Pinch reflex ion diodes on the PBFA-I accelerator

The PBFA-I accelerator has been efficiently coupled to two pinch diodes while operating in two different voltage configurations. In both diodes, the electrons from top and bottom cathode rings pinch under the influence of the diode current to the equator of the anode. The anode is a plastic foil through which the electrons can pass repeatedly while pinching, increasing the efficiency of ion production. In the low voltage mode (0.8 mv), which used 18 lines, prepulse was required to turn on the large area, 42 cm diameter anode. Operating in the full 36 line mode, however, increased the voltage to nearly 2 mv, improving diode performance as the accelerator was tuned to optimize simultaneity and remove prepulse. Best results were obtained with a 26 cm diameter focusing diode, which had a central gas cell for neutralized beam transport. With 9 tw coupled to the diode, 3 tw of protons were produced at 1.9 mv. The brightness was seen to be limited by the 2-30 noncorrectable beam divergence