A shunt impedance measurement method for CRM cyclotron cavity

The characteristic parameters of the cyclotron cavity are crucial for both cyclotron design and commissioning. Among which, the resonance frequency, the quality factor and shunt impedance of the acceleration gap are the three key parameters when identifying a cyclotron RF system. An accurate shunt impedance measurement can lead to a very close estimation of the Dee voltage under giving driven power, includes both maximum quantity and distribution. The difficulties of such measurements are that either the probe will interfere local EM field, or have very limited signal to noise ratio. A new shunt impedance measurement method has been reported in the paper, starting with the definition of scatter parameter of passive network, followed with probe design, measurement setup and result of the CRM cyclotron cavity. Also, the same method has been applied in the measurement of 100 MeV cyclotron cavity, the result has been confirmed by the 3D RF structure computation code in this ease, and the difference is less than one percent. (authors)