Stimulated scattering of man-made E.M. emission from an electron beam injected into ionosphere

Adv. Space Res. Vol. 10. No. 7. pp. (7)151—(7)153. 1990

0273—1177/90 $0.00 + .50 Copyright © 1989 COSPAR

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STIMULATED SCATTERING OF MAN-MADE E.M. EMISSION FROM AN ELECTRON BEAM INJECTED INTO IONOSPHERE Z. Klos,* Z. Zbyszynski,* G. G. Managadze,** N. A. Leonov*** and K. M. Torkart * Space Research Center, Polish Academy of Sciences, ul. Ordona 21, 01-237 Warsaw, Poland * * Space Research Institute, U.S.S.R. Academy of Sciences, Profsoyusnaya 84, 117810 Moscow, U.S.S.R. ***Kiev State University, Kiev, U.S.S.R. tDeparrment of Communications and Wave Propagation, Technical University Graz, !nffeldgasse 12, A—8010 Graz, Austria ABSTRACT On the electron emitting payload Cruaiya.60-Spurt the amplification of the background noise from ground based transmitter was observed during the beam injection. This effect is explained as the stimulated Raman scattering of the incident wave on the electron beam. INTRODUCTION During the high altitude rocket experiment Gruziya-60-SPURT with vertical electron injection 4 = 0.5A, = 6.2KeV on board radio emission measurements were performed with two instruments: the plasma radio spectrometer PRS-1 and high frequency receiver ISKRA covering the frequency range from 0.1.10 MHz and 20-320 MHz, respectively. The electron gun operated with 4.5 sec pauses between 600 rnsee pulses. A sample of the observed emission, related to the rectangular pulse, up to 80 MHz to which frequency signal was not disturbed by telemetric system is presented in Fig. 1. together with the background noises registered in pauses at different altitudes. In these figures the permanent background signal around 72.6 MHz is well manifested.

08

~

‘‘‘‘

260,15 F~:3,10

5~1~jDB

F:0,95 50

50

_______,_~~~_•_,~

0. 0 DB :

50

.~

~

1,60 0

50

OB 50

~

0

0

50

MHZ 213,98

~~~~•N________Q F:1,30

50

0 MHZ 0 ‘3~55~2f0B Fp:4.20E : 50:

,

,,,,.,

50

MHZ 16681 F~=1,15

MHZ 0 50 GRUZIYA-60 -SPURT

MHZ

~

+

,

0

0

M~-1Z

~3~1~flOB

‘‘~

—

50

~

~

Fig. 1. The example of measured spectra by board receiver in the range 20.80 MHz (ISKRA,Db(10~V)) related to the injected rectangular beam pulse and the background emission ( dashed line ) registered in pauses at different altitudes. The backgrond signal around 72.5 MHz is well manifested. (7)15 1

(7)152

Z. Kios

et al.

ELECTRON BEAM EFFECT This background signal, which ISKRA antenna received between electron gun pulses we relate to ground based Radio transmitter. F~onithe observed signal power it was possible to determine signal field strength which is E 0 = 8~iV/cmfor the altitude of 305 km. During the gun pulse the electron beam creates emission up to 80 MHz, as can be seen in Fig. 1.. The intensity and shape of the generated spectrum strongly depends on the altitude (i.e. the ionospheric electron plasma density) /2,3/ .In the cases when the beam generated emission is shifted to lower frequencies (i.e. at 306 km of altitude) the enhancement of intensity around the 72.5 MHz is well separated. It can be seen that during the beam pulse, this signal emission is amplified, and shifted down The additional voltage which is created on the receiver input impedance is 6(U~— Un)] ~ 35D6(lOpV) AU = 201og(10 which is shown in Fig. 2.. So we can conclude that the ground based emission which reaches the payload during the beam pulse is locally amplified.

DB

1511,5608

so

~~0,95

0_: o’’’ DB

‘sb

‘

50

50

MHZ ~ 1361,72 DB

~

0o~

‘

F~:3.10 50

‘

50

MHZ

~0’’

~HZ

MHZ 213,98

~~:1,30 ‘

‘sb’

305,42 :08 F~_4.20 ‘‘~0’’’

‘

‘‘‘‘‘‘

SO

OB

00

‘

260,15

‘

MHZ

166,51 F~:1,15 00

50

M~Z

GRUZIYA-60-SPURT

Fig. 2. The difference between emission related to the beam and background expressed as AU = 20Iog[105(U~ — Un)] MODEL CALCULATION Looking for the physics of this amplification process it seems that stimulated scattering phenomena can serve as a good explanation of this effect. Stimulated scattering of electromagnetic wave by an electron beam was widely considered in literature /1/. In this process the interaction of electrons with the electromagnetic pump wave (WO, k

0)

as well as with electromagnetic scattered wave (i.,,, k8) is unstable. The source of this instabilitie, is related to the ponderomotive force which results in the beam frame as the interaction of the moving electron under the electric field component of incident wave V0 = cEo/mwo with the magnetic component of the scaterred wave Vo x B,. The created low frequency density modulation (w , k) of the beam electrons, as well as scattered wave can grow exponentially. In our experiment when we have the beam parcticles coming back to the payload as well as the injected beam, we have the situation in which the incident wave vector is parallel or antiparallel to the beam velocity. The wave parameters in the beam frame (denoted by prime) and those in the antennapayload system are related as: =w~~ ±V6k0 =~,j,

where, V6

.

the beam velocity.

Stimulated Scattering by Electron Beam Injection

(7)153

We have, too w

0 = ck0 (as ionospheric plasma influence at 70 MHz is not important) and: ±WI

WI, =

hI, = hI, ±il So for frequencies of scattered signal we have the relation. =

tiio(1 ±~i)2 ±

=

4.6 io~cm 3 s~ l4Oircm MHz io~ 4.2 m

In our experiment V6

(Jo = = =

so the thermalisation of the beam not far from the payload is weak ( V 6. where Wp6 . beam plasma frequency. Thus we can expect that mode of the beam 6 >V~ ) and the basic oscillation occurs with w = Wp )‘o > )~o= Vtô/w~ and we have stimulated Rainan scattering process. In that case the instability growth rate, i.e. Raman growth rate

is /1/: —

~

Eo(wI,w~~)~I~ (cw 0)

As for the injected beam f,b

=

27 MHz so for frequencies of scattered signal we find:

for k0 * V6 <0 181 = 68.7 MHz

and

/82

183 = 25.2 MHz

and

f,~=

and for k0 * Vb > 0

=

122.7 MHz 79.2 MHz

Thus in our observation at 305 km of altitude in the range of 20. 80 MHz the frequency f,1 = 68.7 is that at which the enhancement of scattered signal during the beam injection is observed. For this frequency we have FR = 0.1 sec~. The electron beam oscillations and scattered wave fields will grow up to the saturating mechanism switch on. In the case of the Raman scattering that is thermalisation of the beam (Vgô = w /k) which is realized by the beam electron trapping into the potential well of the oscillating field. That is a fluctuation field of the excited beam, that creates a negative a-c power, which is supplied by the kinetic energy of the beam. This negative a-c energy must in turn be converted into electromagnetic energy flow in order to maintain power conservation (as in the travelling-wave tube). As PR <