Simulations of beam loading compensation in a wideband accelerating cavity using a circuit simulator including a LLRF feedback control

Abstract

Magnetic alloy cavities are employed in the J-PARC RCS to generate high accelerating voltages. The cavity, which is driven by a vacuum tube amplifier, has a wideband frequency response and the beam loading in the cavity is multiharmonic. Therefore, the tube must generate a multiharmonic output current. An LTspice circuit model is developed to analyze the vacuum tube operation and the compensation of the multiharmonic beam loading. The model includes the cavity, tube amplifier, beam current, and LLRF feedback control. The feedback control consists of the I/Q demodulator including low pass filters, PI control, and I/Q modulator. In this article, we present the implementation of the LLRF functions in the LTspice simulations. The preliminary simulation results are also presented. The simulations fairly agree with the beam test results.