Performance characteristics of a circular multicusp neutral beam source

The performance of the Heliotron-E neutral beam system, composed of intense cylindrical magnetic multipole bucket sources and beam line facilities, has been investigated. The investigation of the influence of the filament shape on the arc discharge stability shows that a wide-hairpin shaped filament results in more stable arc discharge without increasing the arc voltage than does a narrow-hairpin filament. An electrolytic polishing process has been tested for surface treatment of the Molybdenum grid and found to be very effective in reducing the number of conditioning shots. Beam extraction experiments show that a single bucket source can deliver the total beam current of 35 A at the accelerating voltage of 30 kV with the corresponding power transmission efficiency of more than 85% at the focal point of the grid curvature, the minimum beam divergence is less than 1.15° and the proton yield of the source is above 85%. Measurements of the equivalent gas line density in the neutralizer cell suggest the existence of the gas flow process different from a standard vacuum model.