Superconducting Proton Linac Research Articles

Investigation of random beam trips in a linear accelerator at the Japan proton accelerator research complex for the development of an accelerator-driven nuclear transmutation system

ABSTRACT In a proton linear accelerator (linac), the proton beam is sometimes unexpectedly interrupted because of the electrical discharge caused by radio frequency, device/equipment failure, and other factors. Are these beam trips random? Traditionally, beam trips have been implicitly assumed to occur randomly. In this study, we investigated whether beam trips occur randomly in the Japan Proton Accelerator Research Complex (J-PARC) linac. The aim was to estimate the beam trip frequency in a superconducting proton linac for an accelerator-driven nuclear transmutation system. First, the J-PARC linac was classified into five subsystems. Then, the reliability function for the operation time in each subsystem was obtained by the Kaplan – Meier estimation, a reliability engineering method. This reliability function was used to investigate the randomness of beam trips. Analysis of operational data for five subsystems of the J-PARC linac for five years showed that beam trips occurred randomly in some subsystems. However, the beam trips did not occur randomly in many subsystems of the proton linac, including the ion source and the acceleration cavity, which are the primary subsystems of the proton linac.

Implementation Status of Myrrha Phase 1 (Minerva)

The MYRRHA design for an accelerator driven system (ADS) is based on a 4 mA, 600 MeV CW superconducting proton linac. The construction of the first stage (called MINERVA) by the Belgium Nuclear Research Centre SCK CEN was approved in 2018. It consists of a 100 MeV superconducting RF linac as well as two independent target stations, one for radio-isotope research and production of radio-isotopes for medical purposes, the other one for fusion materials research. This contribution presents the main design choices and current status of the overall project parts (civil engineering, particle accelerator and target facilities)

Firmware and Software Implementation Status of the ICBLM and nBLM Systems for the ESS Facility

The European Spallation Source (ESS) is a neutron source powered by a 5 MW, 2 GeV superconducting proton linac which is currently being constructed in Lund. Due to high beam current, just a few microseconds of operation with a misaligned beam can melt the accelerating cavity wall. Therefore, a Beam Loss Monitor (BLM) system is necessary to protect hardware and personnel from the consequences of beam loss. The BLM’s main function is to inhibit beam production when excessively high beam losses are detected. Besides protection functionality, the system is anticipated to provide the means to monitor the beam losses during all modes of operation with the objective of preventing excessive machine activation. This paper concentrates on implementation for ionization chamber Beam Loss Monitor (ICBLM) and Neutron Sensitive Beam Loss Monitor (nBLM) systems. The required microsecond reaction time has been achieved due to the application of an FPGA. A single detector module was installed and successfully tested at LINAC4 at CERN, in the section where conditions are similar to the ones expected in the ESS linac. The summary of these tests is also included.

Thermal design and performance of low beta cryomodule for CAFe

China initiative Accelerator Driven System (CiADS) has developed several kinds of cryomodules for superconducting proton linac at IMP. The low beta cryomodules had been designed, fabricated, assembled, and tested for the linac. To meet the requirements of minimizing heat transfer and operational stability, the thermal design and performance of low beta cryomodules have been studied. In this paper, finite element analysis and numerical calculation have been carried out on the design of important components such as thermal insulating support, bellows, thermal shield, power coupler, current leads and so on. Then the heat loads at various temperature levels have been summarized. Besides, the performance of the cryomodules including the cool down, equipment operating data, and heat load measurements are reported. The trial test result of low beta cryomodules shows that the various technical indexes satisfied the technical requirements.

Design and Development of the 200-kW Beam Dump

The Chinese Accelerator Front end (CAFe) is a demo superconducting proton linac for an accelerator-driven subcritical system (ADS). It includes an electron-cyclotron resonance ion source, a low-energy transport line, a radio-frequency quadrupole, a medium-energy transport line, a superconducting section, a high-energy transport line, and a beam dump. The design energy and current are 20 MeV and 10 mA, with a beam power of 200 kW. The goal of the CAFe is to demonstrate the 10-mA ability of a full superconducting linac, especially in the low-energy region. In previous beam commissioning, the maximum beam power achieved was 34 kW, which was limited by the capacity of the beam dump. Thus, for the high-power beam commissioning of CAFe, a new 200-kW beam dump has been designed and developed. Based on the thermal analysis, a maximum power density of 200 W/cm2 is adopted for the dump. To avoid a high-level residual dose, the material of the dump is aluminum alloy (Al6063). The dump is a conical structure, with water flow in the interlayer. During beam commissioning, the dump withstood 200-kW proton beam power and collected a total charge of 2049 mAh.

Shielding Assessment and Optimization of the Target Station for Medical Isotope Production Based on Superconducting Proton Linac

In response to the worldwide shortage of 99mTc supply caused by the combined consequence from both decommissioning and maintenance of research reactors worldwide, the Institute of Modern Physics (IMP) of the Chinese Academy of Science and Lanzhou University have launched a collaboration to research and develop a 99mTc production solution based on the 25 MeV high-intensity superconducting proton linear accelerator. Radiation from high-current proton bombardment must be evaluated and considered carefully at the design stage to meet radiation protection (RP) policy and requirements of the shielding for the key device. This work employed FLUKA to conduct the shielding assessment of both prompt and residual radiation fields in several iterations, based on a prototype of the high-power target system. The prompt dose rates outside the target station are lower than the institution’s limit. The residual dose rates inside the station fall below 100 μSv/h at 64 h after the end of beam (EOB); the dominant source term is then the target chamber. The service life of the main actuator is expected to be extended by 2.7 times with the current partial shielding design. The simulation accelerating techniques are applied to balance the accuracy of results and the progress of the project at the same time, which is referential to the shielding assessment of large-scale nuclear facilities. The results can also be used in further study and construction of the target station.

Oak Ridge Spallation Neutron Source superconducting rf linac availability performance and demonstration of operation restoration with superconducting rf cavity off

Recent advances in superconducting rf (SRF) technology allow for increasingly more reliable and higher power hadron linacs. They hold enormous potential for economic, scientific, medical, environmental, and national security fields. Moving this technology from one of a kind laboratory demonstration devices to industrial scale applications imposes strict requirements on the linac performance in terms of its stability, reliability, and availability. The Spallation Neutron Source (SNS) is currently the highest average power superconducting proton linac in the world that has been routinely operated since 2006. We present statistical data on the SNS SRF linac reliability obtained from its practical operational experience during 2020. We analyze the frequency and duration of SRF cavity trips and identify their causes. These data will show that SRF cavity trips are the most common source of single-point failure within the linac. In an industrial environment, where redundancy is a necessity to prevent interruption of facility operation, the linac beam can be quickly restored by redistributing the failed cavity function to downstream energy reserve SRF cavities. We present a practical demonstration of this approach. We intentionally turn off one of the cavities and recover the beam by readjusting the phases of downstream cavities to maintain the same linac beam energy output. We discuss limitations of this approach at SNS and how they can be overcome.

Commissioning experiences with the spoke-based CW superconducting proton linac

Commissioning experiences with the spoke-based CW superconducting proton linac

2 K superfluid helium cryogenic vertical test system for superconducting cavity of ADS Injector I

The accelerator-driven subcritical system (ADS) is the internationally recognized key technology of nuclear waste problem treatment, of which superconducting proton linac is an important part. With the support of the strategic science and technology pilot project of the Chinese Academy of Sciences, the Institute of High Energy Physics of the Chinese Academy of Sciences took the lead in the research of 325 MHz superconducting proton linac, which is called ADS Injector I. The superconducting accelerator part of ADS Injector I mainly consists of 14 spoke-type superconducting cavities with β 0.12. At the same time, the research work of various cavities with different β values and different frequencies is also carried out to lay the technical and technological foundation for ADS main accelerator. The only way to determine whether the superconducting cavity can reach the design target and whether it can be installed into the cryostat is the vertical test at cryogenic. As the only way to test the microwave performance of the superconducting cavity at low temperature, the vertical test can accurately test the acceleration gradient Eacc and the corresponding quality factor Q0 of the superconducting cavity. The design and construction of the superconducting cavity vertical test facility is based on the practical needs of the pilot project and the long-term development of the superconducting accelerator. This paper mainly introduces the design and construction of the cryogenic vertical test system for the superconducting cavity of ADS Injector I, including the system scheme design, process design, heat load analysis, 2 K superfluid helium obtaining method, system commissioning and operation, etc. The static heat leakage at 2 K of the 2 K superfluid helium vertical test system of ADS Injector I is 1.624 W, which has reached the international advanced level. The 2 K superfluid helium vertical test system of ADS Injector I after constructed not only meets the test requirements of ADS pilot project, but also conducts 4 K and 2 K vertical tests for other different types of superconducting cavities and relevant cryogenic experiments.

Commissioning of China ADS demo Linac and baseline design of CiADS project

China Accelerator Driven Subcritical System (C-ADS) program was launched in China in 2011. In the first five-year phase, a 25 MeV demo linac has been successfully built to demonstrate the key technologies of the driven linac. Beam commissioning activities have been carried out to study the high-power beam physics. Followed by the previous phase, China Initiative Accelerator Driven Subcritical System (CiADS) is approved contain a superconducting proton linac with 500 MeV and 5 mA. In this paper, the commissioning results of the demo linac and the beam dynamics design of CiADS linac based on commissioning experiences are presented.

A variable field phase-shifter for recirculating proton linacs

The recirculating superconducting proton linac that has a potential to substantially save accelerator cost was recently proposed. It consists of three sections to accelerate the continues-wave (CW) beam to multiple GeVs. In the first section, the beam passes the linac two times. In the second and third sections, the beam goes through the linac four and six times. A phase-shifter is needed to meet the synchronous acceleration condition for multi-pass acceleration using the same RF cavity due to the phase slippage of the proton beam. Here we present the design of a variable field rectangular bend phase-shifter in which the beam goes to a different path in each pass inside the magnet to meet the synchronous condition.

Overtaking collision effects in a cw double-pass proton linac

The recirculating superconducting proton linac has the advantage of reducing the number of cavities in the accelerator and the corresponding construction and operational costs. Beam dynamics simulations were done recently in a double-pass recirculating proton linac using a single proton beam bunch. For continuous wave (cw) operation, the high-energy proton bunch during the second pass through the linac will overtake and collide with the low-energy bunch during the first pass at a number of locations of the linac. These collisions might cause proton bunch emittance growth and beam quality degradation. In this paper, we study the collisional effects due to Coulomb space-charge forces between the high-energy bunch and the low-energy bunch. Our results suggest that these effects on the proton beam quality would be small and might not cause significant emittance growth or beam blowup through the linac. A 10 mA, 500 MeV cw double-pass proton linac is feasible without using extra hardware for phase synchronization.

Comparison of coaxial higher order mode couplers for the CERN Superconducting Proton Linac study

Higher order modes (HOMs) may affect beam stability and refrigeration requirements of superconducting proton linacs such as the Superconducting Proton Linac, which is studied at CERN. Under certain conditions beam-induced HOMs can accumulate sufficient energy to destabilize the beam or quench the superconducting cavities. In order to limit these effects, CERN considers the use of coaxial HOM couplers on the cutoff tubes of the 5-cell superconducting cavities. These couplers consist of resonant antennas shaped as loops or probes, which are designed to couple to potentially dangerous modes while sufficiently rejecting the fundamental mode. In this paper, the design process is presented and a comparison is made between various designs for the high-beta SPL cavities, which operate at 704.4 MHz. The rf and thermal behavior as well as mechanical aspects are discussed. In order to verify the designs, a rapid prototype for the favored coupler was fabricated and characterized on a low-power test-stand.

Development of Infrastructure Facilities for Superconducting RF Cavity Fabrication, Processing and 2 K Characterization at RRCAT

An extensive infrastructure facility is being established at Raja Ramanna Centre for Advanced Technology (RRCAT) for a proposed 1 GeV, high intensity superconducting proton linac for Indian Spallation Neutron Source. The proton linac will comprise of a large number of superconducting Radio Frequency (SCRF) cavities ranging from low beta spoke resonators to medium and high beta multi-cell elliptical cavities at different RF frequencies. Infrastructure facilities for SCRF cavity fabrication, processing and performance characterization at 2 K are setup to take-up manufacturing of large number of cavities required for future projects of Department of Atomic Energy (DAE). RRCAT is also participating in a DAE’s approved mega project on “Physics and Advanced technology for High intensity Proton Accelerators” under Indian Institutions-Fermilab Collaboration (IIFC). In the R&D phase of IIFC program, a number of high beta, fully dressed multi-cell elliptical SCRF cavities will be developed in collaboration with Fermilab. A dedicated facility for SCRF cavity fabrication, tuning and processing is set up. SCRF cavities developed will be characterized at 2K using a vertical test stand facility, which is already commissioned. A Horizontal Test Stand facility has also been designed and under development for testing a dressed multi-cell SCRF cavity at 2K. The paper presents the infrastructure facilities setup at RRCAT for SCRF cavity fabrication, processing and testing at 2K.

Beam commissioning for a superconducting proton linac

To develop the next generation of safe and cleaner nuclear energy, the accelerator-driven subcritical (ADS) system emerges as one of the most attractive technologies. It will be able to transmute the long-lived transuranic radionuclides produced in the reactors of today's nuclear power plants into shorter-lived ones, and also it will provide positive energy output at the same time. The prototype of the Chinese ADS (C-ADS) proton accelerator comprises two injectors and a 1.5 GeV, 10 mA continuous wave (CW) superconducting main linac. The injector scheme II at the C-ADS demo facility inside the Institute of Modern Physics is a 10 MeV CW superconducting linac with a designed beam current of 10 mA, which includes an ECR ion source, a low-energy beam transport line, a 162.5 MHz radio frequency quadrupole accelerator, a medium-energy beam transport line, and a superconducting half wave resonator accelerator section. This demo facility has been successfully operating with an 11 mA, 2.7 MeV CW beam and a 3.9 mA, 4.3 MeV CW beam at different times and conditions since June 2014. The beam power has reached 28 kW, which is the highest record for the same type of linear accelerators. In this paper, the parameters of the test injector II and the progress of the beam commissioning are reported.

Solenoid-Based Focusing Lens for the Low-Beta Section of a Superconducting Proton Linac

A superconducting solenoid-based focusing lens was designed and built for use in the SSR1 cryomodule of PXIE test facility at FNAL. As the cryomodule contains superconducting spoke-type cavities, one of main goals during design stage was minimization of magnetic field on walls of the cavities. The design also attempted minimization of the uncertainty of the magnetic axis position in the lens. This report describes main features of the design and summarizes results of performance tests and magnetic axis position measurements.

Neutrino super beam based on a superconducting proton linac

We present a new design study of the neutrino Super Beam based on the Superconducting Proton Linac at CERN. This beam is aimed at megaton mass physics, a large water Cherenkov detector, proposed for the Laboratoire Souterrain de Modane in France, with a baseline of 130 km. The aim of this proposed facility is to study CP violation in the neutrino sector. In the study reported here, we have developed the conceptual design of the neutrino beam, especially the target and the magnetic focusing device. Indeed, this beam presents several unprecedented challenges, related to the high primary proton beam power (4 MW), the high repetition rate (50 Hz), and the low kinetic energy of the protons (4.5 GeV). The design is completed by a study of all the main components of the system, starting from the transport system to guide the beam to the target up to the beam dump. This is the first complete study of a neutrino beam based on a pebble-bed target capable of standing the large heat deposition of MW class proton beams.24 MoreReceived 5 December 2012DOI:https://doi.org/10.1103/PhysRevSTAB.17.031001This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

High intensity neutrino oscillation facilities in Europe

The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fr\'ejus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of {\mu}+ and {\mu}- beams in a storage ring. The far detector in this case is a 100 kt Magnetised Iron Neutrino Detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular 6He and 18Ne, also stored in a ring. The far detector is also the MEMPHYS detector in the Fr\'ejus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. However, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.

The design simulation of the superconducting section in the ADS injector II

The high-current superconducting proton linac is being studied for the accelerator-driven system (ADS) project undertaken by the Chinese Academy of Sciences. The injector II will be operated at 162.5 MHz, and the proton out from the RFQ with an energy of 2.5 MeV will be accelerated to 10 MeV by two cryo-modules, which are composed of eight superconducting half wave resonance cavities and nine solenoids. In this paper, the design and beam simulation of the superconducting section of the injector II, the acceptance calculation and a stability analysis are presented.

Optical emission spectroscopy of the Linac4 and superconducting proton Linac plasma generators

CERN's superconducting proton Linac (SPL) study investigates a 50 Hz high-energy, high-power Linac for H(-) ions. The SPL plasma generator is an evolution of the DESY ion source plasma generator currently operated at CERN's Linac4 test stand. The plasma generator is a step towards a particle source for the SPL, it is designed to handle 100 kW peak RF-power at a 6% duty factor. While the acquisition of an integrated hydrogen plasma optical spectrum is straightforward, the measurement of a time-resolved spectrum requires dedicated amplification schemes. The experimental setup for visible light based on photomultipliers and narrow bandwidth filters and the UV spectrometer setup are described. The H(α), H(β), and H(γ) Balmer line intensities, the Lyman band and alpha transition were measured. A parametric study of the optical emission from the Linac4 ion source and the SPL plasma generator as a function of RF-power and gas pressure is presented. The potential of optical emission spectrometry coupled to RF-power coupling measurements for on-line monitoring of short RF heated hydrogen plasma pulses is discussed.