LLRF controls in SuperKEKB Phase-1 commissioning
First beam commissioning of SuperKEKB (Phase-1), which is an asymmetry double ring collider of 7-GeV electron and 4-GeV positron beams, which had started from February, has been successfully accomplished at the end of June 2016, and the desired beam current for Phase-1 was achieved in both rings. This paper summarize the operation results related to low level RF (LLRF) control issues during the Phase-1 commissioning, including the system tuning, the coupled bunch instability and the bunch gap transient effect. RF system of SuperKEKB consists of about thirty klystron stations in both rings. Newly developed LLRF control systems were applied to the nine stations among the thirty for Phase-1. The RF reference signal distribution system has been also upgraded for SuperKEKB. These new systems worked well without serious problem and they contributed to smooth progress of the commissioning. The old existing systems, which had been used in the KEKB operation, were still reused for the most stations, and they also worked as soundly as performed in the KEKB operation.
I/Q フィードバック制御における大電流ビーム負荷での空洞離調に対する 位相補償機能 PHASE COMPENSATION FUNCTION FOR CAVITY DETUNING DUE TO HEAVY BEAM LOADING IN I/Q-FEEDBACK CONTROL
Digital low-level RF control systems, which handle I/Q components of RF signal with FPGAs, had been developed for the SuperKEKB project, and they have worked successfully in the Phase-1 (2016) and Phae-2 (2018) commissioning. However, some issues to be concerned are still remaining for the high beam current to achieve the design luminosity, which is aiming at 40 times higher than the KEKB accelerator. One of the concerned issues is large cavity detuning for compensation of heavy beam loading. Optimum detuning for the normal conducting cavity in SuperKEKB will attain about 30 kHz at the design beam current of 3.6 A. This detuning corresponds to about 70-degree phase change in RF cavity transmission, which makes phase shift in a closed loop of cavity field regulation. Accordingly it is worried that some disturbances make the I/Q feedback control unstable due to the large phase shift inside the loop. Therefore, a new function to compensate the phase shift due to the large detuning was implemented into FPGA of the digital control system. This new function was successfully worked in the Phase-2 commissioning. In this paper, the demonstration result is reported, and also it is discussed that how the large phase shift in an I/Q-feedback loop effects on the cavity regulation control.
A technique for large-field, superficial electron therapy.
The application of electron beams to radiation therapy has received increased attention in recent years. This interest stems largely from the special characteristics of the electron depth-dose distribution; the fall-off in depth dose near the end of the range of the electrons is particularly rapid for electron beams having energies less than about 10 Mev. Such an electron beam is suitable for the treatment of widespread, superficial lesions, where it is desirable to minimize the dose to deep tissues. All the common sources of super-voltage x-rays, apart from radioactive substances, are inherently capable of producing an external beam of electrons, though with varying degrees of complexity. Electrons of about the energy suitable for superficial therapy (several Mev) may be used to produce an x-ray beam which is sufficiently penetrating for the treatment of even the deepest lesions. The Stanford medical linear accelerator was designed to provide both x-rays and electron beams. The accelerator and its applic...