Yasushi Arimoto

A compact SEOP 3He neutron spin filter with AFP NMR

We developed AFP NMR in an aluminum container for polarized noble gas nuclei. The radio frequency magnetic field inside the aluminum container was designed from computer simulations. The polarization loss by the AFP spin flip of 3He was measured to be as low as 3.8×10−4. With this technique, a compact in-situ polarizing 3He neutron spin filter with AFP NMR is demonstrated.

Developments of In-Situ SEOP Polarized 3He Neutron Spin Filter in Japan

We launched the polarized 3He neutron spin filters (NSF) project in order to provide neutron polarization for the pulsed neutron beams in Japan. We adopted the in-situ spin exchange optical pumping (SEOP) technique to polarize the nuclear spin of 3He atoms because it has some advantages for our applications. The overall system size is compact and it avoids the problem of the time decay of nuclear spin of 3He thus suppressing the costs of maintenance and providing other advantages [1, 2] with respect to data analysis and quality. In this paper, we performed pulsed neutron beam tests of our compact in-situ SEOP NSF system at the BL10 beamline in the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC). The polarization of the 3He gas reached was 73 % and a pump-up time constant of 9.5 h was observed. This paper is a status report about the development of in-situ SEOP NSF system for the pulsed beam at J-PARC.

Design and Construction of the SuperKEKB QC1 Final Focus Superconducting Magnets

The construction of SuperKEKB, which consists of 7 GeV electron and 4 GeV positron main rings, is now going on. The final focus superconducting quadrupole magnets in the interaction region have been designed and constructed. From the field qualities of the prototype magnets, the magnet designs were modified, and the manufacturing and assembling methods of the coils were changed to satisfy the design values. The field measurements of the magnets were performed at room temperature, and confirmed that they were acceptable for the beam operation. In the paper, the design and the construction of the final focus quadrupole magnets, QC1, which will be located at the closest position to the beam interaction point, are presented.

Development of HTS Sextupole Magnet for SuperKEKB Interaction Region

The SuperKEKB project underway at KEK will increase the KEKB luminosity by 40 times using nanobeam-interaction-region focusing optics. To achieve this high luminosity, the chromaticity correction of the collision beams is crucial; thus, special sextupole magnets, which can simultaneously produce normal and skew sextupole fields, are required in the straight sections around the interaction point. As a candidate for the sextupole, a cryocooled high-temperature superconducting magnet was proposed; development has begun. Here, the basic magnet design and the results of a small coil test are presented. The test studied the quench characteristics of the REBCO-impregnated coil.

Improvement of 3 He Nuclear Polarization for Neutron Scattering

Nuclear-polarized 3 He gas has recently been widely used in neutron facilities around the world for polarized neutron scattering. The large neutron absorption cross-section of 3 He depends strongly on the 3 He-spin and the neutron-spin directions, and a polarized neutron beam can be easily obtained by passing the beam through polarized 3 He gas, thus constituting a neutron spin filter (NSF). The relationships between neutron polarization Pn, neutron transmission Tn, and 3 He polarization PHe are:

Development of polarized Xe gas target for neutron experiment at J-PARC

At the Materials and Life science experimental Facility (MLF) in J-PARC, an experiment of detecting a neutron polarizing ability caused by a neutron-nuclear spin correlation at a resonant peak of 129Xe is planned. We evaluated measurable quantities based on a neutron optical theorem, developed a polarized Xe gas system, and carried out a feasibility test of our apparatus.

Applications of 3He neutron spin filters on the small-angle neutron scattering spectrometer SANS-J-II

A polarized 3He neutron spin filter has been applied to polarization analysis on the small-angle neutron scattering spectrometer SANS-J-II at JRR-3. Measurements were taken on silver behenate, which has several coherent peaks in the small-angle region with a background of spin incoherent hydrogen scattering. Here we demonstrate that the coherent and spin incoherent scattering were successfully separated by the polarization analysis using the 3He spin filter on the instrument.

Magnetic Field Distribution Control With Anisotropic Inter-Pole Magnetic Field

A novel method to control a magnetic field distribution in a magnet is devised with use of inter-poles made of anisotropic magnet material. One can generate a gradient field in a constant gapped magnet with this technique; the effective length of the magnet can be constant, independent of the entrance position. Such a magnet can have not only constant gap but also smaller fringing field compared with a conventional one that controls its field distribution by changing the gap height

Experimental study on heat transfer through a few layers of multilayer insulation from 300 K to 4.2 K

The final focusing magnet system at the SuperKEKB interaction region has been designed under stringent space constraints and consists of 8 main Superconducting (SC) quadrupole magnets, 4 compensation SC solenoids, and 43 SC correction coils. SC correction coils are directly wound on the inner containment tubes of liquid helium (LHe) vessels, which serve as support bobbins for SC cables. Beam pipes, which are kept at room temperature (~300 K), are inserted into the cold bores of the vessel inner tubes. Between them, the minimal radial gaps are only 3.5 mm. Heat transfer from the warm beam pipes causes the raised operation temperatures of SC cables and increases heat leaks into cryostats. Multilayer insulation (MLI) is adopted to reduce heat flux in the narrow gaps. MLI performance as a function of the layer number was studied with a vertical anti-cryostat of dedicated design. The measurements were carried out by a calorimeter of thermal conduction and a modified LHe boil-off method. This paper presents the cryogenic measurement system and discusses the experimental results for the cryostats of the SuperKEKB final focusing SC magnets.

Design and Performance Test of a Superconducting Compensation Solenoid for SuperKEKB

The construction of a final focusing superconducting magnet system for SuperKEKB is underway. The superconducting magnet system consists of eight quadrupole magnets, four compensation solenoids, and 43 corrector coils. They are installed inside of the particle detector, i.e., Belle-II, which has a superconducting solenoid generating 1.5 T in the magnet center. Four compensation solenoids produce the magnetic field with the opposite direction to the Belle-II solenoid field to reduce the X - Y coupling of the collision beams and achieve the high luminosity of 8 × 1035 cm-2 · s-1. The compensation solenoids are wound with a 1.5-mm-thick and 1-mm-wide NbTi wire, which has a critical current of 1.8 kA at 4.2 K and 4 T. The minimum inner and outer radii of the compensation solenoids are approximately 70 and 200 mm, respectively. The length of the longest compensation solenoid is approximately 1.56 m. The maximum operating current and the maximum magnetic field of the solenoids are designed to be less than 450 A and 4 T, respectively. The construction and performance test of a compensation solenoid are completed. In this paper, the magnet design, excitation test, and magnetic field of the compensation solenoid are presented.