Masanori Ikegami

Simulation of space charge effects in a synchrotron

We have studied space charge effects in a synchrotron with multi-particle tracking in 2-D and 3-D configuration space (4-D and 6-D phase space, respectively). First, we will describe the modelling of space charge fields in the simulation and a procedure of tracking. Several ways of presenting tracking results will be also mentioned. Secondly, it is discussed as a demonstration of the simulation study that coherent modes of a beam play a major role in beam stability and intensity limit. The incoherent tune in a resonance condition should be replaced by the coherent tune. Finally, we consider the coherent motion of a beam core as a driving force of halo formation. The mechanism is familiar in linac, and we apply it in a synchrotron.

XAL online model enhancements for J-PARC commissioning and operation

The XAL application development environment has been installed as a part of the control system for the Japan Proton Accelerator Research Center (J-PARC) in Tokai, Japan. XAL was initially developed at the spallation neutron source (SNS) and has been described at length in previous conference proceedings. Included in XAL is an online model for doing quick physics simulations. We outline the upgrades and enhancements to the XAL online model necessary for accurate simulation of the J- PARC linac and transport system.

Beam commissioning of the J-PARC linac medium energy beam transport at KEK

The construction of the initial part of the J-PARC linac has been started at KEK for beam tests before moving to the JAERI Tokai campus, where J-PARC facility is finally to be constructed. The RFQ and MEBT (Medium Energy Beam Transport) have already been installed at KEK, and the beam test has been performed successfully. In this paper, the experimental results of the beam tests are presented together with simulation results with a 3D PIC (Particle-In-Cell) code.

Beam study with RF choppers in the MEBT of the J-PARC proton linac

A beam study of the RF fast chopper system in the MEBT of the J-PARC linac was successfully performed up to a beam current of 25 mA. The achieved rise/fall time of the chopped beam was about 10 ns. A beam signal during the chopper-on period, measured at the exit of the MEBT, was less than the noise level of the monitor systems. A flexible pattern of the chopped pulse train was achieved, which is useful for various kinds of operating pulse modes of the J-PARC accelerator.

Transverse Tuning Scheme for J-PARC Linac

A transverse matching scheme has been planned for the J-PARC linac beam commissioning with use of wire scanners. The beam diagnosis layout has been determined to realize the planned matching scheme. Continuous monitoring of the matching with beam position monitors is also discussed.

Tuning of RF amplitude and phase for the drift tube linac in J-PARC

The J-PARC linac has three DTL tanks to accelerate the negative hydrogen ions from 3 MeV to 50 MeV. The RF phase and amplitude are adjusted for each cavity with a phase scan method within the accuracy of 1? in phase and 1% in amplitude. The experimental results show a remarkable agreement with the numerical model within a sufficient margin in the tuning of the last two DTL tanks. However, a notable discrepancy between the experiment and the numerical model is seen in the tuning of the first DTL tank. After studying with a three-dimensional multi-particle simulation, the generation of the low energy component and the pronounced filamentation are identified as the main causes of the discrepancy. The optimization of the tuning scheme is also discussed to attain the tuning goal accuracy for the first DTL tank.

RF amplitude and phase tuning of J-PARC SDTL

A fine tuning has been performed for RF phase and amplitude of SDTL (Separate-type Drift Tube Linac) station in the beam commissioning of J-PARC LINAC. A phase-scan method is adopted to carry out the tuning. An adequate set-point is determined by matching measured absolute beam energy with those from a modeling. The tuning goal is satisfied using this method, which required within 1deg for phase and 1% for amplitude. This paper presents detail procedures of RF tuning of SDTL.

Beam Dynamics and Commissioning of the J‐PARC Linac

At the first stage of J‐PARC (Japan Proton Accelerator Research Complex), the linac will accelerate a H− beam to 181 MeV with a peak current of 30mA. A normalized transverse emittance of less than 4πmm⋅mrad and a momentum spread of less than ±0.1% are required at the injection point of the the rapid cycling synchrotron (RCS) following the linac. In order to find out operating points satisfying the above requirements and develop commissioning strategies, intense simulation studies of the linac have been performed. The beam commissioning of the drift‐tube linac tank‐1 (DTL1) has been performed at KEK. Transverse emittances at the DTL1 exit, phase scan property of the DTL1, and so on have been measured to confirm the validity of the simulations and commissioning strategies.

The precise survey and the alignment results of the J-PARC LINAC

J-PARC linear accelerator components have been installed. Before the beam commissioning, a precise survey for alignment has been performed. The reference points were set up on the tunnel wall to built a survey network. Based on the survey results, the magnets in the straight section were re-aligned finely. Then, the results of the displacement are confirmed to be tolerable for the beam commissioning.

Tuning of the RF field of the DTL for the J-PARC

Tuning of the accelerating field of the DTL first tank for the Japan Proton Accelerator Research Complex (J-PARC) has been done. The first DTL tank consists of 75 full drift tubes, 37 post-couplers and 10 fixed tuners. The resonant frequency of the tank is 324 MHz. An uniform accelerating field has been achieved by the fine adjustment of the post-couplers and the fixed tuners. The field stabilization by the post-couplers against perturbations has been confirmed also. In order to achieve the stabilized-uniform distribution of the average field for each accelerating gap, the following techniques have been applied for the post-coupler tuning: (1) non-uniform insertion length of the post-coupler from the tank wall; (2) increment of the diameter of several post-couplers. The recipe of the fine post-coupler tuning is described.