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.