Negative Ion Density Fronts

Kaganovich, Igor

Princeton University. Plasma Physics Laboratory.

关键词: 70 Plasma Physics And Fusion Technology;    Anions;    Ion Density;    Ion Temperature;    Ignition;   

DOI  :  10.2172/772280
RP-ID  :  PPPL-3529
RP-ID  :  AC02-76CH03073
RP-ID  :  772280

美国|英语

来源: UNT Digital Library

【 摘 要 】

Negative ions tend to stratify in electronegative plasmas with hot electrons (electron temperature Te much larger than ion temperature Ti, Te > Ti ). The boundary separating a plasma containing negative ions, and a plasma, without negative ions, is usually thin, so that the negative ion density falls rapidly to zero-forming a negative ion density front. We review theoretical, experimental and numerical results giving the spatio-temporal evolution of negative ion density fronts during plasma ignition, the steady state, and extinction (afterglow). During plasma ignition, negative ion fronts are the result of the break of smooth plasma density profiles during nonlinear convection. In a steady-state plasma, the fronts are boundary layers with steepening of ion density profiles due to nonlinear convection also. But during plasma extinction, the ion fronts are of a completely different nature. Negative ions diffuse freely in the plasma core (no convection), whereas the negative ion front propagates towards the chamber walls with a nearly constant velocity. The concept of fronts turns out to be very effective in analysis of plasma density profile evolution in strongly non-isothermal plasmas.