Improvement in the RF Capture by Using Nonsinusoidal Accelerating Voltages

In order to improve the RF capture in PPA, calculations and experiments have been perfarmed with higher harmonic terms added to the accelerating voltage. Computer calculations of the synchrotron phase space acceptance, using the phase potential, have shown that by adding the second harmonic it should be possible to increase the acceptance of PPA at capture by a factor of 2. Since in PPA the acceptance increases with energy, second harmonic needs to be added only during the first part of the acceleration and a suitable voltage program for the RF has been calculated. Initial experiments with the second harmonic added during the first 300 microseconds of the acceleration cycle showed an intensity gain in excess of 50%. Although only described for PPA, the method can easily be adapted to other machines.