138258874
CONDITION OF MA CORES IN THE RF CAVITIES OF J-PARC SYNCHROTRONS AFTER SEVERAL YEARS OF OPERATION
J-PARC 3 GeV Rapid Cycling Synchrotron (RCS) and 50 GeV Synchrotron (MR) employ the Magnetic Alloy (MA) loaded RF cavities. We observed the impedance reductions of the RF cavities in RCS three times during 3 years of operation. We figured out that the impedance reductions were resulting from the MA core buckling. The MA core buckling was caused by the thermal stress that was enhanced due to the impregnation with epoxy resin. We also observed the impedance reductions of MR RF cavities during 2 years of operation. Opening the RF cavity, we found that the impedance reductions were caused by the corrosion on the MA core cutting surface. The copper ions and colloids in the cooling water might accelerate the corrosion process.
114630141
SIMULATION OF MAGNETIC ALLOY LOADED RF CAVITY AND HOM ANALYSIS
120092838
Longitudinal painting with large amplitude second harmonic rf voltages in the rapid cycling synchrotron of the Japan Proton Accelerator Research Complex
In the rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC), the longitudinal painting is important to alleviate the space-charge effects. It is known that the momentum offset injection and applying the second harmonic rf voltage improves the bunching factor, which is defined as the ratio of average and peak current. Our simulation studies show that the large-amplitude second harmonic, 80% to the fundamental, is optimum, and the second harmonic phase sweep improves the bunching factor at the beginning of the injection period. We performed the beam tests of longitudinal painting in the J-PARC RCS. We proved that the longitudinal painting with the 80% second harmonic, the momentum offset of $\ensuremath{-}0.2%$, and the second harmonic phase sweep improved bunching factors significantly.
121515925
Achievement of very low jitter extraction of high power proton beams in the J-PARC RCS
Abstract The 3 GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) delivers high intensity proton beams to the Materials and Life Science Facility (MLF) and the main ring (MR). The repetition rate of the RCS is 25 Hz. The typical operation period of the J-PARC is 3.2 s, which consists of 80 RCS cycles. Four beam pulses are for the MR and the other pulses are led into the MLF. Since a bucket-to-bucket injection scheme is used for the MR, the beam from the RCS must be injected with a precise phase to the proper rf bucket of the MR. In case of the MLF, the beam has to be synchronized to the Fermi chopper, which has a tolerance of only a few 100 ns. Thus, stable beam timings with a very low jitter are required for both destinations. To realize the stable beam timing, we employ the timing system, which is not synchronized to the AC power line. Also the magnetic-alloy accelerating cavities and the full digital low-level RF control system are the keys for the precise beam phase control. For acceleration of a high power beam, the phase feedback loop, which damps the longitudinal dipole oscillation, is necessary. The phase loop is a cause of the jitter of the beam extraction timing. We apply a gain pattern of the phase loop to avoid the influence on the beam phase at the extraction. We have achieved a very low jitter extraction of a high power beam within 1.7 ns, which corresponds to 1 degree of the rf frequency at the extraction.
9194378
MA cavities for J-PARC with controlled Q-value by external inductor
The original J-PARC RCS cavity design used cut-cores to control the Q-value. Adjusting the distance between the C-shaped core parts the optimum Q=2 is reached. Because of problems related to the cut-core surfaces, the "hybrid cavity" was introduced, using tanks with uncut cores (Q=0.6) in parallel to tanks with cut-cores with a wider gap (Q=4), resulting in total Q=2. Although this was successfully tested, the manufacturing procedure for cut-cores involves more steps than for uncut cores. To reduce risks for long-term operation, the RCS cavities are loaded with uncut cores for day-1 operation. In the following, we describe how we establish Q=2 with parallel inductors.
138147992
DEVELOPMENTS OF MAGNETIC ALLOY CORES WITH HIGHER IMPEDANCE FOR J-PARC UPGRADE
Magnetic alloy cavities are successfully used for JPARC synchrotrons [1]. These cavities generate much higher RF voltage than ordinary ferrite cavities. For future upgrades of J-PARC facilities, a higher field gradient is necessary. It was found that the characteristics of magnetic alloy are improved by a new annealing scheme under magnetic field. A large production system using an old cyclotron magnet is under construction for the J-PARC upgrade. The status of core development will be reported.
26597811
Feshbach-Kerman-Koonin model analysis of preequilibrium (p,p') and (p,n) reactions at 12 to 26 MeV.
Double-differential proton emission cross sections have been measured for proton-induced reactions on [sup 98]Mo and [sup 106]Pd at incident energies around 26 MeV. Several sets of ([ital p],[ital p][prime]) and ([ital p],[ital n]) data for both target nuclei at incident energies from 12 to 26 MeV are analyzed in terms of the multistep-direct (MSD) and multistep-compound (MSC) reaction models of Feshbach, Kerman, and Koonin (FKK). The strength [ital V][sub 0] of the effective [ital N]-[ital N] interaction is extracted from a fit of the calculated MSD spectrum to the experimental data using the subtraction method of isolating and analyzing the MSD component alone. A similar analysis is also applied to ([ital p],[ital p][prime]) and ([ital n],[ital n][prime]) data for [sup 93]Nb in the same energy region. The experimental nucleon emission spectra at 26 MeV are reproduced well by the calculation that includes preequilibrium MSD and MSC emission, direct collective excitation to low-lying discrete levels, and Hauser-Feshbach equilibrium emission in a quantum-mechanical way. The systematic dependence of [ital V][sub 0] on the incident energy and the nature of projectiles and ejectiles is investigated. In addition, the sensitivities to input parameters used in the MSD calculation (the optical model potential parameters, themore » pairing correction, and the nonlocality correction) are examined in order to see their effect on the determination of [ital V][sub 0]. The possibility of gradual absorption of reaction flux from the [ital P] to the [ital Q] chain is also discussed through analyses of preequilibrium ([ital p],[ital p][prime]) and ([ital p],[ital n]) spectra using a phenomenological phase space approach.« less