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Description
A Large Volume Surface Plasma Source with a converter for the Los Alamos linear accelerator was developed. A large gas-discharge chamber with a multipole magnetic wall and 2 heated cathodes can support a discharge generating a plasma. A cooled converter with a diameter of 5 cm and a potential of up to -300 V emits negative ions, accelerates them and focuses in an emission aperture with a diameter of 6.4 mm. From this SPS, up to 18 mA of H- ions are extracted at a duty cycle of up to 10%.
For dependence of an extracted H- beam current on the discharge current is typical a strong saturation through H- destruction in thick layer of discharge plasma. The H- beam intensity and H- generation efficiency can be increased by decrease of plasma layer thickness between converter surface and emission aperture. It is possible to improve beam characteristics by small modification of this converted SPS. It is proposed to used a thin Penning discharge in front of the converter. Magnetic field for Penning discharge is created by permanent magnets. Decrease of plasma end gas between converter and emission aperture can decrease H- beam loss and increase an extracted beam intensity up to 2 times.
