from Wave Probe instrument

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Advances in Space Research 43 (2009) 1904–1909 www.elsevier.com/locate/asr

Experiment VARIANT – first results from Wave Probe instrument Fedir Dudkin a, Valery Korepanov a,*, Georgiy Lizunov b a

Lviv Centre of Institute of Space Research, Laboratory for EM Investigations, 5-A Naukova Street, Lviv 79000, Ukraine b Institute of Space Research, 40, Glushkova Avenue, Kyiv 03680, Ukraine Received 30 October 2007; accepted 22 March 2009

Abstract The international experiment VARIANT was carried out onboard Ukrainian remote sensing satellite SICH-1M launched 2004, December 24. In spite of other than planned satellite orbit and onboard systems failure about 11 telemetric files from VARIANT payload were obtained. Due to episodic and random payload switching the main goal of VARIANT experiment - study of field aligned currents and monitoring of electromagnetic state of the ionosphere – was not possible to realize. However the data analysis from VARIANT instrumentation allowed us to obtain for the first time a reliable confirmation of proper operation in ionospheric plasma of a new device developed for wave activity study – Wave Probe, which consists of compact combination of Split Langmuir Probe working at floating potential and search-coil magnetic field sensor. Such a probe can simultaneously measure variations of one component of spatial current density and a perpendicular component of magnetic field with a spectral sensitivity threshold up to 0.1 pA/(cm2 Hz1/2) and 0.03 pT/Hz1/2, respectively. Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Wave Probe; Current density; Split Langmuir Probe

1. Introduction The international experiment VARIANT (Korepanov et al., 2000) onboard the Ukrainian remote sensing satellite SICH-1M was launched December 24, 2004. Due to the malfunction of the third stage of the launcher instead of supposed circular polar orbit with 650 km altitude, the satellite got elliptic one with apogee about 600 km, perigee 280 km and inclination 83 degrees. Because of so low perigee the available attitude control means appeared to be not efficient and as a result the satellite tumbled around its axis with angular speed about 0.007 degrees of arc per second. Such onboard conditions made impossible the operation of the main satellite payload – remote sensing instrumentation. But low-power piggy-back scientific payload of VARIANT experiment appeared to be in good operation state and, in spite of power supply problem and data processing *

Corresponding author. Tel.: +380 322 639163. E-mail address: [email protected] (V. Korepanov).

complications in rotating reference frame, the telemetric information was reduced to the real values of measured physical parameters. The satellite rotation also complicated additionally the situation creating problem for data transmission to the ground station. In May 2005 due to the on-board battery discharge the satellite ceased its active operation. Unfortunately, due to episodic and random switching of VARIANT payload, the main scientific goals of this project – study of field-aligned currents and monitoring of ionospheric disturbances – appeared not possible to realize. But big enough amount of information collected from sensors allows us to obtain for the first time a reliable confirmation of proper operation in ionospheric plasma of a new device developed for wave activity study – Wave Probe (WP), which consists of Split Langmuir Probe (SLP) working at floating potential and search-coil magnetic field sensor. Combination of such probes in one compact device gives possibility of wave vector simple calculation and obtaining of dispersion relations for wave processes in space plasmas (Korepanov and Dudkin, 1999a,b).

0273-1177/$36.00 Ó 2009 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2009.03.018

F. Dudkin et al. / Advances in Space Research 43 (2009) 1904–1909

Here the analysis of multi-components measurements executed during VARIANT experiment is made in order to prove that WP gave credible results.

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(Korepanov and Dudkin, 1999a) that he signal at amplifier input can be expressed in the form U ¼ KJ ;

ð1Þ

where 2. WP operation principle 2.1. Description of SLP

ð2Þ

K ¼ K 0K 1K 2 is transfer factor, K 0 ¼ SR;

The first SLP design consisted of two conducting plates separated by a thin insulator. The plates were simultaneously swept from negative to positive potentials with respect to the plasma. It was tested for the first time during rocket flight (up to height about 300 km) in 1968 (Bering et al., 1973a,b; Bering and Moser, 1975). SLP has been developed to obtain in situ information about plasma’s current density, bulk flow, electron temperature and density by measuring the current to each plate and the difference current between them. Unfortunately such a design has some principal shortcomings which lead to low sensitivity of SLP in space plasma experiments. The errors of measurements appeared to be very sensitive to plate area differences, plate work function differences, input parameters of preamplifier differences, and probe wake effects. Additionally the sweep voltage of sawtooth waveform applied to the probe created the wideband noise. Such multiple problems probably were the cause why researchers refused this device. More successful version of SLP application for current density measurements in space plasma was proposed later (Vaisberg et al., 1989), which operated only at floating potential in AC frequency range. However, its construction was not enough compact, what is important for combined wave analysis, and the matching with plasma medium was not substantiated good enough. So such measurements gave only qualitative assessments. These shortcomings were overcame in new WP designing (Korepanov and Dudkin, 1996). In the last case the SLP plates of half-cylindrical shape are placed on the body of magnetic field sensor (Fig. 1) and are shunted by resistor R of specified value to obtain the direct proportion between measuring current J and voltage at matching amplifier input U (and not the dependence of U against electric field E). It was shown

Fig. 1. Wave Probe with input amplifiers circuits.

ð3Þ

S is a cross-section area of SLP plate, K 1 ¼ 1=ð1 þ RðY þ Y a ÞÞ

ð4Þ

Y ¼ 1=ðZ e1 þ Z e2 Þ;

ð5Þ

Zei is impedance of SLP plate, i = 1, 2, Ya is an equivalent admittance of amplifier input circuits, K2 is normalized transfer factor of amplifier input circuits (depends on design). We give below a more exact estimation of SLP transfer function K unlike (Vaisberg et al., 1989; Korepanov and Dudkin, 1999b, 2003), taking additionally into account the plasma sheath admittance. In the case of long half-cylindrical plates of WP we can use an elongated ellipsoid approximation (Wait, 1982): 1

Z ei ¼ ð2pcrs Þ ðQðg0 Þ þ ðrs =r  1ÞQðge ÞÞ;

ð6Þ

QðgÞ ¼ lnððg þ 1Þ=ðg  1ÞÞ; 2 0.5

ð7Þ 2 0.5

2

2 0.5

g0 = (1  (a/b) ) , ge = (1  (ae/be) ) , c = (b  a ) , a, b are the minor and major half-axes of ellipsoid, ae = a + s, be = b + s, s is a plasma sheath thickness. For elongated ellipsoid, when be/ae  1, we may accept b = be = c, a is the radius of SLP electrode, L = 2b is the SLP electrode length, 1

Z ei ¼ ð2pLrs Þ ðlnðae =aÞ þ ðrs =rÞ lnðL=ae ÞÞ

ð8Þ

where rs and r are the complex conductivities of plasma sheath and ionospheric plasma, rs ¼ Y s ðf ÞkD =S

ð9Þ

2

kD = (e0jTe/(e ne)) is the electron Debye radius, e0 is absolute dielectric constant of free space, j is Boltzmann

Fig. 2. SLP normalized transfer factor frequency response: (a) |K/K0|; (b) Arg(K/K0) (in degrees).

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constant, Te is electron temperature, e and ne are electron charge and concentration, Ys( f ) is sheath admittance at plasma floating potential. For s  a in Maxwellian plasma without magnetic field Ys( f ) = Yre + jYim (Crawford and Mlodnosky, 1964), where Y re ¼ Se0 u=k2D ; Y im ¼ xC s

ð10Þ

u is the satellite speed, x is angular frequency of current, Cs is SLP electrode sheath capacity, 0:5

0:5

C s ¼ ðSe0 =kD Þð2 lnðu1 ðkT e =ð2pme ÞÞ ÞÞ :

ð11Þ

For non-magnetized plasma approximation r can be written in the form (Swift and Schwar, 1970): r ¼ rre þ jrim ;

ð12Þ

Fig. 3. Magnetic sensor noise.

where rre ¼ ne e2 m= me ðx2 þ m2 Þ 2


2

ð13Þ 2





rim ¼ x e0  ne e = me ðx þ m Þ ;

ð14Þ

m is electron-ion collision frequency, me is electron mass. The normalized SLP amplitude-frequency response (K/K0) calculated for ionospheric plasma at the heights 300–400 km (these of VARIANT experiment is shown in Fig. 2, where curve a is the modulus of the complex function K/K0 and curve b is the argument of K/K0 (in degrees), for the frequency range 1 Hz–15 kHz where the measurements with WP and double Langmuir probe were made in this experiment. For this case Y a ¼ jxC þ 0:5B B ¼ Ra =D; D¼

ð15Þ



1

a11  a12 þ j xs1 a11 þ ðxs2 Þ 1 þ 2a12 þ a212 þ ðxs2 Þ

K 2 ¼ D=ð1 þ jxs1 Þ

2

ð16Þ

 ;

ð17Þ ð18Þ

where C = 3.6 nF is shunt capacitor (in parallel with the measuring resistor R of value 860 X that is chosen for SLP maximum sensitivity at given frequency range), s1 = 1.44  105 s, s2 = 0.36 s are the time constants of amplifier input circuits, a11 = (s1 + s2)/s2, a12 = s1/s2, Ra = 3.6  106 X is amplifier input resistance (see Fig. 1). Proposed design allows avoiding specific problems inherent to early used SLP versions: – no influence of plate area differences because the same current flows between plates and creates a voltage drop proportional to the flowing current and the value of resistor which connects the SLP plates, – no essential influence of work function differences, input parameters differences of preamplifier, and probe wake effects because of both plates are practically at the same potential (value of measuring resistor is small enough). For example, at maximal expected current density 104 pA/cm2 potential difference between SLP plates will be less than 0.7 mV.

The sensitivity threshold of SLP is determined by the factor K0 = SR and input amplifier noise. For WP design S = 77 cm2, so K0  6.6  104 V/(A/cm2) = 66 nV/(pA/ cm2). For amplifier spectral noise density about 9 nV/ Hz0.5 (amplifier model AD620) the spectral sensitivity threshold of SLP will be about 0.14 pA/(cm2 Hz1/2). Such a sensitivity was confirmed during VARIANT experiment (see Section 3, Fig. 4). 2.2. Description of magnetic sensor Search-coil magnetic sensor was designed using developed calculation method (Korepanov and Berkman, 1999) as a part of WP (Fig. 1). Its noise level frequency response is shown in Fig. 3. At frequency 1 kHz noise level is minimal and equals to 0.03 pT/Hz1/2. The magnetic sensor transfer function is flat in working frequency range 1 Hz–15 kHz. The flight data confirmed high sensitivity and low noise of this sensor (see Section 3). 3. Case study: whistler multi-component measurements analysis The determination of dispersion relations for the wave, propagating in space plasmas is an important task of electromagnetic measurements onboard satellites. By this the major problem is to separate the spatial and temporal variations of electromagnetic fields. The solution of this problem, as well as of the measurement of wave vector ~ k ¼~ kðx0 Þ and wave frequency in the resting frame x = x0 + kxVs was proposed by means of simultaneous measurements of components of electric and magnetic fields and current density in space (Vaisberg, 1985; Romanov et al., 1990; Krasnosselskikh et al., 1991; Santolik and Parrot, 1998). During the VARIANT payload operation a set of multi-component registrations of electronic whistlers was obtained. Whistler-like signals suit well for the verification of WP operation by many reasons. First, they have high phase velocity x=k  u, so Doppler effect is negligible. Second, dispersion relations for whistler with

F. Dudkin et al. / Advances in Space Research 43 (2009) 1904–1909

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Fig. 4. Dynamic spectra (a) and waveforms (b) of measured signals.

frequency x allows simple enough calculation of wave number k. Necessary plasma parameters can be taken from the known model of ionosphere. From the other hand, spectral parameters fx; ~ kg may be obtained with the help of Maxwell equation from the amplitudes of fields and curBx ; ~ jx g induced by whistler in space plasma. rents f~ Ex ; ~ Starting from these considerations, the attempt was made to compare the whistler parameters, found by both these ways. If obtained results will be close enough, this will mean the WP proper operating.

Starting from these considerations, the attempt was made to compare the whistler parameters, found by both these ways. If obtained results will be close enough, this will mean the WP proper operating. As an example, we selected the whistler signal received at orbit 1363 over the Horn of Africa region during thunderstorm (March, 23, UT 22:13:35, latitude 13.09, longitude 48.11, height 340.8 km), which was observed simultaneously in channels of double Langmuir probe (EZ component of electric field) and WP (BX component

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of magnetic field, JZ component of current density). The transfer function of EZ-channel is flat in frequency range 1 Hz–15 kHz. The dynamic spectra of these signals are given in Fig. 4a, and corresponding waveforms are shown in Fig. 4b. The measured signals amplitudes for the moment t = 33.7 s filtered at frequency f = 4 kHz are given below: frequency f = 4000 Hz magnetic field BY = 30 pT

electric field EZ = 80 lV/m, electric current density JZ = 30 pA/cm2

As it can be estimated from Fig. 4a, the whistler propagated quasi-longitudinally, at least not very oblique, what allows accepting the angle u between wave vector and magnetic field close to zero and hence cos u  1. Then the dispersion equation for whistler at x  xc can be written as: x¼

xc 2 2 xc c k cos u  2 c2 k 2 ; 2 xp xp

ð19Þ

where xp is Langmuir frequency and xc – electron cyclotron frequency. Their values for the given point in ionosphere are taken from the ionosphere model MSIS-90: xp  3  107 s1; xc  5  106 s1. Then for the selected f = 4 kHz the refraction factor n and wavelength k for the whistler were calculated: ck  85; k ¼ 890 m: ð20Þ x Now let us find the same dispersion characteristics from the available data of current and fields measurements. It is known that longitudinally propagating whistler is a circular right-polarized wave, where the vectors of electric and magnetic fields and current are rotating with frequency x in the plane perpendicular to wave vector. For such a whistler wave the relations between amplitudes of corresponding fields and currents harmonics are described by Maxwell equations:

n¼

1 ~ n~ Ex ; Bx ¼ ~ c ~ J x ¼ ie0 x n2~ Ex ;

ð21Þ ð22Þ

where ~ n ¼ c~ k=x. Taking the signals amplitudes at the frequency f = 4 kHz given above, we calculated from Eq. (21): n¼c

B ¼ 110; E

k ¼ 660 m:

ð23Þ

The comparison of calculated results from Eq. (20) and experimental ones from Eq. (23) gives rather good similarity. Moreover, when we calculate current density using Eq. (22), it gives J = 23 pA/cm2, what is very close to the value J = 30 pA/cm2 measured by SLP (see above). These rough estimations confirm our statement about WP proper operation.

4. Conclusion The dispersion relations are very important for the wave activity study in space plasmas. One of the most effective methods for their analysis is the simultaneous measurement in situ of spatial current density and magnetic field fluctuations during wave processes. Basing on the presented results obtained in frames of experiment VARIANT, we may conclude that the newly developed combined sensor Wave Probe can be used for the measurements of mentioned EM parameters with very high sensitivity in wide frequency range. Such a probe may be effectively used for waves spectral composition restoring. This allows us to propose the Wave Probe for nearest planned space missions (OBSTANOVKA, RADIOASTRON, IONOSAT). Acknowledgements The authors are very grateful to Forrest Moser for fruitful discussion and help with coating and to Stas Klimov for attention to presented results. This work was supported by NSAU contracts 1-02/03, 1-05/03. References Bering, E.A., Kelley, M.C., Moser, F.S. Split Langmuir probe measurements of current density and electric fields in an aurora. J. Geophys. Res. 78 (13), 2201–2213, 1973a. Bering, E.A., Kelley, M.C., Moser, F.S., Fahleson, U.V. Theory and operation of the split Langmuire probe. Planet Space Sci. 21 (11), 1983–2001, 1973b. Bering, E.A., Moser, F.S. A measurement of perpendicular current density in an aurora. J. Geophys. Res. 80 (18), 3961–3972, 1975. Crawford, F.W., Mlodnosky, R.F. Langmuir probe response to periodic waveforms. J. Geophys. Res. 69 (13), 2765–2773, 1964. Korepanov, V., Berkman, R. New approach to the exact design of low noise search-coil magnetometers, XIV IMEKO Word Congress. New measurements – challenges and visions, Tampere, Finland, 1997, vol. IVA. Topic 4, pp. 103–108, 1999. Korepanov, V., Dudkin, F. Combined wave probe for space plasma investigations – theory and first application result (Abstract), 25th General Assembly of the URSI, Lille, France, August 28–September 5, 1996, p. 500, 1996. Korepanov, V., Dudkin, F. Comparative analysis of current density meters operating in space plasmas. Adv. Space Res. 23 (8), 1541–1544, 1999a. Korepanov, V., Dudkin, F. Three independent techniques to study spatial current density. Small Satellites for Earth Observation, Digest of the 2nd Int. Symp. of the Int. Academy of Astronautics, Berlin, April 12– 16, 1999, pp. 235–238, 1999b. Korepanov, V.E., Dudkin, F.L. In-flight characterization of satellite electromagnetic sensors. Adv. Space Res. 32 (11), 2329–2334, 2003. Korepanov, V., Negoda, O., Lizunov, G., Alleyne, H., Balikhin, M., Blecky, J., Dudkin, F., Fedorov, A., Juchniewicz, J., Klimov, S., Krasnosselskikh, V., Lefeuvre, F. Project VARIANT: current and field measurements on board SICH-1M satellite. Adv. Space Res. 25 (7–8), 1337–1342, 2000. Krasnosselskikh, V.V., Natanzon, A.M., Reznikov, A.E., Schyokotov, A.Yu., Klimov, S.I., Kruglyi, A.E., Woolliscroft, L.J.C. Current measurements in space plasmas and the problem of separating between spatial and temporal variations in the field of a plane electromagnetic wave. Adv. Space Res. 11 (9), 37–40, 1991.

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