Volume production of D- negative ions in low-pressure D-2 plasmas- negative ion densities versus plasma parameters

摘要

Pure volume production of D- negative ions is studied in a rectangular arc chamber. Production and control of D-2 plasmas are tested by varying the intensity of the magnetic filter ME The values of electron temperature T-e and electron density n(e) in D-2 plasmas are slightly higher than those in H-2 plasmas. T-e in D-2 plasmas cannot be decreased below 1 eV in the extraction region with the same MF conditions for optimizing H2 plasmas. A stronger MF field is required for controlling T-e in D-2 plasmas. Therefore, the transport in or the production of H2 and D2 plasmas is different, i.e. there is an isotope effect, a consequence of which is that the H- and D- densities have different spatial distributions. Extracted H- and D- currents are primarily determined by H- and D- densities in front of the extraction hole, respectively. According to the estimated rate coefficients and collision frequencies of main collision processes, it is reconfirmed that T-e in the extraction region should be maintained below 1 eV with n(e) kept high for the enhancement of H- and D- production. For the enhancement of D- production, preliminary results on VUV emission measurement are presented and discussed briefly.