Search

The 3-GeV rapid-cycling synchrotron at the Japan Proton Accelerator Research Complex has achieved the highpower beam operation equivalent to 1MW. As a next step, a study of an upgrade is in progress to mitigate the dose exposure of the maintenanceworkers in a high residual dose environment and realize the further high intensity beam power. Regarding the upgrade plan's provisions for radiation protection, a new injection scheme has been proposed to make space available for radiation shielding. The total length of the two shift bump magnets of the four magnets is reduced for this purpose, while the other two magnets in the injection straight section remain unchanged. As a result, the two types of pulse magnets are connected separately in series and are excited by two independent power supplies, which are made possible by splitting the presently installed power supply. A structural analysis of the new shift bump magnet is in progress, including simulations of the effects of eddy currents and the coil temperatures by OPERA-3D. This paper describes preliminary results of this analysis and the outlines the modified power supply design. [ABSTRACT FROM AUTHOR]

The simulation model for a new power supply of the injection bump system magnets refid="ref1"/refid="ref2"/ refid="ref3"/refid="ref4"/ of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Complex) refid="ref5"/, refid="ref6"/ has been constructed. The new power supply requires the reduction of the ripple noise current which will resonate with load and excites a forced beam oscillation at \sim96 kHz in the injection stage. In order to incorporate the load impedance in the simulation model, the impedances of a feeder line and the bump magnet with a ceramic vacuum chamber refid="ref7"/ inside were measured. The RF shield is formed on the ceramic surface along the beam direction. The results were successfully analysed using the OPERA-3D refid="ref8"/ and the circuit simulation code, Micro-Cap refid="ref9"/, and showed a good agreement. It was found the RF shield of a ceramic chamber has a resonant structure corresponding to \sim96 kHz. [ABSTRACT FROM PUBLISHER]

The beam painting injection system of the 3-GeV RCS in J-PARC, which realizes the uniform beam distributions in the ring, consists of four horizontal paint bump magnets and two vertical paint magnets. The power supply of the paint bump magnet is required to excite the current with high accuracy that varies from 17.6 kA to zero during 0.5 ms. The IGBT chopper units, a switching frequency of which is 50 kHz each, are multiply-connected to achieve the effective carrier frequency of 600 kHz. Accordingly, the output accuracy of the exciting current has been achieved to be less than 1.0%. The measurements of the magnetic field with the actual current waveform were performed and the good performance was confirmed. [ABSTRACT FROM AUTHOR]

The four shift bump magnets (BUHS01-04) of the 3-GeV RCS in J-PARC, which are located at the long straight section, produce a fixed main bump orbit to merge the injection beam into the circulating beam. They are realized with four magnets connected in series to form the accurate closed bump orbit. However, the total integrated magnetic field of the four magnets is not zero because of the magnetic field interference between the shift bump magnet and the adjacent quadrupole magnets (Q magnet). In order to measure the magnetic field distribution accurately, the short search coil and the long search coil were used. Furthermore, the imbalance of the total integrated magnetic field has been improvement by inserting 0.3 mm insulators in the median plane of the return yoke of the BUHS02 and 03. The value of the integration has been decreased from 2358.0 G cm to -71.6 G.cm. [ABSTRACT FROM AUTHOR]

New technical issues are initiated in the ITER Toroidal Field (TF) coil manufacturing because of the scale-up by about 3 times from the TF model coil. The major issues are feasibilities of high accuracy, automatic winding, precise prediction of conductor elongation after heat treatment to insert the conductor in narrow groove of a radial plate, and development of insulation system, which can sustain irradiation of a neutron fluence of 1022 n/m2 and, in addition, be impregnated in a suitable duration. One of major parts of automatic winding machine, a bending roller head, was developed and trial winding using short sample conductor was successfully carried out. The elongations of the TF conductor after the heat treatment is evaluated to be in ±0.03% In addition, results of impregnation test using short samples indicate that it will take about 60 h to impregnate TF coil double-pancake by the method developed in the model coil project. New impregnation technique is under development to shorten the impregnation period. [ABSTRACT FROM AUTHOR]

The J-PARC RCS (Rapid Cycling Synchrotron) is designed to inject the H beam from the LINAC, to change their charge from H to H+, to accelerate the H+ beam from 400 MeV to 3 GeV, with 8.3 x 1013 protons per pulse at 25 Hz repetition rate, and to extract the H+ beam after the acceleration to the MLF (Material and Life Science Experimental Facility) and the MR (Main Ring). Thus the RCS has the beam circulating ring and three beam transport lines. The RCS ring consists of several magnets, and the DC magnets are installed for beam injection and extraction. The four steering magnets and two septum magnets are installed at injection line in order to adjust the beam injection point. One quadratic magnet, two steering magnet and two septum magnets are installed at dump line for the part of the beam with their charge not changed from H to H+ at the charge stripping foil. Two deflecting magnets to kick out the beam without exciting the pulse kicker magnets and three septum magnets are installed at the extraction line. Up to now, the DC magnets are developed and manufactured, the field measurements are carried out, and magnets installation into the RCS tunnel are finished. The field distributions of DC magnets are measured by using the new field mapping system with three one-dimensional hall-probes on a 3-axis movable stage. In the case of the quadrupole magnet, the field measurements are not only field mapping but also analyze its magnetic higher order components by the harmonic rotating coil. As a result, the measured field quality meets the design performance requirements of the DC magnets. [ABSTRACT FROM AUTHOR]

3 GeV RCS (Rapid Cycling Synchrotron) at J-PARC (Japan Proton Accelerator Research Complex) comprises with several magnets of different kinds. These include seven septum magnets for the beam injection and extraction at RCS ring. Design requirements for these magnets often conflicts with efforts to minimize leakage magnetic field. Silicon steel sheets set outside of the septum magnets shield leakage magnetic fields so as to keep'proper beam orbits in the ring in most cases. At the beam junction areas for beam injection and extraction, sufficient spacing is not available for installing thick magnetic shields. Vacuum chambers are made by the magnetic stainless steel to reduce the leakage field without a large shield. Results obtained from 3-D field calculations by TOSCA indicate the magnetic leakage field is suppressed down to a few Gauss or less in the present design. All septum magnets and branch structure vacuum chamber made of titanium and magnetic stainless steel are manufactured and assembled successfully. The field measurements of the septum magnets proved that both the strength and also gradient of the magnetic leakage field are diminished. [ABSTRACT FROM AUTHOR]

Installation of the kicker magnets in the extraction section of the RCS in i-PARC facility was completed. They extract a proton beam accelerated up to 3GeV. Since high voltage of 30 kV, which corresponds to 60 kV for charging the pulse forming line, is applied to the magnet every 40 msec, they are installed in vacuum chambers to prevent the electrical breakdown. However, magnetic field mapping is difficult in vacuum. Therefore, we performed the mapping in the air with applying one third of the operational voltage after checking linear dependence of magnetic field to exciting current. A short search coil on the 3-axis stages was used in the magnetic field mapping. The results showed that the good uniformity was achieved in the whole aperture. The magnetic field distribution of the same type of kicker magnet was in good agreement with each other. The excitation test with the operational charging voltage of 60 kV was also performed in vacuum. At the first stage, we were bothered by the electric breakdown. It was noticed that the reduction of outgassing rate by baking was very effective to suppress the discharge. And the continuous excitation was found to have a conditioning effect for the stable operation. [ABSTRACT FROM AUTHOR]

The injection bump system of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) consists of the pulse bending magnets for the injection bump orbit, which are four horizontal bending magnets (shift bump), four horizontal painting magnets (h-paint bump) and two vertical painting magnets (v-paint bump). The shift bump magnets, which are connected in series in order to form a closed bump orbit. The injection bump system needs the power supplies with the high speed and flexible current pattern. Furthermore, the tracking error is required less than 1.0% for 1.0 μs pulse current. The power supplies with the IGBT (Insulated Gate Bipolar Transistor) chopper units, which are controlled by the switching frequency over 60 kHz, realize its performance. The decay time of the shift bump power supply is less than 200 microseconds. [ABSTRACT FROM AUTHOR]

The injection system of the 3-GeV RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) consists of four main orbit bump magnets (shift bump) to merge the injection beam with the circulating beam. In order to control the injection beam with sufficient accuracy, the shift bump magnets need a wide uniform magnetic field. The magnetic field design and the structural analysis of the shift bump magnets have been performed using three-dimensional electromagnetic and mechanical analysis codes. The shift bump magnets have realized a uniform field with less than 0.35% inhomogeneity over a wider area, which is 400 mm in width and 240 mm in height. Furthermore, the magnets operate with a high magnetic field and they are located in high radioactive level area. The flexible bar is applied to the coil as the countermeasure for thermal expansion and the insulator has strong radiation resistance. [ABSTRACT FROM AUTHOR]

Kicker magnets are installed in the extraction section of the RCS (Rapid Cycling Synchrotron) in J-PARC (Japan Proton Accelerator Research Complex) facility. They extract a 3 GeV proton beam and inject it into a downstream beam transport line at a repetition rate of 25 Hz. The power supply is mainly composed of the charging unit, the pulse forming network, and thyratrons as switching device. The maximum charging voltage is 80 kV. The kicker magnet is a distributed (transmission line) twin-C type. The circuit parameters are designed to have the 10 characteristic impedance. The magnets are installed in vacuum chambers to prevent voltage breakdown. In order to accept 1 MW beam power, strict conditions are imposed on the kicker system. In the first part of this paper, we give an outline of the RCS extraction kicker system. Next, we report the specifications and performance of the power source and magnet. In addition, we report the measurements of the vacuum performance and magnetic field. [ABSTRACT FROM AUTHOR]

Septum magnets used in the injection and extraction section of the 3 GeV RCS (rapid cycling synchrotron) of J-PARC (Japan proton accelerator research complex) require a large aperture for low-loss operations of high intensity beam, protection against high radiation, and high durability making unnecessary frequent maintenance after high activation. Therefore, the septum magnets have been designed to work in DC for mechanical stability. Also it works outside the beam vacuum, thus eliminating any trouble due to the leakage of cooling water in the vacuum system. A prototype extraction septum magnet was constructed. Magnetic field in the gap of the yoke and leakage field outside of the magnetic shield were measured with a three dimensional Hall probe. The experimental results were compared with three dimensional magnetic field calculations made by TOSCA. The measurement of the magnetic field in the gap agrees well with a simple 3D model. On the other hand, leakage field of the measurement is larger than that of the model. Because the thickness of the return yoke is not sufficient, the magnetic flux density approaches saturation. After we made a more detailed model, it was confirmed that the many bolt holes which fasten the return yoke narrow the effective cross sectional area, thus reduce the effective permeability, and make the magnetic reluctance and the leakage field larger. This paper also describes the results of heat measurements of the magnet and efficiency of water cooling. [ABSTRACT FROM AUTHOR]

Septum magnets are used in the injection and extraction section of the 3 GeV rapid cycling synchrotron (RCS) of J-PARC (Japan Proton Accelerator Research Complex). The RCS needs seven septum magnets, two for the injection line, two for the beam dump line and three for the extraction line, respectively. These septa require a large aperture for low-loss operation with high intensity beams, and high durability for minimizing maintenance after high activation. For insuring mechanical stability the septum magnets have been designed to work DC. The septa magnets work outside a vacuum, thus eliminating any trouble due to the leakage of cooling water into the vacuum system. We have been designing them by using the three dimensional magnet static field calculation code, TOSCA. This paper describes the flatness of the magnetic field in the gap and reduction of the leakage field of the septum magnets in the RCS. [ABSTRACT FROM AUTHOR]