Compact Accelerator Research Articles

Revealing the dynamics of ultrarelativistic non-equilibrium many-electron systems with phase space tomography

The description of physical processes with many-particle systems is a key approach to the modeling of numerous physical systems. For example in storage rings, where ultrarelativistic particles are agglomerated in dense bunches, the modeling and measurement of their phase-space distribution is of paramount importance: at any time the phase-space distribution not only determines the complete space-time evolution but also provides fundamental performance characteristics for storage ring operation. Here, we demonstrate a non-destructive tomographic imaging technique for the 2D longitudinal phase-space distribution of ultrarelativistic electron bunches. For this purpose, we utilize a unique setup, which streams turn-by-turn near-field measurements of bunch profiles at MHz repetition rates. To demonstrate the feasibility of our method, we induce a non-equilibrium state and show that the phase-space distribution microstructuring as well as the phase-space distribution dynamics can be observed in great detail. Our approach offers a pathway to control ultrashort bunches and supports, as one example, the development of compact accelerators with low energy footprints.

TOUCANS: A versatile Monte Carlo neutron transport code based on GEANT4

This paper reports the development of TOUCANS, a new Monte Carlo neutron transport code fully written using the GEANT4 toolkit. It aims at modeling complex systems easily and rapidly, thanks to a simple key–value input file. While its main focus is the transport of low energy neutrons – below 20 MeV – using evaluated cross-section libraries, it also takes advantage of the state-of-the-art capabilities offered by GEANT4 regarding the modeled cross-sections for practically all particles at all energies. Hence it gives access to non-specialists to a wide variety of applications involving different particles, such as the simulation of compact accelerator based neutron sources (CANS) which initially motivated its development. It leverages on recent implementations performed within GEANT4 to provide both shielding calculation capabilities (using Adaptive Multilevel Splitting, which is a full y automated variance reduction technique) and criticality calculation capabilities (to estimate the keff of a multiplicative system). It also benefits from a tight coupling with CADMesh to readily import CAD models, with NCrystal to extend the support of thermal neutron transport to crystals, with FIFRELIN to increase compound nucleus de-excitation accuracy, and with FUNZ to provide to the user parametric simulation capabilities (such as multi-objective algorithms and calculation of Pareto sets). Thanks to recent improvements of the neutron physics within the GEANT4 Neutron-HP package, the TOUCANS code can be considered on-par with industrial neutron transport codes such as Tripoli-4® or MCNP in term of neutron physics accuracy. Its sources should be released soon amongst GEANT4 advanced examples.

Enhanced ion acceleration from transparency-driven foils demonstrated at two ultraintense laser facilities

Laser-driven ion sources are a rapidly developing technology producing high energy, high peak current beams. Their suitability for applications, such as compact medical accelerators, motivates development of robust acceleration schemes using widely available repetitive ultraintense femtosecond lasers. These applications not only require high beam energy, but also place demanding requirements on the source stability and controllability. This can be seriously affected by the laser temporal contrast, precluding the replication of ion acceleration performance on independent laser systems with otherwise similar parameters. Here, we present the experimental generation of >60 MeV protons and >30 MeV u−1 carbon ions from sub-micrometre thickness Formvar foils irradiated with laser intensities >1021 Wcm2. Ions are accelerated by an extreme localised space charge field ≳30 TVm−1, over a million times higher than used in conventional accelerators. The field is formed by a rapid expulsion of electrons from the target bulk due to relativistically induced transparency, in which relativistic corrections to the refractive index enables laser transmission through normally opaque plasma. We replicate the mechanism on two different laser facilities and show that the optimum target thickness decreases with improved laser contrast due to reduced pre-expansion. Our demonstration that energetic ions can be accelerated by this mechanism at different contrast levels relaxes laser requirements and indicates interaction parameters for realising application-specific beam delivery.

Present status of the YU-AMS system and its operation over the past 10 years

In 2009, Yamagata University installed a compact 14C accelerator mass spectrometry (YU-AMS) system and an automated graphitization line. The YU-AMS system is based on a 0.5 MV pelletron accelerator (1.5SDH-1) developed by National Electrostatics Corporation (NEC). A second automated graphitization line and an additional ion source of the YU-AMS system were installed in 2014. Approximately 2,000 samples have been measured per year using the system since 2010. The long-term stability of the system from 2010 to 2021 was assessed by measuring the IAEA-C6 and IAEA-C7 standard samples graphitized by the automated graphitization line.

Monte Carlo Study of an Electron-Based Neutron Source for Bragg Edge Imaging

Neutron imaging is a powerful and nondestructive tool for testing materials in industrial and research applications. Compact accelerator neutron sources are gaining interest in neutron application techniques, such as Bragg edge transmission imaging. Delivering a high neutron flux with a narrow pulse width and suppressed photons at the sample position are fundamental factors for designing a neutron source for Bragg edge imaging. In this study, Monte Carlo calculations were performed to simulate a 40-MeV electron beam impinging on a cylindrical tungsten target. Different target moderator and reflector (TMR) geometries were investigated to produce cold neutrons, and their results were compared. Polyethylene (PE) and graphite were used as the moderator and the reflector, respectively. The structures and dimensions of the moderator and reflector were optimized using a Monte Carlo simulation with the PHITS-3.28 code. The effect of the PE moderator temperature on the cold neutron flux was investigated. The results showed that the optimum size of the PE at 77 K inside the reflector was 3 × 15 × 15 cm3 to achieve the wavelength resolution of 1.05% and the neutron flux of 1.16 × 104 n/cm2/s at 1000 cm from the target station by assuming the electron beam current of 275 µA. In addition, the FLUKA 4-2.1 code was used to calculate the neutron spectrum from the designed neutron production target at room temperature, and the results were consistent with the PHITS calculations. The neutron spectrum together with its pulse width from the designed TMR were used to simulate the Bragg edges of an α -Fe sample, and it was concluded that the TMR is suitable for performing Bragg edge imaging.

Hybridised production of technetium-99m and technetium-101 with fluorine-18 on a low-energy biomedical cyclotron

New modes of production and supply of short-lived radioisotopes using accelerators are becoming attractive alternatives to the use of nuclear reactors. In this study, the use of a compact accelerator neutron source (CANS) was implemented to explore the production of 99mTc and 101Tc. Irradiations were performed with neutrons generated from a 16.5 MeV cyclotron utilising the 18O(p, n)18F reaction during routine 18F-fluorodeoxyglucose (FDG) production in a commercial radiopharmacy. Natural molybdenum targets in metal form were employed for the production of several Tc isotopes interest via (n, γ) reactions on 98Mo and 100Mo. The production of 99mTc and 101Tc under these conditions is considered and discussed.

Simultaneous Determination of Transuranium Radionuclides for Nuclear Forensics by Compact Accelerator Mass Spectrometry.

Accelerator mass spectrometry (AMS) is one of the most sensitive techniques used to measure the long-lived actinides. This is particularly of interest for determination of ultra-trace transuranium nuclides and their isotopic fingerprints for nuclear forensics. In this work, a new method was developed for simultaneous determination of transuranium nuclides (Np, Pu, Am, and Cm isotopes) by using 300 kV AMS after a sequential chemical separation of each group of actinides. 242Pu and 243Am were utilized as tracers for Np/Pu and Am/Cm yield monitoring. The results show that the chemical behaviors of Np and Pu on the TK200 column and those of Am and Cm on the DGA column were very consistent in 8-9 mol/L of HNO3 and 0.015-0.03 mol/L of NaNO2 media during the radiochemical separation. The AMS detection efficiencies for transuranium nuclides were also evaluated. The detection limits for all radionuclides are below femtogram level and even in attogram level for Pu and Cm isotopes. The established method has been successfully applied to accurately measure various transuranium nuclides in a single actinide radionuclide solution, demonstrating its feasibility for nuclear forensic investigation.

Status report: A decade of traditional radiocarbon dating applications by DirectAMS

DirectAMS debuted as an affordable, high-throughput radiocarbon dating service at AMS-12 in 2011. A dedicated pretreatment laboratory has been in operation since 2012 in conjunction with an NEC 1.5SDH-1 Compact Pelletron Accelerator Mass Spectrometer installed in 2006. Over 60,000 14C radiocarbon dating targets have been measured over the last decade. The status of the laboratory and performance from routinely measured standard, reference, and blank materials are presented.

Uniformization of a large beam spot using sextupole magnets for a compact multiple-energy electron accelerator

We have commissioned a multiple-energy electron accelerator that illuminates an 800 mm × 800 mm target. The energy of the beam ranges from 0.5 to 5 MeV. A beamline following the accelerator has horizontal and vertical sections that include an alpha dipole and a “focus sextupole”. In the horizontal section, the alpha magnet, having a bend angle of 270° and a field index of 0.8, provides both vertical collimation and energy selection. In the vertical section, a focus sextupole converts the initial Gaussian beam distribution to a uniform distribution in one dimension without beam loss. We used a scanning magnet just ahead of the target to expand the beam in the orthogonal dimension. Using the French code TraceWin, we simulate the beam dynamics in this beamline by integrating electron trajectories through field maps of the magnets. We have determined experimentally that the focus sextupole creates a horizontal strip beam on target having a current density uniformity of better than 90 %. By scanning this strip beam vertically, we have achieved a two-dimensional current density uniformity of better than 90 %.

Bottleneck-Stationary Compact Model Accelerator With Reduced Requirement on Memory Bandwidth for Edge Applications

State-of-the-art compact models such as MobileNets and EfficientNets are structured using a linear bottleneck and inverted residuals. Hardware architecture using a single dataflow strategy fails to balance the required memory bandwidth with the given computational resources. This work presents a heterogeneous dual-core accelerator that performs a block-wise pipelined process as a unit using a bottleneck-stationary (BS) dataflow. The BS greatly relieves the requirement on DRAM bandwidth and on-chip SRAM capacity. A look-behind-only attention is also proposed as a co-optimized algorithm. Compared to the state-of-the-art hardware scheme, the proposed accelerator demonstrates a reduction of 1.8- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.9\times $ </tex-math></inline-formula> in latency and 2.2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\times $ </tex-math></inline-formula> in energy consumption, respectively.For verification, the accelerator with a 16-bit integer precision was implemented using 28nm CMOS process. Measurements show energy efficiencies of 0.5-to-3.75 TOPS/W in a supply voltage range of 0.55-to-1.15V.

Creation and direct laser acceleration of positrons in a single stage

Relativistic positron beams are required for fundamental research in nonlinear strong field QED, plasma physics, and laboratory astrophysics. Positrons are difficult to create and manipulate due to their short lifetime, and their energy gain is limited by the accelerator size in conventional facilities. Alternative compact accelerator concepts in plasmas are becoming more and more mature for electrons, but positron generation and acceleration remain an outstanding challenge. Here, we propose a new setup where we can generate, inject, and accelerate them in a single stage during the propagation of an intense laser in a plasma channel. The positrons are created from a laser-electron collision at 90\ifmmode^\circ\else\textdegree\fi{}, where the injection and guiding are made possible by an 800-nC electron beam loading which reverses the sign of the background electrostatic field. We obtain a 17-fC positron beam, with GeV-level central energy within 0.5 mm of plasma.

Introduction of Research Work on Laser Proton Acceleration and Its Application Carried out on Compact Laser–Plasma Accelerator at Peking University

Laser plasma acceleration has made remarkable progress in the last few decades, but it also faces many challenges. Although the high gradient is a great potential advantage, the beam quality of the laser accelerator has a certain gap, or it is different from that of traditional accelerators. Therefore, it is important to explore and utilize its own features. In this article, some recent research progress on laser proton acceleration and its irradiation application, which was carried out on the compact laser plasma accelerator (CLAPA) platform at Peking University, have been introduced. By combining a TW laser accelerator and a monoenergetic beamline, proton beams with energies of less than 10 MeV, an energy spread of less than 1%, and with several to tens of pC charge, have been stably produced and transported in CLAPA. The beamline is an object–image point analyzing system, which ensures the transmission efficiency and the energy selection accuracy for proton beams with large initial divergence angle and energy spread. A spread-out Bragg peak (SOBP) is produced with high precision beam control, which preliminarily proved the feasibility of the laser accelerator for radiotherapy. Some application experiments based on laser-accelerated proton beams have also been carried out, such as proton radiograph, preparation of graphene on SiC, ultra-high dose FLASH radiation of cancer cells, and ion-beam trace probes for plasma diagnosis. The above applications take advantage of the unique characteristics of laser-driven protons, such as a micron scale point source, an ultra-short pulse duration, a wide energy spectrum, etc. A new laser-driven proton therapy facility (CLAPA II) is being designed and is under construction at Peking University. The 100 MeV proton beams will be produced via laser–plasma interaction by using a 2-PW laser, which may promote the real-world applications of laser accelerators in malignant tumor treatment soon.

Development of a compact linear accelerator to generate ultrahigh dose rate high-energy X-rays for FLASH radiotherapy applications.

In recent years, the FLASH effect, in which ultrahigh dose rate (UHDR) radiotherapy (RT) can significantly reduce toxicity to normal tissue while maintaining antitumor efficacy, has been verified in many studies and even applied in human clinical cases. This work evaluates whether a room-temperature radio-frequency (RF) linear accelerator (linac) system can produce UHDR high-energy X-rays exceeding a dose rate of 40Gy/s at a clinical source-surface distance (SSD), exploring the possibility of a compact and economical clinical FLASH RT machine suitable for most hospital treatmentrooms. A 1.65m long S-band backward-traveling-wave (BTW) electron linac was developed to generate high-current electron beams, supplied by a commercial klystron-based power source. A tungsten-copper electron-to-photon conversion target for UHDR X-rays was designed and optimized with Monte Carlo (MC) simulations using Geant4 and thermal finite element analysis (FEA) simulations using ANSYS. EBT3 and EBT-XD radiochromic films, which were calibrated with a clinical machine Varian VitalBeam, were used for absolute dose measurements. A PTW ionization chamber detector was used to measure the relative total dose and a plane-parallel ionization chamber detector was used to measure the relative normalized dose of each pulse. The BTW linac generated 300-mA-pulse-current 11 MeV electron beams with 29kW mean beam power, and the conversion target could sustain this high beam power within a maximum irradiation duration of 0.75 s. The mean energy of the produced X-rays was 1.66 MeV in the MC simulation. The measured flat-filter-free (FFF) maximum mean dose rate of the room-temperature linac exceeded 80Gy/s at an SSD of 50cm and 45Gy/s at an SSD of 67.9cm, both at a 2.1cm depth of the water phantom. The FFF radiation fields at 50cm and 67.9cm SSD at a 2.1cm depth of the water phantom showed Gaussian-like distributions with 14.3 and 20cm full-width at half-maximum (FWHM) values, respectively. This work demonstrated the feasibility of UHDR X-rays produced by a room-temperature RF linac, and explored the further optimization of system stability. It shows that a simple and compact UHDR X-ray solution can be facilitated for both FLASH-RT scientific research and clinical applications.

Experimental validation of cold neutron source performance with mesitylene moderator installed at RANS

The RANS (RIKEN Accelerator driven Neutron Source), one of compact accelerator neutron sources (CANS), tries to expand its performance by installing a cold neutron which may provide new opportunities in many applications. RANS is a low power CANS with a proton beam of 7 MeV and 100 µA at maximum. A moderator system was constructed based on results of optimization design study with mesitylene. Recently, we have done performance tests aiming at showing characteristics as cold neutron source. Cryogenic mesitylene moderator was installed on a plug with a new target moderator reflector configuration of RANS. Experiment using a gas electron multiplier (GEM) detector was carried out to measure neutron spectra of the cold moderator. This paper describes performance of the cold moderator in terms of 1) Cold neutron gain of optimization design with respect to a polyethylene moderator, 2) Temperature dependency of cold neutron spectrum flux regarding scattering kernel (SK), and 3) comparison between experiment and calculation. A note is given for comparison between calculations with different SKs available. Also, two-dimensional imaging of cold and thermal neutron spectrum flux on the viewed surface is shown with a pinhole slit configuration.

Simulation and design of an IPHI-based neutron source, first steps toward SONATE

Facilities providing bright thermal neutron beams are of primary importance for various research topics. At CEA-Saclay, a compact accelerator driven neutron source, SONATE, is investigated in taking advantage of the IPHI accelerator able to deliver a 3 MeV proton beam with an intensity up to 100 mA. To optimize the performances of such a neutron source, it is necessary to maximize the thermal neutron flux while minimizing the contribution of other particles. In this work, optimization has been performed using the Monte Carlo code TOUCANS, a neutron transport code based on Geant4 developed at CEA-Saclay. This latter has been coupled to PROMETHEE, a software allowing multi-objective optimization for many simulation software. In this work the Kriging metamodel based approach is used to optimize a neutron beamdump. To take into account the various constraints, noise on the detection system and radiation protection issues, several beamdump configurations are evaluated. The variation of beamdump parameters makes it possible to identify the set of optimal solutions, the Pareto front. It allows to focus on the set of best choices and to choose wisely the best configurations. After describing the validation of TOUCANS on experimental tests performed from 2016 to 2022, the capability of such an approach will be presented.

Microscopic origin of the abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals: An extended ab initio study

As a promising next-generation material for superconducting radiofrequency cavities, superconducting Nb3Sn, once developed for fabricating a high-field magnet, has attracted tremendous research interest due to the significant potential for both compact and large scale accelerator applications. However, the intrinsic physical origin, especially at atomic and electronic scale, of the abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals is still controversial and not fully understood yet. Through an extended atomic and electronic modelling of electronic structure evolution arising from the perturbation of lattice strain and temperature, we proposed an analytical model for depicting the abnormal temperature-dependent elastic constants and transition resistivities of superconducting Nb3Sn. The extended ab initio modeling takes into account the interaction of the d electrons with the strain, the strain-modulated electronic structure evolution and the accompanied variations in the density of states at the Fermi level, and the competition between the lattice contribution and the electron contribution in governing the abnormal elastic response along with the superconducting transition of Nb3Sn. The model predictions of the elastic constants and the superconducting phase transition resistivities of single crystal and polycrystalline Nb3Sn qualitatively agree with the experimental observations. The extended ab initio studies indicate the abnormal changes in the elastic properties and the transition resistivity response characteristics are intrinsically correlated, the contribution arising from the d-band electrons determines the cross-scale abnormal elastic behavior accompanying the superconducting transition in Nb3Sn crystals.

Determination of ultra-low level of 239, 240Pu in grass/vegetable sample by compact accelerator mass spectrometry

Determination of ultra-low level of 239, 240Pu in grass/vegetable sample by compact accelerator mass spectrometry

Photonic flatband resonances for free-electron radiation.

Flatbands have become a cornerstone of contemporary condensed-matter physics and photonics. In electronics, flatbands entail comparable energy bandwidth and Coulomb interaction, leading to correlated phenomena such as the fractional quantum Hall effect and recently thosein magic-angle systems. In photonics, they enable properties including slow light1 and lasing2. Notably, flatbands support supercollimation-diffractionless wavepacket propagation-in both systems3,4. Despite these intense parallel efforts, flatbands have never been shown to affect the core interaction between free electrons and photons. Their interaction, pivotal for free-electron lasers5, microscopy and spectroscopy6,7, and particle accelerators8,9, is, in fact, limited by a dimensionality mismatch between localized electrons and extended photons. Here we reveal theoretically that photonic flatbands can overcome this mismatch and thus remarkably boost their interaction. We design flatband resonances in a silicon-on-insulator photonic crystal slab to control and enhance the associatedfree-electron radiation by tuning their trajectory and velocity. We observe signatures of flatband enhancement, recording a two-order increase from the conventional diffraction-enabled Smith-Purcell radiation. The enhancement enables polarization shaping of free-electron radiation and characterizationof photonic bands through electron-beam measurements. Our results support the use of flatbands as test beds for strong light-electron interaction, particularly relevant for efficient and compact free-electron light sources and accelerators.

Out-of-Field Dose Measurement by TLD Dosimetry and Estimation of Radiation-Induced Secondary Cancer Risk of Thyroid and Breast from Head Radiotherapy.

Radiation therapy, the most common form of cancer treatment, can result in late complications, such as secondary breast and thyroid cancers. This study aimed to evaluate the risk of secondary cancers using two radiobiological models of Excess Absolute Risk (EAR) and Excess Relative Risk (ERR) in patients with brain cancer undergoing radiotherapy for improved survival rates of cancer patients. In this expository cross-sectional study, 45 patients under the age of 40 years underwent Whole Brain Radiotherapy (WBRT) using a compact accelerator in Shahid Ramezanzadeh Hospital, Yazd, Iran. Out-of-field organ dose measurement was performed using a Thermoluminescent Dosimeter (TLD) to determine the dose to thyroid and breast tissues. The risk of secondary cancers in these organs was calculated 3, 5, 10, 15, and 20 years after radiation therapy. The mean values of thyroid cancer risk in men and women were 0.418±0.509 and 0.274±0.306, respectively. ERR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women undergoing radiation therapy were 1.084±2.938, 0.594±1.407, 0.248±0.497, 0.138±0.248, and 0.091±0.148, respectively. EAR values of breast cancer in 3-, 5-, 10-, 15-, and 20-year women following radiation therapy were 0.064±0.060, 0.077±0.071, 0.119±0.100, 0.178±0.248, and 0.259±0.178, respectively. After irradiation, the risk of secondary cancer is affected by factors, such as the patient's age and gender. The secondary thyroid cancer is higher than that of other organs, such as the breast, in the patients undergoing WBRT.

Determination of Radiocarbon Content in Bio-Oil Samples by Mini Carbon Dating System in the Gliwice Radiocarbon and Mass Spectrometry Laboratory

Abstract The applications of isotopes are used by many European countries to investigate environmental changes. A compact modern accelerator mass spectrometry (AMS) system known as Mini Carbon Dating System (MICADAS) is used in Gliwice Radiocarbon and Mass Spectrometry Laboratory for determining the 14C content in different environmental samples including liquid fuels. For radiocarbon measurement using MICADAS, the liquid samples are accurately prepared using the tin capsules for liquids for combustion in elemental analyser (EA) and graphitisation in the AGE system. In this study, the determination of 14C content in three different bio-oil samples and one reference sample of 100% biomass was conducted. Bio-oil samples were prepared using tin capsules for liquids sealed in the second capsules for solids to avoid sample evaporation while the reference sample was prepared using the tin capsule for solids for combustion in EA and graphitisation in the AGE system. Based on the 14C measurement results, one of the bio-oils was not produced from the analysed reference biomass. Two others were determined as a mixture of bio- and fossil components, and based on 14C the bio-carbon content was calculated. For all samples, the 14C measurement showed reproducible and reliable results.