  A large volume surface plasma source (SPS) with a biased converter was
developed for the Los Alamos linear accelerator. A large gas-discharge chamber
with a multipole magnetic wall and 2 heated cathodes can support a discharge
generating plasma. A cooled converter with a diameter of 5 cm and a potential
of up to -300 V bombarded by positive ions and emits secondary 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%. The emitted H- beam current is attenuated through H- destruction in thick
layer of gas and discharge plasma. The H- beam intensity and H- generation
efficiency can be increased by decreasing the gas and plasma layer thickness
between the converter surface and the emission aperture. It is possible to
improve beam characteristics by making a small modification to the converted
SPS. We propose to use a thin Penning discharge in front of the converter. The
magnetic field for the Penning discharge is created by permanent magnets.
Decreasing the plasma end gas layer between the converter and the emission
aperture can decrease the H- beam loss and thus increase the extracted beam
intensity up to 2 times
