Osamu Araoka

Construction of Superconducting Magnet System for the J-PARC Neutrino Beam Line

Following success of a prototype R&D, construction of a superconducting magnet system for J-PARC neutrino beam line has been carried out since 2005. A new conceptual beam line with the superconducting combined function magnets demonstrated the successful beam transport to the neutrino production target.

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.

Commissioning Results of Superconducting Magnet System for the Neutrino Beam Line

The first commissioning of a magnet system for the neutrino beam line in the J-PARC has been performed from January to March, 2009. The magnet system could be cooled down successfully in 9 days. RRRs of all the magnets and joint resistances in the magnet string were measured to be reasonable values. The magnet string composed of 28 superconducting combined function magnets could be excited up to 5000 A after several shutdown tests without a spontaneous quench. A quench protection scheme with a magnet safety system developed by CEA/SACLAY were verified to work properly. As for beam commissioning, the proton beams could pass through the arc section including the superconducting magnet string on the first attempt, and the magnet protection system were verified to work quite well even in a beam induced quench test.

Status of Superconducting Magnet System for the J-PARC Neutrino Beam Line

A superconducting magnet system for the J-PARC neutrino beam line has been under construction since 2004. The system consists of 14 doublet cryostats; each contains 2 combined function magnets (SCFM). The SCFM uses two single layer left/right asymmetric coils that produce a dipole field of 2.6 T and quadrupole of 19 T/m. The SCFMs had been developed by 2004, mass-produced since 2005, and completed by summer 2008. The system is being installed since Feb. 2008 till the end of 2008. The paper summarizes the system overview including cryogenics and safety peripheries. The paper also reports the production and installation status.

CRYOGENIC SYSTEM FOR J‐PARC NEUTRINO SUPERCONDUCTING MAGNET BEAM LINE—DESIGN, CONSTRUCTION AND PERFORMANCE TEST

A helium cryogenic plant has been constructed in the proton accelerator research complex, J‐PARC, to cool a string of superconducting magnets in the neutrino beam line since 2005. It consists of a screw compressor with a capacity of 160 g/s at 1.4 MPa, a 1.5 kW refrigerator, a centrifugal SHE pump with a flow rate of 300 g/s and peripherals. After system integration, performance tests have been carried out. In a preliminary cooling test without magnets, the cryogenic system attained a cooling capacity of 522 W by circulating supercritical helium flow of 300 g/s at 0.4 MPa and at 4.5 K. Afterwards a full system test with the magnets was carried out. The magnets were successfully charged up to an ultimate current of 5000 A beyond a nominal current of 4400 A. This paper describes the plant design and the result of performance measurements.

Performance Tests of Superconducting Combined Function Magnets in the First Full-Scale Prototype Cryostat for the J-PARC Neutrino Beam Line

The first full-scale prototype magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment was successfully developed and tested. Two superconducting combined function magnets have been installed into the cryostat. The magnets were successfully cooled down to 4.5 K by forced flow supercritical helium and excited up to the current of 7345 A which is the nominal current of 50 GeV proton beam. The spot heater quench test showed that the quench characteristics in the supercritical helium were very similar to that in the liquid helium at 4.2 K, 1 atm. The quench protection scheme with both cold diodes and quench protection heaters was tested, and it has been verified that the magnet can be protected with safe margin.

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

Fabrication and cold tests of 32 superconducting combined function magnets including 4 backup magnets for the J-PARC neutrino have been completed. All the magnets reached 7700 A, 105% of maximum operation current, without any spontaneous quenches. Quench protection performance was also confirmed to be safe. In the field measurement during cold tests, all the magnets showed sufficient field quality to fulfill the specification. Reproducibility of the field quality was evaluated to be about the same order of that observed in ordinary cos-thetas magnets, indicating good manufacturing reproducibility.

Magnetic Field Measurement System in Superconducting Combined Function Magnets for the J-PARC Neutrino Beam Line

Magnetic field measurements have been performed for the first full-scale magnet system assembled with the cryostat for the J-PARC proton beam line of neutrino experiment. In the measurement system, the probe position with respect to magnet central axis is measured by a Helium Neon laser and a position sensitive detector, PSD, in order to obtain an exact dipole field strength. Errors associated with the PSD misalignment and influences on the PSD signals by the magnetic field were evaluated. The measured dipole components approached to the design values by compensating those with the probe position. The latest beam simulation indicated that the measured values of magnetic field were good enough for the primary proton beam transport.

Cryogenic characteristics of a large thin superconducting solenoidal magnet cooled by forced two-phase helium

Abstract A prototype thin superconducting solenoidal magnet for the SDCdetector (Solenoidal Detector Collaboration for the former SSC project) was developed. The magnet was cooled down and excited up to 12,000A in the performance test at KEK. The magnet is 3.8 m in diameter, 2 m in length with a total cold mass of 4.5 tonnes. It was cooled by using indirect two-phase helium flow passing through a 64 m serpentine cooling path. The hydrodynamic characteristics has been investigated. The measured result and preliminary analysis are discussed.

Pressure drop of two-phase helium flowing in a large solenoidal magnet cooling path and a long transfer line

Abstract The pressure drop of two-phase helium flowing in a 64 m cooling path of a magnet and a 58 m connecting transfer line was investigated. A large thin superconducting solenoidal magnet, which was developed for the SDC detector (Solenoidal Detector Collaboration for the former SSC project), was used for this experiment. The magnet is 3.8 m in diameter, 2 m in length with a total cold mass of 4.5 tons. It was cooled by two-phase helium flow passing through a serpentine cooling path. The pressure drops of single-phase gas helium flow during cool down and two-phase helium flow in steady cooling were measured and compared with predictions. The measured pressure drop of single-phase helium agreed well with the prediction; however, the measured pressure drop of two-phase helium was much larger than the predictions based on separated and homogeneous flow models. In the high mass-flow region of two-phase flow, slight pressure oscillations were observed in the inlet, outlet and differential pressures of the magnet. The magnet temperature was stable and not affected by those oscillations.