Masahito Tomizawa

Design of dynamic collimator for J-PARC main ring

The J-PARC main ring has a beam collimator section downstream of the injection area. The allowed beam loss is about 450 W. The beam halo generated before acceleration can be scraped by a standard collimator scheme. However the beam halo can grow during the acceleration. Such a halo may cause a serious beam loss at the extraction. A collimation during acceleration (dynamic collimator) is useful to reduce the beam loss at the extraction. We propose the dynamic collimator scheme and show the performance expected from the simulations.

Opposite field septum magnet system for the separation of charged particle beams

The Japan Hadron Facility (JHF) accelerator complex comprises a 50-GeV main synchrotron, a 3-GeV rapid-cycling synchrotron, and a 400-MeV linac. The accelerators provide high-intensity, high-energy proton beams for various scientific fields. These high-intensity, high-energy accelerators, especially the 50-GeV main synchrotron, impose tight demands on the injection/extraction septum magnets for a thin structure, large aperture and high operating field. But to manufacture high field septum magnets on the condition of a large aperture is very difficult because of its extraordinarily strong electromagnetic force due to the self-field. To cope with these tight demands, new design concepts of septa are required. An opposite-field septum magnet system is one of the solutions to realize a thin septa or very high-field septum magnets.

Manufacturing and Operation of the Magnetic Septa for the Slow Beam Extraction From the J-PARC 50 GeV Proton Synchrotron

The magnetic septa have been developed for the slow beam extraction from the 50 GeV Proton Synchrotron to the Hadron Experimental Hall at J-PARC (Japan Proton Accelerator Research Complex). The magnetic septa consist of two thin magnetic septa, four medium thick magnetic septa and four thick magnetic septa. The typical operating current is 3000 A and the total kick angle is 77 mrad with the 30 GeV proton beam. All parts of the thin and of the medium thick septum magnets are made of inorganic materials to resist high radiation environment. The positions of the thin and medium thick septa can be aligned remotely in the horizontal range of ±5 mm, which enables us to minimize the beam loss at the magnetic septum section. The septa were installed in the synchrotron ring in December, 2008, after a test at KEK (High Energy Accelerator Research Organization), and were successfully operated in the beam time for the slow beam extraction in January and February, 2009, which resulted in the first 30 GeV slow extracted beam delivery to the Hadron Experimental Hall.

New optics design of injection/fast extraction/abort lines of J-PARC main ring

The J-PARC Main Ring has three straight sections for injection, slow extraction and fast extraction. Injection line has been redesigned so as to give a higher reliability for the thin septa. The magnetic field can be reduced by adding an extra kicker. Alternative optics for the fast extraction with a larger acceptance has been proposed. In this design, the thin septa are replaced by kickers with a large aperture. Beam with an arbitrary energy can be aborted from opposite side from the fast extraction. An external abort line has been designed to deliver the beam aborted at an arbitrary energy to a dump just by using a static quadrupole doublet for the focus.

Hardware R&D of the KEK/JAERI 50 GeV synchrotron fast extraction kicker magnets

The fast extraction kicker magnets of the 50 GeV synchrotron are now in an intensive R&D stage. In the 50 GeV ring, the fast extraction system is designed to deliver the 50 GeV beam to the downstream neutrino oscillation experiment beam line with the Super-Kamiokande detector. At the same time, the fast extraction line is required to function as a beam abort, in case of hardware failure during acceleration of the beam from 3 GeV to 50 GeV. In order to fulfill both demands, the extraction system is designed to accommodate bipolar beam extraction. A new technology to make the bipolar kicker magnet system, using a symmetric Blumlein pulse forming network (SBPFN) system, has been introduced. Its validity is being investigated, both theoretically and experimentally. R&D programs aimed at establishing some of the important technical elements in the fast extraction kicker system are presently in progress. This R&D includes experimental studies of the bipolar kicker principle and the development of IGBT switching modules that satisfy full switching capability of the designed current and voltage.

Study of EP instability for a coasting proton beam in circular accelerators

We discuss interactions between a coasting proton beam and electrons. The electrons, which are created near the beam position, are considered in this paper. A coasting proton beam traps the electrons eternally, if there are no perturbations nor diffusion mechanisms. Therefore electrons are accumulated and their density could arrive above a threshold value for the instability, finally: i.e., a coasting proton beam is always unstable. However the instability affects both of the beam and electrons. Electrons may be diffused by the instability, in which the beam still has a small oscillation amplitudes, with the result that the beam amplitude may be kept in the small level, and may be stable in actual operations of accelerators. We study the ep instability with focusing the electron diffusion using a computer simulation method

Hardware for Beam Injection and Extraction

The injection and extraction beam‐lines of the 50 GeV synchrotron in the JHF project are described. The 50 GeV ring is equipped with one injection line from the preceding 3 GeV ring and three extraction lines for experimental facilities and for beam aborts. Some of the characteristic features on the injection/extraction hardware components, particularly on the kickers, are mentioned. These features are intended to fulfill two important demands on the kicker design, namely, a reduction of reflected waveforms and a bipolar fast extraction by the fast reverse of the kick direction.

Radiation Handling in the Slow Extraction of the JHF 50 GeV Ring

In the slow extraction of the JHF 50GeV ring, about 1 is expected to hit the ESS(Electro Static Septum). The beam loss in the scattering is about 1% corresponding to the beam power of 7.5kW. Considering the tolerable beam loss(0.5∼1W/m), careful study of the beam loss of the scattering beam is indispensable. To evaluate the radiation level around ESS, simulation study with MARS14(00), was carried out. In addition, the beam loss distribution in the ring was studied combining MARS14(00) and single particle tracking. The result shows that the radiation level around ESS is suppressed to the tolerable level. In addition, it was found that the actual beam loss is much smaller than the loss of 1% which hit the ESS wire.

Electron cloud simulations for the main ring of J-PARC

The simulation of beam instabilities is a helpful tool to evaluate potential threats against the machine protection of the high intensity beams. At Main Ring (MR) of J-PARC, signals related to the electron cloud have been observed during the slow beam extraction mode. Hence, several studies were conducted to investigate the mechanism that produces it, the results confirmed a strong dependence of the beam intensity and the bunch structure in the formation of the electron cloud, however, the precise explanation of its trigger conditions remains incomplete. To shed light on the problem, electron cloud simulations were done using an updated version of the computational model developed from previous works at KEK. The code employed the signals of the measurements to reproduce the events seen during the surveys.

Design Study of Superconducting Transmission Line Magnet for J-PARC MR Upgrade

In order to enhance the beam efficiency of the J-PARC main ring, installation of a new ring is being considered. The new ring, which can accommodate up to 30-GeV proton beam, enables to operate the fast and slow extractions simultaneously with the maximum throughput. Use of superconducting transmission line magnets is proposed as bending magnets for the new ring. Design study of the magnets has started. This paper reports on the brief concept of the new ring, requirements to the magnets, and the status of the design study