Hirohiko Someya

Design of RCS magnets for J-PARC 3-GeV synchrotron

The 3-GeV synchrotron proposed in the JAERI/KEK Joint Project (J-PARC) is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400 MeV to 3 GeV at a repetition rate of 25 Hz. The 3-GeV synchrotron is used to produce pulsed spallation neutrons and muons. It also works as an injector for a 50-GeV synchrotron. The 3-GeV synchrotron consists of 24 dipole magnets, 60 quadrupole magnets, 18 sextupole magnets and 52 steering magnets. Since the magnets for the 3-GeV synchrotron are required to have a large aperture in order to realize the large beam power of 1 MW, one of the serious issue is a large fringe field at a pole end comparing to usual synchrotron magnet. Therefore, we carefully estimated not only the magnetic field but also the effect of multi-pole components in the fringing field. In this paper, we would report the results of the field calculation and mechanical design of RCS magnets.

Eddy Current Effects of the J-PARC RCS Sextupole Magnets

Sextupole magnets for the chromaticity correction of the rapid-cycling synchrotron of the Japan Proton Accelerator Research Complex have a large bore of 330 mm and a relatively short length of 320 mm. The end effect, therefore, was not negligible and a three-dimensional magnetic field calculation was necessary to achieve the required field quality of inside the radius of 141.2 mm for the designed maximum field gradient of 18.6 T/m. Eddy current effect on the field quality and temperature rise was considered because the magnets were to be excited with a current pattern of a frequency of 25 Hz. Measurement using harmonic coils confirmed that the required field quality was achieved. Measurement results of the sextupole component and 18-pole component field were reproduced with the magnetic field calculation program OPERA3d/ELEKTRA.

Eddy current effect of magnets for J-PARC 3-GeV synchrotron

The 3-GeV synchrotron proposed in the JAERI/KEK Joint Project (J-PARC) is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400-MeV to 3-GeV at a repetition rate of 25-Hz. The 3-GeV synchrotron is used to produce pulsed spallation neutrons and muons. It also works as an injector for a 50-GeV synchrotron. Since the magnets for the 3-GeV synchrotron are required to have a large aperture in order to realize the large beam power of 1 MW, there is a larger fringing field at a pole end than for a usual synchrotron magnet. In addition, the 25 Hz ac field induces eddy currents in magnet components: e.g., in the coil, magnet end plates, etc. The eddy current induced in the end plates is expected to be large. Therefore, it is important to investigate the effect of large leakage field and eddy current on the beam motion around the magnet end part. We have measured the eddy loss and the eddy current field at the edges of the dipole and quadrupole magnets. In this paper, we report the comparison between the results of the measurements and the two-dimensional eddy current model developed for this study.

Beam position measurement using linac microstructure at the KEK booster synchrotron

The position information of the most recently injected beam from the linac is obtained by picking-up the signal of the harmonic component of the beam, if the bunch structure disappears during one turn due to the momentum spread. The experiment for 201 MHz pickup was performed in the KEK booster ring, and is compared with the simulation. The possible application of this method to the 3 GeV rapid cycling synchrotron in the Japan Proton Accelerator Research Complex (J-PARC) is also addressed.

Linear Coupling Resonance Correction of the J-PARC Main Ring

To reach higher beam power, a linear coupling resonance [1, 2] in the J-PARC Main Ring (MR) should be corrected. The resonance is caused by alignment error of quadrupole magnets and vertical closed orbit distortion in sextupole magnets. To reduce the resonance effect, four skew quadrupole magnets have been installed at front and end of straight sections for injection and fast extraction as shown in Fig. 1. Before manufacturing the skew quadrupole magnets, strength of the resonance was measured by scanning vertical local bump at sextupole magnets. With the measurement, required properties of the skew quadrupole magnets had been fixed. As the first step for correcting the resonance, the MR operating tune was set on the resonance to observe the beam loss, and then we searched good operating currents of the skew quadrupole magnets without accelerating (3GeV DC mode at injection energy). For the next step, the MR was switched to acceleration mode up to 30GeV, and the good operating patterns of the magnets were found successfully. In this paper, design and field measurement of the skew quadrupole magnets, simulated results of the linear coupling resonance, and results of beam study will be shown.

Field Measurement and Machinery Placement of the J-PARC RCS Magnets

The 3 GeV synchrotron in the Japan Proton Accelerator Research Complex (J-PARC) is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400 MeV to 3 GeV at a repetition rate of 25 Hz. RCS is composed of 24 dipole magnets, 60 quadrupole magnets and 18 sextupole magnets. Field measurement was performed for all magnets and adequate results were obtained. In this paper, we will report the results of field measurement and machinery placement of the magnets performed based on those results.

Design and Fabrication of an RCS Magnet Coil Using a Stranded Conductor of J-PARC 3-GeV Synchrotron

The 3-GeV synchrotron now being constructed in the JAERI/KEK Joint Project is a rapid-cycling synchrotron (RCS), which accelerates a high-intensity proton beam from 400-MeV to 3-GeV at a repetition rate of 25-Hz. Magnet coils of the RCS synchrotron are fabricated by using a stranded conductor. As a magnet coil, a hollow conductor that has a cooling water channel is widely used. However since RCS magnet is excited with a rapid cycle, heat of coil conductor caused by eddy current becomes a problem. Therefore, in order to reduce eddy current loss of coil conductor, we used a stranded conductor that consists of many electrically-isolated thin wires wrapped around a cooling water pipe as a coil conductor. This is a conductor developed at KEK as a coil conductor excited with a rapid cycle and was further developed to the stage of mass production. In this paper, we will report design and fabrication of an RCS magnet coil using a stranded conductor.

How to decrease the rise time of a current from a thyratron housing

Abstract Means of decreasing the rise time of the output current from a thyratron housing are discussed. An equivalent circuit, from which calculated results are in good agreement with measurements, is introduced. The simulation shows that the main cause of an increased rise time is not the inductance but the capacitance of the floating housing associated with the cathode heaters and grid supplies. By inserting a large inductance in series with the floating capacitance, the rise time achieved can be very close to that calculated from an ideal circuit which has no floating capacitance or inductance.

Transverse Bunched Beam Instability in KEK Booster

A transverse bunched beam instability has been observed over the past few years in the KEK booster synchrotron, and the kicker magnet for the fast beam extraction has been thought to be responsible for this instability. To check this supposition, the instability was observed quantitatively using a spectrum analyzer and its growth rate was compared with calculations assuming various termination conditions at the feeding end of the coaxial cable of the kicker. The variation of the growth rate with time for a realistic case is well explained by the reflection of the current induced in the kicker at the feeding end of the cable.