Fumihiko Tamura

Lowlevel RF Control System of J-PARC Synchrotrons

We present the concept and the design of the low level RF (LLRF) control system of the J-PARC synchrotrons. The J-PARC synchrotrons are the rapid cycling 3-GeV synchrotron (RCS) and the 50-GeV main ring (MR) which require very precise and stable LLRF control systems to accelerate the ultra-high proton beam current. The LLRF system of the synchrotron is a full-digital system based on direct digital synthesis (DDS). The functions of the system are (1) the multi-harmonic RF generation for the acceleration and the longitudinal bunch shaping, (2) the feedbacks for stabilizing the beam, (3) the feedforward for compensating the heavy beam loading, and (4) other miscellaneous functions such as the synchronization and chopper timing. The LLRF system of the RCS is now under construction. We present the details of the system. Also, we show preliminary results of performance tests of the control modules.

High power test of MA cavity for J-PARC RCS

We have been testing the RF cavities for the J-PARC RCS, so that we can operate the cavities without severe problems. Before some MA cores were damaged, then we found such cores have low ribbon resistance. After that we have tested the cavities loaded with cores which have improved ribbon resistance.

Dual Harmonic Operation with Broadband MA Cavities in J-PARC RCS

In the J-PARC RCS RF system, the fundamental rf acceleration voltage and the 2nd higher harmonic one are applied to each cavity. This is possible, because the magnetic alloy loaded cavities have a broadband characteristic and require no resonant frequency tuning. The tube amplifier provides both rf components. We calculate the operation of the tube under the condition of the dual harmonic, the non-pure resistive load and the class AB push-pull mode. We also describe about the single harmonic operation from the view point of the higher harmonic push-push mode.

Realizing a high-intensity low-emittance beam in the J-PARC 3-GeV RCS

The J-PARC 3-GeV rapid cycling synchrotron is now developing beam studies to realize a high-intensity lowemittance beam with less beam halo. This paper presents the recent experimental results while discussing emittance growth and its mitigation mechanisms.

Present Status and Future Upgrades of the J-PARC Ring RF Systems

J-PARC facility is the multipurpose research institutes. 10 years have passed since the user operation started. We have been considering the accelerator upgrades for the future and the target beam powers for 3 GeV rapid cycling synchrotron (RCS) and 30GeV Main ring (MR) are 1.5MW and 1.3MW, respectively. To achieve a 1.5MW of RCS output beam power, increasing the number of Linac proton particles is necessary. For accelerating such higher beam current, the ring rf systems in the RCS need to upgrade an accelerating voltage and to take into account for heavier beam loading compensation. In case of the MR, increasing the number of proton particles is not appropriate from the viewpoint of space charge effects. We choose to shorten the MR cycle time to increase an output beam power. The required accelerating voltage becomes almost double. All nine systems were replaced to realize the required voltages with the higher accelerating gradient RF systems using a newly developed magnetic alloy material. At present, the proton beam of 470 kW is being delivered to the T2K experiment with a cycle time of 2.48 s. Beam powers of MR will plan to aim first at 750 KW after replacing the magnet power supplies. But, to realize a 1.3 MW of the target beam power, the upgrade of RF power sources will be necessary. We report the present status of the ring RF systems and the upgrades for the future.

Baseband simulation model of the vector rf voltage control system for the J-PARC RCS

Vector rf voltage feedback control for the wideband magnetic alloy cavity of the J-PARC RCS is considered to be employed to compensate the heavy beam loading caused by high intensity proton beams. A prototype system of multiharmonic rf vector voltage control has been developed and is under testing. To characterize the system performance, full rf simulations could be performed by software like Simulink, while the software is proprietary and expensive. Also, it requires much computing power and time. We performed the simplified baseband simulations of the system in z-domain by using free software, the Python control library. It seems to be beneficial for searching the parameters that the baseband simulation can be performed quickly. In this presentation, we present the setup and results of the simulations. The simulations well reproduce the open and closed loop responses of the prototype system.

Recent Progress of 1-MW Beam Tuning in the J-PARC 3-GeV RCS

This paper presents the recent progress of 1-MW beam tuning in the J-PARC 3-GeV RCS, especially focusing on our approaches to beam loss issues.

The Second Harmonic RF System for J-PARC MR Upgrade

Power upgrade scenario of J-PARC Main Ring includes replacement of RF cavities with higher field gradient using magnetic alloy, Finemet ®-FT3L, cores than the present ones. It also needs to install the second harmonic RF cavity in the other section where dedicated water system for RF cavities is not available. Installation scenario of the second harmonic RF will be presented.

The Path to 1 MW: Beam Loss Control in the J-PARC 3-GeV RCS

The J-PARC 3-GeV RCS started a 1-MW beam test in October 2014, and successfully achieved a 1-MW beam acceleration in January 2015. Since then, a large fraction of our effort has been concentrated on reducing and managing beam losses. In this paper, recent progresses of 1-MW beam tuning are presented with particular emphasis on our approaches to beam loss issues.

Optics Tuning for Beam Collimation in the J-PARC 3-50 Beam Transport Line

The Japan Proton Accelerator Research Complex (J-PARC) 3-50 Beam Transport line (3-50BT) is a beam transport line from 3-GeV rapid-cycling synchrotron (RCS) to 50-GeV main ring (MR). The RCS is a high-intensity proton accelerator, where the designed beam power is 1 MW, and has the complex source of space charge effect and beam instability, etc. Therefore, the uncontrolled emittance growth and beam halo increase nonlinearly with the beam power ramp up. Additionally, the physical aperture of 81  mm mrad in the MR is smaller than physical aperture of 486  mm mrad in the RCS. Therefore, the 3-50BT line has the collimators in order to remove the unwanted beam tail or halo from the RCS. The designed collimator aperture is 54  mm mrad. It is required to measure and optimize the optics parameters in the collimator area for taking full advantage of the beam collimation. Especially, it is very important to make the dispersion functions free in the collimator area and optimize the beta function to remove beam tail or halo over predefined transverse emittance. This paper introduces the method of optics measurement and reports the results of the measurement and optimization based on an accelerator model.