High-intensity Beam Research Articles

Halo formation and emittance growth for an intense sheet beam

In this paper, halo formation and emittance growth caused by an initial envelope mismatch on high-intensity sheet beams are investigated. An estimate for the maximum energy that a halo particle can achieve is obtained using a nonlinear Hamiltonian approach. Based on a kinetic description of the beam, a theoretical framework is developed to predict the final stationary state achieved after the envelope oscillations are completely damped. The theory allows for the determination of relevant quantities like the final particle distribution and total emittance growth. The results are compared to self-consistent numerical simulations of the sheet beam.

Photonic jet generated by a silicon nitride spherical particle with shaped beam illumination

Photonic jets (PJs) are generated by the interaction between beams and dielectric particles, resulting in narrow, high-intensity beams produced behind the medium. Silicon nitride exhibits excellent optical properties; we aim to explore the potential of silicon nitride in PJ applications. In this paper, the beam is expanded by spherical vector wave functions with the framework of the generalized Lorenz–Mie theory (GLMT). Numerical simulations are performed to investigate the PJs generated by silicon nitride spherical particles illuminated by the plane wave, Gaussian beam, and zero-order Bessel beam under water; the effects of various parameters on the characteristics of PJs are further examined.

Source of instability in the rapid cycling synchrotron of the China spallation neutron source

The rapid cycling synchrotron (RCS) of the China spallation neutron source accumulates 1.56 ×1013 protons and accelerates them from 80 MeV to 1.6 GeV at a repetition rate of 25 Hz, delivering a 100 kW proton beam to the target. Despite predictions that no instabilities would occur at high beam intensity, an unexpected coherent oscillation of the beam was observed during the beam commissioning. To confirm and address the instability, a series of systematic measurements and studies were conducted, revealing that the issue is a transverse coupled bunch instability and identifying a narrow-band impedance with a low frequency in the RCS. Further bench measurements confirmed that ceramic chambers with RF shields are the source of this impedance, which is consistent with the analysis of the experimental data. Based on these findings, a tune curve during the ramping process and chromaticity optimization have been implemented to completely mitigate the instability in the RCS at 100 kW.

Photopyroelectric tweezers for versatile manipulation.

Optical tweezers and related techniques offer extraordinary opportunities for research and applications in physical, biological, and medical fields. However, certain critical requirements, such as high-intensity laser beams, sophisticated electrode designs, additional electric sources, or low-conductive media, significantly impede their flexibility and adaptability, thus hindering their practical applications. Here, we report innovative photopyroelectric tweezers (PPT) that combine the advantages of light and electric field by utilizing a rationally designed photopyroelectric substrate with efficient and durable photo-induced surface charge-generation capability, enabling diverse manipulation in various working scenarios. These PPTs allow for remote and programmable manipulation of objects with diverse materials (polymer, inorganic, and metal), different phases (bubble, liquid, and solid), and various geometries (sphere, cuboid, and wire). Furthermore, the PPT is not only adaptable to high-conductivity media but also applicable to both portable macroscopic manipulation platforms and microscopic manipulation systems, enabling cross-scale manipulations for solid objects, liquid droplets, and biological samples. The high-level flexibility and adaptability of the PPT extend to broad applications in manipulating hydrogel robots, sorting particles, assembling cells, and stimulating cells. By surpassing the limitations of conventional tweezers, the PPT bridges the gap between macroscopic and microscopic manipulations, offering a revolutionary tool in robotics, colloidal science, biomedical fields, and beyond.

Dosimetric study of synchrotron rapid beam off control and skip spot function for high beam intensity proton therapy.

All Hitachi proton pencil beam scanning facilities currently use discrete spot scanning (DSS). Mayo Clinic Florida (MCF) is installing a Hitachi particle therapy system with advanced technologies, including fast scan speeds, high beam intensity, rapid beam off control (RBOC), a skip spot function, and proton pencil beam scanning using dose driven continuous scanning (DDCS). A potential concern of RBOC is the generation of a shoulder at the end of the normal spot delivery due to a flap spot (FS) with a flap dose (FD), which has been investigated for carbon synchrotron but not for proton delivery. While investigated, for instance, for Hitachi's installation at MCF, this methodology could be applicable for all future high intensity proton deliveries. No Hitachi proton facility currently uses the proposed RBOC. This study aimed to understand the dosimetric impact of proton FD at MCF by simulating the FS with a Hitachi proton machine in research mode, reflecting the higher proton intensities expected with RBOC at MCF. Experiments were conducted to simulate MCF RBOC at Kyoto Prefecture University of Medicine (KPUM) in research mode, reducing delay time (Td) from 1.5ms to 0.1ms. 5,000 contiguous spots were delivered on the central axis for proton energies of 70.2, 142.5, and 220.0MeV; at normal, high dose rate (HDR), and ultra-high dose rate (uHDR) intensities; and at vertical and horizontal gantry angles for different Td. Measurements were taken using a fast oscilloscope and the nozzle's spot position monitor (SPM) and dose monitor (DM). A model was developed to predict FD dependence on beam intensity and assess the dosimetric impact for prostate and brain treatment plans. Two simulation types were planned: a flap DSS plan with FS at every spot and a flap DDCS plan with FS only at the end of each layer. FD was observed for RBOC with Td=0.1ms, showing no gantry angle dependence. FD increased with higher delayed dose rate (DDR), that is, beam intensity. The planning study showed dose volume histogram deterioration with increased FD compared to the clinical plan, but it was only significant for uHDR intensities. Deterioration was marginal in flap DSS plans for the HDR intensities planned at MCF, and flap DDCS plans were even less sensitive than flap DSS plans. MCF is installing proton DDCS with higher beam intensities, a skip spot function, and fast beam-off control. The resulting FD had an insignificant impact on dose distribution for two patient plans with both DSS and DDCS at the anticipated MCF intensities. However, significant dependence was observed in the case of uHDR. A method to measure the position and dose of the FS during commissioning is described in addition to recommendations for regular QA and log-based proton patient-specific quality assurance.

Simulation of dark scalar particle sensitivity in $\eta$ rare decay channels at HIAF

Abstract Searching dark portal particle is a hot topic in particle physics frontier. We present a simulation study of an experiment targeted for searching the scalar portal particle at Huizhou $\eta$ factory. The HIAF high-intensity proton beam and a high event-rate spectrometer are suggested for the experiment aimed for the discovery of new physics. Under the conservative estimation, $5.9\times 10^{11}$ $\eta$ events could be produced in one month running of the experiment. The hadronic production of $\eta$ meson ($p + ^7\text{Li} \rightarrow \eta X$) is simulated at beam energy of 1.8 GeV using GiBUU event generator. We tend to search for the light dark scalar particle in the rare decay channels $\eta \rightarrow S \pi^0 \rightarrow \pi^+ \pi^- \pi^0$ and $\eta \rightarrow S \pi^0 \rightarrow e^+ e^- \pi^0$. The detection efficiencies of the channels and the spectrometer resolutions are studied in the simulation. We also present the projected upper limits of the decay branching ratios of the dark scalar particle and the projected sensitivities to the model parameters.

Half-Integer Random Resonance Compensation for Further Beam Power Ramp-up in the 3-GeV Rapid Cycling Synchrotron of the Japan Proton Accelerator Research Complex

Abstract A comprehensive study on random resonances was conducted to mitigate beam losses and ensure sufficient tunability of the operating point for further beam power ramp-up in the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex. Low-intensity beam studies revealed considerable excitation of the half-integer random resonance. This half-integer random resonance was successfully compensated for using trim quadrupole magnets without exciting other higher-order resonances. By implementing a conventional theoretical procedure based on resonance driving terms, we identified the leakage field from extraction magnets as the primary source of the error field driving the random resonance. High-intensity beam studies confirmed that our resonance compensation approach substantially mitigated beam loss in higher-tune regions, making it highly effective in improving operating point tunability.

Inorganic Nanorods Enable the Memorization of Photoinduced Microlens Arrays in Dye-Doped Liquid Crystals.

The photoinduced molecular reorientation of liquid crystals (LCs) caused by their nonlinear optical responses has attracted much attention due to their large refractive index change, leading to promising applications in optical devices. This reorientation is typically induced by light irradiation above a threshold intensity and is temporary, with the initial orientation recovering unless the LCs are polymerized and cross-linked. Our report highlights the memory effect of molecular reorientation in LCs. The high-intensity laser beam irradiation of dye-doped LCs containing polymer-grafted ZnO nanorods resulted in the molecular reorientation of the LCs. The effect was maintained even after the light was turned off. This memorized molecular orientation functioned as a polarization-dependent microlens due to the self-phase modulation and self-focusing effect of the propagating light. The polarization selectivity of the microlens allows for innovative optical applications, including security printing and anticounterfeiting.

Utilization strategies of beam dumps for High energy FRagment Separator (HFRS) at HIAF

The construction of the High Intensity heavy-ion Accelerator Facility (HIAF) is currently underway, with the High Energy FRagment Separator (HFRS) serving as a critical component. The HFRS, a next-generation in-flight radioactive separator, is designed to produce, separate, and purify rare isotopes with a maximum magnetic rigidity of 25 Tm, facilitating experimental studies on very short-lived and neutron-rich isotopes. To protect the environment and equipment, beam dumps are essential for intercepting high-intensity primary beams with different charge states post-target. Utilizing the beam optics of the HFRS and beam parameters after the target, Geant4 ion tracking simulations were employed to determine the ion trajectories of both primary beam and secondary beam. The interception efficiency for the primary beam and the transmission efficiency for the secondary beam were calculated, providing strategies and movement range for beam dump utilization. These findings are expected to contribute to the future operation of the HFRS.

A versatile setup for hydrogen isotope permeation studies.

The Testbed for Analysis of Permeation of Atoms in Samples (TAPAS) is an experimental setup for ion-driven permeation studies with a focus on investigating wall materials for nuclear fusion devices. A monoenergetic, mass-filtered high-intensity keV ion beam is focused and directed onto the permeation sample by electrostatic ion optics and decelerated to the desired ion energy by a dedicated set of apertures close to the sample. We were able to obtain ion energies as low as 170 eV/D with a D3+ ion beam with an ion flux density of the order of 1020 D/m2s on a beam-wetted area of ∼33mm2. These conditions avoid sputtering of W targets by the ion beam and are representative of the particle flux and energy spectrum impinging on the first wall of a prospective nuclear fusion power reactor. Permeation samples can be heated up to 1000K in an ultra-high vacuum. The design of the deceleration system, together with a high pumping speed in the loading chamber, ensures a low pressure of recycling hydrogen isotope molecules in front of the sample. In addition to ion-driven permeation, TAPAS provides a limited capability for gas-driven permeation at low pressures up to nearly 1mbar. Permeating hydrogen isotopes are detected with a quadrupole mass spectrometer in the downstream ultra-high vacuum chamber. After a detailed description of the setup and calibration procedures for implanted particle flux, mass spectrometer, and neutral gas pressure, benchmark experiments on recrystallized, 50μm thick tungsten foils are shown, demonstrating that diffusion-limited boundary conditions for permeation were reached.

Response function measurement for a non-destructive gas-sheet beam profile monitor.

A gas-sheet beam profile monitor enabling non-destructive two-dimensional profile measurements of a high-intensity beam by capturing an image of a beam-induced fluorescence was developed. For quantitative profile measurements, the monitor's response function comprising, e.g., the gas sheet density distribution and the detector's sensitivity distributions must be experimentally clarified because the monitor output is a converted profile with the response function. A response function measurement method was devised based on the beam-profile-measurement method formula of the monitor. The response function was obtained by injecting a thin electron beam into the developed monitor and scanning its center position in transverse. The measured response function was evaluated by the J-PARC 3MeV, 60 mA H- beam profile measurement. The 2-D beam profile was successfully reconstructed with the measured response function within the 2.74% residual of the least-squares method and 6.01% experimental statistic deviation. The projected 1-D profiles agreed well with those measured using a wire-scanning-type profile monitor.

Rate-induced aging effects on Parallel-Plate Avalanche Counter (PPAC) caused by heavy ion beams

The Facility for Rare Isotope Beams (FRIB) is one of the premier scientific user facilities for nuclear science with radioactive beams, capable of producing most (approximately 80%) of the isotopes expected to exist, from oxygen to uranium, at energies up to 200 MeV/u. With the increase in beam power from the present 10 kW to the planned 400 kW, FRIB experiments are about to enter a new era. An unprecedented rate capability as well as stable performance of all the planned instrumentation intended for beam diagnostics and beam tuning is required at the expected high beam intensities (>1 MHz). A summary of aging phenomena at high heavy-ion beam rates observed in the Advanced Rare Isotope Separator (ARIS) detectors for beam diagnostics, including Parallel Plate Avalanche Counters (PPAC) and plastic scintillation for time-of-flight measurements, is discussed. Current research and development project to mitigate rate-induced aging are presented.

Performance Evaluation of Electron Multiplier Tubes as a High-Intensity Muon Beam Monitor of Accelerator Neutrino Experiments

Abstract Upgrade work towards increasing the beam intensity of the neutrino beamline at the Japan Proton Accelerator Research Complex (J-PARC) is underway. Monitoring tertiary muon beams is essential for stable operation of the beamline. Accordingly, we plan to replace the present muon monitor sensors with electron multiplier tubes (EMTs). We investigated the radiation tolerance and linearity response of EMTs using a 90 MeV electron beam. EMTs were irradiated with electrons up to 470 nC. EMTs show higher radiation tolerance than the Si sensors which are presently used as one of the muon monitor detectors for the Tokai-to-Kamioka (T2K) long-baseline neutrino experiment at J-PARC. The integrated charge yield decrease is found to be less than 8% after a beam irradiation equivalent to 132 days of operation at the future J-PARC beam power of 1.3 MW. The EMTs show linearity better than $\pm$5% up to the future beam intensity. The observed yield decrease is likely due to dynode deterioration, based on detailed investigation. The studies described here confirm that EMTs can be used as a high-intensity muon beam monitor. Owing to the reported results, we are proceeding with the installation in the J-PARC neutrino beamline.

Measurement of the 116Sn(18O, 18Ne)116Cd double charge exchange reaction at 276 MeV

The measurement of the 116Sn(18O, 18Ne)116Cd double charge exchange reaction cross section at very forward angles was performed for the first time at INFN-LNS using the MAGNEX magnetic spectrometer. This study, carried out at 276 MeV beam energy, provides a cross section of 34 nb ([9, 44] nb at 95% confidence level), confirming the tiny values recently obtained for the same reaction in other nuclides. This result has a major impact on the forthcoming systematic investigation of 0νββ decay candidates carried out by the NUMEN project, since it allows to properly tailor future experiments with high-intensity beams. The ultimate goal of this exploration is to experimentally access information about nuclear matrix elements relevant to the 0νββ decay rate.

New operation analysis method for vacuum tube driving a tuned cavity

The rf system of China Spallation Neutron Source (CSNS) Rapid Cycling Synchrotron (RCS) utilizes vacuum tubes to drive the ferrite-loaded cavities. Ensuring stable tube operation in the rf system is crucial for the acceleration of high-intensity beams, as any instability may impede further increases in beam power. Therefore, the operation of the vacuum tube under heavy beam loading has attracted significant attention, particularly in the case of CSNS-II RCS, where the circulating beam current is expected to reach up to 15.25 A, imposing a substantial burden on the vacuum tube for beam loading compensation. Thus, a comprehensive analysis of tube operation is imperative. However, current methods for the tube operation analysis are developed based on wideband rf cavities, which are inadequate when the load of the tube is a narrowband ferrite-loaded cavity equipped with a tuning system. The presence of a tuning system renders the modeling method for wideband rf cavities inapplicable for ferrite-loaded cavities. Therefore, the development of a new method is necessary. This paper introduces a novel method for analyzing operation of vacuum tube driving a tuned cavity. The effectiveness of the method is validated by comparing the analysis results with measurements under beam loading conditions. Furthermore, an estimation of tube operation under 500 kW beam loading for CSNS-II is provided. Published by the American Physical Society 2024

The thermal dynamic simulation and microstructure characterization of micro-arc oxidation (MAO) films on magnesium AZ31 irradiated by high-intensity pulsed ion beam

The micro-arc oxidation (MAO) film on AZ31 magnesium alloy was irradiated by high-intensity pulsed ion beam (HIPIB) at the energy density of 1–5 J/cm2 to enhance its corrosion resistance. The temperature and stress field was simulated by numerical model established by Marc.Mentat software to explore the surface modification mechanism of the irradiated MAO films. The experimental results show that the pores on the MAO film surface decreased, and obvious remelting phenomenon was observed on the irradiated film surface at 4 and 5 J/cm2. X-ray diffraction (XRD) detection indicated that HIPIB irradiation had little effect on the phase structure of the MAO films, except for grain refinement on MgO and Mg3(PO4)2. The wettability of the MAO films changed from hydrophilicity to hydrophobicity by irradiation characterized by contact angle results. From the potentiodynamic analysis, the corrosion potential of irradiated MAO films was significantly higher than that of the original ones, the maximal value of the corrosion potential was obtained at 4 J/cm2, which is increased by 57 mV compared with that of the original ones. The simulated results show that the surface temperature of MAO film increases rapidly during the irradiation process, and the maximum surface temperature reaches the boiling point of MgO 3873 K up to 4 J/cm2. At 4 J/cm2, the MAO film exhibited melting and ablation, with depths of 1.8 μm and 0.6 μm, respectively. The high temperature field and thermal stress by irradiation lead to surface melting of MAO film, which promotes the decrease of the number and dimension of the pores on the MAO film surface. The densification and less porosity of MAO film by HIPIB irradiation inhibited the infiltration of the corrosive liquid to the substrate, which is mainly responsible for the modification of MAO film corrosive performance.

Wideband High-Intensity Self-Bending Bessel-Like Beam Metasurface-Based Launcher for Wireless Applications

Wideband High-Intensity Self-Bending Bessel-Like Beam Metasurface-Based Launcher for Wireless Applications

Harnessing quantum light for microscopic biomechanical imaging of cells and tissues

The biomechanical properties of cells and tissues play an important role in our fundamental understanding of the structures and functions of biological systems at both the cellular and subcellular levels. Recently, Brillouin microscopy, which offers a label-free spectroscopic means of assessing viscoelastic properties in vivo, has emerged as a powerful way to interrogate those properties on a microscopic level in living tissues. However, susceptibility to photodamage and photobleaching, particularly when high-intensity laser beams are used to induce Brillouin scattering, poses a significant challenge. This article introduces a transformative approach designed to mitigate photodamage in biological and biomedical studies, enabling nondestructive, label-free assessments of mechanical properties in live biological samples. By leveraging quantum-light-enhanced stimulated Brillouin scattering (SBS) imaging contrast, the signal-to-noise ratio is significantly elevated, thereby increasing sample viability and extending interrogation times without compromising the integrity of living samples. The tangible impact of this methodology is evidenced by a notable three-fold increase in sample viability observed after subjecting the samples to three hours of continuous squeezed-light illumination, surpassing the traditional coherent light-based approaches. The quantum-enhanced SBS imaging holds promise across diverse fields, such as cancer biology and neuroscience where preserving sample vitality is of paramount significance. By mitigating concerns regarding photodamage and photobleaching associated with high-intensity lasers, this technological breakthrough expands our horizons for exploring the mechanical properties of live biological systems, paving the way for an era of research and clinical applications.

Proposal for a Ramsey Neutron-Beam Experiment to Search for Ultralight Axion Dark Matter at the European Spallation Source.

High-intensity neutron beams, such as those available at the European Spallation Source (ESS), provide new opportunities for fundamental discoveries. Here, we discuss a novel Ramsey neutron-beam experiment to search for ultralight axion dark matter through its coupling to neutron spins, which would cause the neutron spins to rotate about the velocity of the neutrons relative to the dark matter halo. We estimate that experiments at the HIBEAM beamline with a 50m free flight path at the ESS can improve the sensitivity to the axion-neutron coupling compared to the current best laboratory limits by up to 2-3 orders of magnitude over the axion mass range 10^{-22} eV-10^{-16} eV.

Design and development of vacuum system for electron beam powder bed fusion process

A vacuum system is one of the crucial components of the Electron Beam-Powder Bed Fusion Process (EB-PBF). It ensures the generation of a high-intensity electron beam. This paper presents a vacuum system design for the EB-PBF process. The work chamber and EB gun chamber have been designed and verified using ANSYS workbench for stress, strain, and deformation limits and found satisfactory. The analytical calculations have been performed for all the pumps, considering the various gas loads during the process. After the design, the vacuum system has been fabricated and tested for its stability, ultimate vacuum, and leak rate. The helium leak test results show that all the joints have a leak rate better than 1 × 10−8 mbar l/s. Further, the analytical results of each pump have been compared with experimental results and found almost in line with the theoretical results. The results show that a pressure lower than 1 × 10−5 mbar and 5 × 10−6 mbar can be achieved in the work chamber and EB gun chamber in less than 23 min and 10 min respectively. The chamber was evacuated multiple times and found that the chamber could still hold pressure better than 1 × 10−2 mbar after 48 h.