mm high temperature shock tube has been used to produce a uniform plasma. In order to get the attenuation of the electromagnetic wave through the plasma ...
ACTA MECHANICA SINICA, Vol.20, No.3, June 2004 The Chinese Society of Theoretical and Applied Mechanics Chinese Journal of Mechanics Press, Beijing, China Allerton Press, INC., New York, U.S.A.
ISSN 0567-7718
A N I N V E S T I G A T I O N OF E L E C T R O M A G N E T I C WAVE P R O P A G A T I O N IN P L A S M A B Y S H O C K TUBE* ZHU Naiyi (~-7~) t LI X u e f e n ( ~ ) HUANG Lishun (i~) Y U Xilong ( ~ : ~ ) YANG Qiansuo(~t~.)
(Laboratory of High Temperature Gas Dynamics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, China) ABSTRACT: This paper presents the electromagnetic wave propagation characteristics in plasma and the attenuation coefficients of the microwave in terms of the parameters n~, v, w, L, cab. The r m m high t e m p e r a t u r e shock tube has been used to produce a uniform plasma. In order to get the attenuation of the electromagnetic wave through the plasma behind a shock wave, the microwave transmission has been used to measure the relative change of the wave power. The working frequency is f = (2 ~ 35) GHz (ca = 27rf , wave length A = 15 cm ~ 8 mm). The electron density in the plasma is nr = (3 x 10 l~ ~ 1 x 1014 ) c m -3. The collision frequency v ---- (1 x l0 s ~ 6 • 101~)Hz. The thickness of the plasma layer L -----(2 ,.~ 80) cm. The electron circular frequency cab = eBo/m~, magnetic flux density B0 = (0 ~ 0.84)T. The experimental results show t h a t when the plasma layer is thick (such as L/A >_ 10), the correlation between the attenuation coefficients of the electromagnetic waves and the parameters he, v, ca, L determined from the measurements are in good agreement with the theoretical predictions of electromagnetic wave propagations in the uniform infinite plasma. When the plasma layer is thin (such as when both L and A are of the same order), the theoretical results are only in a qualitative agreement with the experimental observations in the present parameter range, but the formula of the electromagnetic wave propagation theory in an uniform infinite plasma can not be used for quantitative computations of the correlation between the attenuation coefficients and the parameters n~, v, ca, L. In fact, if ca < cap, v 2 cap, v 2 _ 10), the cor-
c a n n o t be used for q u a n t i t a t i v e c o m p u t a t i o n s of the correlation b e t w e e n the a t t e n u a t i o n coefficients a n d
r e l a t i o n b e t w e e n the a t t e n u a t i o n coefficients of the e l e c t r o m a g n e t i c waves a n d the p a r a m e t e r s n , , v, w, L
the p a r a m e t e r s n~, v, w, L. I n fact, if w < Wp, v 2 wp, v 2
