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

•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/m2 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.