A short cylindrical antenna as a diagnostic probe for measuring collision frequencies in a collision-dominated non-Maxwellian plasma

Abstract

o t t a n d B. R a m a R a o S c i e n t i f i c R e p o r t No. 3 M a r c h 1969P r e p a r e d u n d e r G r a n t NGR 2 2 -0 0 7 -0 5 6 D i v i s i o n of E n g i n e e r i n g a n d A p p l i e d P h y s i c s H a r v a r d U n i v e r s i t y , C a m b r i d g e , M a s s a c h u s e t t s Investigations have been m a d e to d e t e r m i n e the effects of i n t e rp a r t i c l e collisions on t h e a n t i r e s o n a n t impedance c h a r a c t e r i s t i c s of a n e l e c t r i c a l l y s h o r t , c y l i n d r i c a l antenna in t h e vicinity of t h e p l a s m a f r equency of a n i s o t r o p i c non-Maxwellian p l a s m a , T h e dependence of t h e e l e c t r o n -n e u t r a l collision f r e q u e n c y on t h e e l e c t r o n e n e r g y h a s been t a k e n into account, T h e e x p e r i m e n t a l r e s u l t s have been c o m p a r e d with 1 2 t h e t h e o r i e s p r o p o s e d by King e t al. and Balmain.T h e u s e of t h i s antenna a s a diagnostic p r o b e f o r m e a s u r i n g e l e c t r o n -n e u t r a l collision f r e q u e n c y and e l e c t r o n density has b e e n investigated. E l e c t r o n -n e u t r a l collision f r e q u e n c i e s f o r H e l i u m m e a s u r e d by t h i s technique a r e i n good a g r e e m e n t with t h e o r e t i c a l r e s u l t s calculated f r o m t h e collision c r o s ss e c t i o n d a t a of Golden and Bandel, 3

Measurement of the impedance of a linear antenna in a magnetoplasma

“…(i) We assume that the electron temperature is equal to zero; this allows the use of the cold plasma model, which may be a good approximation for the input impedance under collision dominated conditions. As mentioned in section 4, the effective collision frequency obtained by using the curve fitting technique [Scott and Rao, 1969;Bhat and Rao, 1973] is rather large in the present experiments.…”

Effective coffision frequency and electron temperature in a weakly ionized argon plasma

“…According to Frost & Phelps (1964), Golden & Bandel (1965), Molmud (1959) and Scott & Rao (1969), the hard-sphere model is especially suited to a helium plasma, whose thermally averaged momentum exchange cross-section q is nearly constant over the temperature range of interest, 3000 °K < T e < 10000 °K. With constant cross-section q, the thermally averaged collision frequency V depends linearly on the relative velocity v r between the interacting particles.…”