Study on the plasma characteristics in the extraction region of hybrid negative ion source

Abstract

To experimentally investigate the beam optics performance of negative hydrogen ion sources under filament-arc(FA) discharge and radio-frequency (RF) discharge, the NBI group at Southwestern Institute of Physics(SWIP) has designed a negative hydrogen ion source, on which the researchers can independently carry out filament-arc discharge, RF-driven discharge, as well as simultaneous FA-RF hybrid discharge. When the plasma diffuses through the extraction region, the electron energy distribution function(EEDF) and spatial characteristics of the plasma are of primary interest to the researchers. In the SWIP FA-RF hybrid negative hydrogen ion source, a Langmuir probe installed in the extraction region is used to measure the fundamental parameters of the plasma, and the calculation of EEDF follows the Druyvesteyn analysis. Furthermore, the evolution process of plasma parameters in the extraction region during cesium seeding has also been investigated. Experimental results indicate that stochastic heating is the main mechanism for electron heating in the FA-RF hybrid negative hydrogen ion source. Increasing RF power substantially enhances both electron density and electron temperature. However, electron temperature remains unchanged when increasing the arc power. It has been found that the electron density decreases gradually throughout the cesium seeding process, while electron temperature remains relatively stable.