Dai Arakawa

Acceleration of the polarized proton beam at the KEK 12 GeV ps

Abstract Acceleration of the polarized proton beam at the KEK PS up to 3.5 GeV is described. In the booster synchrotron, 75% of the linac beam polarization was preserved without any correction for the depolarizing resonances. In the main ring, almost 100% of the booster beam polarization was preserved at 3.5 GeV by the fast passage method for the intrinsic resonances and by the closed orbit correction for the imperfection resonances. The KEK PS is the first cascaded synchrotron which has demonstrated acceleration of a polarized beam.

Polarized deuteron beam acceleration at the KEK-PS

Abstract Polarized deuteron acceleration tests were performed at the KEK-PS. There is one weak intrinsic resonance at 8 GeV. The polarization was measured by an external polarimeter at 2 GeV following two patterns. The beam was extracted after deceleration to 2 GeV from 10.2 GeV in pattern 1 and just after acceleration up to 2 GeV in pattern 2. The polarization was almost the same in the two patterns, meaning that a polarized deuteron beam has been successfully accelerated up to 10.2 GeV at the KEK-PS.

Internal Polarimeters for the Polarized Proton Beam at the KEK 12 GeV PS

An internal polarimeter was constructed to detect the beam polarization in KEK proton synchrotron (PS) from TP = 500 MeV to 12 GeV. The polarimeter was installed in the main ring and successfully used for the measurement of the beam polarization at 500 MeV. We report the design and the performance of this polarimeter and the results of this first measurement. In addition to that, we also report the design of another internal polarimeter for monitoring the depolarization in the booster.

Induction Acceleration of a Single RF Bunch in the KEK PS

Results of the induction acceleration of a single RF bunch in the KEK PS are reported.

Progress of 7-GeV SuperKEKB Injector Linac Upgrade and Commissioning

KEK injector linac is being upgraded for the SuperKEKB project, which aims at a 40-fold increase in luminosity over the previous project KEKB. SuperKEKB asymmetric electron and positron collider with its extremely high luminosity requires a high current, low emittance and low energy spread injection beam from the injector. Electron beams will be generated by a new type of RF gun, that will inject a much higher beam current to correspond to a large stored beam current and a short lifetime in the storage ring. The positron source is another major challenge that enhances the positron bunch intensity from 1 to 4 nC by increasing the positron capture efficiency, and the positron beam emittance is reduced by introducing a damping ring, followed by the bunch compressor and energy compressor. The recent status of the upgrade and beam commissioning is reported.

Performance of the Digital LLRF Systems at KEK cERL

A compact energy recovery linac (cERL), which is a test machine for the next generation synchrotron light source 3-GeV ERL, was constructed at KEK. In the cERL, a normal conducting (NC) buncher cavity and three superconducting (SC) two-cell cavities were installed for the injector, and two nine-cell SC cavities were installed for the main linac (ML). The radiofrequency (RF) fluctuations for each cavity are required to be maintained at less than 0.1% rms in amplitude and 0.1° in phase. These requirements are fulfilled by applying digital low-level radio-frequency (LLRF) systems. During the beam-commissioning, the LLRF systems were evaluated and validated. A measured beam momentum jitter of 0.006% shows that the target of the LLRF systems is achieved. To further improve the system performance, an adaptive feedforward (FF) control-based approach was proposed and demonstrated in the beamcommissioning. The current status of LLRF system and the adaptive FF approach for LLRF control in the cERL are presented in this paper. INTRODUCTION At KEK, a compact energy recovery linac (cERL), as a test facility for future 3-GeV ERL project, was constructed, and the first beam-commissioning was carried out at June, 2013 [1, 2]. The cERL is a 1.3 GHz superconducting radio-frequency (SCRF) machine that is operated in continuous-wave (CW) mode. As shown in Fig. 1, the cERL consists of an injector part and a main linac (ML) part. A normal conducting (NC) cavity (buncher) and three two-cell superconducting (SC) cavities (Inj. 1, Inj. 2, and Inj. 3), were installed in the injector, and two main nine-cell SC cavities (ML1 and ML2) were installed in the main linac (ML). For lowemittance beam, the requirements of the RF field stabilities are 0.1% rms in amplitude and 0.1° in phase in the cERL. This requirements are fulfilled by applying digital low-level radio-frequency (LLRF) systems. The LLRF system in the cERL is disturbed by various disturbances include the 50-Hz microphonics, the 300-Hz high-voltage power supply (HVPS) ripples and the burst mode beam-loading [3-4]. The current LLRF system is not sufficient to reject all of these disturbances. In view of this situation, we have proposed a disturbance observer (DOB)-based approach for suppress the main disturbances in the cERL [3]. Based on this approach, the disturbances can be reconstructed by the cavity pickup signal and then removed from the feedforward (FF) table in real-time. Therefore, in terms of function, this approach is just like an adaptive FF control. In this paper, we first introduce the LLRF system in the cERL, and then present the measured LLRF stability and beam momentum jitter during the cERL beamcommissioning. In the next stage, we describe the basic idea of the proposed adaptive FF approach for disturbances rejection. Finally, we present the preliminary result of this adaptive FF approach for microphonics rejection in the cERL commissioning. Main linac 2 8 kW SSA Nine-cell SC 8 kW SSA Main linac 1 Two-cell SC SC SC 300 kW Kly. 25 kW Kly. 8 kW SSA Vector-sum Controlling ~8.5 MV/m for main linac Cavities ~3 MV/m for Injector Cavities ~ 20 MeV Dump 16 kW SSA Figure 1: Layout of the cavities in the cERL. The marked values of beam energy and accelerating field indicate the current state in the cERL beam-commissioning. HLRF SYSTEM RF power sources including 25 kW klystron, 300 kW klystron, 8 kW solid state amplifier (SSA) and 16 kW SSA were employed in the cERL. Figure 1 shows the layout of the cavities and corresponding power sources in the cERL. Table 1 gives the loaded Q value, required RF power, and RF sources for each cavity. It should be mentioned that, in the Inj .2 and Inj .3, a vector-sum control method is applied. All of these RF sources are stable and reliable in the beam commissioning. Table 1: Cavity Parameters of the cERL Cav. QL f1/2 [Hz] RF power [kW] RF source Bun. 1.1×10 57000 3 8 kW SSA Inj. 1 1.2×10 540 0.53 25 kW Kly. Inj. 2 5.8×1

Head-tail instability and microwave instability in the KEK-PS

Head-tail instability and microwave instability has been studied and cured in the course of the intensity up-grade program of the KEK-PS. Experimental results, its interpretations and cures are given on the head-tail instabilities, emerging just after the acceleration start, and the microwave instability, arising after the transition energy in the 12 GeV PS main ring.