Improvement of Velocity Distribution Function Measurement of Hydrogen Atoms in ion Source Discharges

Abstract

The efficiency of negative hydrogen (H-) ion surface production in an ion source should be highly dependent upon the velocity distribution function of neutral atomic hydrogen (H0) striking the plasm grid (PG). A system composed of forming an atom beam, rotating beam chopper, ionizer and pulse count unit has been constructed to measure H0 velocity distribution functions. The background noise due to stagnation of hydrogen gas in the region between the beam formation skimmer and the ion source PG was improved by inserting a flow reflection structure. The short life time of the secondary electron emission detector (SEM) was prolonged by properly setting the hydrogen ion trajectories from the ionizer to the the first dynode of the SEM. The system is running stably to record the velocity distribution function but statistical noise synchronized to the trigger pulse of the chopper must be removed before the measurment of change in H0 velocity distribution functions dependin upon the type of discharge.