Effect of argon additive on H− density and temperature in volume negative ion source

Abstract

Various plasma parameters were measured for several hydrogen-argon mixtures in the multicusp H Ϫ ion source Camembert III, equipped with tantalum filaments. The density and the temperature of electrons were measured with the Langmuir probe situated in the center of the source and associated with the photodetachment diagnostics. The two-laser photodetachment diagnostics was used to obtain the temperatures of the two negative ion populations. At low hydrogen pressure ͑0.8 mTorr͒ a small concentration of argon additive enhances the hydrogen negative ion density ͑by approximately 60%͒, it also increases the electron density. The negative ion population fractions having the high-and low-temperature values behave differently when varying the total pressure in pure hydrogen and in hydrogen with argon additive. Several possible explanations of the drastic change of the relative ratio of negative ion populations when the argon fraction is increased, are proposed. Another interesting phenomenon observed during the experiments is the decrease with time of the H Ϫ density in the presence of argon. After adding the argon during the time interval of ϳ1 h the H Ϫ density goes down and finally establishes at a minimum value. The final H Ϫ density is lower than the H Ϫ density in pure hydrogen plasma before adding argon. This ''poisoning'' is discussed in terms of wall production of vibrationally excited H 2 molecules.

Negative hydrogen ion production mechanisms

“…[112][113][114][115][116][117] This concept was earlier predicted by Hiskes et al 118 Several research efforts were made to study the effect on the H À ion density by mixing argon and other inert gases to hydrogen. [119][120][121][122] Work on the performance improvement of large RF driven hydrogen negative ion sources for fusion integrated the idea of mixing argon or other inert gases to hydrogen and was initiated at IPP and described in 1999 by Speth et al 123 In this source, the RF antenna was located near the back plate. It was found that the negative ion yield increased with pressure but saturated with rf power.…”

Experimental study on dynamic effects of H- and D- negative ions in an ECR-plasma source

“…To the best of our knowledge, the most indicative reports on the application of this process are the Refs. [4][5][6][7][8][9], concerning filament-driven sources. More recently, Kado et al [10] proposed a novel and simple method to measure thermal and flow velocities of negative ions by making use of the photodetachment technique in a steady-state linear divertor/edge plasma simulator MAP (material and plasma)-II.…”

New developments in multicusp H− ion sources for high energy accelerators (invited)

“…Systems with higher frequencies have also been used. Electron cyclotron resonance ͑ECR͒ heating 10 with modified standard sources 11,12 and seven small ECR systems 13 in a multicusp source were tested. Microwave sources were used and even tandem combinations of a microwave source with a multicusp source 14 were tried.…”