Development of an advanced ‘‘volume’’ H− source for neutral beam application

Abstract

Based on recent experimental results made on the large and small multicusp volume H− sources, a new multicusp source has been designed to generate high-brightness H− or D− beams for high duty factor or dc operations. Cesium will be introduced into the source plasma to enhance the H− output current. Arrangements for reducing the electrons as well as capturing them in the preaccelerator electrodes will be incorporated into the new source geometry.

A small radius hydrogen discharge: An effective source of volume produced negative ions

“…However, the rf source in its present design of a large-scale two-chamber source does not ensure efficiency high enough for volume production of the ions, and currently it is considered as a source with surface production of the ions. [2][3][4] The design of the rf sources of negative hydrogen ions is based on the experience accumulated during many years of work on the dc filament sources [5][6][7][8][9][10][11][12][13][14] starting in the 1980s, the time when the idea for the tandem type of the source arouse. The idea is for a design that ensures spatial separation in the source of two regions, respectively, of high-and low electron temperature, and it originates from the conclusion that such a design provides conditions favoring the two-step reaction of the volume production of the negative ions: excitation of the molecules to highly vibrationally excited states that requires high-energetic electrons and production of negative ions via dissociative attachment of electrons to the vibrationally excited molecules that requires low-energetic electrons.…”

Magnetic filter operation in hydrogen plasmas

“…The magnetic filter is a localized transverse magnetic field. Its effect for cooling the electrons has been proved both experimentally [3,6,7,13,[20][21][22][23][24][25][26], by probe diagnostics and measurements of the current density of the extracted negative ions, and theoretically [6-12, 15, 27] by modelling and discussions on the mechanisms governing the operation of the filter. The fluid-plasma models [6][7][8][9][10]15] of the magnetic filter involve the importance of the transport processes.…”

Negative hydrogen ion maintenance in small radius discharges: Two-dimensional modeling

“…The idea is that the region of high-electron temperature favors the vibrational excitation of the hydrogen molecules, whereas the region of low-electron temperature supports high concentration of negative ions produced via dissociative attachment of electrons to vibrationally excited molecules. Such a concept stems from early studies on dc discharge sources [13][14][15][16][17][18][19][20][21] and it is based on an assumption for locality in the discharge behavior which in dc discharges is fulfilled, at least, in the longitudinal direction. However, the recent development of the concept toward construction of the tandem source as a big-size two-chamber rf driven source 22 failed with regard to the volume production of the ions.…”