-
Author(s):
Y. Takeiri, A. Ando, O. Kaneko, Y. Oka and T. Kuroda
-
Title:
Negative Ion Extraction Characteristics of a Large Negative Ion Source with Double-Magnetic Filter Configuration
Date of publication:
May 1992
-
Key words:
negative ion source, negative-ion-based NBI, volume production, magnetic filter, double-magnetic filter configuration
-
Abstract:
A multi-ampere hydrogen negative ion source with a large extraction area of 25 cm x 25 cm has been developed. This negative ion source is a volume-production-type bucket ion source which is operated with double-magnetic filter configuration. In this configuration, the fast electrons, which produce the vibrationally excited molecules, are trapped near the chamber wall by the cusp field, which is the first magnetic filter. In the central region of the arc chamber, there exist only the thermal electrons with low temperature. As a result, the negative ions are produced in the central region by dissociative attachment. A rod magnetic filter in front of the plasma grid, which is the second magnetic filter, is utilized for reducing the population of the electrons in the vicinity of the plasma grid, which are extracted together with the negative ions. By this structure the extracted electron current can be controlled independently of the H^- ion current. So far, a 1.4A of H^- ion current has been obtained with the energy of 34 keV. Negative ion extraction characteristics of this ion source, such as the arc power dependence and the gas pressure dependence, are presented.
-
|
