Universal electronic phaseshifter

Future time-sharing operation of the UNILAC for low energy experiments and injection into the Synchrotron SIS requires varying the amplitudes and phases of the accelerating structures' rf from pulse to pulse with a 50 Hz repetition rate. Fast variation of the amplitude is already provided, but the phaseshifting is done so far by coaxial relays and trombones. The UNILAC consists of accelerating structures with operating frequencies of 27 MHz and 108 MHz, bunchers at 9 and 27 MHz an choppers down to 1.5 MHz. For a new high current injector, structures with frequencies of 13.5 and 54 MHz are also being considered. A new electronic phaseshifter with a range of +/- 1800 should be usable with minimal changes at all these frequencies. The selected principle was a digital phase-locked loop circuit. Besides the necessary speed, the realized circuit has several additional advantages. Phaseshifters at 9, 4.5 and 1.5 MHz have been in operation for one year without problems. A prototype of a 108 MHz phaseshifter is under test