High Intensity Proton Accelerator Research Articles

Radiation safety design for the J-PARC project

The High-Intensity Proton Accelerator Project, named J-PARC, is in progress, with the aim of enabling studies on the latest basic science and the advancement of nuclear technology. In the project, a high-energy proton accelerator complex with the world's highest instantaneous intensity is under construction. In order to establish a reasonable shielding design, both simplified and detailed design methods were used in the shielding design of J-PARC. This paper reviews the present status of the radiation safety design study for J-PARC.

Derivation of Simple Evaluation Method for Thermal Shock Damage on Accelerator Materials Caused by Out-of-control Beam Pulses and its Application to 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.

Science with High Intensity Hadron Machines

Future high intensity proton accelerators are introduced and sciences explored at the facilities are reviewed.

Scientific Reviews: 1-MW Pulse Sapllation Neutron Source (JSNS) of J-PARC

The J-PARC project has been in progress concerning the construction of experimental facilities along with high intensity proton accelerators, aimed at scientific breakthroughs in materials and life sciences, nuclear and elementary physics research, and the technological development of an accelerator-driven transmutation system [1]. Most of the 3–GeV protons are extracted to be injected into a facility called the Materials and Life Science Experimental Facility (MLF), in which a 1-MW pulse neutron source (JSNS) and a muon production target are located, sharing the beam in tandem fashion [2]. A neutron beam with high performance of time resolution, along with high intensity in the 1-MW regime, will open realistic technological breakthroughs in the sciences of microscopic molecular dynamics; surface physics, magnetism; polymer; biology; structure and its functions; precise methods for analysis; dynamic visualization techniques; many industrial applications; and even evolution in cosmology and astrophysics.

Surface production dominating Cs-free H− ion source for high intensity and high energy proton accelerators

A Cs-free negative hydrogen (H−) ion source driven by pulsed arc plasma with a LaB6 filament is being operated for the beam tests of the Japan Proton Accelerator Research Complex (J–PARC) linac. A peak H− current of 38 mA, which exceeds the requirement of the J–PARC first stage, is stably extracted from the ion source with a beam duty factor of 0.9% (360 μs×25 Hz) by principally optimizing the surface condition and shape of the plasma electrode. The sufficiently small emittance of the beam was confirmed by high transmission efficiency (around 90%) through the following 324 MHz 3 MeV J–PARC radio frequency quadrupole linac (M. Ikegami et al., Proc. 2003 Part. Accel. Conf. 2003, p. 1509). The process of the optimization, which confirms the validity of hypothesis that H− ions are produced by surface reaction on a Mo plasma electrode dominantly in the ion source, is presented.

Particle and nuclear physics at J-PARC

Abstract The construction of a high-intensity proton accelerator complex (J-PARC) is now under way in Japan. It will provide a variety of beams of neutrinos, kaons, pions, muons and primary protons etc. Diverse physics topics will be addressed here with the first beam scheduled for the year 2007. In this talk, the most important particle and nuclear physics objectives there will be presented.

Benchmark Experiments of Dose Distributions in Phantom Placed Behind Iron and Concrete Shields at the TIARA Facility

To verify the calculation methods used for the evaluations of neutron dose at the radiation shielding design of the high-intensity proton accelerator facility (J-PARC), dose distributions in a plastic phantom of 30 x 30 x 30 cm3 slab placed behind iron and concrete test shields were measured by using a tissue equivalent proportional counter for 65-MeV quasi-monoenergetic neutrons generated from the 7Li(p,n) reactions with 68-MeV protons at the TIARA facility. Dose distributions in the phantom were calculated by using the MCNPX and the NMTC/JAM-MCNP codes with the flux-to-dose conversion coefficients prepared for the shielding design of the facility. The comparison results show the calculated results were in good agreement with the measured ones within 20%.

Research and development on accelerator-driven transmutation system at JAERI

Abstract Japan Atomic Energy Research Institute carries out research and development on accelerator-driven system (ADS) to transmute minor actinides and long-lived fission products in high-level radioactive waste. The system is composed of high intensity proton accelerator, lead-bismuth spallation target and lead-bismuth cooled subcritical core with nitride fuel. About 2500 kg of minor actinide is loaded into the subcritical core. Annual transmutation amount using this system is 250 kg with 800 MW of thermal output. This transmutation amount corresponds to the amount of minor actinides produced from 10 units of 1GWe power reactors annually. A superconducting linear accelerator with the beam power of 20–30 MW is connected to drive the subcritical core. To maximize the transmutation efficiency, the nitride fuel without uranium, such as (Np, Am, Pu)N, is selected. The nitride fuel irradiated in the ADS is reprocessed by pyrochemical process followed by the re-fabrication of nitride fuel. Many research and development activities are under way and planned in the fields of subcritical core design, spallation target technology, lead-bismuth handling technology, accelerator development, and minor actinide fuel development. Especially, to study and evaluate the feasibility of the ADS from physics and engineering aspects, the transmutation experimental facility (TEF) is proposed under a framework of the High-Intensity Proton Accelerator Project.

加速器駆動による核変換工学技術(NP4 核燃料サイクル・バックエンド技術)

It will be an innovative technology to transmute a minor actinide (MA) and long-lived fission products to stable or short-lived nuclei by accelerator-driven system (ADS). The benefit is a reduction of burden to the environment. The system consists of a high intensity proton accelerator with sub-critical fast reactor. Lead-bismuth eutectic is a spallation target and coolant in the reactor. Engineering issues for nuclear transmutation are Lead-bismuth technology, radiation damage of the materials due to proton and neutron and corrosion-erosion.

Nuclear Science and Engineering Expected in High-Intensity Proton Accelerator Facility (J-PARC)

Nuclear Science and Engineering Expected in High-Intensity Proton Accelerator Facility (J-PARC)

Optimization of a micro-strip gas chamber as a two-dimensional neutron detector using gadolinium converter

Abstract A micro-strip gas chamber (MSGC) has been under development as a two-dimensional position sensitive detector for neutron scattering experiments at the high-intensity proton accelerator facilities. The MSGC requirements as a neutron detector are high counting rate, high detection efficiency, high positional resolution, stability and large area coverage. The purpose of this paper is to verify the properties of Gadolinium as a MSGC converter. The arrangements of a capillary plate and MSGC gas pressure have been optimized by simulation of a Gadolinium converter. As a result of that, a position resolution of 160 μm and n/γ ratio of 200 were obtained at the gas pressure of 0.02 atm. In view of γ-ray sensitivity, the further improvement is required for practical applications.

Physics prospects with high intensity proton accelerator (J-PARC) at Tokai

Abstract From Japanese fiscal year JFY01, which started on April 1, 2001, a new accelerator project to provide high-intensity proton beams proceeded into its construction phase. This project, which is now called the J-PARC (Japan Proton Accelerator Research Complex) project, is conducted under a cooperation of two institutions, KEK and JAERI. We set a goal to achieve 1 MW proton beams at 3 GeV and 0.75 MW beams at 50 GeV. The project will be completed within six years, with the anticipated first beams in the spring of 2007. In this article I will describe a) the project itself, b) sciences to be pursued at this new accelerator complex and c) the present status and future plans of the project.

Prospects of very long baseline neutrino oscillation experiments with the KEK-JAERI high intensity proton accelerator

We study the physics potential of very long baseline neutrino-oscillation experiments with a high intensity proton accelerator which will be completed by the year 2007 in Tokai-village, as a joint project of KEK and JAERI (Japan Atomic Energy Research Institute). The 50 GeV proton synchrotron at J-PARC (Japan Proton Accelerator Research Complex) will deliver neutrino beams in the range of a few GeV with an intensity about two orders of magnitude higher than the present KEK beam for the K2K experiment. As a sequel to the proposed J-PARC--to--Super-Kamiokande experiment, we study the impact of experiments with a 100 kton-level detector and a baseline length of a few-thousand km. The pulsed narrow-band ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ beams allow us to measure the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e}$ transition probability and the ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ survival probability through counting experiments at a large water-\ifmmode \check{C}\else \v{C}\fi{}erenkov detector. We study the sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, the three angles, and one $\mathrm{CP}$ phase of the three-generation lepton-flavor-mixing matrix. We find that experiments at a distance between 1000 and 2000 km can determine the sign of the larger mass-squared difference ${(m}_{3}^{2}\ensuremath{-}{m}_{1}^{2})$ if the mixing between ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{3}$ (the heaviest-or-lightest neutrino) is not too small: $4|{U}_{e3}{|}^{2}(1\ensuremath{-}|{U}_{e3}{|}^{2})\ensuremath{\gtrsim}0.03.$ The $\mathrm{CP}$ phase can be constrained if the $|{U}_{e3}|$ element is sufficiently large: $4|{U}_{e3}{|}^{2}(1\ensuremath{-}|{U}_{e3}{|}^{2})\ensuremath{\gtrsim}0.06,$ and if the smaller mass-squared difference ${(m}_{2}^{2}\ensuremath{-}{m}_{1}^{2})$ and the ${U}_{e2}$ element are in the preferred range of the large-mixing-angle solution of the solar-neutrino deficit. The magnitude $|{m}_{3}^{2}\ensuremath{-}{m}_{1}^{2}|$ and the matrix element ${U}_{\ensuremath{\mu}3}$ can be precisely measured, but we find little sensitivity to ${m}_{2}^{2}\ensuremath{-}{m}_{1}^{2}$ and the matrix element ${U}_{e2}.$

KEK/JAERI Joint Project on high-intensity proton accelerators

Abstract From JFY01, which started on April 1, 2001, a new accelerator project to provide high-intensity proton beams proceeded into a construction phase. This project is conducted under a cooperation of two institutions, KEK and JAERI. The accelerator complex will provide 1 MW proton beams at 3 GeV and 0.75 MW beams at 50 GeV. The project will be completed within 6 years. In this article I will describe (a) the project itself, (b) sciences to be pursued at this new accelerator complex and (c) the present status and future plans of the project.

Possibility of the LBL experiment with the high intensity proton accelerator

We study physics possibility of Very Long Base-Line (VLBL) Neutrino-Oscillation Experiments with the High Intensity Proton Accelerator, which will be completed by the year 2007 in Tokai-village, Japan. As a target, a 100 kton-level water-Cerenkov detector is considered at 2,100 km away. Assuming the pulsed narrow-band nu_mu beams, we study sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, one CP phase and three angles of the lepton-flavor-mixing matrix. We find that experiments at a distance 2,100 km can determine the neutrino mass hierarchy if the mixing matrix element U_{e3} is not too small. The CP phase and U_{e3} can be constrained if the large-mixing-angle solution of the solar-neutrino deficit is realized.

Measuring the CP-violating phase by a long base-line neutrino experiment with Hyper-Kamiokande

Abstract We study the sensitivity of a long-base-line (LBL) experiment with neutrino beams from the High Intensity Proton Accelerator (HIPA), that delivers 1021 POT per year, and a proposed 1 Mt water Cerenkov detector, Hyper-Kamiokande (HK) 295 km away from the HIPA, to the CP phase (δMNS) of the three-flavor lepton mixing matrix. We examine a combination of the νμ narrow-band beam (NBB) at two different energies, 〈pπ〉=2, 3 GeV, and the ν μ NBB at 〈pπ〉=2 GeV. By allocating one year each for the two νμ beams and four years for the ν μ beam, we can efficiently measure the νμ→νe and ν μ → ν e transition probabilities, as well as the νμ and ν μ survival probabilities. CP violation in the lepton sector can be established at 4σ (3σ) level if the MSW large-mixing-angle scenario of the solar-neutrino deficit is realized, |δMNS| or |δMNS−180°|>30°, and if 4|Ue3|2(1−|Ue3|2)≡sin22θRCT>0.03 (0.01). The phase δMNS is more difficult to constrain by this experiment if there is little CP violation, δMNS∼0°or 180°, which can be distinguished at 1σ level if sin22θRCT≳0.01.

ICONE11-36485 R & D Status of Superconducting Proton Linear Accelerator for ADS at JAERI

An accelerator driven nuclear transmutation system (ADS) requires high intensity proton beam; the energy is about 1GeV and the beam power is several tens MW. A superconducting proton linear accelerator is most promising option to provide the high power proton beam. R&D of the superconducting proton linear accelerator began in 1995 at JAERI in collaboration with High Energy Accelerator Research Organization (KEK). As the first step of the R&D, 600MHz superconducting single-cell and 5-cell cavities of beta (ratio of the beam velocity to the light velocity)=0.5,0.6 and 0.9 were fabricated and tested. Surface peak fields (Esp) of the cavity up to 51 and 40 MV/m were obtained at 2K for the single-cell and 5-cell cavities, respectively. The results are good enough for utilization of a high intensity proton accelerator. As the next step of the R&D work, prototype cryomodule has been fabricated in order to demonstrate the cavity performance in the cryomodule. The cryomodule includes two 5-cell cavities of beta=0.6 and is designed to perform 2K operation. Assembly and installation of the cavities in the cryomodule were carried out in the clean room to avoid dust contamination. The design field strength of Esp=16MV/m were obtained in the preliminary test of the cryomodule. The High Intensity Proton Accelerator Project is promoting by JAERI and KEK. A superconducting proton linear accelerator is planned in the energy range from 400 to 600 MeV. The proton beams of 600 MeV will be delivered to the Transmutation Experimental Facility. System design of the superconducting proton linac has been carried out; a cryomodule includes two 972MHz 9-cell cavities and 11 cryomodules are necessary for the acceleration from 400 to 600 MeV at Esp=30 MV/m. Total length of the superconducting linear accelerator is designed to be 58m.

真空用Ｏリソグのγ線による劣化具合の調査

The high-intensity proton accelerator being constructed by JAERI and KEK will generates greater beam power than conventional accelerators. The radiation emission due to beam losses will therefore increase. Since vacuum O-rings installed in the accelerator will be degraded badly by the radiation, there is need to find an O-ring that has more resistant to radiation. To find an O-ring that has better radiation resistant than that of the fluororubber used for conventional accelerators in general, some O-rings which are expected to have enough resistant to the radiation were irradiated, and estimated a degradation by measurement of outgassing rate, hardness, permeation time of helium gas, and an outward observation. Most of the O-rings were irradiated in an oxygen free atmosphere and in the air. The irradiations were carried out at room temperature in Co-60 gamma irradiation facility until a dose of 1 MGy was reached. The radiation resistance of PURE-UBBER O-ring showed somewhat better than that of the fluororubber O-ring.

Physics potential of future long baseline neutrino oscillation experiments with KEK-JAERI HIPA

We study physics potential of Very Long Base-Line (VLBL) Neutrino-Oscillation Experiments with the High Intensity Proton Accelerator, which will be completed by the year 2007 in Tokai-village, Japan. As a target, a 100 kton-level water-Čerenkov detector is considered at 2,100 km away. Assuming the pulsed narrow-band ν μ beams, we study sensitivity of such experiments to the neutrino mass hierarchy, the mass-squared differences, one CP phase and three angles of the lepton-flavor-mixing matrix. We find that experiments at a distance 2,100 km can determine the neutrino mass hierarchy if the mixing matrix element | U e3 | is not too small. The CP phase and | U e3 | can be constrained if the large-mixing-angle solution of the solar-neutrino deficit is realized.

Flavor physics at the high intensity proton accelerator project in Japan

Abstract Possible flavor physics programs at the Joint KEK-JAERI project of High Intensity Proton Accelerators (JKJ) will be described. In particular, physics with kaons, muons, and neutrinos is mentioned.