Beam Parameters Research Articles

Potential of the CLARA test facility for VHEE radiotherapy research

The Compact Linear Accelerator for Research and Applications (CLARA) is a test facility at the STFC Daresbury Laboratory, which is capable of delivering ultra-bright electron bunches of up to 250 MeV beam energy. A new beam line has been designed to maximise the exploitation of the CLARA facility in a variety of scientific fields, including novel acceleration and new modalities of radiotherapy. In this paper, we present the specification and design of this beam line to explore the possibilities of pursuing R&D in very high-energy electron (VHEE) radiotherapy and VHEE with FLASH radiotherapy. We describe the beam line design, including the flexibility of the beam optics to focus the beam in a range of locations and present results from preliminary start-to-end simulations using Monte Carlo tracking codes. We highlight advantages of this beam line, including rapid access to the shielded experimental hutch and the possibilities for the installation of different experimental setups in two dedicated chambers. The beam line includes focussing magnets, extensive diagnostics, and allows in-air installation within the experimental beam line. The facility will allow an experimental programme towards addressing many outstanding issues related to this new radiotherapy modality. We also describe the available flexibility in beam parameters for both conventional dose rates and those entering into the FLASH regime. The possibility of both living cells and treatment planning studies is anticipated to be conducted at this world-class facility.

Coupling efficiency of electromagnetic hermite non-uniformly correlated beams into a single-mode fiber in a turbulent atmosphere

We present a theoretical formula to analyze a single-mode fiber coupling efficiency of electromagnetic hermite non-uniformly correlated (EMHNUC) beams propagating through the turbulent atmosphere and investigate the effects of initial beam parameters, including the beam width, coherence length, beam order, and ratio of field amplitude on fiber-coupling efficiency. We find that a single-mode fiber coupling efficiency initially decreases, increases sharply to the maximum value, and gradually decreases after a long propagation distance. This behavior is attributed to the co-work of the characteristics of such vector non-uniform correlated structural beam and their diffraction broadening in atmospheric turbulence. Adjusting beam parameters can effectively improve the single-mode fiber-coupling efficiency. Our results will benefit the fiber-coupling systems in free-space optical communication.

Analysis of the dynamic responses of a piezothermoelastic microbeam resonator under dual-phase-lag heat conduction

Thermoelastic vibration responses of a piezothermoelastic (PTE) microbeam resonator have been investigated in the present work under simply supported boundary conditions. The basic governing equations for a transversely isotropic piezothermoelastic solid are formulated by assuming the Euler–Bernoulli beam theory with hyperbolic dual-phase-lag (DPL) heat conduction model. Later on, non-dimensionalization of the variables have been carried out for simplicity to obtain the set of coupled governing equations for thermal deflection, electric field, and thermal moment. Initial and boundary conditions are defined to solve for the non-dimensional thermal deflection and thermal moment by using Laplace transform technique along with the finite Fourier sine transform. Closed-form solutions of the problem are obtained. Moreover, an attempt is made to illustrate the analytical results through numerical simulations by taking a PTE material of Lead Zirconate Titanate (PZT-5A). The influence of the quadratic term of the phase-lag parameter of heal flux in the DPL model is investigated to compare the effects of phase-lags under parabolic and hyperbolic DPL models. In addition, the long-term and short-term vibration responses of thermal moment and thermal deflection are analyzed in detail to observe the impact of different factors which characterize the piezoelectric phenomena and dual-phase-lag effects. Comparative analysis of different well-known models for responses of thermal moment and thermal deflection is also presented for short- and long-time ranges. Some important observations about how piezoelectric parameters, dual-phase-lag parameters, and beam parameters affect the behavior of piezothermoelastic vibrations have been highlighted.

Numerical study on the flexural and shear behavior of steel fiber and high‐strength steel combination in ultra‐high‐performance fiber‐reinforced concrete beams under cyclic loading

AbstractFiber‐reinforced concrete consists of hydraulic cement, water, aggregate, and discrete fibers, making it a composite material. These fibers, available in different shapes, sizes, and materials such as steel, polymer, glass, and natural fibers, are commonly utilized in structural applications. The tensile strength of conventional concrete tends to decrease as micro‐cracks develop rapidly under applied stresses. However, incorporating closely spaced fibers can hinder the progression of micro‐cracks, leading to a substantial improvement in both tensile and flexural strengths of concrete. Furthermore, fibers can delay the initiation of tensile cracks, effectively enhancing concrete's ability to withstand tensile strains before failure. As a result, fiber‐reinforced concrete exhibits increased durability and enhanced resistance to impacts compared to plain concrete. This study aims to evaluate and compare the cyclic flexural behavior of a cantilever beam constructed from ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) using reinforcing bars made of high‐strength steel (HSS). The beams contain varying relative proportions of longitudinal reinforcement and steel fibers. Various key performance parameters of the cantilever beam were thoroughly examined, such as load capacity, flexural ductility, failure mode, hysteresis response, energy dissipation, and hardness. The study demonstrated that UHPFRC beams with HSS exhibit good cyclic flexural performance prior to failure.

Impact of beam asymmetries at the Future Circular Collider e+e−

In this paper, we present detailed simulations with asymmetric initial beam settings in the context of the proposed Future Circular Collider e+e− (FCC-ee) using the framework. We compare simulated equilibrium bunch sizes and luminosities against an already existing analytical model, which shows remarkably good agreement for realistic small perturbations. We investigate the longitudinal top-up injection, the currently preferred injection scheme for the FCC-ee, using self-consistent simulations featuring beam-beam collisions with beamstrahlung and the injection process for the first time. We present and assess the sensitivity and required precision of the nominal beam parameters in a potential real-life operation by providing first estimates of the tolerances in the initial asymmetry of several machine parameters, with respect to the 3D flip-flop mechanism, obtained from parameter scan simulations. Published by the American Physical Society 2024

Efficiency-enhanced TM-mode gyrotron with down-taper interaction structure

Recent advancements have shown that transverse magnetic (TM)-mode gyrotrons are feasible under specific conditions, yet their capabilities remain insufficiently explored. This article systematically investigates a W-band TM11-mode gyrotron within the down-tapered structure(s) to uncover its limitations and underlying physics. 2D interaction-efficiency maps are scanned as functions of the tube's geometrical parameters or beam parameters under magnetic-field tuning. An oversized tube integrated with short two-stage down tapers enhances the output efficiency of the fundamental axial mode and effectively alleviates the axial-mode competition. The peak electron-beam efficiency of the TM11 mode exceeds 50% with an idealized cold beam. The 3D particle-in-cell simulations are utilized to validate the real-time scheme including multiple transverse modes. Incorporating realistic beam spread, the first-harmonic TM11 mode effectively suppresses the second-harmonic and third-harmonic transverse electric modes with a maximum steady output of 130 kW, corresponding to an interaction efficiency of 37%. Complex dynamics regarding the mode-competing and mode-forming processes are revealed and discussed. This study not only facilitates the exploration of TM-mode gyrotrons but also provides insights into the harmonic gyrotron using the axis-encircling electron beam, where TM modes have more chances to be excited and dominate oscillations.

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.

Seismic Resistance of Reinforced Concrete Building Frames Based on Interval Assessment of the Coefficient of Permissible Damage

The main method for assessing the seismic resistance of buildings in the standards of most countries is the linear-spectral method. This method allows for the calculation of the spatial model of a building for seismic load in the elastic range without resorting to direct integration of the equations of motion. Nonlinear characteristics of reinforced concrete structure materials are usually considered integrally using the reduction factor. However, the values of this factor in the Russian standards are not sufficiently substantiated, as the later studies show. To determine the coefficient of permissible damage (reduction factor), six reinforced concrete frames were considered, with different parameters such as span length, number of spans, and number of floors. The design parameters of beams and columns (section sizes, reinforcement, etc.) were preliminarily selected based on the calculation using the linear-spectral method. In the second stage, numerical modeling was carried out in the OpenSEES PC to implement the pushover analysis procedure. Then, the coefficient of permissible damage was estimated by processing the capacity curves obtained on the basis of nonlinear static calculation. The value of the sought coefficients is practically not affected by the number of stores of the frame; however, with an increase in the number of spans, the coefficient K1 increases, which is explained by a decrease in the plasticity of the system. On average, for the frames under consideration, the coefficient K1 was 0.526, which is 1.5 times greater than the coefficient proposed in modern Russian standards, K1 = 0.35. The results obtained on the basis of pushover analysis are compared with the coefficients K1 determined through the values of the average degree of damage (d) of the buildings according to the modified seismic scale MMSK-86. For various types of reinforced concrete frame buildings, K1 = 0.51 was obtained. It is recommended that the coefficient K1 for reinforced concrete frame buildings should be increased to a value of at least K1 = 0.5 in the Russian standard.

Theory of bunched beam transverse Schottky signals with stationary rf system and high-order chromaticity

Theory of bunched beam transverse Schottky signals with stationary rf system and high-order chromaticity

Evaluation of the stress-strain state of the RC beam with the use of DIC

Abstract The article presents the results of adapting the digital image correlation method for the possibility of diagnosing reinforced concrete structures. Reinforced concrete (RC) bending elements are the most widely used in construction practice, which determines the importance of reliable estimation of their stress-strain state. The purpose of this study includes reliable theoretical and experimental investigation of the strength and deformability parameters of the RC beam. The experimental study was conducted using digital image correlation and sub-micron contactless gauges. Experimental data was verified with the calculation of the stress-strain state of the RC beam according to DBN V.2.6-98:2009 and Eurocode 2 and the finite-element modelling (FEM). As a result, the values of deflections, concrete and rebar strains were obtained and presented as corresponding diagrams. The results of all the methods are within the same ranges. Also, the form and character of corresponding diagrams are very similar. The indicated deviations were within acceptable limits. It was noted that the theoretical calculation generally provides lower strain values, which is a satisfactory result, as it indicates the bearing capacity reserves provided by the current regulations. The propagation of cracks was monitored during the experiment and the measured cracks opening was compared with theoretical assumptions. Theoretical values are higher than experimental, which shows certain conservativity of valid normative regulations. The experimental and theoretical results were in good correspondence, which confirms their reliability. It was concluded, that the proposed in the study complex theoretic-experimental approach provides essential information about the strength and deformability of the structure.

Divertor Tokamak Test: Impact of NBI shine-through and beam-plasma interaction on Divertor Tokamak Test facility

IntroductionIn this work, we aim to explore numerically the behavior of beam energetic particles in the Divertor Tokamak Test (DTT), a superconductive device equipped with a Neutral Beam Injection (NBI) system capable of injecting neutrals up to 510 keV.MethodWe explore beam ionization and beam slowing down for different DTT plasma scenarios. Numerical simulations are performed using the ASCOT suite of codes, including a wide-range scan of plasma density and beam injection energy. For different plasma conditions, we estimate shine-through losses, including the heat fluxes on the first wall thanks to dedicated particle tracing simulations. Orbits of newly-born fast ions are characterized by means of the constant of motion phase space, showing how trapped energetic particles’ population and prompt losses change with plasma density and NBI energy.Results and discussionSlowing down simulations show that NBI injection at 510 keV is well coupled to DTT plasmas. DTT NBI will be one of the sources of auxiliary ion heating, with an absorbed power ratio of up to ∼50% depending on plasma and beam parameters. At low plasma densities, energetic particle confinement is less efficient, and NBI power and/or energy reduction is expected.

Unraveling the propagation dynamics of radially polarized anomalous vortex beams in turbulent maritime atmospheres

Based on the unified theory of coherence-polarization, we utilize the extended Huygens-Fresnel principle to derive analytical expressions for the average intensity distribution of a radially polarized anomalous vortex beam (RPAVB) propagating through non-Kolmogorov maritime atmospheric turbulence. The hollow structure of the RPAVB can be sustained over long distances by manipulating the self-focusing point position, which depends on the initial beam parameters. This manipulation effectively mitigates the effect of maritime atmospheric turbulence. Additionally, the RPAVB undergoes a transition into a Gaussian form at significant distances, which can be intentionally slowed down by increasing the beam order, topological charge, beam width, or reducing the turbulent strength.

Experimental investigation on high heat flux plasma parameters of HIT-PSI device in argon discharges

Abstract Researches on plasma-facing materials/components (PFMs/PFCs) have become a focus in magnetic confinement fusion studies, particularly for advanced tokamak operation scenarios. Similarly, spacecraft surface materials must maintain stable performance under relatively high temperatures and other harsh plasma conditions, making studies of their thermal and ablation resistance critical. Recently, a low-cost, low-energy-storage for superconducting magnets, and compact linear device, HIT-PSI, has been designed and constructed at Harbin Institute of Technology (HIT) to investigate the interaction between stable high heat flux plasma and PFMs/PFCs in scrape-off-layer (SOL) and divertor regions, as well as spacecraft surface materials. The parameters of the argon plasma beam of HIT-PSI are diagnosed using a water-cooled planar Langmuir probe and emission spectroscopy. As magnetic field rises to 2 T, the argon plasma beam generated by a cascaded arc source achieves high density exceeding 1.2×1021 m−3 at a distance of 25 cm from the source with electron temperature surpassing 4 eV, where the particle flux reaches 1024 m−2s−1, and the heat flux loaded on the graphite target measured by infrared camera reaches 4 MW/m2. Combined with probe and emission spectroscopy data, the transport characteristics of the argon plasma beam are analyzed.

Optimization of process parameters of electron beam welded Nimark 300 for weld bead analysis

Electron beam welding (EBW) offers an excellent capability of introducing the desired weld properties in similar and dissimilar welds. The high depth-to-width ratio enables exceedingly concentrated attention to the weld area, resulting in a smaller HAZ, making it one of the finest welding techniques. This study thus optimizes the basic input parameters of the machine based on weld quality, which incorporates weld penetration and geometry. The EBW was performed on Maragine steel (Nimark 300), a given alloy widely utilized in aerospace sensing applications. In analyzing the input variables associated with machining, this research employed the Taguchi optimization tool by zeroing in weld penetration and geometry. Then, variance analysis (ANOVA) was used for further study. Lastly, we conducted a verification test to compare the experimental results with the theoretically predicted values and thoroughly scrutinized the mathematical modelling. The machine parameters as voltage were 40, 50 and 60 KV, and the welding current was selected as 2, 4 and 6 mA. The welding speed for joining was chosen as 300, 600 and 900 mm/min. The maximum penetration was obtained at 50KV, 6mA current and 300 mm/min. The maximum bead width (BW) was obtained at 60 KV, 6 mA and 600 mm/min.

Exact boundary-value solution for an electromagnetic wave propagating in a linearly varying index of refraction

The propagation of electromagnetic waves in a linearly varying index of refraction is a fundamental problem in wave physics, being relevant in fusion science for describing certain wave-based heating and diagnostic schemes. Here, an exact solution is obtained for a given incoming wavefield specified on the boundary transverse to the direction of inhomogeneity by performing a spectral, rather than asymptotic, matching. Two case studies are then presented: a Gaussian beam at oblique incidence and a speckled wavefield at normal incidence. For the Gaussian beam, it is shown that when the waist $W$ is sufficiently large, oblique incidence manifests simply as rigid translation and focal shift of the corresponding diffraction pattern at normal incidence. The destruction of the hyperbolic umbilic caustic (corresponding to a critically focused beam) as $W$ is reduced is then demonstrated. The caustic disappears once $W \lesssim \delta _a \sqrt {L}$ ( $L$ being the medium length scale normalized by the Airy skin depth $\delta _a$ ), at which point the wave behaviour is increasingly described by Airy functions, but experiences less focusing as a result. To maximize the intensity of a launched Gaussian beam at a turning point, one should therefore minimize the imaginary part of the launched complex beam parameter while having the real part satisfy critical focusing. For the speckled wavefield, it is shown that the transverse speckle pattern only couples to the Airy longitudinal pattern when the coupling parameter $\eta = \sqrt {L}/f_{\#}$ is large, with $f_{\#}$ being the f-number of the launching aperture. When $\eta \ll 1$ , a reduced description of the total wavefield can be obtained by simply multiplying the incoming speckle pattern with the Airy swelling.

Creation of color centers in MgF2 single crystals by swift heavy ions: Energy loss and fluence dependence

Ion-solid interaction leads to significant modifications in the surface and bulk of different materials. MgF2 of a rutile crystalline structure is an important optical material for a large variety of applications. The single crystals were irradiated with energetic heavy ions of various kinetic energies and fluences. After irradiation, we utilized optical spectroscopy to study the ion-induced defects and their evolutions as a function of ion beam parameters. The absorption spectra show the creation of different types of ion-induced defects, namely F-, F2-, and F3-centers. The concentrations of the observed color centers as well as their creation efficiency are studied in terms of ion energy loss and fluence. The results are of high importance for understanding the degradation of optical materials in space environments.

Propagation characteristics of a circular Airyprime Gaussian beam in a gradient refractive index medium

In this paper, the focusing characteristics of a circular Airyprime Gaussian beam (CAPGB) propagating in a gradient refractive index (GRIN) medium is studied for the first time, to the best of our knowledge, and some interesting features are observed. We find that the CAPGB exhibits periodic focus–defocus behavior and completes a period propagation process with two focal points within a half variation period L/2 of the GRIN medium. Meanwhile, the CAPGB has singularity at the positions of z=(2j+1)L/4 on the optical axis. The focal lengths of bifocal points, the distance between two focal points, the focal intensity, and the focusing ability can be manipulated by beam parameters and the GRIN factor. It is noteworthy that the number (one or two) of focal points in one focusing period, and the focusing period or frequency of the CAPGB in the GRIN medium could be controlled by the beam distribution factor and GRIN factor, respectively. Moreover, the focusing ability of the CAPGB is much higher than that of a circular Airy Gaussian beam in the GRIN medium.

The design of high-brightness ERL-FEL injector based on VHF electron gun

In the past decade, the fourth-generation light source based on the combination of Energy Recovery Linac (ERL) and Free-Electron Laser (FEL) using superconducting linear accelerators has garnered significant attention. It holds immense potential, particularly in generating high-power Extreme Ultraviolet (EUV) light sources. This article primarily focuses on the physical design of an injector for ERL-FEL, based on a Very High Frequency (VHF) electron gun with a charge of 100 pC. The beam energy is accelerated to 10 MeV using 3-cell superconducting cryomodule. The optimization of beam parameters is conducted through employment of BMad and ASTRA simulations, incorporating the concept of Merger optimization. The beam emittance is less than 0.6 mm mrad, and the peak current at the injector exit exceeds 18 A. We present a new method to evaluate the Longitudinal Space Charge (LSC) effects in merger sections, which can be readily applied in design work. Furthermore, we introduce a novel type of merger. The performance of this new merger is comparable to the previously known optimum, the zigzag merger, offering a potential alternative solution for injectors in ERLs.

Cavity-based bunch length measurement study for the Super Tau-Charm Facility transport line

In this paper, a nondestructive cavity-based scheme is proposed to achieve high-resolution bunch length measurement in the Super Tau-Charm Facility (STCF) transport line. By extracting the TM010 and TM020 mode signals excited by the beam within a single pillbox cavity, a beam spectrum can be obtained to deduce the Root-Mean-Square (RMS) bunch length. This scheme is more spatially compact compared to the traditional method using double cavities. In this study, the basic principles of the cavity-based bunch length measurement method are explained, the monitor layout is introduced, and the design methods for the cavity and electronics are described. A prototype cavity was machined. Offline tests demonstrate that the eigenmodes in the cavity meet the design requirements and can be used for the bunch length measurements. Based on the online signal characteristics of the Cavity Beam Position Monitors (CBPMs) and the beam parameters of the STCF, the performance of this measurement method is evaluated. For picosecond-level bunches in the STCF transport line, this scheme can provide a bunch length measurement resolution of 233.5 fs at 1.5 nC.

On the acceptance, commissioning, and quality assurance of electron FLASH units.

FLASH or ultra-high dose rate (UHDR) radiation therapy (RT) has gained attention in recent years for its ability to spare normal tissues relative to conventional dose rate (CDR) RT in various preclinical trials. However, clinical implementation of this promising treatment option has been limited because of the lack of availability of accelerators capable of delivering UHDR RT. Commercial options are finally reaching the market that produce electron beams with average dose rates of up to 1000Gy/s. We established a framework for the acceptance, commissioning, and periodic quality assurance (QA) of electron FLASH units and present an example of commissioning. A protocol for acceptance, commissioning, and QA of UHDR linear accelerators was established by combining and adapting standards and professional recommendations for standard linear accelerators based on the experience with UHDR at four clinical centers that use different UHDR devices. Non-standard dosimetric beam parameters considered included pulse width, pulse repetition frequency, dose per pulse, and instantaneous dose rate, together with recommendations on how to acquire these measurements. The 6- and 9-MeV beams of an UHDR electron device were commissioned by using this developed protocol. Measurements were acquired with a combination of ion chambers, beam current transformers (BCTs), and dose-rate-independent passive dosimeters. The unit was calibrated according to the concept of redundant dosimetry using a reference setup. This study provides detailed recommendations for the acceptance testing, commissioning, and routine QA of low-energy electron UHDR linear accelerators. The proposed framework is not limited to any specific unit, making it applicable to all existing eFLASH units in the market. Through practical insights and theoretical discourse, this document establishes a benchmark for the commissioning of UHDR devices for clinical use.