Yasushi Arimoto

High Energy Accelerator Research Organization | KEK · Accelerator Laboratory

A prototype high-temperature superconducting （HTS） sextupole magnet for the SuperKEKB interaction region has been designed, fabricated and tested. The magnet consists of two types of sextupole coils, normal and skew coil, wound with a REBCO coated conductor 4 mm in width. The design field gradients of the normal and skew coil are 200 T/m² and 20 T/...

A new muon beamline is under construction for the COMET Phase-I experiment at J-PARC. The experiment requires a negative muon beam with the world-highest intensity to search for muon-electron conversion processes. The muon beamline consists of a series of superconducting solenoid magnets to generate muons by 8 GeV pulsed proton beam from MR of J-PA...

The International Linear Collider (ILC) main linac comprises a series of 12 m-long cryomodules. The cryomodule contains eight 9-cell superconducting (SC) RF (SRF) cavities and an SC quadrupole magnet combined with dipole correctors to focus and steer electron and positron beams. The magnets are installed between the SRF cavity string and at the lon...

Along the beam lines of the SuperKEKB main rings, 218 conventional sextupole magnets are installed, and they are used for tuning the chromaticity of the accelerator rings. Especially, 16 sextupole magnets in the beam straight lines in the Tsukuba area are quite essential for the Crab Waist beam colliding. To make the beam tuning process finer, we a...

The COMET experiment, currently under construction at J-PARC, aims to explore the process of muon-to-electron conversion in a nucleus. This phenomenon, known as charged-lepton flavor violation, is an elementary process beyond the Standard Model. The muon beam is produced from pion decays generated by bombarding a proton beam on a target and correct...

SuperKEKB, which is currently in operation at the KEK Tsukuba campus, is operated by squeezing the electron and positron beams at the interaction point (IP) to β * y = 1 mm and β * y = 60 mm. Eight superconducting (SC) quadrupole magnets squeeze the two beams at IP. When the SC quadrupole magnets were re-energized, we observed a change of vertical...

In the main linac of the International Linear Collider (ILC), superconducting magnets for beam focusing and steering will be located periodically in superconducting RF (SRF) cavity string for beam acceleration in common cryomodules. A concept of conduction cooling of the combined-functioned, splittable superconducting magnets has been proposed and...

SuperKEKB is an electron-positron asymmetric-energy double-ring collider, which was built in Japan. It has been operated to explore new phenomena in B-meson decays. Hence, extremely higher luminosity is required. A collision scheme of low emittance with a large Piwinski angle called a "nano-beam scheme" has been adopted to achieve higher luminosity...

SuperKEKB is an electron–positron asymmetric-energy double-ring collider, which was built in Japan. It has been operated to explore new phenomena in B-meson decays. Hence, extremely higher luminosity is required. A collision scheme of low emittance with a large Piwinski angle called a “nano-beam scheme” has been adopted to achieve higher luminosity...

The SuperKEKB was designed and constructed as the upgraded accelerator of KEKB. In this accelerator design, the nano-beam scheme of collision was applied and a luminosity of 8 × 10³⁵ cm⁻²s⁻¹ was targeted. In the design, the beam final focus system was the key component in the accelerator hardware elements. This final focus system consists of 55 sup...

A prototype ${\rm{REBa_{2}Cu_{3}O_{y}}}$ (REBCO) sextupole coil was designed and fabricated for the chromaticity correction of an asymmetric—energy collider, named SuperKEKB. The REBCO sextupole coil consists of the six two-layer-rectangular coils, which are wound with a 4-mm-wide coated conductor and impregnated with the epoxy resin. The inner b...

A final focus quadrupole system (QCS) was installed into the interaction region (IR) of SuperKEKB, and was aligned to accelerator coordinates on February 2017. QCS is a superconducting magnet system consisting of eight quadrupole magnets and four compensation solenoids. We performed measurements of magnetic centers and roll-angles of all quadrupole...

The 55 SuperKEKB final focusing superconducting magnets are assembled into two cryostats, located at the left side and the right side of the accelerator interaction point, respectively. The two cryostats are cooled by sub-cooled liquid helium at 0.16 MPa with two independent refrigerators of about 250 W cooling capacity. From August 2016, the two c...

A prototype high-temperature superconductor (HTS) sextupole magnet for the SuperKEKB Interaction Region was fabricated and tested in order to gain the experience in the fabrication of the HTS magnets as well as to understand their characteristics. The designed field strength of the sextupole magnet is 200 $\rm T/m^2$ at 30 K. The coil of the magn...

The construction of a final focusing superconducting magnet system for SuperKEKB has been completed. The superconducting magnet system consists of eight quadrupole magnets, four super-conducting compensation solenoids and 43 corrector coils. These magnets are installed in two cryostat, QCS-L and QCS-R. QCS-L and QCS-R are inserted into the particle...

The SuperKEKB electron-positron collider is an accelerator that has been upgraded for the KEKB. This collider is designed to explore New Physics beyond the Standard Model of particle physics in the B meson regime. The target of SuperKEKB is to attain a luminosity that is 40 times higher than that of the KEKB. To accomplish this, a new beam final fo...

The PRISM-FFAG ring, which consists of 10 scaling radial sector magnets, has been designed to store muons with large emittance and momentum spread. The FFAG magnets differ from conventional dipole magnets in that they have a magnetic field that varies strongly with radius and the vertical direction of the magnetic field alternates. Each magnet is c...

SuperKEKB is an asymmetric-energy electron-positron collider designed to achieve 40 times luminosity of KEKB B-factory. The phase-2 commissioning was carried out from 19th March to 17th July 2018 to confirm the “nano-beam” scheme collision. In the early stage of the phase-2 commissioning, the basic functionality of the final focus quadrupole double...

The beam final focus system in the SuperKEKB in-teraction region, IR, consists of 55 superconducting magnets in-cluding 8 main quadrupole magnets. Two cryostats for these mag-nets were required to be operated inside the Belle-II particle detec-tor because of the magnet positions by the SuperKEKB beam op-tics. The cryostats were designed under const...

A remote monitoring system was developed based on the software infrastructure of the Experimental Physics and Industrial Control System (EPICS) for the cryogenic system of superconducting magnets in the interaction region of the SuperKEKB accelerator. The SuperKEKB has been constructed to conduct high-energy physics experiments at KEK. These superc...

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...

Forty-three superconducting (SC) correction coils with maximum currents of about 60 A are installed in the SuperKEKB final focusing magnet system. Current leads to energize the SC correction coils should have an affordable heat load and fit the spatial constraints in the service cryostat where the current leads are installed. To address the require...

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...

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 ma...

The SuperKEKB B-Factory at KEK (Japan), after few years of shutdown for the construction and renovation, has finally come to the Phase-1 commissioning of the LER and HER rings, without the final focus system and the Belle II detector. Vacuum scrubbing, optics tuning, and beam related background measurements were performed in this phase. Low emittan...

To energize the SuperKEKB final focus superconducting (SC) magnets, 110 current leads in total will be equipped in the two service cryostats. For the SC quadrupoles and solenoids, 22 leads are the conventional vapor cooled type and the others for the SC correction coils employ an HTS section at the cold ends. The qualification program on the leads...

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 met...

A new time projection chamber (TPC) was developed for neutron lifetime measurement using a pulsed cold neutron spallation source at the Japan Proton Accelerator Research Complex (J-PARC). Managing considerable background events from natural sources and the beam radioactivity is a challenging aspect of this measurement. To overcome this problem, the...

Low energy neutrons can be accelerated or decelerated by the technique of AFP-NMR with RF in a gradient magnetic fields. The neutrons have magnetic moments, hence their potential energy are not cancelled before and after passage of magnetic fields and their kinetic energy change finally when their spins are flipped in the fields. Nowadays most meas...

A final focus magnet system of SuperKEKB consists of 4-superconducting (SC) quadrupole doublets, 43 SC-correctors, 4 SC-compensation solenoids. They are aligned in a detector (Belle-II) solenoid which generates a longitudinal field of 1.5 T. These magnetic components are separately designed and the beam optics simulation has been performed with the...

He-3 neutron spin filters require a homogeneous magnetic field, otherwise the nuclear polarization of the He-3 gas will easily be lost by small magnetic field gradients. Magnetic cavities with field gradients of 10(-4)/cm or better are often in demand, and many such cavities - Helmholtz coils, solenoids, permanent magnet circuits, etc - have been d...

A polarized He-3 neutron spin filter requires a suitably homogeneous magnetic environment to avoid depolarization of He-3 nuclear spin. In the present study, we discussed the required performance of the magnetic shield for an in-situ spin exchange optical pumping neutron spin filter system and designed a magnetic shield with T-1mag > 100 h under a...

The SuperKEKB project requires a positron and electron collider with a peak luminosity of 8 x 10(35) cm(-2) s(-1). This luminosity is 40 times that of the KEKB B-factory, which operated for 11 years up to 2010. SuperKEKB is an asymmetry-energy and double-ring collider; the beam energy of the positron (LER) is 4 GeV and that of the electron (HER) is...

Ultra cold neutrons (UCN), which have energies less than 300 neV, can be accelerated or decelerated by controlling static magnetic and RF fields. Neutron kinetic energies can inclease or declease when their spin flip. This method can be used to rebunch a pulsed beam of neutrons to a storage bottle that can store UCN with high density. High UCN dens...

A neutron beamline for the study of fundamental physics has been constructed at the spallation neutron source of the Japan Proton Accelerator Research Complex (J-PARC). In-flight measurement of the neutron lifetime and the development of the transport optics of ultracold neutrons are in progress. The present status of the beamline and these experim...

Space-time focusing was demonstrated by a neutron accelerator. Test experiments were performed by using very slow neutrons at High-Flux Reactor at Institut Laue-Langevin. Focusing of neutrons at the detector position through the accelerator was observed. Focusing neutrons enables us to transport the neutrons while maintaining density from source to...

Using a transportable 3He spin filter neutron polariser, we have constructed a polarised thermal neutron diffraction (PND) instrument on a powder neutron diffractometer. To minimise the inhomogeneity of the magnetic fields around the 3He spin filter, an optimised compact non-adiabatic two-coil spin flipper for the PND instrument was developed. Magn...

Ultra-cold neutron (UCN) is attractive for a search of the neutron electric dipole moment (nEDM). It is crucial to store UCNs with high density in a bottle for nEDM measurement apparatus. To increase the density, time focusing technique can be useful, where slow neutrons are accelerated and fast neutrons are decelerated by using magnetic potential....

The spin-exchange cross-section, σ se, was measured for a 6.33 keV/amu 3He+ ion incident on a polarized Rb atom. The result is σ se = −0.26+0.27 × 10−15 cm2, which is unexpectedly an order of magnitude smaller than the theoretical value σ se = 5.9 × 10−15 cm2 evaluated by the semiclassical impact parameter method assuming formation of a single mole...

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 feasibilit...

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...

Acceleration control for neutrons was demonstrated. Ultra cold neutrons (UCN) -neutrons with energies less than 300 neV - can be accelerated or decelerated by means ofstatic magnetic and RF fields. Neutrons have a magnetic dipole moment, and hence theirkinetic energies vary depending on their spin in magnetic fields. Their kinetic energiesare resto...

A gradient DC magnet is designed using 3D magnetic field analysis code. This magnet, referred to as a B0 magnet, is one of the key elements of a time-focusing device for ultra-cold neutrons (UCNs) based on a radio frequency gradient flipper – a so-called rebuncher. The magnet generates a guide and a potential field that interacts with the magnetic...

In spin-exchange optical pumping, there is unknown excess relaxation, called the X-factor, that limits attainable 3He polarization. It is known that the X-factor depends on the glass containers. Hence, it is expected that there are cell-to-cell variations in microscopic structure among the cells and that these variations affect the attainable 3He p...

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 i...

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 an...

Polarized neutron spin filters are being developed based on spin-exchange optical pumping. In the present study a high-power diode laser (85 W) was used to excite Rb atoms and the laser linewidth was narrowed using an external cavity. The optics in the external cavity were designed by ray tracing. The ray-trace calculations demonstrated that a doub...

We have begun the development of an in-situ spin-exchange optical pumping (SEOP) system aiming to use it as a neutron spin filter for incident beam polarization at the Japan Proton Accelerator Research Complex (J-PARC). To use it, it is recommended that the optics be adjusted easily, have high stability, and have a small size. In this paper we impr...

We measured the neutron beam polarization of the BL05/NOP (Neutron Optics and Physics) beamline at J-PARC with an accuracy of less than 10−3 using polarized 3He gas as a neutron spin analyzer. Precise polarimetry of the neutron beam is necessary to understand the beamline optics as well as for the asymmetry measurements of the neutron beta decay, w...

Polarized 3He neutron spin filters are suitable devices for polarizing neutrons at spallation neutron facilities because of the wide coverage in energy range and the large solid-angles. The glass cell plays an important role in the 3He spin filters. In order to get good quality of glass cells, the investigation on the microscopic structure would be...

We have developed thin film Fresnel lenses made of a hydrogen-free amorphous polymer for neutron focusing purposes. A neutron beam test showed the strong focusing of a cold neutron beam, and an increase of the neutron intensity was observed to be more than 50 times.

The PRISM–FFAG ring, which consists of 10 scaling-radial-sector magnets, has been designed to store muons with large emittance and momentum spread. The FFAG magnets differ from conventional dipole magnets in that they have a magnetic field that varies strongly with radius and the vertical direction of the magnetic field alternates. Each magnet is c...

A test experimental line at SPring-8 has been constructed for the generation of backward Compton scattered (BCS) γ-rays by head-on collision between an 8 GeV electron beam and a far-infrared (FIR) laser. For the FIR laser, we use a continuous-wave methanol laser optically pumped by a carbon dioxide (CO2) laser. The FIR laser output power achieved i...

The magnetic field of three scaled-radial-sector fixed field alternating gradient (FFAG)-magnets has been measured. The magnets have very large horizontal (1 m) and vertical (0.3 m) apertures to store muons and achieve phase rotation in an FFAG ring. The measurements results are compared to a three-dimensional field analysis using the TOSCA code; t...

The magnetic field of three scaled-radial-sector fixed field alternating gradient (FFAG)-magnets has been measured. The measurements results are compared to a three-dimensional field analysis using the TOSCA code; the generated magnetic field agrees satisfactorily with the TOSCA calculation in a range of 0.5%. Tracking simulation with the measured-...

Unwanted particles produced in various acceleration stages are detrimental for delayed coincidence experiments involving rare decays such muon to electron conversion. A new monitoring scheme is proposed to realize the beam extinction lower than 10 -6 for a bunched proton beam. Dissociation of hydrogen molecules into hydrogen atoms is detected by co...

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 const...

A large-aperture FFAG magnet for the PRISM has been designed. The performance of this magnet is simulated by a particle tracking. The R&D status will be presented.

In order to produce MeV photons (γ-ray) by the laser Compton scattering (LCS), a high power optically pumped far infrared (FIR) laser has been developed at SPring-8. We obtained about 1.6 W of maximum output power of FIR laser at CH3OH 119 μm lasing line pumped by 9P(36) branch line of CO2 laser. In case of the SPring- 8 storage ring, the momentum...

A novel type of magnet equipped with magnetically anisotropic interpoles is designed for the PRISM-FFAG. The magnetic field is calculated for the magnet and used for particle tracking simulation. The performance of the magnet is compared to a normal type magnet.

An ultra-high field gradient RF system has been designed for the PRISM project. This paper will report the status of R&D.

The (7Li,7Be) charge-exchange spin-flip reaction was for the first time used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of deuteron from the analogous B(GT) distribution. The obtained distribution is in agreement with recent photodisintegration measurements and effective-field calculations.

The ({sup 7}Li,{sup 7}Be) charge-exchange spin-flip reaction was for the first time used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of deuteron from the analogous B(GT) distribution. The obtained distribution is in agreement with recent photodisintegration measurements and effective-field calculation...

The (7Li,7Be) charge-exchange spin-flip reaction was for the first time used to deduce the distribution of the B(M1) reduced matrix elements for the photodisintegration of deuteron from the analogous B(GT) distribution. The obtained distribution is in agreement with recent photodisintegration measurements and effective-field calculations.

A proposal is presented on the polarized 3He ion source based on the spin-exchange collisions of the low-energy 3He+ ion with polarized alkali-metal atoms (Rb) which are optically pumped under the strong magnetic field. To transfer the electron polarization of 3He+ ion to the 3He nucleus, we offer to use the Sona transition based on a non-adiabatic...

A magnet design for a PRISM-FFAG synchrotron is pre-sented. The magnet type adopted for the PRISM-FFAG is a scaled-radial-sector and DFD triplet. The design was done by using a 3D calculation code. Tracking simulations were performed with the calculated magnetic-field mapping.

For MeV γ-ray production by the backward Compton scattering (BCS), a high power optically-pumped far infrared (FIR) laser has been developed at the synchrotron radiation facility of SPring-8. We obtained about 1.6-W of output power of FIR laser at CH3OH 119-μm lasing line pumped by 9P(36) branch line of CO2 laser. We have constructed a test beamlin...

Resonances above the t+t threshold in ${}^{6}\mathrm{He}$ have been studied via the ${}^{6}\mathrm{Li}$${(}^{7}\mathrm{Li},$ ${}^{7}\mathrm{Be}$ $t)$${}^{3}\mathrm{H}$ reaction at $0\ifmmode^\circ\else\textdegree\fi{}$ taken with a ${}^{7}\mathrm{Li}$ beam of 65 MeV/nucleon. By observing the binary triton decay, a new prominent resonance is found a...

Resonances above the t+t threshold in 6He have been studied via the 6Li(7Li, 7Be t)3H reaction at 0° taken with a 7Li beam of 65 MeV/nucleon. By observing the binary triton decay, a new prominent resonance is found at Ex=18.0±0.5MeV with a width of 7.7±1.0MeV. The branching ratio for the binary triton decay from this resonance is deduced to be 90±1...

A di-triton cluster state at highly excited energies in 6He has been investigated via the (7Li,7Be) reaction with an incident energy of 65 MeV/A. Decay charged-particles from excited states in 6He were measured in coincidence with 7Be ejectiles using solid-state detectors. A prominent bump was observed at Ex = 18 MeV in the binary triton decay chan...

The relaxation rates of the polarized rubidium (Rb) vapor were measured by using a chopped pumping laser to investigate the depolarization mechanism of a high density Rb vapor in a strong magnetic field. The measurement was carried out in a range of the magnetic field from 1 to 5 T and the Rb cell temperature from 90 to 130 °C which corresponds to...

Spin-exchange cross sections between a 3He+ ion and a Rb atom were calculated in a 3He+ impact-energy range from 0.01 to 10 keV/amu by the semiclassical close-coupling method based on the molecular-orbital expansion. The previous calculation in which only two states of the 3He+ (1s 2S)+Rb(5s 2S) system were taken into account overestimated the expe...

A triton cluster structure in ^6He was investigated in the ^6Li(^7Li,^7Be)^6He(tt) reaction at E/A = 65 MeV at RCNP of Osaka University. Outgoing ^7Be were detected at 0^circ with the high resolution spectrometer Grand Raiden in coincidence with tritons. Those were detected with 14 Si counter telescopes mounted inside a target chamber. A binary dec...

A long history is presented on the polarized 3He ion source being developed at RCNP for nuclear physics research at an intermediate energy region. A particular emphasis is placed on how to solve serious problems encountered in each phase of the development, i.e., OPPIS (Optical Pumping Polarized Ion Source) [phase 1], EP-PIS (Electron Pumping Polar...

We investigated the spatial distribution of a polarization in 3He beam expected from a novel polarized 3He ion source based on electron pumping, i.e., multiple electron capture and stripping collisions of an incident fast 3He+ ion with a polarized Rb vapor in a strong axial magnetic field. For this purpose, a Monte Carlo simulation was carried out...

Spin-exchange cross sections between a 3He+ ion and a Rb atom were calculated in a 3He+ impact-energy range from 0.01 to 10 keV/amu by the semiclassical close-coupling method based on the molecular-orbital expansion. The previous calculation in which only two states of the 3He+ (1s 2S)+Rb(5s 2S) system were taken into account overestimated the expe...

The spin-exchange cross-section, σ se, was measured for a 6.33 keV/amu 3He+ ion incident on a polarized Rb atom. The result is σ se = −0.26+0.27 × 10−15 cm2, which is unexpectedly an order of magnitude smaller than the theoretical value σ se = 5.9 × 10−15 cm2 evaluated by the semiclassical impact parameter method assuming formation of a single mole...

A He-3(+) beam with nuclear polarization was produced by passing a fast He-3(+)-ion beam through a thick polarized Rb vapor target in a strong magnetic field. Observed polarization transfer coefficients as a function of the Rb vapor thickness are qualitatively explained by an electron pumping model based on multiple processes of electron capture an...

The isovector electric monopole resonance (NMR) was studied by the Ni-60(Li-7,Be-7)Co-60 reaction at 65A MeV and at forward scattering angles including zero degrees. We confirmed the existence of the IVMR at an excitation energy of 20 +/- 2 MeV with a width of 10 +/- 2 MeV in Co-60, which is an analog of the T-0 + 1 isospin component of the IVMR es...

The charge-exchange 71Ga(3He,tγ)71Ge reaction was used to study the spin-isospin (Gamow Teller: GT) excitations relevant to the axial-vector charged-weak response for solar neutrinos. High-lying GT states in 71Ge with excitation energies up to one MeV above the neutron threshold were found to have finite γ-decay branches to low-lying states. The GT...

A novel type of polarized 3He ion source based on “electron pumping” was recently proposed. This ion source requires multiple electron capture and stripping collisions of 3He+ ions with polarized alkali atoms under a strong magnetic field (2–3 T). Since these processes may induce a serious increase in the emittance and reduction of polarized beam i...

We constructed a new polarized 3He ion source in order to establish a meth