THPM2Y01
IMP/CAS, Lanzhou, People's Republic of China
The frequency detuning as large as 10 kHz observed on the RFQ of the Injector II of the CIADS when the beam passed by couldn’t be explained by the beam loading theory based on the equivalent circuit analysis, which is a mainstream theory being widely used in the analysis of beam loading nowadays. By introducing the concept of beam-cavity system, together with the impedance model of the beam, the beam induced detuning of the beam-cavity system was proved to be amount to the optimum detuning of the cavity under the given beam condition in a very straightforward way and the problem was therefore converted to the calculation of the optimum detuning of the RFQ. With the introduction of the new notions of effective synchronous phase and RF phase, the existing beam loading theory is extended to the analysis of the more complex accelerating structures, such as RFQ, which has many accelerating cells and with different synchronous phase in each cell, along with more than one dominant mode coexisting in the cavity. The numerical result obtained from the extended beam loading theory was well agreed with the experiment result mentioned at the beginning.
