Alexander Schnase

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.

Simulation of Phase Modulation for Longitudinal Emittance Blow-Up in J-PARC MR

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method[1,2,3,4] by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency as shown in Fig. 1, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM as shown in Fig. 2. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Simulation of Debunching for Slow Extraction in J-PARC MR

The J-PARC MR delivers a proton beam for nuclear physics experiments with slow extraction. The beam is debunched at flat top to obtain a coasting beam by turning off the rf voltage. The beam loading effect can disturb the uniformity of the debunching at the flat top. We describe the results of the particle tracking simulation including the beam loading effect.