First Beam Extraction Experiment From A Prototype Filament-Arc Driven Negative Ion Source

A prototype negative ion source has been designed and constructed, in order to initialize investigations on physical and engineering problems of a negative ion source which is a key component of a negative-ion-based neutral beam injector. Driven by filament-arc discharge, experiments have been carried out to validate that this ion source is able to produce and extract negative ions. In pure hydrogen discharge without Cesium (Cs), diagnostics by a single Langmuir probe indicates that electron temperate is around 0.5-0.7 eV at the beam extraction region and the strength of the filter field is enough to cool electrons down. By applying extraction and acceleration voltages to the accelerator, beam extraction experiment has been performed. The maximum acceleration current with Cs reaches 1.22 A, corresponding a beam current density of 6.42 mA/cm2. The current ratio of electrons to negative ions is 0.28 - 0.44 depending on the arc power. The arc efficiency is affected by the partial pressure of water, increment in which brings decrement in arc efficiency.