An Instrument for Measuring Betatron Resonant Frequencies

An instrument has been developed to measure betatron tunes with a minimum of disturbance to normal operation. In one mode of operation, the beam is driven by a frequency sweeping voltage controlled oscillator (VCO). The output of this VCO is compared to (1-¿) feedback from the beam in a phase-sensitive demodulator. The dc output of this demodulator helps to control the frequency of the VCO, thus closing a loop around the beam. At frequency coincidence between the (1-¿) feedback and the VCO, a pulse is generated which stops the VCO frequency sweep and allows phase lock on the beam if desired. This pulse also activates measuring and digitizing circuitry to record pertinent data at the instant of frequency coincidence. Other modes of operation permit measurement of, and phase lock to, unexcited or "natural" resonances.