In the main linac (ML) of the compact energy recovery linac at KEK, two 1.3 GHz nine-cell superconducting cavities (ML1 and ML2) with high loaded Q (QL > 1×10) are operated in continuous wave mode. Because of the narrow bandwidth of these cavities, the microphonics detuning have a significant impact on the achievable RF field stability. In this paper, we have analysed the microphonics performance of the two ML cavities. According to our study, a “field level dependence microphonics” phenomenon is observed on the ML1 cavity. Several frequency components higher than 500 Hz were suddenly excited if the cavity field is above an onset field (~3 MV/m). Although the mechanism for the phenomenon remains obscure, the onset field is probably related with the cavity quench limits. Finally, we confirmed that the deteriorated RF stabilities (due to the deteriorated microphonics) can be improved by applying a disturbance observer based control approach.

In the SuperKEKB Phase2 operation, the beam injection phase from the injector LINAC to rings drifts several degrees or more per day. The monitoring and compensation system of the phase drift between the LINAC master oscillator (MO) and the ring MO is important for stable beam injection. The frequency of LINAC MO and the ring MO is 571.2 MHz and 508.9 MHz, respectively. Both MO signals are monitored by the direct sampling technique using the same sampling frequency (clock). There are several combinations of the clock generation. In this paper, the possible three combinations will be compared including the clock jitter performance and the short-term phase stability and the combination 1 is selected for the phase difference monitor system. The 1ms short-term phase stability is 0.04 deg. (RMS) without digital filter and 0.005 deg. (RMS) with 10 kHz bandwidth digital filter for both MO signals in the laboratory. Finally, the long-term phase drift between LINAC MO and ring MO is monitored at the injector LINAC. INTRODUCTION The luminosity of the SuperKEKB upgrade project is 40 times higher than KEKB. The lower-emittance and highercurrent beam is required. The beam injection phase stabilization between the injector LINAC to rings is very important for stable beam injection. Figure 1 shows the master oscillator (MO) system for LINAC, damping ring (DR) and main ring (MR). The MO of the LINAC and the rings is 571.2 MHz and 508.9 MHz, respectively. They are synchronized by 10 MHz trigger but the phase drift between them was found to be several degrees per day [1].

The procedure for induction acceleration of a heavy ion beam of A/Q=4 in the KEK digital accelerator is reported. This paper discusses essential issues associated with induction acceleration of ion beams from low energies, including injection error, relatively large closed orbit distortion, and a fully predictive control method for the acceleration.

A low level RF (LLRF) design is being currently developed within the compact Energy Recover Linac (cERL) at KEK. One challenging task is to achieve the high amplitude and high phase stability required by the accelerating fields of up to 0.1% and 0.1°, respectively. To improve the performance of the LLRF system, a gain scanning experiment for determining the optimal controller gain was carried out on the cERL. Furthermore, as a substitute for the traditional PI controller, a more robust H∞-based multiple input multiple output (MIMO) controller was realized. This controller requires more detailed system information (transfer function or state equation), which can be acquired by using modern system identification methods. In this paper, we describe the current status of these experiments on the cERL.

This paper reports on a present status of a positron injector linac upgrade for SuperKEKB. A development status of a flux concentrator for positron focusing is shown. An influence of offset layout of the flux concentrator and the target on a positron yield is described. Positron capture by L-band and large aperture S-band accelerating structures are compared in a viewpoint of satellite bunch elimination. Beam optical design compatible to electrons and positrons of different beam energies is discussed.

The J-PARC RCS is a 25 Hz Rapid-Cycling proton Synchrotron and its designed beam power is 1 MW. The beam position monitor (BPM) system at J-PARC RCS is described in this paper. The pre-defined diameter of the BPM detectors is larger than 250 mm, however, the system has to measure the beam position very accurately. In addition, it is necessary to have a large dynamic range. The system should work not only for the high intensity but also for low intensity, such as during beam commissioning, when the intensity is below 1% of the design intensity.There are 54 BPM detectors around the ring and most of them are placed inside steering magnets because of quite limited space. The BPM detector is an electro-static type and it has four electrodes, and a pair of electrodes gives a good linear response with a diagonal cut shape to detect the charge center precisely. The signal processing units, which are equipped with 14-bit 40 MS/s ADC and 600 MHz DSP, have been developed. They are accessed via shared memory space and controlled by EPICS. Such a processing unit is capable of recording the full 25 Hz pulse data for the so-called "COD mode" (averaged beam position calculation) and it can also store the whole waveform data for further analysis, like turn-by-turn position calculation. The resolution was estimated to be 20 mu m for "COD mode" and to be 0.3 mm for the turn-by-turn mode with relatively low intensity of 8 x 10(11) ppp. The position accuracy is estimated to be about 0.5 mm using a newly developed Beam Based Alignment (BBA) method. (C) 2012 Elsevier B.V. All rights reserved.