Strangeness nuclear physics at J-PARC

The Japan Atomic Energy Agency (JAEA) has designed a Transmutation Physics Experimental Facility (TEF-P) as an experimental facility in the Japan Proton Accelerator Research Complex (J-PARC). The TEF-P is a critical assembly driven by a low-power proton beam, a maximum of 10 W, which is extracted from a high-power beam source, such as 250 kW of 400 MeV proton beam of the J-PARC linac. To extract such a low-power proton beam from the high-power proton beam, we developed a laser charge exchange (LCE) device and employed its technique, which is one of the non-contact beam extraction techniques. To confirm the performance of the LCE device, a low-power proton beam was extracted using a negative-hydrogen linac having an energy of 3 MeV, and a bright continuous laser. A 0.57 mW proton beam was successfully extracted with a laser stripping efficiency of 2.3 × 10 − 5 . These values obtained are in good agreement with the estimated values.

Development of high-reflectivity neutron supermirrors using an ion beam sputtering technique

J-PARC (Japan Proton Accelerator Research Complex) is a multi-purpose research facility for materials and life sciences, nuclear and particle physics, and nuclear engineering with extremely high power proton beams of 1 MW. The accelerator complex consists of a 400-MeV linac, a 3-GeV Rapid Cycling Synchrotron (RCS), and a 50-GeV Main Ring synchrotron (MR). Its goals are to provide MW-class beams at 3 GeV and at several 10 GeV, while it is a challenge to localize and suppress beam loss to the level to allow hands-on maintenance of accelerator components. The RCS scheme is adopted to realize them, which is advantageous over conventional Accumulation Ring (AR) regarding less beam loss problems due to lower beam current and easier construction and operation of a linac. RCS, however, required various challenging technologies such as ceramic ducts to reduce eddy current effects, high field Radio Frequency (RF) system, and paint injection technique (an injection scheme to reduce phase space density of the beam) to reduce space charge effects. The linac has also unique technologies to minimize beam loss, such as compact electromagnet Drift Tube Quadrupoles (DTQ’s) to control beam envelopes precisely, and a fast beam suspending system in Machine Protection System (MPS) with Radio Frequency Quadrupole linac (RFQ). The beam commissioning of the linac started in Nov. 2006, and its design energy of 181 MeV in the first construction phase was achieved in Jan. 2007. RCS beam commissioning started in Sep. 2007 and the beam was accelerated to the designed energy of 3 GeV in Oct. 2007. MR beam commissioning started in May 2008, and the beam acceleration to 30 GeV was established in Dec. 2008. The first neutron and muon beams were produced in May and Sep. 2008, respectively, at Materials and Life science experimental Facility (MLF). The linac commissioning has resulted in very stable beam with short down time. RCS commissioning quickly achieved beam acceleration and extraction, and paint injections are being studied intensively. RCS recorded the highest beam power of 0.21 MW in Sep. 2008 with beam loss well localized at the collimators. The linac beam energy will be upgraded to 400 MeV with Annular Coupled Structure linac (ACS) in order to increase the beam power to 1 MW. In the second construction phase, upgrade of the linac with 600-MeV Super-Conducting Linac (SCL) for Accelerator-Driven nuclear waste transmutation System (ADS) and upgrade of MR energy from 30 to 50 GeV are planned.Copyright © 2009 by ASME

Radiation shielding calculations were performed for the shielding design around beam injection and beam extraction areas at the 3-GeV proton synchrotron in the Japan Proton Accelerator Research Complex (J-PARC) with the PHITS Monte Carlo code. Prompt dose rates outside the shields were obtained from calculated neutron energy spectra and flux-to-dose conversion coefficients prepared for the shielding design in J-PARC. The thicknesses of shields were determined from the comparison results of the prompt dose rates with the criteria of dose limit for the design in J-PARC.

In recent years, experiments in particle physics and nuclear physics have required faster data collection systems and advanced trigger systems as the beam intensity has been increased. The current data acquisition (DAQ) system at the Japan Proton Accelerator Research Complex (J-PARC) Hadron Experimental Facility (HEF) uses fixed- and low-latency triggers with dedicated hardware to reduce data and event-building software that merges data into a single endpoint. This conventional DAQ system is expected to be inadequate for future experiments. It has to be replaced with a new simplified but powerful system called streaming DAQ, which collects the detector signals and filters them with software running on many computers. Therefore, we developed a prototype of streaming DAQ software for the J-PARC HEF using FairMQ and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Redis</i> as middleware. The key features include simplicity and a low learning cost to develop and be operated by a small number of people. The software can be used in a fully streaming readout system and in the triggered DAQ and the combined DAQ of the hardware and software triggers.

ABSTRACTA mercury target system to produce neutron beams has been operated at the spallation neutron source in the Japan Proton Accelerator Research Complex (J-PARC). Pressure waves are generated in mercury by rapid heat generation due to bombardment by high-intensity short-pulse proton beams. The pressure waves not only cause cyclic stress but also induce the cavitation damage on the target vessel. Reduction of these pressure waves is important from the viewpoint of extending the lifetime of the target vessel in future power-up operations. The injection of microbubbles into mercury is effective for reducing pressure waves. Accordingly, a microbubble generator was installed in the mercury target vessel and an in situ diagnostic system that measures the displacement velocity of the target vessel induced by the pressure waves was also set up in J-PARC to investigate the effect of proton beam condition and the effect of the microbubbles. Consequently, we found that the peak displacement velocity of the target vessel decreased owing to microbubble injection. The ratios of the peaks obtained with bubble injection to that without bubble injection were 1/3 and 2/3 when the injected gas fractions were 0.4% and 0.1%, respectively.

Neutron scattering experiments are a powerful probe to investigate a phenomenon of the materials and life science. The Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC) is the one of the most intense pulsed neutron experimental facility in the world. In MLF, 18 neutron experimental instruments have already been under operation and various measurements are carried out by many users. These instruments are composed of neutron detectors, sample environment and neutron optics devices. The signals from these components and the neutron source are transformed into the digital signals by the data acquisition (DAQ) electronics [1] and recorded as the event data with the time in the DAQ computers by “DAQ Middleware” [2]. The DAQ system produces the enormous measurement event data (~GB) under various measurement conditions. Simultaneously, the measurement meta-data indicating each measurement condition is recorded in XML format by the MLF control software framework “IROHA” [3]. These measurement event data and meta-data are collected in the MLF common storage and cataloged by the MLF Experimental Database based on the commercial XML database. The database system provides the web interface for the experiment data management and the remote data analysis for users. In this presentation, we will show the details of the DAQ system and the experiment data management system at MLF, J-PARC.

Development and test of SEOP neutron spin filter in Japan

ABSTRACTNeutron flux per pulse reached world record at neutron source in Japan Proton Accelerator Research Complex (J-PARC). In the J-PARC, mercury target system is used as a spallation neutron source. A target vessel has a multi-walled protection system that comprises a mercury vessel enclosed with a double-walled water shroud. This is to prevent the leakage of the mercury outside the target vessel. The multi-walled structure needed to be complicated with a lot of welding lines. However, during the operation, we faced an unscheduled shutdown due to water leakage to the intermediate layer between the mercury vessel and water shroud. An investigation on the cause of the leakage was carried out. It is deduced that the leakage path was formed due to the crack propagation from welding defects that are caused by the complicated multi-walled structure. The crack propagation is attributed to the repeated stress by pressure waves generated in the mercury target. Based on the investigation results, the design was improved to remove the welding line on the complicated structure and to realize the stable operation with 1 MW proton beam, which is the final design value of the neutron source in J-PARC.

A cesium (Cs) free H(-) ion source driven with a lanthanum hexaboride (LaB(6)) filament was adopted as an ion source for the first stage of the Japan Proton Accelerator Research Complex (J-PARC). At present, the maximum H(-) ion current produced by the ion source is 38 mA, using which J-PARC can produce a proton beam power of 0.6 MW by accelerating it with the 181 MeV linac and the 3 GeV rapid cycling synchrotron. In order to satisfy the beam power of 1 MW required for the second stage of the J-PARC in the near future, we have to increase the ion current to more than 60 mA. Therefore, we have started to develop a Cs-seeded ion source by adding an external Cs-seeding system to a J-PARC test ion source that has a structure similar to that of the J-PARC ion source except for the fact that the plasma chamber is slightly larger. As a result, a H(-) ion current of more than 70 mA was obtained from the ion source using a tungsten filament instead of a LaB(6) filament with a low arc discharge power of 15 kW (100 V, 150 A).

This Progress Report describes the operation of the Los Alamos Meson Physics Facility (LAMPF) and the research programs carried out there for the years 1992 and 1993. The accelerator operated for over 100 days in 1992, providing beams of H{sup +}, H{sup {minus}}, and polarized H{sup {minus}} for a rich and varied research program in nuclear physics. The accelerator had only fair beam availability in 1992 (for example, the average H{sup +} beam availability was 72%), caused largely by problems in the 201-MHz rf system. A major effort was expended to address these problems before the 1993 run. These efforts were rewarded by good beam availability in 1993 and few problems with the 201-MHz system. LAMPF operated remarkably smoothly during 1993, in the midst of a period of great uncertainty in the future of the facility and the downsizing of MP Division, which led to the loss of a large number of key people to positions elsewhere in the Laboratory. The H{sup +} intensity had to be held to no more than {approximately} 800{mu}A because of a vacuum leak in the A2 target. Nevertheless, the accelerator operated very.reliably and the summer run in 1993 proved to be extremely productive. This report discusses the research conducted on: Nuclear and particle physics; atomic physics; radiation effects; materials science; astrophysics; and theoretical physics.

Since Japanese fiscal year JFY01, which started on April 1, 2001, the Japan Proton Accelerator Research Complex (J‐PARC) has been in construction under a cooperation of two institutions, KEK and Japan Atomic Energy Research Institute (JAERI). After a short introduction of the whole project, I report on the current status of the construction and the initial research programs at J‐PARC.

Hadron Physics at J-PARC

In high-intensity proton accelerator facilities, a failure of an electromagnet that steers beam pulses may result in thermal shock damage to the accelerator material by injecting an out-of-control pulse. It is important that a Machine Protection System (MPS) is appropriately designed to prevent this damage in the facilities such as the Japan Proton Accelerator Research Complex (J-PARC). In this study, a simple evaluation method for the allowable injection time before the operation of the MPS was derived from the relation between the thermal stress and the yield stress of materials. As the first step in the derivation, the upper limit of heat generation was formulated for various kinds of materials without beam experiments. Second, the allowable injection time was evaluated on the basis of the upper limit of heat generation, assuming a Gaussian distribution in the beam current density. The derived evaluation method was then applied to J-PARC. The allowable injection time ranged from 1.5 to 330 μs for the incident energy above 25 MeV. This time was longer than the beam pulse width for the 3-GeV RCS ring, and some beam-transport lines. On the other hand, the injection of the whole pulse was not permitted for the other accelerating systems of J-PARC.

The Japan Proton Accelerator Research Complex (J-PARC) 3-50 Beam Transport line (3-50BT) is a beam transport line from 3-GeV rapid-cycling synchrotron (RCS) to 50-GeV main ring (MR). The RCS is a high-intensity proton accelerator, where the designed beam power is 1 MW, and has the complex source of space charge effect and beam instability, etc. Therefore, the uncontrolled emittance growth and beam halo increase nonlinearly with the beam power ramp up. Additionally, the physical aperture of 81  mm mrad in the MR is smaller than physical aperture of 486  mm mrad in the RCS. Therefore, the 3-50BT line has the collimators in order to remove the unwanted beam tail or halo from the RCS. The designed collimator aperture is 54  mm mrad. It is required to measure and optimize the optics parameters in the collimator area for taking full advantage of the beam collimation. Especially, it is very important to make the dispersion functions free in the collimator area and optimize the beta function to remove beam tail or halo over predefined transverse emittance. This paper introduces the method of optics measurement and reports the results of the measurement and optimization based on an accelerator model.