J-PARC Neutrino Beam Line Research Articles

Performance evaluation of 3 inch PMT for Hyper-Kamiokande

Hyper-Kamiokande is a next generation water Cherenkov detector for the study of neutrino oscillations including the search for leptonic CP violation. In order to reduce the systematic uncertainty, a 1 kton scale intermediate water Cherenkov detector (IWCD) is planned to be constructed at around 1 km downstream the J-PARC neutrino beamline. The multi-PMT modules, which consist of 19 3 inch PMTs will be installed in the IWCD to improve the detector performance with their higher granularity. We have measured the characteristics of candidate 3-inch PMTs such as gain, peak to valley ratio, timing resolution and after pulses, and checked the impact to the detector performance.

R&D on the gas injection system of Beam Induced Fluorescence Monitor toward MW beam power at the J-PARC Neutrino Beam-line

A Beam Induced Fluorescence (BIF) monitor is being developed as an essential part of the monitor update toward MW beam power operation at the J-PARC neutrino beam line, where a 30 GeV proton beam is extracted, bent and struck onto a 90-cm-long graphite target to produce an intense and nearly pure muon (anti-)neutrino beam for the Tokai-to-Kamioka(T2K) experiment. A BIF monitor can measure the proton beam profile non-destructively and continuously spill-by-spill with fluorescence light produced by proton-N 2 interactions. In order to generate enough light to measure the profile precisely, it is necessary to temporarily increase the vacuum pressure near the BIF interaction point up to ~ 10−2 Pa during each beam spill while keeping the average pressure low (10−4 to 10−6 Pa) at other locations to protect vacuum equipment. Therefore, R&D of a pulsed gas injection system satisfying these requirements is in progress. We will report the recent R&D status of the gas injection system and prospects toward operation of a prototype monitor which we plan to install this fall 2019.

Study of neutrino charged current interactions on iron in the NINJA experiment

Emulsion Cloud Chamber with 65kg iron target was exposed to the neutrino beam at J-PARC neutrino beam line in 2016. It is capable of detecting short proton tracks down to 200 MeV/c. Data presented in this document corresponds to 0.40×1020 POT. The 194 neutrino-iron charged current interactions were successfully reconstructed in the target. Numbers of protons and charged pions in the final state of each event were measured and compared with those of a Monte Carlo simulation.

First neutrino event detection with nuclear emulsion at J-PARC neutrino beamline

Precise neutrino--nucleus interaction measurements in the sub-multi GeV region are important to reduce the systematic uncertainty in future neutrino oscillation experiments. Furthermore, the excess of ${\nu_e}$ interactions, as a possible interpretation of the existence of a sterile neutrino has been observed in such an energy region. The nuclear emulsion technique can measure all the final state particles with low energy threshold for a variety of targets (Fe, C, H${_2}$O, and so on). Its sub-$\mu$m position resolution allows measurements of the ${\nu_e}$ cross-section with good electron/gamma separation capability. We started a new experiment at J-PARC to study sub-multi GeV neutrino interactions by introducing the nuclear emulsion technique. The J-PARC T60 experiment has been implemented as a first step of such a project. Systematic neutrino event analysis with full scanning data in the nuclear emulsion detector was performed for the first time. The first neutrino event detection and its analysis is described in this paper.

The new experiment WAGASCI for water to hydrocarbon neutrino cross section measurement using the J-PARC beam

The T2K (Tokai-to-Kamioka) is a long baseline neutrino experiment designed to study various parameters that rule neutrino oscillations, with an intense beam of muon neutrinos. A near detector complex (ND280) is used to constrain non-oscillated flux and hence to predict the expected number of events in the far detector (Super-Kamiokande). The difference in the target material between the far (water) and near (scintillator, hydrocarbon) detectors leads to the main non-canceling systematic uncertainty for the oscillation analysis. In order to reduce this uncertainty a new water grid and scintillator detector, WAGASCI, has been proposed. The detector will be operated at the J-PARC neutrino beam line with the main physics goal to measure the charged current neutrino cross section ratio between water and hydrocarbon with a few percent accuracy. Further physics program may include high-precision measurements of different charged current neutrino interaction channels. The concept of the new detector will be covered together with the actual construction plan.

The graphite target for J-PARC neutrino beam-line

The graphite target of the J-PARC neutrino beam-line for the long base-line neutrino-oscillation experiment, T2K is developed. The graphite target is designed to withstand the exposure of high intensity protons beam from J-PARC accelerator. The Helium gas cooling is adopted to minimize the radiation damage of the graphite. J-PARC neutrino beam-line is operated from April 2009. The first target was used for 6.7 × 1020 protons-on-target without significant trouble, while the maximum number of protons per pulse is 1.2 × 1020 with 2.48 s cycle.

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

The Great East Japan earthquake that occurred on March 11, 2011 resulted in devastating damages to J-PARC. Although damages to the superconducting magnet system for the J-PARC neutrino beam line appeared to be relatively small, a long recovery procedure was required to resume the operation. Except for this long shutdown period, the system has been operated stably ensuring good accumulation of the physics data. The paper reports on the operation status including the damages by the earthquake and its recovery process. Repair of the insufficient cooling of steering corrector coils, which was present prior to the earthquake, was also performed during the recovery process. The paper also reports on the repair.

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

The superconducting magnet system for the J-PARC neutrino beam line for the T2K experiment has been served for the beam operation without serious disturbance since April 2009. Present most concern of the system is the operational current limit of superconducting corrector magnets for beam steering due to systematic quenches at lower currents. Operational experience of the magnet system and examples of troubleshoot including countermeasures against the corrector magnet quenches are presented.

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.

Superconducting Magnet System for the J-PARC Neutrino Beam Line

Superconducting combined-function magnets have been utilized for the 50-GeV, 750-kW proton beam line in the J-PARC neutrino experiment. The magnets are designed to provide a dipole field of 2.6 T combined with a quadrupole field of 19 T/m in a coil aperture of 173.4 mm at a nominal current of 7,345 A. Following the success of a prototype R&D project, a superconducting magnet system for the J-PARC neutrino beam line has been constructed since 2005. Using a new conceptual beam line with the superconducting combined-function magnets has demonstrated successful beam transport to the target neutrino production.

Superconducting Magnet System for J-PARC Neutrino Beam Line

A helium cryogenic system has been constructed to circulate 300 g/s of Supercritical Helium (SHe) at 4.5 K through a series of superconducting magnets for a neutrino beam line at J-PARC. The conceptual cryogenic system design, considering the cooling characteristics of the magnets, was defined in 2005. The engineering design was subsequently carried out by Taiyo Nippon Sanso Corp. The main elements are a screw compressor with a capacity of 160 g/s at 1.4 MPa, a refrigerator with a capacity of 1.5 kW at 4.5 K and a centrifugal SHe pump with a flow rate of 300 g/s. After system integration in 2008, performance tests were conducted. In a preliminary cooling test to confirm the cryogenic capacity, the cryogenic system successfully performed to the required specifications by circulating a supercritical helium flow of 300 g/s at 0.4 MPa and 4.5 K through a bypass line with a simulated heat load of 520 W and simulated pressure drop of 0.85 MPa. Following this, a full system test with the magnets was carried out. The magnets were pre-cooled from the ambient temperature for eight days and were kept below 4.8 K by circulating pumped SHe. The measured heat leakage at the magnets during these tests, including SHe transfer lines, was 210 W. Since the maximum beam loss predicted is 150 W, the cooling capacity of the cryogenic system is large enough to manage beam operations expected in the future.

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

The Great East Japan earthquake that occurred on March 11, 2011 resulted in devastating damages to J-PARC. Although damages to the superconducting magnet system for the J-PARC neutrino beam line appeared to be relatively small, a long recovery procedure was required to resume the operation. Except for this long shutdown period, the system has been operated stably ensuring good accumulation of the physics data. The paper reports on the operation status including the damages by the earthquake and its recovery process. Repair of the insufficient cooling of steering corrector coils, which was present prior to the earthquake, was also performed during the recovery process. The paper also reports on the repair.

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.

Future possibilities with the J-PARC neutrino beam

The J-PARC neutrino beam line is under construction. The next generation neutrino oscillation experiments, including the T2K experiment, will observe evidence for a finite θ13, if sin2 2θ13 > 0.01. In this case, it is likely that future long baseline experiments with the conventional but strong neutrino beam can measure important neutrino parameters such as the CP violation phase and the mass hierarchy. In this paper, possible future neutrino oscillation experiments to be carried out using the J-PARC neutrino beam are discussed.

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.

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 Combined Function Prototype Magnets for the J-PARC Neutrino Beam Line

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

J-PARC neutrino beam line and target development

J-PARC neutrino beam line and target development

Quench Stability Against Beam-Loss in Superconducting Magnets at the 50 GeV Proton Beam Line for the J-PARC Neutrino Experiment

The heat load on superconducting magnets induced by beam loss is a major subject to be solved for stable operation of the 50 GeV-0.75 MW J-PARC neutrino beam line. Heat load for a 10 W/point beam loss in an actual coil was calculated using the MARS code which simulates the actual magnet. Calculated heat load was up to 20 kJ/m/sup 3//pulse. Instantaneous heating of 0-40 kJ/m/sup 3//pulse was induced in Rutherford type cable in an experiment, and the thermal characteristic measured using SHe. The cable specimen for an experimental verification used the same structure as the superconducting cable for the magnet in the test. It was found that a heat pulse of 20 kJ/m/sup 3/ caused an instantaneous temperature rise of 0.25 K in the experiment and will not induce a quench according to the quench simulation calculation.