High Intensity Proton Accelerator Facility Research Articles

Gas sheet beam induced fluorescence based beam profile measurement for high intensity proton accelerators

The paper describes the design simulations, developmental details and characterization results of a dual gas sheet generator system for non-invasive beam profile measurement of high-intensity proton beams. The system is being developed for the Low Energy High Intensity Proton Accelerator facility at Bhabha Atomic Research Centre, India. To our knowledge, this is the first time an intense low energy proton beam was used to directly view the beam induced fluorescence of a gas sheet. The system works by generating two thin nitrogen gas sheets which produces fluorescence when a charged particle beam passes through them, thereby providing a visual representation of the beam's intensity profile. The gas sheets are generated at 45° to the beam axis, which allows the fluorescence created by the interaction to be viewed directly through a viewport or camera capture. The beam profile measurements were carried out with a typically 20 keV, 10 mA pulsed proton beam from an ECR ion source under different operating parameters like gas sheet pressure, beam current, beam energy and focusing magnetic field. The Geant4 simulation has been performed to study the scintillation process and optical transport. It may become useful to study methods of reconstructing the beam profile from image obtained.

Measurement of displacement cross-sections of Nb irradiated by protons with kinetic energy range between 0.4 and 3 GeV

In high-intensity proton accelerator facilities, it is crucial to evaluate the damage of beam-interception materials and accelerator components, such as a superconducting magnet coil and cavity. The displacement per atom (dpa) is used as a damage index derived by integrating the particle flux and the displacement cross section. Although the dpa is employed as the standard, the experimental data of displacement cross section are scarce for a proton in the energy region above 20 MeV. To obtain the data for superconducting materials for high-intensity accelerators and magnets, we measured the displacement cross section of Nb for proton irradiation with a kinetic energy range between 0.4 and 3 GeV at J-PARC. The present experimental results were compared with the calculation of PHITS code and Karlsruhe Institute of Technology (KIT) evaluation using both NorgerttRobinson-Torrens (NRT) and the athermal recombination corrected dpa (arc-dpa) models. The experiment showed that the widely utilized NRT model overestimates the cross section by 50%. It is also found that the arc-dpa model shows remarkably good agreement with the present data.

Design of the 590 MeV proton beamline for the proposed TATTOOS isotope production target at PSI

IMPACT (Isotope and Muon Production with Advanced Cyclotron and Target Technologies) is a proposed initiative envisaged for the high-intensity proton accelerator facility (HIPA) at the Paul Scherrer Institute (PSI). As part of IMPACT, a radioisotope target station, TATTOOS (Targeted Alpha Tumour Therapy and Other Oncological Solutions) will allow the production of terbium radionuclides for therapeutic and diagnostic purposes. The proposed TATTOOS beamline and target will be located near the UCN (Ultra Cold Neutron source) target area, branching off from the main UCN beamline. In particular, the beamline is intended to operate at a beam intensity of 100 μA, requiring a continuous splitting of the main beam via an electrostatic splitter. Realistic beam loss simulations to verify safe operation have been performed and optimised using Beam Delivery Simulation (BDSIM), a Geant4 based tool enabling the simulation of beam transportation through magnets and particle passage through the accelerator. In this study, beam profiles, beam transmission and power deposits are generated and studied.

The High Intensity Proton Accelerator Facility

The High Intensity Proton Accelerator Facility at PSI routinely produces a proton beam with up to 1.4 MW power at a kinetic energy of 590 MeV. The beam is used to generate neutrons in spallation targets, and pions in meson production targets. The pions decay into muons and neutrinos. Pions and muons are used for condensed matter and particle physics research at the intensity frontier. This section presents the main physics and technology concepts utilized in the facility. It includes beam dynamics and the control of beam losses and activation, power conversion, efficiency aspects, and performance figures, including the availability of the facility.

Iterative learning control-based adaptive beam loading compensation implementations in the J-PARC LINAC

Abstract The Japan Proton Accelerator Research Complex (J-PARC) is a multi-purpose high-intensity proton accelerator facility that consists of a 400 MeV linear accelerator (LINAC), a 3 GeV rapid-cycling synchrotron (RCS), a 30 GeV main ring synchrotron (MR), and experimental facilities. In 2018, to achieve the goal of a 1 MW beam power at the RCS, the beam current of the LINAC was increased from 30 to 50 mA. Based on the beam loading effect, such a strong beam current can cause a significant drop in the accelerating gradients. Although both feedback and normal static feedforward control schemes were used in the low-level radio frequency (LLRF) system to suppress the beam loading effect, the peak-to-peak stability of the RF field still does not meet the requirements of the LINAC (i.e., ± 0.5% amplitude and ± 0 . 5 ° phase). To solve this problem, an iterative learning control (ILC) scheme was studied and implemented in the J-PARC LINAC. The beam loading compensation experiments demonstrate that the inclusion of the ILC controller improves the performance of the control system significantly. As the number of iterations increase, the tracking error of the system decreases monotonously. For the accelerating field with beam operation, compared to the performance with static feedforward control, the peak-to-peak stability of amplitude improves from greater than ± 1% to less than ± 0.4%, and the peak-to-peak stability of phase improves from ± 1°to ± 0 . 2 ° .

Induced radioactivity studies of the shielding and beamline equipment of the high intensity proton accelerator facility at PSI

The Paul Scherrer Institute (PSI) is the largest national research center in Switzerland. Its multidisciplinary research is dedicated to a wide ↓eld in natural science and technology as well as particle physics. The High Intensity Proton Accelerator Facility (HIPA) has been in operation at PSI since 1974. It includes an 870 keV Cockroft-Walton pre-accelerator, a 72 MeV injector cyclotron as well as a 590 MeV ring cyclotron. The experimental facilities, the meson production graphite targets, Target E and Target M, and the spallation target stations (SINQ and UCN) are used for material research and particle physics. In order to ful↓ll the request of the regulatory authorities and to be reported to the regulators, the expected radioactive waste and nuclide inventory after an anticipated ↓nal shutdown in the far future has to be estimated. In this contribution, calculations for the 20 m long beamline between Target E and the 590 MeV beam dump of HIPA are presented. The ↓rst step in the calculations was determining spectra and spatial particle distributions around the beamlines using the Monte-Carlo particle transport code MCNPX2.7.0 [1]. To perform the analysis of the MCNPX output and to determine the radionuclide inventory as well as the speci↓c activity of the nuclides, an activation script [2] using the FISPACT10 code with the cross sections from the European Activation File (EAF2010) [3] was applied. The speci↓c activity values were compared to the currently existing Swiss exemption limits (LE) [4] as well as to the Swiss liberation limits (LL) [5], becoming e↑ective in the near future. The obtained results were used to estimate the total volume of the radioactive waste produced at HIPA and have to be reported to the Swiss regulatory authorities. The comparison of the performed calculations to measurements is discussed as well.

Experimental investigation of the radiation shielding efficiency of a MCP detector in the radiation environment near Jupiter’s moon Europa

Neutral Ion Mass spectrometer (NIM) is one of the instruments in the Particle Environmental Package (PEP) designed for the JUICE mission of ESA to the Jupiter system. NIM, equipped with a sensitive MCP ion detector, will conduct detailed measurements of the chemical composition of Jovian icy moons exospheres. To achieve high sensitivity of the instrument, radiation effects due to the high radiation background (high-energy electrons and protons) around Jupiter have to be minimised. We investigate the performance of an Al–Ta–Al composite stack as a potential shielding against high-energy electrons. Experiments were performed at the PiM1 beam line of the High Intensity Proton Accelerator Facilities located at the Paul Scherrer Institute, Villigen, Switzerland. The facility delivers a particle beam containing e−, μ− and π− with momentum from 17.5 to 345MeV/c (Hajdas et al., 2014). The measurements of the radiation environment generated during the interaction of primary particles with the Al–Ta–Al material were conducted with dedicated beam diagnostic methods and with the NIM MCP detector. In parallel, modelling studies using GEANT4 and GRAS suites were performed to identify products of the interaction and predict ultimate fluxes and particle rates at the MCP detector. Combination of experiment and modelling studies yields detailed characterisation of the radiation fields produced by the interaction of the incident e− with the shielding material in the range of the beam momentum from 17.5 to 345MeV/c. We derived the effective MCP detection efficiency to primary and secondary radiation and effective shielding transmission coefficients to incident high-energy electron beam in the range of applied beam momenta. This study shows that the applied shielding attenuates efficiently high-energy electrons. Nevertheless, owing to nearly linear increase of the bremsstrahlung production rate with incident beam energy, above 130MeV their detection rates measured by the MCP detector compares to the MCP rate of the incident electron beam. We define key performance parameters for the shielding and show direction of its improvements by introducing additional layer of material to attenuate γ-rays and reduce the MCP sensitivity to the penetrating radiation. The experiments also verify the predictions by modelling tools used currently for optimisation of shielding against high-energy particles.

Thermal analysis and neutron production characteristics of a lowpower copper beam dump-cum-target for LEHIPA

Monte Carlo simulations of heat deposition and neutron production have been carried out for the low power beam dump-cum-target for the 20 MeV Low Energy High Intensity Proton Accelerator (LEHIPA) facility at BARC using GEANT4 and FLUKA. Thermal analysis and heat transfer calculations have also been carried out using the computational fluid dynamics code CFD ACE+. In this work we present the details of the analysis of the low power beam dump-cum-target designed for conditioning of the accelerator upto a maximum power of 600 kW with a duty cycle of 2% which corresponds to an average power of 12 kW in the first phase.

Detection efficiency of microchannel plates for e(-) and π(-) in the momentum range from 17.5 to 345 MeV/c.

High-energy e(-) and π(-) were measured by the multichannel plate (MCP) detector at the PiM1 beam line of the High Intensity Proton Accelerator Facilities located at the Paul Scherrer Institute, Villigen, Switzerland. The measurements provide the absolute detection efficiencies for these particles: 5.8% ± 0.5% for electrons in the beam momenta range 17.5-300 MeV/c and 6.0% ± 1.3% for pions in the beam momenta range 172-345 MeV/c. The pulse height distribution determined from the measurements is close to an exponential function with negative exponent, indicating that the particles penetrated the MCP material before producing the signal somewhere inside the channel. Low charge extraction and nominal gains of the MCP detector observed in this study are consistent with the proposed mechanism of the signal formation by penetrating radiation. A very similar MCP ion detector will be used in the Neutral Ion Mass (NIM) spectrometer designed for the JUICE mission of European Space Agency (ESA) to the Jupiter system, to perform measurements of the chemical composition of the Galilean moon exospheres. The detection efficiency for penetrating radiation determined in the present studies is important for the optimisation of the radiation shielding of the NIM detector against the high-rate and high-energy electrons trapped in Jupiter's magnetic field. Furthermore, the current studies indicate that MCP detectors can be useful to measure high-energy particle beams at high temporal resolution.

Quadruple Stacked Elliptical Supermirror Device for One Dimensional Neutron Focusing

Focusing neutron beam with wide wavelength range is an indispensable technique used to compensate for weak signals from tiny samples in various experiments using pulsed neutron beam generated from high intensity proton accelerator facilities, such as J-PARC. Aspherical supermirror device is one of the most effective optical devices for focusing neutron beam with wide wavelength range since it has no chromatic aberration. Stack of aspherical supermirror enables us to focus neutron beams with wide divergence. Thin mirrors with a millimeter thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of the other mirrors. Previously, we developed a fabrication process of a precise millimeter-thick elliptical supermirror. This process consists of noncontact figuring by the numerically controlled local wet etching technique, the finishing of surface without degrading mirror shape by low-pressure polishing, and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report fabrication of elliptical supermirror with a thickness of 1 mm and development of multiply-arranged neutron focusing mirror device using stacked 4 fabricated elliptical supermirror with a thickness of 1mm.

Figuring of Aspherical Metal Mirror Substrate for Neutron Focusing by Numerically Controlled Electrochemical Machining

Neutron beam generated by high intensity proton accelerator facility is powerful tool to investigate characteristics of soft and hard materials. However, neutron beam is not major tool for material science since intensity of neutron beam is very weak compared to that of X-rays. Neutron focusing device is required to increase in intensity of neutron beam. Aspherical supermirror is effective for neutron focusing with wide wavelength range without chromatic aberration. In this research, we proposed a fabrication process for large and cost-effective aspherical mirror substrate made of aluminum alloy because metal can be figured coarsely at low cost by using conventional machining. The mirror fabrication process proposed by us consists of grinding for coarse figuring, numerically controlled electrochemical machining (NC-ECM) to correct objective shape with form accuracy of sub-micrometer level and low-pressure polishing to decrease in surface roughness to sub-nanometer level. In the case of figure correction of the mirror substrate by NC-ECM, deterministic correction is realized because NC-ECM is a non-contact electrochemical removal process for metal materials, without workpiece deformation. In this paper, we report fundamental machining characteristics of ECM, which uses electrode with a diameter of 10 mm and NaNO3 electrolyte.

High pressure experiments with the Engineering Materials Diffractometer (BL-19) at J-PARC

J-PARC, a high-intensity proton accelerator facility in Japan, has been open to public use since December 2008, and various high-pressure experiments are expected to be conducted using its high-intensity pulsed neutron beam. The first test experiment using a Paris-Edinburgh (PE) press was performed with the Engineering Materials Diffractometer "TAKUMI". The powder diffractions of standard samples in the press were successfully obtained using two different geometries (vertical scattering geometry and horizontal scattering geometry). Although the signal was weak and there are still many issues to be solved, it has been confirmed that in situ high-pressure neutron powder diffraction is feasible at J-PARC.

Estimation of Radioactivity Produced in Cooling Water at High-Intensity Proton Accelerator Facility

The radioactivity produced in accelerator cooling water was estimated to determine the maintenance scenario of Japan Proton Accelerator Research Complex (J-PARC) accelerators. The PHITS and the MCNPX codes were used to calculate the proton and neutron fluxes in water-cooled accelerator components. The activation cross-section sets of oxygen for high-energy protons and neutrons were evaluated from the available experimental data and theoretically calculated data by the INC/GEM and the LAHET codes. The radioactivity from corrosion products was also estimated by scaling of the measurements at the High Energy Accelerator Research Organization 12 GeV Proton Synchrotron Experiment (KEK-PS) and Los Alamos Meson Physics Facility (LAMPF). The tritium estimation is an acceptable level for disposal to the environment, while short-lived nuclides at the 3-GeV synchrotron may raise the dose rate in the machine room.

Electrostatic separator for K1.8 beam line at J-PARC

The new electrostatic (ES) separator to select and deliver 1–2GeV/c kaon beams is made for the secondary beam line at the high intensity proton accelerator facility. The ES separator will generate a 75kV/cm electrostatic field between parallel electrodes of 10cm gap and 6m in length along the beam direction. The K−/π− ratio of the line is expected to have a larger value than 1. It is designed so as to be radiation-proof and to lower spark rate comparing with the present separators.

Shield Penetrating Water Cooled Bus Ducts for Radiation Resistant Magnets at J-PARC

The high intensity proton accelerator facility J-PARC is now in its final stage of construction. Soon intense primary proton beams will be slowly extracted to an experimental hall (HD-hall) and transported to a production target. Since the radiation level around the target will be very high, the beam line tunnel needs to be surrounded by 2.5 m-5 m thick concrete shields in the HD-hall. Radiation resistant magnets for handling high intensity beams are buried inside these thick concrete shields. This structure, however, brought us a problem of leading electric power lines to the magnets. For a solution to this problem, we have developed water cooled bus ducts penetrating radiation shield. These bus ducts enable us to connect the power supplies placed outside the shields to the magnets in the shortest power line length without any deterioration of protection ability of radiation shielding. The maximum power capacity of the bus duct is over 5000 A. The bus ducts plays an important part in our radiation resistant magnet system.

Evaluation of the radioactivity of the pre-dominant gamma emitters in components used at high-energy proton accelerator facilities

At a high-energy, high-intensity proton accelerator facility, the accelerator components inside the beam-line tunnel and the concrete wall of the tunnel are activated due to beam loss during operation. During maintenance work inside the tunnel, radiation emitted from these activated materials can cause exposure to radiation workers. In this study, the relation between the surface dose rate of activated materials and the induced radioactivity was considered, and an evaluation of the major radioactivity using the surface dose rate was made. It has been revealed that (22)Na in Al samples and (54)Mn in Fe samples, (60)Co and (54)Mn in Fe samples, and (60)Co in Fe and Cu samples are principal residual radionuclides after a few hundred days of cooling about a few years of cooling and approximately 10 y of cooling, respectively.

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.

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%.

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

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.