ENHANCED PRODUCTION OF NEGATIVE-IONS IN LOW-PRESSURE HYDROGEN AND DEUTERIUM DISCHARGES

A new approach to enhance the production of negative ions in low-pressure hydrogen and deuterium discharges is described. The procedure, which requires on-off modulation of the discharge current, is applied to a conventional magnetic multicusp or "bucket" volume negative-ion source. The extracted D- current from a 15-A discharge at a filling pressure of 2.4 mTorr is increased from 0.5 to 2.0 mA/cm2 by discharge-current modulation at 10 kHz and 23% duty cycle. The D- beam current is not significantly modulated ( < 5%). The extracted electron current density and average discharge current are reduced by over a factor of 4. The work is relevant to production of D- beams for neutral-beam injectors.