plasmas [3,4,5] subject to resonance absorption heating and/or parametric instabi- lities. Second, in ... d i s t r i b u t i o n f(v7 proportional t o exo-(v/v )m with m=5. Dashed s t r a i g h t ... Fokker Planck simulations [15). Above 1/2 M,V~ =.
JOURNAL DE PHYSIQUE, Colloque C6, supplQment au n o 10, Tome 47, octobre 1986
ELECTRON EXCITATION RATES IN NON-MAXWELLIAN PLASMAS
M. LAMOUREUX, P. ALATERRE* and J.P. MATTE* Laboratoire de Spectroscopie Atomique et Ionique, Bdt. 350, Universite Paris-Sud, F-91405 Orsay Cedex, France ' ~ n s t i t u tNational de la Recherche Scientifique-Energie. Universite du Quebec, C.P. 1020, Varennes, Quebec, JOL 2P0, Canada
RdsumQ. Nous 6tudions l'excitation collisionnelle relative 2 des transitions permise et interdites d'ions h6liumoi'des dans deux types de plasmas non-llaxwelliens : plasmas presentant une population suprathermique et plasmas ayant ) ~ taux s'avbrent Btre extr8une distribution d'blectrons en ~ X ~ - ( V / V ~ Les rnement affect& par le caractbre non-Maxwellien pour les valeurs moyennes et Qnerpie du seuil ) . I1 faudrait tenir compte de ce fait prandes deX/kTe et 6ventuellement en tirer partie dans les dtudes de modslisation de l'amplification X rsalisges dans de tels milieux.
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(z:
Abstract. Electron excitation rates relative to allowed and forbidden transitions of He-like ions are evaluated for two current types of non-bTaxwellian plasmas : plasmas witha suprathermal population and plasmas with electron distribution functions of the form e ~ ~ - ( v / v ~ The ) ~ rates are shown to be strongly affected by the non-Maxwellian character for moderate and larpe values of the ratio x/kTe ,%being the threshold enerpy. This should be taken into account and hopefully taken advantage of when modellinp X-ray amplifications in such plasmas.
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1. Introduction. In many natural and laboratory plasmas, the free electrons do not follow a Maxwellian distribution with kinetic temperature Te. First, in an extended group of plasmas, a tail of b(axwel1ian suprathermal electrons has to be affixed to the cold Maxwellian distribution. This situation is found in astrophysical plasmas [I], Z pinch plasmas [2] , tokamak plasmas with runaway electrons as well as in laser plasmas [ 3 , 4 , 5 ] subject to resonance absorption heating and/or parametric instabilities. Second, in another group of plasmas, the distribution is genuinely non-Maxwellian over the whole velocity range and takes the form e~~-(v/v,)~ with 2 < m < 5. This is the case in plasmas perturbed by ion acoustic turbulences [63 and in laser Last plasmas where " classical absorption " is the dominant heating mechanism [7,8]. situation occurs when using short wavelength lasers, as is usually done to curb the generation of suprathermal electrons deleterious from the viewpoint of inertial fusion. Whichever the cause and the nature of the non-Faxwellian character of the plasma, it will affect the properties which predominantly depend on electrons of energies for which the distribution is far from Yaxwellian, that is on electrons energetic in comparison to the average kinetic energy kT e' 2. Calculation of the excited rates for He-Fike ions. We consider electron collisional excitations in He-like ions, one Is electron beinp: brought to a 2s or 2p subshell. We study the allowed transitions ls2 IS +]P
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986608
JOURNAL DE PHYSIQUE
and t h e t h r e e f o r b i d d e n t r a n s i t i o n s + l ~ , 3 ~ 3,s f o r t h e a t o m i c numbers Z= 3 , 6 , 8 , and 14. F o r each e x c i t a t i o n c o n s i d e r e d , we u s e t h e c o l l i s i o n s t r e n g t h o b t a i n e d from a c l o s e c o u p l i n g model (1) [93 and e x p r e s s e d i n a p a r a m e t r i c way. I n t h e f o l l o w i n g ,
Fig.
1
E l e c t r o n d i s t r i b u t i o n f u n c t i o n s f o r two t y p e s o f non-Maxwellian ~ l a s m a sa t t h e ( c o l d ) k i n e t i c t e m p e r a t u r e kTe- S o l i d upper c u r v e : plasma w i t h a s u p r a t h e r m a l ~ o ~ u l a t i o n5 , % of t h e e l e c t r o n s c o r r e s ~ o n d i n gt o t h e hot Dash-dotted lower c u r v e : plasma w i t h t h e e l e c t r o n temperature 8 kT d i s t r i b u t i o n f ( v 7 p r o p o r t i o n a l t o exo-(v/v )m w i t h m=5. Dashed s t r a i g h t m l i n e : r e f e r e n c e Maxwellian c a s e .
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X
i s t h e e x c i t a t i o n t h r e s h o l d e n e r g y , E= 112 M , V ~ t h e i n c i d e n t e l e c t r o n energy and x = E/X t h e reduced energy. The r a t e s amount t o
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