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Particle orbit optimization in the beam extraction region of a cold cathode PIG negative ion source for electrostatic tandem accelerators

When using a PIG (Penning Ion Gauge) type ion source for production of negative ions, these ions must be extracted from a hole on the side of the anode cylinder, perpendicularly to the magnetic field for plasma confinement. As a result, unnecessary deflection force works on the extracted beam. This study aims to improve the ion extraction efficiency of a cold-cathode PIG negative-ion source. The idea is to reduce the beam loss by cancelling the stray magnetic field from the source by placing small dipole magnets in the extraction electrode. Through the measurement of the magnetic field distribution and beam trajectory calculation, it was numerically confirmed that the beam trajectory can be corrected by this small dipole magnet with a peak magnetic field of about 50 mT under the present experimental condition.