A 30hyphen;kV triode accelerator has been constructed to test the design and operating characteristics of accelerators for negative hydrogen ion beams. Incorporating both a quadrupole electron trap and an octupole electron suppressor, the accelerator has been used to extract, accelerate, and focus Hminus;ion beams of up to current densities of 20 mA cmminus;2. The results suggest that this accelerator design is capable of focusing across a wide range of ion current densities (0ndash;20 mA cmminus;2) and acceleration voltages (15ndash;30 kV) using the variation of a singlehyphen;gap potential to achieve the required focusing. Applying a bias voltage of up to 2 V between the beam forming electrode and the anode of the source suppresses electrons and has allowed accelerator power efficiencies of over 73percnt; to be obtained for all ion current densities up to 20 mA cmminus;2so far extracted. Initial evidence that the extracted and accelerated negative ion beam may be undergoing selfhyphen;focusing is discussed.
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