High-power Proton Beam Research Articles

Beam Profile Measurement Using the Highly-Oriented Pyrolytic Graphite

The mitigation of heat loading is one of the important issues for beam instrumentation to measure the high-power proton beam. Recently, the highly-oriented pyrolytic graphite (HOPG) material was used for the target probe of the bunch-shape monitor at the front end in the Japan Proton Accelerator Research Complex (J-PARC). Since the thermal conductivity of the HOPG is high, it is suitable to measure both transverse and longitudinal beam profiles under the condition of high heat loading. As an application of the HOPG, for example, the thin HOPG may be used as a substitutive material of the target wire for the transverse profile monitor such as the wire scanner monitor. The possibility of the HOPG target for both transverse and longitudinal beam profile monitors is discussed from some results of the test experiment using the 3 MeV negative hydrogen ion beam at the test stand.

Design and performance of the shielded DTL4 Faraday cup for the commissioning of the high-power ESS proton linac

The final as-built version of the DTL4 Faraday cup for the ESS proton accelerator is presented; the beam-interceptive device acted as beam dump to support the commissioning and tuning of the ESS proton accelerator up to the DTL4 section. The DTL4 Faraday cup was designed, optimized and validated via MCNPX/ANSYS simulations in order to dump [21, 74] MeV protons, proton pulses up to 50 μs long, repetition rates up to 14 Hz and an unprecedented proton beam current up to 62.5 mA. The maximum volumetric power density was computed to be 20 GW/cm3 and 25 MW/cm3 for 21 MeV and 74 MeV protons, respectively.During the DTL4 commissioning, the DTL4 Faraday cup absorbed and safely dissipated the proton beam power, measured in real-time the proton beam current as well as the pulse duration. Examples of measured proton pulses are included to demonstrate the transport and acceleration of the high-power proton beam all the way down to the ESS DTL4 section. The control system for the data acquisition, operation under vacuum, motion control and cooling water system was based on EPICS. The operational parameters are presented following the results of thermo-mechanical calculations. In the most demanding operational condition, the predicted temperature of the core was around 1010 °C. The cooling water temperature was continuously monitored and remained below 23 °C during the operational period.Neutronics simulations were performed in order to quantify the activation, residual dose rates, radiation shielding and necessary decay time to be waited after the end of the commissioning. After four weeks of decay, a residual dose rate of 1.1 mSv/h was measured at 30 cm from the device. The DTL4 Faraday cup and its shielding were uninstalled in order to proceed with the installation of the DTL5 section. The Faraday cup is planned to be permanently installed in the DTL4 intertank once the DTL5 section is in place.

Insights into radiation resistance of titanium alloys from displacement cascade simulations

Radiation damage in beam window materials limits the use of high power proton beams in high energy physics research. The alloy Ti-6Al-4V is presently used as a beam window material but a prospective alternative, Ti-15V-3Cr-3Sn-3Al has been proposed. Since both these alloys contain dual phases at room temperature, we compare the radiation damage in the α and β-phases of these two materials via primary knock-on atom (PKA) cascade simulations in the 10–40 keV energy range. At PKA energies 30 and 40 keV, the number of Frenkel pairs in the ballistic stage is higher in the β-phase of Ti-6Al-4V than that in the β-phase of Ti-15V-3Cr-3Sn-3Al almost by a factor of 2. The α-phase, of both these alloys, by far outperforms the β-phases of the two alloys, both in terms of damage during the ballistic stage and in terms of the surviving defects. The average displacement threshold energy (Ed) in the α-phase of both alloys was found to be 66 eV while that in the β-phase of Ti-15-3-3 was 55 eV and in the β-phase of Ti-6-4 was 46. While the number of surviving defects is almost equal in both alloys, the vacancy and interstitial clustering mechanisms differ notably, which can impact the degree of radiation hardening and loss of ductility. Our simulations show larger vacancy and interstitial clusters form in Ti-6Al-4V as compared to that in Ti-15-3-3-3 alloy. These results indicate that Ti-15-3-3-3 alloys may be a promising candidate for next generation beam window material with a higher radiation tolerance than the existing Ti-6-4 alloy.

A novel methodological study for monitoring proton beam spot using back-streaming secondary neutrons from the high-power target

The power of the proton beam of a high-power spallation neutron source generally ranges from 100 kW to several MW. The distribution of the power density of the beam on the target is critical for the stable operation of the high-power spallation target. This study proposes a beam monitoring method that involves restoring the image of a high-power proton beam spot on a target based on the principle of pinhole imaging by using the back-streaming of secondary neutrons from the spallation target. Fast and indirect imaging of the beam spot can be achieved at a distance of tens of meters from the target. The proposed method of beam monitoring can flexibly adjust the size of the pinhole and the measurement distance to control the intensity of flux of the secondary neutrons according to the demands of the detection system, which is far from the high-radiation target area. The results of simulations showed that the proposed method can be used to restore the beam spot of the incident proton by using the point response function and images of the secondary neutrons. Based on the target and the Back-n beamline in the CSNS, the effectiveness of this method has also been confirmed by means of Monte Carlo simulation.

Improved vacuum system for high-power proton beam operation of the rapid cycling synchrotron

The vacuum system in the rapid-cycling synchrotron of the Japan Proton Accelerator Research Complex has been operated for more than 10 years. It becomes evident that the high-power beam operation has more powerful effects on the vacuum system than expected at the time of the design. Those effects of the high-power beam are categorized into two types of events, the malfunction of vacuum equipment and the large pressure rise. A specific example of the former event is the failure of the turbomolecular pump (TMP) controller by the full loss of a single-shot high-intensity beam. The TMP itself is also damaged by a bearing crush due to a touch down without braking the rotor. We have developed a TMP controller that can connect with long power and control cables of more than 200 m lengths. This length makes the controller be installed in a control room where there is no radiation influence. The TMP with high-strength bearing has been also developed. The TMP system becomes tolerant to a large loss of the high-intensity beam by using such a controller and a TMP. The latter event is an extreme pressure rise with increasing the beam power. The dynamic pressure behaviors during the beam operations are investigated to understand the outgassing mechanism by the beam. It is indicated that the pressure rise mechanism is a result of the ion-stimulated gas desorption. The analytical calculation based on the ion-stimulated gas desorption model well reproduces the measured dynamic pressure. The calculation also shows that, among the parameters, a larger pumping speed per unit length $s$ and a smaller initial surface density of the adsorbed molecules ${q}_{0}$ are required to suppress the extreme pressure rise. The nonevaporable getter (NEG) pumps are additionally installed to obtain the larger $s$ and smaller ${q}_{0}$. It is confirmed by simulating the beam line pressure distribution that the additional NEG pumps are effective to obtain the larger $s$ in every position along the beam line. The ability of the NEG pump to keep a low pressure during the vacuum system shutdown, which can contribute to maintain the small ${q}_{0}$, is examined by the buildup test. It is finally confirmed that the dynamic pressure during the high-power beam is effectually suppressed.

Multiple length-scale microstructural characterisation of four grades of fine-grained graphite

Multiple length-scale microstructural characterisation has been conducted on four different grades of unirradiated fine-grained graphite: CL 2020, IG 430, SGL R7650 and POCO ZXF-5Q, which are the potential candidates as high-power proton beam intercepting materials (secondary particle-production targets). Micrometre and sub-micrometre sized porosity structures have been characterised by X-ray micro-computed tomography (µXCT) and focused ion beam-scanning electron microscopy tomography (FIB-SEM tomography). Results show that these four grades of graphite have distinct porosity structures with a substantial amount of interconnected pores; POCO-ZXF-5Q has the most uniform porosity size and spatial distribution out of the four at these length scales examined. As a direct measurement of the total number and volume of nano-sized Mrozowski cracks is currently not readily feasible, the characteristic crystalline size La reflecting the coherent scattering length at nano-scale was evaluated using micro-Raman spectroscopy. It has been found that a significant reduction in average characteristic crystalline size had been induced by sample preparation. Further measurements on freshly fractured sample surfaces excluding these damages suggested that IG430 graphite has the largest average crystallite size (~290 nm) while POCO-ZXF-5Q has the smallest average crystallite size (~80 nm) with a narrow distribution. These results from un-irradiated graphite were used to further understand the proton irradiated behaviour of these four grades of graphite.

High power particle accelerator for driving the nuclear waste transmutation system at nuclear power plant

The existing technology for treatment of NPP nuclear waste is a deep geological disposal technology. But this technology is still has possibility of leakage due to heating caused by radioactivity process from long lived elements of nuclear waste. The development of high power particle accelerator technology which can produce high power proton beam to induce nuclear spallation reaction has introduced a new accelerator-based technology for treatment of nuclear waste from NPP named the Accelerator-driven Transmutation Waste (ATW). This paper describes result of study on status of accelerator based transmutation system for NPP nuclear waste. ATW is subcritical nuclear reactor combined with high power proton accelerator for transmutation of nuclear waste utilizing neutrons from spallation reaction due to collision of high power proton beam with heavy metal material as spallation target. The types of accelerators used for ATW are cyclotron, linac and synchrotron which able to produce proton beam of 10 up to 100 MW beam power, 10 up to 100 mA beam current and 0.6 up to 1.5 GeV beam energy. Demonstration scale ATW requires 1 up to 2 MW of proton beam power to generate 50 up to 100 MWth of thermal power in subcritical reactor. Whereas industrial ATW requires 10 up to 75 MW of proton beam power to generate hundred MWth of thermal power in subcritical reactor. Several countries have roadmap of ADS research and development which the main goal of nuclear waste transmutation using ADS called ATW. ATW also can be used for electrical energy production which is safer and more reliable.

Low-power proton beam extraction by the bright continuous laser using the 3-MeV negative-hydrogen linac in Japan Proton Accelerator Research Complex

ABSTRACT 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 . These values obtained are in good agreement with the estimated values.

Lifetime assessment of functional components in the ESS target environment during beam energy ramp up

The Target Station at the European Spallation Source (ESS) is designed to convert high power proton beam to high brightness neutron beams, for studying fundamental properties of materials. Upon commissioning of the ‘beam on target’ planned in 2022, the ESS linac will deliver lower energy proton beam than the design value of 2 GeV, for neutron production. The beam energy will then be gradually ramped up, with the sequential commissioning of the downstream part of the superconducting cryomodules. During neutron production, the beam intercepting devices and moderators are exposed to intense flux of primary and secondary particles, suffering from radiation induced structural degradation. The extent of the radiation damage depends on the energy and intensity of the impinging protons. Currently, the lifetime criteria determined for these components are based on the 2 GeV beam energy. To secure availability and reliability of the neutron production during the beam energy ramp-up phase, the radiation damage rates in these components should be reassessed and the lifetime criteria be adjusted. In this paper, we present the lifetime criteria for the beam intercepting devices and moderators for different beam energies, to serve for the planning of the maintenance and replacement schedule during the proton energy ramp-up phase.

Preliminary Study of the High Temperature Superconducting Solution for 2 GeV CW FFAG Magnet

Proton beam with an average power of 5 MW-10 MW have important applications in particle physics towards the intensity frontier, as well as in the advanced energy, and material science. The fixed field alternating gradient (FFAG) accelerator combines the advantages of existing accelerators, which has a higher limitation of beam energy than high power cyclotron and has a higher beam-to-grid efficiency than existing high power linac and synchrotron, thus is considered as a good candidate for high power proton machine. By utilizing the strong focusing and large acceptance features of FFAG in the theoretical framework of the fixed field and fixed frequency of isochronous cyclotron, a continue wave FFAG capable of producing 2 GeV/3 mA protons (with an beam power of 6 MW) has been proposed in China Institute of Atomic Energy (CIAE). Due to the beam loss of high power proton beams, the resulting high radiation will deposit a large amount of radiation dose and heat load on the superconducting (SC) magnet. As the high temperature superconductors (HTS) have a much larger thermal margin due to high critical temperature (> 90 K) and high upper critical field (>100 T) than the traditional low temperature superconductors, and have been also considered have the lower overall construction costs and power consumption than the conventional magnet, currently the HTS magnet is the favorable solution for the 2 GeV FFAG magnet design. In this paper, the lattice design along with the requirements on the F-D-F magnet of the 2 GeV FFAG design is briefly introduced first. Then, the design of the F-D-F magnet is outlined. The details of the HTS coil design utilizing ReBCO conductor and operating at ~30 K is also included.

Radiation hardness study for the COMET Phase-I electronics

Radiation damage on front-end readout and trigger electronics is an important issue in the COMET Phase-I experiment at J-PARC, which plans to search for the neutrinoless transition of a muon to an electron. To produce an intense muon beam, a high-power proton beam impinges on a graphite target, resulting in a high-radiation environment. We require radiation tolerance to a total dose of 1.0kGy and 1MeV equivalent neutron fluence of 1.0×1012neqcm−2 including a safety factor of 5 over the duration of the physics measurement. The use of commercially-available electronics components which have high radiation tolerance, if such components can be secured, is desirable in such an environment. The radiation hardness of commercial electronic components has been evaluated in gamma-ray and neutron irradiation tests. As results of these tests, voltage regulators, ADCs, DACs, and several other components were found to have enough tolerance to both gamma-ray and neutron irradiation at the level we require.

Multi-Ribbon Profile Monitor for high power proton beam at J-PARC MR Abort Line

Japan Proton Accelerator Research Complex (J-PARC) Main Ring (MR), the world-class high intensity proton synchrotron, provides proton beam to two experimental facilities with two extraction modes: Fast extraction (FX) and Slow extraction (SX). The number of protons per pulse (ppp) in MR recorded the world highest value of 2.7 × 1014 in the FX mode. Now we are planning to increase the ppp further up to 3.3 × 1014 in near future. The beam profile is one of the most important parameters to discuss the high intensity beam dynamics in MR. Monitors using multi-wires /ribbons are effective to measure the beam profile with good accuracy and wide dynamic range. However, they cause significant beam losses by interactions with high-intensity circulating beam in synchrotrons. Recently, we installed new multi-ribbon profile monitor (MRPM) in an abort line in MR. The abort line is one of the extracted beam lines of the FX system. It has a quadrupole doublet which is called Abort Q and transports extracted beam to a beam dump. The FX system can extract the circulating beam in MR with an arbitrary energy. Performing the single-pass measurement with MRPM and changing the transfer matrix by sweeping field strength of Abort Q, the emittance of the extracted beam can be measured. In this paper, we present the design, manufacturing, and results of the first beam test of newly installed MRPM system.

A fresh look at ALP searches in fixed target experiments

A significant number of high power proton beams are available or will go online in the near future. This provides exciting opportunities for new fixed target experiments and the search for new physics in particular. In this note we will survey these beams and consider their potential to discover new physics in the form of axion-like particles, identifying promising locations and set ups. To achieve this, we present a significantly improved calculation of the production of axion-like particles in the coherent scattering of protons on nuclei, valid for lower ALP masses and/or beam energies. We also provide a new publicly available tool for this process: the Alpaca Monte Carlo generator. This will impact ongoing and planned searches based on this process.

Temperature control for spallation target in accelerator driven system

In an accelerator driven critical or sub-critical system (ADS), a spallation target is irradiated by high-power proton beam to drive a reactor. To continuously produce very intense neutrons, it is very important to ensure that the target operates in a setting temperature environment. This paper reports several techniques of temperature control for the spallation target in China initiative ADS system, where tungsten granules in the target container are used as both coolant and target materials. In order to avoid high temperatures at the target center due to the Gaussian distribution of beam intensity, the proton beam should be scanned on the surface of the target to provide a high degree of uniformity in energy deposition. The target temperature can be controlled by adjusting automatically the speed of the coolant. If the speed attains the maximum setting value, the beam intensity will be decreased for a given value to reduce the heat generation. To evaluate the proposed control techniques, the heat transfer model of particles has been employed to investigate the spatio-temporal variations of the target temperatures. The simulation results indicate that the beam scanning technique reduces dramatically the temperatures. The target temperatures can be controlled by adjusting automatically both the granular speed and the beam intensity. The target can operate normally in the setting working temperature range even if the target is irradiated by the proton beam with the maximum power.

Overtemperature protection systems for spallation target in China initiative accelerator driven sub-critical system

In an accelerator driven sub-critical system (ADS), a spallation target is irradiated by high-power proton beam to drive a sub-critical reactor. To continuously produce very intense neutrons, it is very important to prevent the unsafe operation of the target. This paper reports an over-temperature protection system for the spallation target in China initiative ADS system, where tungsten granules in the target container are used as both coolant and target materials. In order to protect the target from abnormal irradiation by the accelerator's beam when the granules are blocked or when the beam deviates from the target center, 12 sets of thermocouples are mounted inside the target container to monitor the target temperature. To evaluate the protection functions of these thermocouples, the heat transfer model of particles has been employed to investigate the spatio-temporal variations of the target temperatures when tungsten granules stay static in the target. The simulation results indicate that the temperatures of the thermocouples increase with the irradiation time and the granular blockage can be detected by analyzing the temperatures of these thermocouples. On the other hand, when the beam center deviates from the target center, the azimuthal distribution of the target temperature becomes non-uniform, and the temperature of the thermocouple close to the beam center increases faster. Finally, in the monitoring system for the over-temperature protection, 12 thermocouples divided into 3 groups which are fixed within the target in the upper, central and lower parts of the target, and 4 thermocouples in each group are located in four directions of east, south, west, and north. If two or more channels of four directions in one group exceed the set point, the protective function of granular blockage will be initiated; if two or more channels in one direction are greater than the set point, the protective function of beam deviation will be triggered.

Thermal-Hydraulic Analysis of the LBE Spallation Target Head in JAEA

To perform basic research and development to realize future accelerator-driven systems, a lead-bismuth eutectic (LBE) alloy spallation target will be installed within the framework of the Japan Proton Accelerator Research Complex (J-PARC) project, Japan Atomic Energy Agency. The target will be bombarded by high-power pulsed proton beams (250 kW, 400 MeV, 25 Hz, and 0.5 ms in pulse duration). The beam window (BW) of the spallation target is critical because it should survive under severe conditions that occur, i.e., high temperature, high irradiation, intense stress, and various kinds of damage. Therefore, the target vessel should be carefully designed to obtain an adequate safety margin. Our previous research indicates that there is a stagnant flow region in the LBE at the BW tip due to the symmetric configuration of the target, which causes high temperature and concentration of stress on the BW. On the basis of our previous work, three types of upgraded target head designs are studied in the current research to reduce/move the stagnant flow region from the BW tip and to increase the target safety margin. Thermal-hydraulic analyses and structural analyses for the target head designs are carried out numerically under a steady-state condition. Results illustrate that the designs can almost eliminate the stagnant flow region in the LBE. As a consequence, the concentration of thermal stress on the BW is released and greatly decreased. The safety margin of the target is improved through this study.

Status of the COMET experiment

The COMET experiment, currently under construction at J-PARC, is designed to search for the the neutrinoless flavour-changing charged-lepton process μ- + A → e- + A, which is a promising channel to look for new physics. The experiment will make use of the high-power proton beam available at the J-PARC Main Ring to achieve a sensitivity orders of magnitude better than the current limits. The experiment will be staged, with ‘Phase-I’ scheduled to begin commissioning soon while the ‘Phase-II’ design is refined in parallel. A description the design of both Phases is presented, along with the latest developments.

Radiation studies for the MOMENT target station**Supported by National Natural Science Foundation of China (11425524, 11527811, 11575226) and Strategic Priority Research Program of the Chinese Academy of Sciences (XDA10010100)

The discovery of the neutrino mixing angle θ13 opens new opportunities for the discovery of leptonic CP violation at high intensity neutrino beams. MOMENT, a future neutrino facility with a high-power proton beam of 15 MW from a continuous-wave linac, is focused on that discovery. The high power of the proton beam causes extreme radiation conditions for the facility and especially for the target station, where the pion capture system of five superconducting solenoids is located. In this paper initial studies are performed for the effects of the radiation on the solenoid structure and the area surrounding it. A concept cooling system is also proposed.

The mechatronic design of a fast wire scanner in IHEP U-70 accelerator

This paper presents the mechatronic design of a fast wire scanner based on a servomotor. The design of the wire scanner is motivated by the need to measure the transverse profile of the high power proton and carbon beams at the IHEP U-70 accelerator. This paper formulates the requirements to the fast wire scanner system for the high intensity proton beam at the U-70 accelerator. The results on the design of electro-mechanical device for the wire scanner with a wire traveling speed 10–20m/s are presented. The solution consists in a brushless servomotor and standard motor control electronics. High radiation levels in the accelerator enclosure dictate the use of a resolver as the position feedback element.

Magnet Design of an 800 MeV High Power Proton Cyclotron

The high-power proton beam has wide applications in neutron and neutrino physics, radioactive ion-beam production, ADS systems, proton radiography, and nuclear data measurement, etc. Cyclotrons are intrinsic in continuous-wave beam mode, which has the characteristics of high efficient power conversion rate, compact structure, and relatively low construction cost. A high-power 800-MeV proton cyclotron was proposed by CIAE, and the prestudy on the cyclotron was carried out since the year of 2009. The main magnet is among the most crucial and challenging subsystems. In contrast to low beam current cyclotron, the main magnet system of high beam current cyclotron needs to provide very strong vertical focusing force to avoid the beam blowup caused by dangerous resonances and space charge effects. In this paper, the 3-D modeling and optimizing work on this large-scale magnet system are presented in detail.