Prospects for light amplification in the far ultraviolet (review)

Abstract

A Monte Carlo model solving only in velocity space is proposed to investigate a low recycling scrape-off layer (SOL) plasma. In the model, the effects of Coulomb collisions are accurately described by a non-linear Monte Carlo collision operator; a conductive heat flux into the SOL is effectively modelled via randomly exchanging the source particles and the SOL particles; secondary electrons are included. A steady state SOL plasma, which satisfies the particle and energy balances and the neutrality constraint, is determined in terms of the total particle and heat fluxes across the separatrix, the edge plasma temperature, the secondary electron emission coefficient and the SOL size. The model gives gross features of the SOL, such a~ plasma temperatures and densities, the total sheath potential drop and the sheath energy transmission factor. Simulations neglecting unlike collisions are performed. It is found that the potential drop and the electron energy transmission factor in collisional SOL plasmas are in close agreement with theoretical predictions. The present model primarily provides useful information about collisionless SOL plasmas that is difficult to obtain analytically.

Kinetics of charge-exchange interaction of dense flows

“…Later, the empirical limitations used turned out to be overestimated by several orders of magnitude. For example, the maximum ion flow that can effectively exchange charge with neutral particles Jmax = niV/ = 3 9 10 is cm -2 9 sec -t [4] is three orders of magnitude smaller than the one obtained in [5] Jexp = nil// = 3-1021 cm -2 9 sec -1. The limitation on the charge-exchange length (Lp/Vi > 10 -7 sec), related to development of possible instabilities, was overestimated by two orders of magnitude.…”

“…In view of the exponential dependence of the value of ~? on N ~ and N ~ for dense flows, the maximum charge-exchange rate (at a specified time) is at the point of maximum interpenetration, which, according to (4), is determined by the condition N ~ = N ~ For the coordinate of this point, we obtain the expression…”

“…The problem is to determine the dynamics and properties of tim region of intense interpenetration of flows (usually, a flow of highly charged ions moving through a medium of neutral particles). The only estimates were obtained by Bunkin et al [4]. It was shown that the maximum effectiveness of mixing does not exceed 25% and is reactmd at half concentrations of the reagents, and the structure of the interaction region is determined not only by the structures of the fronts but also by the charge-exchange length.…”

The 4d–4p transitions and soft X-ray laser wavelengths in Si-like ions

“…Most of the proposed schemes have relied on high-power visible lasers to produce the high temperature and high density required to produce population inversion against short radiative lifetimes [1,2]. In spite of the tremendous progress in the development of X-ray lasers over the last years, only two pumping mechanisms, collisional excitation and recombination, have been used to create gain and produce laser output [3].…”

Table-top Soft X-Ray Lasers

“…The recombination rate is also extremely sensitive to the electron temperature R 3br ϰT e Ϫ4.5 . 157 Therefore, the generation of large population inversion by recombination requires a dense and relatively cold plasma.…”