Tetsuhiro Obana

Design of superconducting combined function magnets for the 50 GeV proton beam line for the J-PARC neutrino experiment

Superconducting combined function magnets will be utilized for the 50 GeV-750 kW proton beam line for the J-PARC neutrino experiment and an R&D program has been launched at KEK. The magnet is designed to provide a combined function with a dipole field of 2.59 T and a quadrupole field of 18.7 T/m in a coil aperture of 173.4 mm. A single layer coil is proposed to reduce the fabrication cost and the coil arrangement in the 2D cross-section results in left-right asymmetry. This paper reports the design study of the magnet.

Concept of magnet systems for LHD-type reactor

Heliotron reactors have attractive features for fusion power plants such as having no need for current drive and a wide space between the helical coils for the maintenance of in-vessel components. Their main disadvantage was considered to be the necessarily large size of their magnet systems. According to the recent reactor studies based on the experimental results in the Large Helical Device, a major radius of plasma of 14?17?m with a central toroidal field of 6?4?T is needed to attain the self-ignition condition with a blanket space thicker than 1.1?m. The stored magnetic energy is estimated at 120?140?GJ. Although both the major radius and the magnetic energy are about three times as large as ITER, the maximum magnetic field and mechanical stress are comparable. In the preliminary structural analysis, the maximum stress intensity including the peak stress is less than the 1000?MPa that is allowed for strengthened stainless steel. Although the length of the helical coil is more than 150?m, that is about five times as long as the ITER TF coil, cable-in-conduit conductors can be adopted with a parallel winding method of five-in-hand. The concept of the parallel winding is proposed. Consequently, the magnet systems for helical reactors can be realized with a small extension of the ITER technology.

Superconducting magnet system at the 50 GeV proton beam line for the J-PARC neutrino experiment

A neutrino oscillation experiment using the J-PARC 50 GeV 0.75 MW proton beam is planned as a successor to the K2K project currently being operated at KEK. A superconducting magnet system is required for the arc section of the primary proton beam line to be within the space available at the site. A system with 28 combined function magnets is proposed to simplify the system and optimize the cost. The required fields for the magnets are 2.6 T dipole and 19 T/m quadrupole. The magnets are also required to have a large aperture, 173.4 mm diameter, to accommodate the large beam emittance. The magnets will be protected by cold diodes and cooled by forced flow supercritical helium produced by a 4.5 K, 2/spl sim/2.5 kW refrigerator. This paper reports the system overview and the design status.

Development and Test of JT-60SA Central Solenoid Model Coil

A central solenoid (CS) model coil (CSMC) was manufactured by using real manufacturing jigs and procedure to validate the CS manufacturing processes for JT-60SA. The winding accuracy and the temperature control precision during the heat treatment met the requirements. The vacuum pressure impregnation process was also successfully finished. The cold test of the CSMC was performed as a final check of the manufacturing process. The joint resistance, the Ic, and the pressure drop measurements were conducted as the verification test. The results of verification test satisfied the design requirements. These results indicate that the manufacturing processes of the JT-60SA CS has been established. The manufacturing of real CS pancakes just started after finishing the CSMC test.

Development of Central Solenoid for JT-60SA

Several components for central solenoid (CS) of JT-60 Super Advanced (JT-60SA) were newly developed and tested. The butt-type joint, the electrical resistance of which is about 2 nΩ, was developed to increase the winding diameter. The insulation system, which consists of Glass/Kapton/Glass tape and Bisphenol A diglycidyl ether (DGEBA) epoxy, showed sufficient tensile strength after the irradiation of 100 kGy. Insulation characteristics of 4 × 4 winding stack sample after the compression of 705 kN 36 000 times was able to withstand voltages larger than 21 kV. The heat treatment and transfer of the CS model coil with superconductor were conducted. The pancake temperature during flat top was maintained at 923 ± 4 K. The maximum temperature difference in the pancake was 30 K. All manufacturing processes were confirmed so that the mass production of CS will be started in 2013.

Test Results of Superconducting Combined Function Prototype Magnets for the J-PARC Neutrino Beam Line

Superconducting combined function magnets are adopted for the 50 GeV, 750 kW proton beam line for the J-PARC neutrino experiment, and two full-scale prototype magnets have been developed successfully at KEK. In the cold tests, both prototypes were excited up to 7700 A without spontaneous quenches. The measured field quality of the both prototypes agreed well with the design field, indicating that the fabrication process has no major problem. The heater quench tests of the first prototype, however, showed that the magnet was not self-protected. Consequently, the design was revised and quench protection heaters were adopted. In quench heater tests of the second prototype magnet using small sheet heaters, the fundamental characteristics of the quench protection heaters were studiedSuperconducting combined function magnets for the J-PARC (Japan Proton Accelerator Research Complex) neutrino experiment have been successfully developed at High Energy Accelerator Research Organization, KEK. The first prototype magnet reassembled for the quench protection studies, and the cold test result indicated that the eight quench protection heaters are effective for the safe protection of the magnet. Three production magnets have been fabricated and tested at 4.5 K, 1 atm, in a vertical cryostat, and the excellent excitation and quench performances are observed. In the field measurement during cold tests, all the magnets indicated the field qualities good enough to fulfill the specification. The field measurement at room temperature has been also performed with the three production magnets for checking the dipole field component. The results are consistent with the computation.

Development of a prototype of Superconducting combined function magnet for the 50 GeV proton beam line for the J-PARC neutrino experiment

Superconducting combined function magnets will be utilized for the 50 GeV, 750 kW proton beam line for the J-PARC neutrino experiment and an R&D program has been launched at KEK. The magnet is designed to provide a combined function of a dipole field of 2.6 T with a quadrupole field of 19 T/m in a coil aperture of 173.4 mm. Critical magnet components including glass-fiber reinforced phenolic plastic spacers have been successfully developed. The mechanical design has been verified by a 100 mm long short-cut model, and coils have been wound for the first full-length prototype.

Development of Curved Combined-Function Superconducting Magnets for a Heavy-Ion Rotating-Gantry

Combined-function superconducting magnets are designed for a heavy-ion rotating gantry. The superconducting coils of these magnets have a surface winding coil structure. To minimize sagitta, the superconducting magnets as well as their coils have a curved shape. Ten superconducting magnets are installed on the rotating gantry. With the superconducting magnets, the rotating gantry can transport carbon ions having 430 MeV/u to a patient with irradiation angles of over ±180 degrees, and is further capable of performing three-dimensional raster-scanning irradiation. Since the superconducting magnets would be rotated by ±180 degrees, compact cryocoolers are employed for cooling of the superconducting coil. Because the coil has quadrupole and dipole layers, the superconducting magnets can provide both quadrupole and dipole magnetic field. Using the combined-function superconducting magnets, we can design a compact rotating gantry, while keeping a large scan size at the isocenter; the length and the radius of the gantry would be approximately 13 and 5.5 m, respectively, which are comparable to those for the existing proton gantries. In this paper, we report the design of the superconducting magnets as well as results of some tests.

Superconducting combined function magnet system for J-PARC neutrino experiment

The J-PARC Neutrino Experiment, the construction of which starts in JFY 2004, will use a superconducting magnet system for its primary proton beam line. The system, which bends the 50 GeV 0.75 MW proton beam by about 80 degrees, consists of 28 superconducting combined function magnets. The magnets utilize single layer left/right asymmetric coils that generate a dipole field of 2.6 T and a quadrupole field of 18.6 T/m with the operation current of about 7.35 kA. The system also contains a few conduction cooled superconducting corrector magnets that serve as vertical and horizontal steering magnets. All the magnets are designed to provide a physical beam aperture of 130 mm in order to achieve a large beam acceptance. Extensive care is also required to achieve safe operation with the high power proton beam. The paper summarizes the system design as well as some safety analysis results.

Stability and Quench Test for NbTi CIC Conductor of JT-60SA Equilibrium Field Coil

The EF coil conductors of JT-60SA are designed with the NbTi cable in conduit conductor because the maximum magnetic field goes up to 6.2 T. The prototype NbTi conductor was developed and tested to confirm the capability of the real conductor. The prototype conductor was proven to have enough Tcs margin under the operating conditions investigated in previous test. In this study, the quench test was operated to measure the stability margin and the normal state propagation. Firstly, the MQE under the Tcs margin of 0.2 K was found to be 80 mJ/cc-strand which is almost the same as that of the previous CIC conductor to result in enough stability margins on EF coil operation. Secondly, the propagation velocity to upstream direction and downstream direction were found to be about 0.47 m/s and 0.54 m/s, respectively. Finally, the quench analysis was conducted to calculate the maximum temperature during quench. The analysis results showed that the maximum temperature reached about 70 K, which is within the permissible value of 150 K for the EF coils.