A Pulsed Synchrocyclotron Ion Source Using a Single Cold Cathode

During a development program to improve the beam current accepted by the Nevis Synchrocyclotron, a new source using a single cold cathode was developed. The change to a single cold cathode has resulted in a marked improvement in the performance of the source compared to operation as a PIG source with the same chimney and extraction geometry. The extracted H+ current was greater than 90% compared to about 70% for the PIG source, and the vertical emittance was improved by over a factor of 2. Pulsed beam currents of up to 80 mA were extracted from a slit of 1.6 mm by 6.25 mm high. Although the extracted current was less than the current from the PIG source (≈ 150mA), the charge per pulse accepted by the accelerator (as measured by an internal probe at a radius corresponding to 30 MeV) increased from 20 to as high as 100 nanocoulombs/pulse.