Beam Intensity Research Articles

New online beam intensity synchronous monitoring system in scanning transmission X-ray microscopy.

The scanning transmission X-ray microscopy (STXM) platform based on synchrotron radiation has achieved nanoscale imaging with chemical sensitivity using spectro-microscopy techniques. However, the quality of STXM imaging is affected by the stability of the beam intensity. The top-up operation mode of synchrotrons to maintain a constant electron beam intensity introduces periodic fluctuations in the X-ray beam intensity, leading to notable imaging noise that decreases both contrast and precision. To address this issue, a high-speed real-time beam intensity monitoring system was designed and implemented at the BL08U1A beamline of the Shanghai Synchrotron Radiation Facility. This system utilizes an yttrium-aluminium-garnet crystal along with dual detectors having an acquisition frequency of up to 1 MHz and a synchronization error of less than 20 ns between them. This system can precisely and synchronously monitor the X-ray beam intensity variations which are used to remove noise due to electron injection from STXM images, thereby markedly improving the quality of STXM imaging.

Influence of microwave parameters on the xenon afterglow beam currents of a superconducting electron cyclotron resonance ion source.

Heavy ion synchrotron accelerators rely on intense pulsed beams of highly charged ions. The production of these pulsed beams from an electron cyclotron resonance (ECR) ion source is predominantly achieved through the afterglow mode. However, the influence of microwave parameters on the characteristics of afterglow beams in high-frequency, high-power, and large plasma-volume ion sources remains unexplored. Recently, a series of experiments have been conducted with a third-generation superconducting ECR ion source. The effects of key microwave parameters, including the power level and pulse length of the secondary microwave source, as well as the RF-off time of the primary microwave radiation, on xenon afterglow beam currents are systematically examined. The experimental results and conclusions derived from the data are presented in this article.

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.

Optical emission spectroscopy and imaging of low-pressure N2 plasmas generated by intense fast-pulsed electron beams

An optical emission spectroscopic (OES) and imaging characterization is conducted on N2 plasmas generated by a 100 keV fast-pulsed electron beam. The electron beams are injected into an N2 gas filled volume with a current of 4.5 kA (300 A/cm2) and a 100 ns pulse width. The characterization is conducted at the pressures, 1 Torr and 0.1 Torr, corresponding to two distinct regimes that exhibit significantly different plasma dynamics. Beam impact ionization is shown to be a primary mechanism for producing low temperature plasmas at 1 Torr during beam output. After beam termination, ionization by an inductive electric field becomes the primary mechanism for plasma formation later in time for both pressures. OES and plasma imaging are used in this work as a diagnostic tool to track the distribution of electronic, vibrational, and rotational state transitions and ionized species. This is achieved with the use of a multi-resolution suite of spectrometers capable of acquiring time-resolved spectra. Vibrational and rotational bands of the N2 second positive system (C3Πu→B3Πg) and the N2+ first negative system (B2Σu+→X2Σg+) are identified in both regimes as well as N+ states exclusively in the lower pressure regime. Vibrational and rotational spectra are shown to track the evolution of the time-varying plasma current. Plasma imaging also reveals spatially nonuniform plasma emission at 0.1 Torr. A few hundred shots are recorded to fully characterize the emissions, and results are shown to be highly reproducible (≤±1% with 2σ confidence).

Transient temperature measurement of electron beam bombarded stainless steel via nanosecond two-color pyrometry.

A two-color pyrometer is presented that enables detection of a temperature rise with temporal resolution of 17.5ns. It is geared toward extreme environments where fast electrical electron pulses or currents may push the temperature of a metal surface to melt on a 100ns time scale. The developed pyrometer, which utilizes an internal gain of 100x, has been tested for SS304 surfaces subjected to an intense electron beam in vacuum. The two-color pyrometer is calibrated using a quasi-calibration method by heating a graphite disk and measuring this temperature with a FLIR TG297 thermal camera. The quasi-calibration method supports the pyrometer to be within 3% accuracy of absolute temperature. The measured temporal temperature profile of the SS304 surface was derived from the pyrometer output data through a detailed gray-body analysis utilizing empirical emissivity data from publicly available literature.

Novel design of a high-frequency radio frequency quadrupole accelerator for medical application

Proton therapy is an advanced particle radiotherapy technology. Lanzhou University recently designed a new linear accelerator system for proton therapy. In the system, a 750[Formula: see text]MHz radio frequency quadrupole (RFQ) accelerator was used to complete the initial acceleration of particles. The RFQ can accelerate a proton beam intensity of 1[Formula: see text]mA from 30[Formula: see text]keV to 3[Formula: see text]MeV kinetic energy within a length of 2[Formula: see text]m. This paper aims to complete the physical design of this high-frequency RFQ, including beam dynamics design, radio frequency (RF) design, and multiphysics analysis. In the dynamics design, a novel design strategy for controlling the longitudinal emittance was adopted to improve the output beam quality of the RFQ. The simulation results showed that the RFQ outlet longitudinal emittance was controlled below 0.1 [Formula: see text] mm mrad. In the RF design, the pi-mold rod structure was applied to RFQ at such high frequencies for the first time. After the whole cavity simulation, it was found that the separation between the operating frequency of the RFQ cavity and its closest dipole mode reached 58.3[Formula: see text]MHz, and its quality factor reached 6352. Finally, a multiphysics analysis was performed. The analysis showed that the maximum temperature rise of the RFQ cavity was less than [Formula: see text]C and the frequency drift due to heating was 18[Formula: see text]kHz. This paper presents the current status of the design of this new linear accelerator. Compared with previous RFQs, the new RFQ has a very high transmission efficiency and higher RF stability.

Sub-micrometer scale synchrotron x-ray fluorescence measurements of trace elements in teeth compared with laser ablation inductively coupled plasma mass spectrometry.

Elemental analysis of teeth allows for exposure assessment during critical windows of development and is increasingly used to link early life exposures and health. The measurement of inorganic elements in teeth is challenging; laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is the most widely used technique. Both synchrotron x-ray fluorescence (SXRF) and LA-ICP-MS have the capability to measure elemental distributions in teeth with each having distinct advantages and disadvantages. In our study, we compared these two methods for teeth elemental quantification. SXRF was able to achieve spatial resolutions of 0.3 µm and is non-destructive while giving similar elemental quantification results to LA-ICP-MS. For particular elements, SXRF can offer lower detection limits but depends on the specific beam intensity. The comparison between methods revealed less than 10% disagreement between quantification results from LA-ICP-MS and SXRF. Synchrotron x-ray fluorescence can be used to effectively quantify elemental distributions in teeth at a nanoscale resolution and is comparable to current laser ablation inductively coupled plasma mass spectrometry. Both methods offer advantages and disadvantages with LA-ICP-MS offering in-lab analyses, whereas SXRF offers much finer spatial and temporal scales and better detection capabilities. For studies focused on fine scale changes in structure, SXRF is more appropriate than LA-ICP-MS.

Neutrino electromagnetic properties and the weak mixing angle at the LHC Forward Physics Facility

The LHC produces an intense beam of highly energetic neutrinos of all three flavors in the forward direction, and the Forward Physics Facility (FPF) has been proposed to house a suite of experiments taking advantage of this opportunity. In this study, we investigate the FPF’s potential to probe the neutrino electromagnetic properties, including neutrino millicharge, magnetic moment, and charge radius. We find that, due to the large flux of tau neutrinos at the LHC, the FPF detectors will be able to provide more sensitive constraints on the tau neutrino magnetic moment and millicharge than previous measurements at DONUT, by searching for excess in low recoil energy electron scattering events. We also find that, by precisely measuring the rate of neutral current deep inelastic scattering events, the FPF detectors have the potential to obtain the strongest experimental bounds on the neutrino charge radius for the electron neutrino, and one of the leading bounds for the muon neutrino flavor. The same signature could also be used to measure the weak mixing angle, and we estimate that sin2θW could be measured to about 3% precision at a scale Q∼10 GeV, shedding new light on the longstanding NuTeV anomaly. Published by the American Physical Society 2025

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.

Establishing and Investigating an Effective Atmosphere‐Ocean Cross‐Medium Propagation Model Based on GSM Beams

AbstractUsing the Gaussian‐Schell model (GSM) beam as the light source, this study creates a blue‐green beam atmosphere‐ocean cross‐medium propagation model (AOCPM) based on the extended Huygens‐Fresnel principle and the linear filtering method. The closed expression of the Cross Spectral Density Function (CSDF) of the GSM beam after propagation through atmospheric turbulence, atmosphere‐ocean interface, and ocean turbulence are derived. And the correctness of the model is verified by simulating the changes in intensity, relative beam width, and speckle normalized intensity autocorrelation function during the propagation of the GSM beam through the atmosphere‐ocean cross‐medium under different parameters. The findings demonstrate that the intensity of the GSM beam after being propagated through the atmosphere‐ocean medium presents a speckle‐like Gaussian distribution, the intensity of the GSM beam gradually attenuates, the relative beam width gradually grows, and the speckle normalized intensity autocorrelation function gradually decreases as the turbulence intensity and propagation distance increase. In addition, the increase in wind speed at rough sea surface mainly leads to the attenuation of intensity. The work of this paper provides a new idea for the study of atmosphere‐ocean cross‐medium propagation of blue‐green beams.

Cumulant method for identifying spatial distributions of laser beam intensity

Cumulant method for identifying spatial distributions of laser beam intensity

Development and evaluation of an in-beam PET system for proton therapy monitoring

Objective. In-beam positron emission tomography (PET) has important development prospects in real-time monitoring of proton therapy. However, in the beam-on operation, the high bursts of radiation events pose challenges to the performance of the PET system.Approach. In this study, we developed a dual-head in-beam PET system for proton therapy monitoring and evaluated its performance. The system has two PET detection heads, each with6×3Plug&Imaging (PnI) detection units. Each PnI unit consists of6×6lutetium-yttrium oxyorthosilicate crystal arrays. The size of each crystal strip is3.95×3.95×20 mm3, which is one-to-one coupled with a silicon photomultiplier. The overall size of the head is15.3×7.65 cm2.Main results. The in-beam PET system achieved a single count rate of 48 Mcps at the activity of 144.9 MBq, an absolute sensitivity of 2.717%, and a spatial resolution of approximately 2.6 mm (full width at half maximum) at the center of the field-of-view. When imaging a Derenzo phantom, the system could resolve rods with a diameter of 2.0 mm. Time-dynamic [18F]-Fluorodeoxyglucose mouse imaging was performed, demonstrating the metabolic processes in the mouse. This shows that the in-beam PET system has the potential for biology-guided proton therapy. The in-beam PET system was used to monitor the range of a 130 MeV proton beam irradiating a polymethyl methacrylate (PMMA) phantom, with a beam intensity of6.0×109p s-1and an irradiation duration of one minute. PET data were acquired only during the one-minute irradiation. We simulated the range shift by moving the PMMA and adding an air gap, showing that the error between the actual and the measured range is less than 1 mm.Significance. The results demonstrate that the system has a high count rate and the capability of range monitoring in beam-on operation, which is beneficial for achieving real-time range verification of proton beams in the future.

Calibration of optical particle spectrometers using mounted fibres

Abstract. Calibrations of optical particle spectrometers (OPSs) are non-trivial and conventionally involve aerosolisation techniques, which are challenging for larger particles. In this paper, we present a new technique for OPS calibration that involves mounting a static fibre within the instrument sample area, measuring the scattering cross section (SCS), and then comparing the SCS with a calculated value. In addition, we present a case for the use of generalised Lorenz–Mie theory (GLMT) simulations to account for deviations in both minor- and major-axis beam intensity, which has a significant effect on particles that are large compared with the beam waist, in addition to reducing the need for a “top-hat” spatial intensity profile. The described technique is OPS independent and could be applied to a field calibration tool that could be used to verify the calibration of instruments before they are deployed. In addition to this, the proposed calibration technique would be suited for applications involving the mass production of low-cost OPSs.

Long-term Outcomes of Definitive Chemoradiation With Proton Therapy for Treatment of Carcinoma of the Anal Canal: Combined Analysis of 2 Prospective Trials.

Although definitive chemoradiation therapy (CRT) with 5-fluorouracil (5-FU) and mitomycin-C (MMC) (5-FU/MMC) remains the standard of care for localized anal cancer, treatment is associated with significant acute and late toxicity. Proton radiation therapy (RT) may potentially reduce such toxicity. Here, we assess the long-term outcomes of patients with anal cancer treated with CRT using proton RT in 2 prospective pilot studies. Patients with stage I to III anal cancer treated with proton RT (pencil beam scanning or intensity modulated proton therapy) per Radiation Therapy Oncology Group (RTOG) 0529 dose schema with concurrent 5-FU/MMC (2 cycles) in 2 prospective, single-arm trials were followed. Locoregional failure, distant metastases, colostomy-free survival, disease-free survival, and overall survival were assessed. Physician-graded late toxicity (>90 days from CRT) was assessed per National Cancer Institute Common Terminology Criteria for Adverse Events version 4. Late toxicities were compared with RTOG 0529 via Fisher exact test. Patient-reported outcomes were analyzed. Between 2013 and 2020, 39 patients were treated; 37 (95%) patients completed treatment per protocol. The median follow-up was 63 months. The 5-year locoregional failure, distant metastases, colostomy-free survival, disease-free survival, and overall survival were 21%, 19%, 72%, 69%, and 75%, respectively. The worst late treatment toxicities were grade 1 in 38%, grade 2 in 24%, grade 3 in 19%, grade 4 in 3%, and no grade 5. Compared to RTOG 0529, rates of overall grade 2+ late toxicities were significantly lower (46% vs 75%, P = .01), attributed to lower dermatologic toxicities (0% vs 25%, P < .01), but there was no significant difference in overall grade 3+ toxicities (22% vs 20%, P = 1.00). No statistically significant correlations between organ-at-risk dosimetry and late toxicities were noted. Available patient-reported outcomes demonstrated that significant proportion of patients had persistent gastrointestinal symptoms at long term. Definitive CRT with proton RT with concurrent 5-FU/MMC for the treatment of anal cancer resulted in comparable long-term disease control and grade 3+ late toxicities compared to RTOG 0529. Future studies should evaluate additional measures to minimize treatment toxicity and subsets of patients who are most likely to benefit from proton RT.

The MeerKAT Fornax Survey. IV. A close look at the cluster physics through the densest rotation measure grid

Using the Square Kilometre Array (SKA) mid precursor MeerKAT, we acquired broadband spectro-polarimetric data in the context of the MeerKAT Fornax Survey to study the Fornax cluster's magnetic fields in detail by building the densest rotation measure (RM) grid to date. Here, we present the survey, the analysis, and a discussion of the RM grid properties. We analyzed a circular region centered on the Fornax cluster center with a radius of ∼1.4^∘; that is, rm∼ 0.73 R_ vir . The mosaics have a resolution of 13arcsec and cover the frequencies between 900,MHz and 1.4,GHz, reaching an average noise of 16muupJy beam^-1 in total intensity and 3muupJy beam^-1 in the Q and U Stokes images. With these data, we detected 508 polarized sources over an area of ∼6.35 deg^2 corresponding to a density of ∼80 polarized sources/deg^2. This is the densest RM grid ever built. Of the polarized sources, five are cluster sources. Excluding the cluster sources, we built the Euclidean-normalized differential source counts in polarization and we went a factor of ten deeper than previous surveys. We tentatively detect for the first time an increment in the differential source counts at low polarized flux densities; that is, ∼9,muupJy at 1.4,GHz. The average degree of polarization of about 3--4% suggests that the sub- population is not dominated by star-forming galaxies, typically showing a degree of polarization lower than 1%. The majority of the polarized sources are Faraday simple; in other words, their polarization plane rotates linearly with the wavelength squared. The RM shows the typical decrement going from the center to the outskirts of the Fornax cluster. However, interesting features are observed both in the RM grid and in the RM radial profiles across different directions. A combination of the cluster physics and large-scale structure filaments surrounding the Fornax cluster could explain the RM characteristics.

ViPErLEED package I: Calculation of I(V) curves and structural optimization

Low-energy electron diffraction (LEED) is a widely used technique in surface-science laboratories. Yet, it is rarely used to its full potential. The quantitative information about the surface structure, contained in the modulation of the intensities of the diffracted beams as a function of incident electron energy, LEED I(V), is underutilized. To acquire these data, only minor adjustments would be required in most experimental setups, but existing analysis software is cumbersome to use and often computationally inefficient. The ViPErLEED (Vienna package for Erlangen LEED) project lowers these barriers, introducing a combined solution for user-friendly data acquisition, extraction, and computational analysis. These parts are discussed in three separate publications. Here, the focus is on the computational part of ViPErLEED, which performs highly automated LEED-I(V) calculations and structural optimizations. Minimal user input is required, and the functionality is significantly enhanced compared to existing solutions. Computation is performed by embedding the existing Erlangen tensor-LEED package (). ViPErLEED manages additional parallelization, monitors convergence, and processes all input and output. This makes LEED I(V) more accessible to new users while minimizing the potential for errors and the manual labor. Added functionalities include intelligent structure-dependent defaults for most calculation parameters, automatic detection of bulk and surface symmetries and their relationship, automated search procedures that preserve the symmetry and speed up convergence, adjustments to the code to handle larger systems than before, as well as parallelization and optimization. Modern file formats are used as input and output, and there is a direct interface to the atomic simulation environment (ASE) package. The software is implemented primarily in (version ≥3.7) and provided as an open-source package (GNU GPLv3 or any later version). A structure determination of the α-Fe2O3(11¯02)−(1×1) surface is presented as an example for the application of the software. Published by the American Physical Society 2025

How simply one can considerably improve performance of the Gas Stripper at the GSI UNILAC

In this report, we propose a simple way how considerably improve the performance of the gas stripper setup at the GSI Universal Linear Accelerator (UNILAC) in Germany. In our proposed approach, we replace inside the main GSI stripper chamber the current nozzle and the short windowless storage gas cell (for the pulsed gas jet operation mode) with a simple conical diverging nozzle combined with a gas catcher tube placed on the gas jet axis at some distance downstream from the nozzle exit. As a result, the background pressure in the main and differentially pumped adjacent vacuum chambers of the gas stripper at the GSI UNILAC dramatically reduces, making it possible to achieve the required optimal thickness of the gas targets. The pulsed gas stripper operation is realized by implementing a commercially available fast gas valve connected to the nozzle entrance. Moreover, the ion beam pulse repetition rate can be increased, allowing for a considerably higher average intensity of the ion beams extracted from the GSI UNILAC. We explored the performance of the proposed GSI UNILAC gas stripper modification by means of detailed computer experiments, which provide a realistic description of supersonic gas jets flowing out of the nozzle into the vacuum. The results of these computer experiments have presented and discussed.

Isotopologue-selective laser cooling of molecules

Abstract Direct laser cooling of molecules has made significant progress in recent years. However, the selective cooling and manipulation of generic molecular samples based on their isotopic composition, which is ubiquitous in atomic laser cooling, has not yet been achieved. Here, we demonstrate such isotopologue-selective laser cooling and near-arbitrary control over the isotopic composition of a molecular beam, using barium monofluoride (BaF) as an example. The manipulation of the rare and previously uncooled 136 BaF is achieved in the presence of several isotopologues of significantly higher natural abundance. Our results enable intense molecular beams, high fidelity detection and manipulation of select low-abundance isotopologues or isotopic mixtures. Such beams are a first step towards isotopologue-selective molecular trapping and will be useful for applications in trace gas analysis, cold collisions and precision tests of fundamental symmetries.

Simulation investigation of a Ka-band phase-locked klystron-type coaxial relativistic Cherenkov generator

To achieve coherent power combination of Ka-band high-power microwave (HPM), a phase-locked klystron-type coaxial relativistic Cherenkov generator (PKC-RCG), which combines the advantageous characteristics of weak dimensional sensitivity of RCG and low input power ratio of relativistic triaxial klystron amplifier (TKA), is proposed and investigated in this paper. The PKC-RCG is composed of two parts: a pre-modulation region adapted from TKA and an energy exchange region adapted from RCG. The pre-modulation region is used for initial speed modulation of intense relativistic electron beams (IREB), ensuring that the output frequency is consistent with the input frequency. The energy exchange region is used for deep clustering of the IREB and achieving efficient beam–wave energy conversion. Phase locking of the output HPM is accomplished through phase delivery of the modulated IREB. Specially designed reflectors and cascaded single-gap bunching cavities with active suppression of asymmetric TM mode are employed in the pre-modulation region to suppress energy coupling and achieve a lower input power ratio. Disk-loaded slow-wave structure with smooth inner conductor is employed in the energy exchange region to further decrease the dimensional sensitivity of RCG. By the proposed Ka-band PKC-RCG, an HPM with a power of 550 MW and a frequency of 29.0 GHz is obtained with ohmic loss being taken into account. Moreover, the input power ratio and phase-locking bandwidth of the proposed Ka-band PKC-RCG are −51.4 dB and 30 MHz, respectively.

Advancing dynamic quantum crystallography: enhanced models for accurate structures and thermodynamic properties.

X-ray diffraction (XRD) has evolved significantly since its inception, becoming a crucial tool for material structure characterization. Advancements in theory, experimental techniques, diffractometers and detection technology have led to the acquisition of highly accurate diffraction patterns, surpassing previous expectations. Extracting comprehensive information from these patterns necessitates different models due to the influence of both electron density and thermal motion on diffracted beam intensity. While electron-density modelling has seen considerable progress [e.g. the Hansen-Coppens multipole model and Hirshfeld Atom Refinement (HAR)], the treatment of thermal motion has remained largely unchanged. We have developed a novel method that combines the strengths of the advanced charge-density models [Aspherical Atom Models (AAMs), such as HAR or the Transferable Aspherical Atom Model (TAAM)] and the thermal motion model (normal modes refinement, NoMoRe). We denote this approach AAM_NoMoRe, wherein instead of refining routine anisotropic displacement parameters (ADPs) against single-crystal X-ray diffraction data, we refine the frequencies obtained from periodic density functional theory (DFT) calculations. In this work, we demonstrate the effectiveness of this model by presenting its application to model compounds, such as alanine, xylitol, naphthalene and glycine polymorphs, highlighting the influence of our method on the H-atom positions and shape of their ADPs, which are comparable with neutron data. We observe a significant decrease in the similarity index for H-atom ADPs after AAM_NoMoRe in comparison to only AAM, aligning more closely with neutron data. Due to the use of aspherical form factors (AAM), our approach demonstrates better fitting performance, as indicated by consistently lower wR2 values compared to the Independent Atom Model (IAM) refinement and a significant decrease compared to the traditional NoMoRe model. Furthermore, we present the estimation of a key thermodynamic property, namely, heat capacity, and demonstrate its alignment with experimental calorimetric data.