A HIGH-SENSITIVITY PHASE STABILIZING SYSTEM AND BEAM CURRENT MONITOR

A 5 MHz phase stabilizing systems and beam current monitor for the superconducting linac ALPI at Laboratori Nasionali di Legnaro (LNL) was designed, constructed and tested. The system, based on a 5 MHz resonant phase detector, provides stabilization of the phase of the beam bunches produced by the LNL double drift buncher. In addition, the system gives a non-destructive reading of the pulsed beam current in the range between 0.3 and 140 nA. The high impedance coupling of the preamplifier to the resonant phase detector allows for a sensitivity of 1 mV/nA, which is two orders of magnitude higher than previously reported for this kind of devices. The fast phase stabilization is performed by means of a voltage controlled phase shifter; the long term drifts are corrected using a digitally controlled delay. An automatic phase adjustment of the resonator amplifier output was included, in order to correct for any phase shift generated by the amplifiers due to changes of the input signal level. A general expression of the phase in response in resonant phase detectors is evaluated and discussed.