Negative ion beam extraction in volume mode on the RF negative ion source at ASIPP

Abstract

• A test equipment of RF negative ion source was modified according to the commissioning results of negative ions extraction. • The negative ion beam current density without Cs seeding was increased to 25 A/m 2 at 50 kW RF power. • The extracted H- current tended to be saturated at high RF power, but the co-extracted electron current kept increasing. • The e/H- ratio is monotonously decreased with the rising bias voltage. Hefei utility negative ions test equipment with RF source (HUNTER) has been developed at the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP), in order to study the RF negative ion source for neutral beam injection application. This paper reports on several recent modifications made to HUNTER, including magnetic confining field, magnetic filter field, extraction area, pumping system, RF generator, high voltage power supply. And then, the performance of negative hydrogen ion beam extraction in volume mode without Cs seeding was reviewed and compared to the former commissioning results. The current of extracted negative ions and co-extracted electrons were recorded by the Hall current sensors installed on the electric wires connecting to the extraction grid, and ground grid and calorimeter. A similar extraction experiment from argon plasma verified the effective deflection and absorption of co-extracted electrons on the extraction grid, where the leaking electrons were less than 2%. The characteristic of negative ion beam extraction in volume mode was analyzed in different RF power, extraction voltage, bias voltage. The extracted negative ion density of 25 A/m 2 was achieved and the corresponding ratio of electron and negative ion current I e /I H- was 9.1, with the RF power of 50 kW and the bias voltage of 29 V. The extracted H − current saturated with RF power, while the co-extracted electron current increased. The current experimental results indicated the HUNTER source was operated on a right trace and is ready for the surface mode operation with Cs seeding.