Investigation of the composition of an ion beam produced using a multi arc ion source

Complementing the diode and beam transport optimization studies currently performed in FZK/Karlsruhe on the proton-beam-facility PROFA [1,2], side investigations were run at the St. Petersburg State University which focused on ion beam divergence and composition measurements using TOF techniques. To ensure direct transferability of the results to the PROFA facility, these measurements were made on a scaled down replica of the PROF A diode, comprising an array of small polyethylene flash-over plasma sources and a grid extraction system. Presented here are only the results of the beam composition measurements, which allow the following conclusions: (i) The ion beam contains H and C ions and heavier constituents that still have to be identified. (ii) The beam composition changes significantly with the total number of shots: While in the start phase of the experiments H⁺ ions predominated, heavier components outweighed these later on in the experiments, supposedly due to hydrogen depletion of the surface layer of the anode polyethylene units. (iii) Reconditioning of the polyethylene units seems possible by running the diode at higher currents (self cleaning) or by cutting off a surface layer.