Maximum Beam Current Research Articles

Beam injection and beam quality in injector LINAC and in beam transport lines at SuperKEKB

At SuperKEKB, the maximum beam currents and the luminosity could be limited by the beam injection in the near future. We estimated requirements to the beam injection to achieve the next target luminosity of 1 × 1035cm-2s-1. Two cases of β y * = 1 mm and 0.8 mm are considered. A simulation shows that we need to suppress the emittance growth of the injecting positron beam in the beam transport (BT) line down to its design value to meet the requirement with β y * = 1 mm. In the case of β y * = 0.8 mm, we need to improve dynamic aperture of LER in addition to the suppression of the emittance growth. Efforts to improve the beam quantity and quality in LINAC and in BT are summarized. The present most serious problem concerning quality of the injecting beams is emittance growth in the BT lines for both electron and positron beams. Simulations and experiments show that the effects of ISR and CSR in the BT lines cause a large horizontal emittance growth of the electron beam. Several measures to suppress the emittance growth are under considerations.

Machine learning-based optimization of storage ring injection efficiency

Since the DELTA accelerator facility does not use a White circuit-driven fast topping-up mode, each software-driven injection ramp cycle takes about 7 seconds. Depending on the injection efficiency, 150 to 200 ramp cycles are required to reach the maximum beam current of 130 mA in the storage ring. Thus, for fast post-injection, a high electron transfer rate is crucial. During the injection process, a large number of parameters (e. g., magnet settings, timings of pulsed elements) have to be adjusted manually. The injection efficiency depends mainly on the settings of the booster extraction elements, the T2 transfer line magnets, and the storage ring injection components. In order to automate the injection procedure and to improve the electron transfer efficiency, the application of innovative machine learning concepts was studied.

First beam extraction from a superconducting azimuthally varying field cyclotron for proton therapy

A 230 MeV superconducting azimuthally varying field (AVF) cyclotron SC230 was developed by Sumitomo Heavy Industries Ltd., Japan. With a yoke diameter, height and weight of 2.8 m, 1.7 m and 65 t, respectively, it is currently the most compact isochronous cyclotron for proton therapy. Size reduction was achieved by a high magnetic field using cryogen-free superconducting coils. It adopts not only a superconducting magnet, but also sectors with a narrow pole gap and large spiral angle, two dees with low power consumption, and beam extraction using the precessional extraction method. It has a maximum beam current of 1 μA. The total power consumption of its system is lower than 200 kW. After each component, including the magnet, was fabricated, the cyclotron was moved to a new test site, and a vacuum test and conditioning of some components were conducted. The beam commissioning started, and the first extracted beam was successfully observed. In this paper, the processes and results of the beam commissioning and the basic performance of the first beam are reported.

PETRA III Operation with High Availability

The Synchrotron Light Source PETRA III at DESY is one of the most brilliant storage-ring based X-ray sources for high-energy photons worldwide, which offers scientists unique X-ray experiments in a wide range of fields since 2009. The light source is operated mainly in two operation modes with 480 and 40 bunches at a beam energy of 6 GeV with a maximum beam current of up to 120 mA. High reliability is one of the key requirements for a synchrotron radiation facility. The key performance indicators, availability and mean time between failures (MTBF), could be significantly improved during the operation periods of the last years. As the final milestones of the extension project that started in 2014, a new undulator was installed for the beamline P62 in the Paul P. Ewald hall in 2020, and a new dipole beamline (P66) have been installed in the North East section of PETRA III in 2021.

A novel metamaterial slow wave structure with larger space-charge-limited current

This article proposes a new type of metamaterial slow wave structure with larger space-charge-limited current for high-power microwave sources. In order to avoid the anisotropy effect and improve the uniformity of electromagnetic field distribution, the slow wave structure consisted of two all-metal units arranged by a modified method of broadside-coupled complementary split ring resonant (CSRR) geometry. Moreover, the conductor on the periphery of the CSRR has been removed, and a short shift tube was added to the units for the purpose of obtaining larger space-charge-limited current. High-frequency analysis shows that the new slow wave structure has the basic characteristics of metamaterials, including double negative electromagnetic parameters, peculiar dispersion, and high coupling impedance. More importantly, transmission simulation shows that the space-charge-limited current of the structure is at least 12 kA, which is about twice the maximum beam current that the hollow circular waveguide of the same size can transmit, and it proves that the design method is effective and feasible. Applying the structure to a microwave source will achieve the goal of high-efficiency and high-power output.

Filling pattern dependence of regenerative beam breakup instability in energy recovery linacs

Beam breakup instability is a potential issue for all particle accelerators and is often the limiting factor for the maximum beam current that can be achieved. This is particularly relevant for Energy Recovery Linacs with multiple passes where a relatively small amount of charge can result in a large beam current. Recent studies have shown that the choice of filling pattern and recirculation scheme for a multi-pass energy recovery linac can drastically affect the interactions between the beam and RF system. In this paper we further explore this topic to study how filling patterns affect the beam breakup instability and how this can allow us to optimise the design in order to minimise this effect. We present a theoretical model of the beam-RF interaction as well as numerical modeling and show that the threshold current can vary by factors of 2-4, and potentially even more depending on the machine design parameters. Therefore a judicious choice of filling pattern can greatly increase the onset of BBU, expanding the utility of future ERLs.

Neutronics design for molten salt accelerator-driven system as TRU burner

Treatment of plutonium separated from spent fuel has been one of the most important issues in the utilization of nuclear power in Japan. This study investigates a molten salt accelerator-driven system (ADS) to transmute transuranic (TRU) nuclides to address the issue. This study proposes the MARDS (Molten salt AcceleratoR Driven System) concept which has four features: employment of chloride, no dedicated spallation target, non-contact between beam window and fuel salt and modularized core. Neutronics calculation for the MARDS concept was performed for a condition of 400 MW thermal power with 800 MeV proton beam. The calculation results showed that the maximum proton beam current was about 7 mA and about 100–120 kg plutonium could be transmuted during one-year operation. The result indicates that the MARDS concept can employ a circular accelerator instead of LINAC and transmute TRU effectively.

Enhancement of charge breeding efficiency for rare isotope beam with the control of magnetic field profile and electron beam energy in EBIS

The magnetic field in the ion trap of electron beam ion source (EBIS) determines the current density of electron beam and thus the depth of trap potential, which affects the charge breeding efficiency to desired charge state. An EBIS charge breeder has been constructed to be used for the Rare Isotope Science Project in Korea. A 6 T superconducting solenoid is used for the trap, and uniform magnetic field is extended with correction coils at the ends. The effect of field uniformity on the electron current density is evaluated using TRAK, and it is shown sizable improvement in the charge breeding efficiency for rare isotope beams can be obtained by elaborate magnetic design. Furthermore, the electron beam energy affects the ionization efficiency. The electron energy is often reduced in the trap for optimal matching with charge striping cross section. However, virtual cathode formation can appear in the process of energy reduction. Maximum beam currents limited by electron energy are studied analytically and by TRAK simulation in the view of improving the charge breeding efficiency.

Lossless Monochromation for Electron Microscopy with Pulsed Photoemission Sources and Radio-Frequency Cavities

Resonant radiofrequency cavities enable exquisite time-energy control of electron beams when synchronized with laser driven photoemission. We present a lossless monochromator design that exploits this fine control in the one-electron-per-pulse regime. The theoretically achievable maximum beam current on target is orders of magnitude greater than state-of-the-art monochromators for the same spatial and energy resolution. This improvement is the result of monochromating in the time domain, unconstrained by the transverse brightness of the electron source. We show analytically and confirm numerically that cavity parameters chosen to minimize energy spread perform the additional function of undoing the appreciable effect of chromatic aberration in the upstream optics. We argue that our design has significant applications in both ultra-fast and non-time-resolved microscopy, provided photoelectron sources of sufficiently small size and laser sources of sufficiently high repetition rate. Our design achieves in simulations more than two orders of magnitude reduction in beam energy spread, down to single digit meV. Overcoming the minimum probe-size limit that chromatic aberration imposes, our design clears a path for high-current, high-resolution electron beam applications at primary energies from single to hundreds of keV.

Effect of Air Pressure on Parameters of Beam Current and X-Ray Radiation Generated in a Gas Diode

Parameters of a beam of runaway electrons and X-ray radiation generated in a gas diode at different atmospheric pressures are studied. It is shown that the maximum beam currents and intensities of X-ray radiation are generated at an air pressure of about 102 Pa. Distribution of beam electrons with respect to energy is determined by the method of attenuation of beam current using aluminum filters with different thicknesses. The maximum of such a distribution corresponds to an electron energy of about 100 keV. The maximum exposure dose of X-ray radiation behind a copper-foil anode with a thickness of 30 μm is about 107 mR. It is shown that the beam electrons absorbed by elements of an X-ray detector affect the shape and amplitude of the desired signal at beam currents of greater than 35 A/cm2.

Design of a CW linac for the Compact Intense Fast NEutron Facility

Abstract The proposed Compact Intense Fast NEutron Facility (CIFNEF) will have a wide range of applications, including the investigation of the exotic structure of neutron-rich nuclei, data for the nuclear fission , and the simulation of the neutron field in a star. To satisfy aims of producing high-intensity fast neutrons and forward neutrons with very low environmental background, the CIFNEF linac should have the capacity of accelerating continuous wave (CW) deuteron (D + ), hydrogen ( H 2 + ) and lithium (7Li 3 + ) beams to 2.5 MeV/u with maximum beam currents of 10 mA, 5 mA and 10 uA, respectively. Based on the above requirements, we proposed a novel compact linac using a combination of RFQ and DTL structures. The dynamics of RFQ and DTL are completed to meet all requirements and start-to-end simulation results show that the three ion species can be accelerated to the final energy with transmission efficiency above 99% as well as good beam quality with lower emittance growth. In addition, we performed error sensitivity analysis and combined error study to evaluate the error tolerance limits of the obtained design.

SuperKEKB main ring vacuum system status until the end of Phase-2 commissioning

SuperKEKB is an electron–positron collider with asymmetric energies at KEK aiming at a high luminosity of 8.0 × 1035 cm–2 s–1. The main ring (MR) consists of two rings: a 4 GeV positron ring (low-energy ring, LER) and a 7 GeV electron ring (high-energy ring, HER). During the Phase-1 commissioning of the MR from February to June 2016 and the Phase-2 commissioning from March to July 2018, the vacuum system worked well overall. By the end of Phase-2, the total beam doses (integrated beam currents) were 1113 and 1002 Ah, and the maximum beam currents were approximately 1010 and 870 mA for the LER and HER, respectively. The increase in pressure per unit beam current decreased steadily. The photodesorption coefficients reached approximately 1 × 10−6 and 7 × 10−8 molecules photon−1 with photon doses of 5.88 × 1024 and 9.27 × 1024 photons m−1 for the LER and HER, respectively. The beam lifetime was limited by the Touschek effect in both rings. Various new vacuum components, including those installed after the Phase-1 commissioning, such as the beam pipes for the Belle II particle detector, beam collimators, and so on, have been functioning well so far. The electron cloud effect was observed in the LER during Phase-1, but it was suppressed by additional countermeasures applied before Phase-2. Regarding the pressure bursts accompanied with beam losses, which were frequently observed during Phase-1, the frequency of the pressure bursts drastically decreased during Phase-2, but the longer operation time with lower beam currents during Phase-2 than Phase-1 should be taken into account. Several new problems, such as the heating of stainless-steel beam pipes due to the synchrotron radiation emitted from the final focusing quadrupole magnets at the collision point, were found during Phase-2, and countermeasures are being prepared for the Phase-3 commissioning, which will commence in March 2019. SuperKEKB has been accumulating various data and information that will facilitate the design and operation of the vacuum systems in future high-current accelerators.

Study on the maximum stable output of a novel s-band micro-pulse electron gun

A novel S-Band Micro-Pulse electron Gun (MPG) which works at the left crossover point energy EcI on the Secondary Electron Yield (SEY) curve was proposed. The working principles of the MPG were presented. The maximum output beam current limited by space charge effects and beam loading effects was investigated by theoretical analysis. The result shows that the maximum beam current is decided by the parameters of the MPG such as resonant frequency, cavity length, shunt impedance and the secondary emission property of the cathode and grid, having nothing to do with the power flowed into the cavity. The low shunt impedance and the low slope of the SEY curve can help increasing the maximum beam current. According to the principles, a MPG with the frequency of 2.856 GHz has been designed and constructed. The steady working state was achieved by using oxygen free copper and molybdenum grid with different transmission coefficient. It was found a good agreement between the analysis and the experiments.

Magnetic field test of superconducting coils for the compact proton therapy cyclotron

The superconducting cyclotron for proton therapy that is under design by ASIPP (Hefei, China) and JINR (Dubna, Russia) will be able to accelerate protons to the energy 200 MeV with the maximum beam current of 1 μA. The performance of superconducting magnets is the key to the superconducting cyclotron, and it will directly affect the quality of the proton beam and the therapeutic effect. To measure the magnetic induction intensity of the superconducting coil with the cryogenic Hall probes on the testing platform. As the current has been increased from 0 to 160 A, the measurement error of probes decreases obviously whose tendencies are consistent. By comparing the measuring results with the theoretical results, we can confirm the quality of superconducting coil and the installation location. Meanwhile, the basic operation of cryogenic Hall probes and data acquisition system is grasped, and the experimental experience for the magnetic intensity test of superconducting cyclotron has been accumulated.

Conceptual design study of beam window for accelerator-driven system with subcriticality adjustment rod

The design of the beam window of the spallation target is one of the critical issues in the accelerator-driven system (ADS) design. This study aims to perform the coupled analysis for the feasible beam window concept. To mitigate the design condition, namely to reduce the necessary proton beam current, subcriticality adjustment rod (SAR) was installed to the ADS core. The burnup analysis was performed for the ADS core with SAR and the results indicated that the maximum proton beam current during the burnup cycle was reduced from 20 to 13.5 mA.Based on the burnup analysis result, the coupled analysis; particle transport, thermal hydraulics and structural analyses, was performed. As the final result, the most robust beam window design; the hemisphere shape, the outer radius = 235 mm, the thickness at the top of the beam window = 3.5 mm and the factor of safety for the buckling = 9.0, was presented. The buckling pressure was 2.2 times larger than the previous one and more feasible beam window concept was presented through this study.

Compact high current proton cyclotron and associated beam dynamics

A compact proton cyclotron of 1 MeV, 5 mA is being developed at VECC is an R{&}D project to study and settle various problems related with the transport, injection and acceleration of high current beams in a cyclotron. Proton beam from 2.45 GHz microwave ion source (already operating with 8 mA @ 80 keV) will be first bunched using a sinusoidal buncher and then will be injected axially in the central region of the cyclotron where a spiral inflector will place the beam on the proper orbit. In this paper we discuss the design of the magnet of 1 MeV cyclotron, simulation results of beam transmission through the spiral inflector and the results of studies on the behaviour of transverse envelopes of space charge dominated beam along the accelerated orbits. Efforts have been made to obtain the proper matching conditions at the central region by optimizing the input beam parameters of the injected beam. The maximum beam current that can be accelerated through the available aperture of the cyclotron focusing channel has also been estimated.

Reduction of RF accelerating voltage of Pohang Light Source-II superconducting RF cavity for stable top-up mode operation

The Pohang Light Source-II (PLS-II) is currently providing a top-up mode user-service operation with maximum available beam current of 400 mA and a beam emittance of below 10 nm-rad. The dimension of the beam bunch shortened to accomplish a low beam emittance of below 10 nm-rad from a high beam current of 400 mA increases the bunch charge density. As a result, the electron beam lifetime is significantly degraded and a high gradient of power is lost in the vacuum components of the storage ring. A study on how to reduce the bunch charge density without degrading beam emittance found that reducing the RF accelerating voltage (Vacc) can lower the bunch charge density by lengthening the bunch in the longitudinal direction. In addition, the Vacc required for stable operation with beam current of 400 mA can be reduced by lowering the external cavity quality factors (Qext values) of the superconducting cavities (SCs). To control the Qext values of SCs gradually without accessing the accelerator tunnel, a remote control motorized three-probe-tuner was installed in the transmission line of each SC. The optimum installation position of the three-probe-tuner was determined by using a finite-difference time-domain (FDTD) simulation and by experimenting on various installation positions of the three-probe-tuner. The Qext values of all the SCs were lowered to 1.40 × 105, and then, the Vacc required to store the beam current of 400 mA was decreased from 4.8 MV to 4.2 MV, which corresponds to 10% lengthening of the beam bunches. The stable operation with the reduced Vacc was confirmed during a 400 mA ten-day top-up mode user-service. Currently, the RF system of the PLS-II storage ring delivers the user-service operation with lowered Qext values to reduce the power loss at the vacuum components as well as the cryogenic heat load of SCs, and no significant problems have been found. This method of reducing the Vacc may also be applied in other synchrotron facilities.

Development of three-dimensional reactor analysis code system for accelerator-driven system, ADS3D and its application with subcriticality adjustment mechanism

ABSTRACTIn order to perform the parametric survey for an accelerator-driven system (ADS) core with the subcriticality adjustment mechanism, a new calculation code system, ADS3D, was developed on MARBLE which is a comprehensive and versatile framework for reactor analysis. The application of ADS3D was also demonstrated on the neutronics design of ADS operated by control rod (CR) movement. Through the neutronics calculation, it was shown that the maximum proton beam current was decreased from 20.5 to 11.6 mA due to the switch from beam-operated to CR-operated core.

The deuteron accelerator preliminary design for BISOL

BISOL, which was named as Beijing_ISOL before (Cui et al., 2013), is the abbreviation of Beijing Isotope-Separation-On-Line neutron beam facility. It is proposed jointly by Peking University (PKU) and China Institute of Atomic Energy (CIAE) for basic science study and application. It is a double driven facility that can be driven by a reactor or a deuteron accelerator. The deuteron driver accelerator should accelerate the deuteron beam up to 40MeV with maximum beam current of 10mA. Proton beams up to 33MeV and He2+ beams up to 81.2MeV can also be accelerated in this accelerator. The accelerator can be operated on either CW (continuous waveform) or pulsed mode, and the ion energy can be adjusted in a wide range. The accelerator will also allow independent operation of the RIB (Radioactive Ion Beams) system. It will be mainly charged by PKU group. Details of the deuteron accelerator preliminary design for BISOL will be given in this paper.

Monte Carlo simulations for high-rate fast neutron flux measurements made at the RAON neutron science facility by using MICROMEGAS

RAON is a Korean heavy-ion accelerator complex that is planned to be built by 2021. Deuterons (53 MeV) and protons (88 MeV) accelerated by using a low-energy driver linac (SCL1) are delivered to the neutron production target in the Neutron Science Facility (NSF) to produce high-energy neutrons in the interval from 1 to 88 MeV with high fluxes of the order of 1012 n/cm2-sec. The repetition rate of the neutron beam ranges from 1 kHz to 1 MHz, and the maximum beam current is ~12 μA at 1 MHz. The beam width is 1 ~ 2 ns. The high-energy and high-rate fast neutrons are used to estimate accurate neutron-induced cross sections for various nuclides at the NSF. A MICROMEGAS (MICRO Mesh Gaseous Structure), which is a gaseous detector initially developed for tracking in high-rate, high-energy physics experiments, is tentatively being considered as a neutron beam monitor. It can be used to measure both the energy distribution and the flux of the neutron beam. In this study, a MICROMEGAS detector for installation at the NSF was designed and investigated. 6Li, 10B, 235U and 238U targets are being considered as neutron/charged particle converters. For the low-energy region, 6Li(n,α)t and 10B(n,α)7Li are used in the energy range from thermal to 1 MeV. 235U(n,f) and 238U(n,f) reactions are used for high-energy region up to 90 MeV. All calculations are performed by using the GEANT4 toolkit.