LLRF Controller Upgrade for the J-PARC 400 MeV LINAC

The output energy of the J-PARC proton LINAC will be upgraded from 181 to 400 MeV in the next two years by adding high-β acceleration sections. The upgrade of the FPGA-based digital LLRF controller for the 400 MeV LINAC will be presented in this paper. This new LLRF controller works for both the 324-MHz low-β and 972-MHz high-β sections. Many functions have been added into the LLRF controller, such as 1) working for different RF systems, 2) gradually increasing the feedback gains in the feedback loop instead of fixed ones, 3) automatic chopped beam compensation, 4) automatically switching the beam loading compensation in accordance with different beam operation mode, 5) input RF-frequency tuning to match the RF cavities during RF start-up, and 6) auto-tuning of the RF cavity tuner by detecting the phase curve of the RF cavity during the field decay instead of the phase difference between the cavity input and output signals. INTRODUCTION The energy of the J-PARC proton LINAC will be upgraded from 181 to 400 MeV, by adding 972-MHz high-β acceleration sections. The layout of the RF systems of the J-PARC 400 MeV LINAC is shown in Fig. 1. For both the 324-MHz low-β and 972-MHz high-β sections, the RF signals are controlled by the FPGA-based digital feedback control systems installed in a compact PCI (cPCI), as shown in Fig.2. It consists of the CPU, IO, DSP with FPGA, Mixer & IQ modulator, and RF & CLK boards [1-4]. The hardware for the 324 and 972 MHz systems is basically the same, except the RF board and Mixer & IQ board, working for different frequency [5]. The software for the two systems is completely the same. Both the hardware and software have been developed and tested. A very good stability of the accelerating fields has been successfully achieved about ±0.2% in amplitude and ±0.2 degree in phase, much better than the requirements of ±1% in amplitude and ±1 degree in phase. This paper mainly describes progresses of the LLRF controller for the J-PARC LINAC, especially for the 972-MHz high-β systems. Figure 2: Digital feedback control system installed in a compact PCI. LLRF SOFTWARE FOR THE WHOLE 400 MeV LINAC During the development of the LLRF software for the 400 MeV LINAC, the different facility conditions and operation requirements between the 324-MHz low-β and 972-MHz high-β sections have been considered, and a uniform LLRF software is designed to apply for the whole 400 MeV LINAC. In the LLRF controller, all of the different conditions between the two sections are just set as input parameters of the controller, so that the software could run for different conditions. Figure 1: Layout of the RF systems of the J-PARC 400 MeV LINAC. TUPEA046 Proceedings of IPAC’10, Kyoto, Japan 1434 07 Accelerator Technology