A Small Helium-3 Cyclotron

Abstract

A 27-inch AVF cyclotron of fourfold symmetry designed specifically for use in helium-3 activation analysis is now in operation at the Lawrence Radiation Laboratory in Berkeley. The fixed energy and modest beam quality requirements have resulted in an instrument of minimum size, weight, power consumption, and fabrication costs. New techniques were developed to construct edge-cooled tape-wound magnet coils which are housed inside the vacuum chamber. Other unusual design features include: unit construction dee liners hydraulically pressed to the pole tip contours; two 55° dees-in-valleys operating in pushpull; a removable top yoke assembly which allows complete access to the pole area; a narrow gap with an average spacing of 1.5 inches making possible maximum utilization of the pole diameter for stable orbits. In conjunction with the tape coils, the use of this small gap also results in a magnet of very high efficiency. The cyclotron operates with an average field of 16.6 kG and a grounded-grid triode provides 40 kV dee-to-ground (150 keV/turn). Power is supplied by 220 V, 3-phase service. The magnet requires 17 kW, the HF system uses 17 kW, and the remaining instruments, pumps, and controls use an additional 6 kW. The complete system, including vacuum pumps and power supplies, weighs 10.7 tons and occupies a floor space of 37 × 64 inches.