Particle Accelerator Systems Research Articles

HVE ion sources for medium and high-energy accelerator systems

Since decades, High Voltage Engineering (HVE) manufactures particle accelerator systems for research and industry. HVE’s product line includes Singletron and Tandetron accelerator systems with terminal voltages of up to 6 MV. They are dedicated to a wide range of applications including ion implantation and irradiation, Ion Beam Analysis (IBA), Accelerator Mass Spectrometry (AMS), and neutron reference fields. In this paper, we give an overview of the different positive and negative ion sources that are applied in these systems. We focus especially on the recent development and the performance of a compact 2.45 GHz permanent magnet ECR bipolar ion source (HVE Model SO-160), used for negative light-ion injection into tandem accelerators. It generates high-current, low-emittance light-ion beams at 30 keV energy. The novelty in the design of this ion source is that it combines direct negative extraction for H − with positive extraction for He + that is followed by charge exchange to He − in a Na-based electron donor canal. The source produces in excess of 250 eµA of H − and more than 20 eµA of He −. It is expected the design allows for substantially higher currents, especially for H −.

Orbital angular momentum detection device for vortex microwave photons

Orbital angular momentum (OAM), which was first discovered in the optical field, represents a new dimension of electromagnetic waves. However, the detection of OAM microwave photons, i.e., vortex microwave photons, at room temperature is difficult due to their low energy. Here we report a prototype of a vortex microwave photon detection device based on vortex electrons. Our OAM detection device efficiently distinguishes the intrinsic OAM in the microwave band, which is helpful for exploring new physical dimensions. In addition, the detection device can be enhanced with a vortex electron sorting device designed with electron holograms so that OAM microwave photon demultiplexing can be achieved. Finally, the OAM detection device has high practicability; i.e., not only it can be used at room temperature, but also it is much smaller than a particle accelerator system. To illustrate the significance of this method, we demonstrate an on-off keying transmission system based on our OAM detection device.

IsoDAR@Yemilab: A report on the technology, capabilities, and deployment

IsoDAR@Yemilab is a novel isotope-decay-at-rest experiment that has preliminary approval to run at the Yemi underground laboratory (Yemilab) in Jeongseon-gun, South Korea. Here, we describe in detail the considerations for installing this compact particle accelerator and neutrino target system at the Yemilab underground facility. Specifically, we describe the caverns being prepared for IsoDAR, and address installation, shielding, and utilities requirements. To give context and for completeness, we also briefly describe the physics opportunities of the IsoDAR neutrino source when paired with the Liquid Scintillator Counter (LSC) at Yemilab, and review the technical design of the neutrino source.

Differentiable Preisach Modeling for Characterization and Optimization of Particle Accelerator Systems with Hysteresis.

Future improvements in particle accelerator performance are predicated on increasingly accurate online modeling of accelerators. Hysteresis effects in magnetic, mechanical, and material components of accelerators are often neglected in online accelerator models used to inform control algorithms, even though reproducibility errors from systems exhibiting hysteresis are not negligible in high precision accelerators. In this Letter, we combine the classical Preisach model of hysteresis with machine learning techniques to efficiently create nonparametric, high-fidelity models of arbitrary systems exhibiting hysteresis. We experimentally demonstrate how these methods can be used insitu, where a hysteresis model of an accelerator magnet is combined with a Bayesian statistical model of the beam response, allowing characterization of magnetic hysteresis solely from beam-based measurements. Finally, we explore how using these joint hysteresis-Bayesian statistical models allows us to overcome optimization performance limitations that arise when hysteresis effects are ignored.

Investigation on the Effect of Cable Length on Pulse Shape of High Voltage High Pulse Power Supply

In the present scenario of pulse power applications, transmission of high voltage pulses varies as per load condition. In the early days of its application, High Voltage High Pulse Power Supply (HVHPPS) design saw short distance between load and source, where the effect of cable length was not taken into account for design. This paper presents the effect of cable length on pulse shape of High Voltage High Pulse Power Supply. The load under observation is Klystron based high energy particle accelerator system. The performance of pulse power systems were observed continuously on a daily basis throughout the year and detailed analysis was carried out. This paper generates the model of pulse forming system and provides details of pattern distortion of the pulse shape due to various dynamic parameter changes i.e. impedance, Load Voltage, Load Current, Cavity Dimensional Changes (Microwave components) due to temperature variations and performance of the power supply. The results were analysed and validated with hardware results across a range of actual industrial loads.

New Commissioning Results of the MIST-1 Multicusp Ion Source

For the sterile neutrino experiment IsoDAR (Isotope Decay-At-Rest), we have developed a compact particle accelerator system delivering a 10 mA, continuous wave (cw) proton beam at 60 MeV to a neutrino production target. The accelerator comprises a compact isochronous cyclotron, an RFQ embedded in the cyclotron yoke, and an ion source. To reduce space charge effects during injection and acceleration, we are accelerating H+ 2 instead of protons. To produce the needed cw H+ 2 beam current of 10 mA (nominal) at the required purity and quality, we have built a new filament driven, multicusp ion source (MIST-1). Here we report commissioning results for long-time running at reduced power, demonstrating the feasibility of the design. Highlights include an H+ 2 beam current density of ≈ 10 mA/cm2, ≈ 80% H+ 2 fraction, and extrapolated emittances of 0.05 π-mm-mrad (RMS, normalized) after extraction. We also present high fidelity simulations that are in good qualitative and quantitative agreement with emittance measurements in our test beam line.

Experimental Evaluation of Sub-Sampling IQ Detection for Low-Level RF Control in Particle Accelerator Systems.

The low-level radio frequency (LLRF) control system is one of the fundamental parts of a particle accelerator, ensuring the stability of the electro-magnetic (EM) field inside the resonant cavities. It leverages on the precise measurement of the field by in-phase/quadrature (IQ) detection of an RF probe signal from the cavities, usually performed using analogue downconversion. This approach requires a local oscillator (LO) and is subject to hardware non-idealities like mixer nonlinearity and long-term temperature drifts. In this work, we experimentally evaluate IQ detection by direct sampling for the LLRF system of the Polish free electron laser (PolFEL) now under development at the National Centre for Nuclear Research (NCBJ) in Poland. We study the impact of the sampling scheme and of the clock phase noise for a 1.3-GHz input sub-sampled by a 400-MSa/s analogue-to-digital converter (ADC), estimating amplitude and phase stability below 0.01% and nearly 0.01°, respectively. The results are in line with state-of-the-art implementations, and demonstrate the feasibility of direct sampling for GHz-range LLRF systems.

CyberKnife radiation therapy as a platform for translational mouse studies

Purpose Radiation therapy (RT) is a common nonsurgical treatment in the management of patients with cancer. While genetically engineered mouse models (GEMM) recapitulate human disease, conventional linear particle accelerator systems are not suited for state-of-the-art, imageguided targeted RT (IGRT) of these murine tumors. We employed the CyberKnife (CK; Accuray) platform for IGRT of GEMM-derived non-small cell lung cancer (NSCLC) lesions. Material and methods GEMM-derived KrasLSL-G12D/+/Trp53fl/fl -driven NSCLC flank tumors were irradiated using the CK RT platform. We applied IGRT of 2, 4, 6, and 8 Gy using field sizes of 5–12.5 mm to average gross tumor volumes (GTV) of 0.9 cm3 using Xsight Spine Tracking (Accuray). Results We found that 0 mm planning target volume (PTV) margin is sufficient for IGRT of murine tumors using the CK. We observed that higher RT doses (6–8 Gy) decreased absolute cell numbers of tumor infiltrating leukocytes (TIL) by approximately half compared to low doses (2–4 Gy) within 1 h, but even with low dose RT (2 Gy) TIL were found to be reduced after 8–24 h. Conclusion We here demonstrate that the CK RT system allows for targeted IGRT of murine tumors with high precision and constitutes a novel promising platform for translational mouse RT studies.

Electromagnetic effects of equatorially misaligned RF cavities

One of the most challenging problems in modern particle accelerator systems is the manufacture of RF cavities within the desired tolerance limits. In this study experimental and computational investigations to quantify the effects of transversal half-cell misalignments on the fundamental accelerator cavity parameters and beam dynamics are presented. Equivalent circuit components of an equatorially misaligned single-cell aluminum elliptical cavity are obtained from the measured data and are employed to calculate longitudinal impedance and modal wake function. Critical coupling and bead-pull measurements are performed at the TM010-like mode frequency, 2.45 GHz for the quality factor and shunt impedance of the high-β cavity. We report equivalent circuit analysis for higher-order modes and variations of the equivalent circuit components with respect to considered misalignment errors for the MICE experiment's muon cooling cavity. It is shown that using the equivalent circuit model decreases the computational load significantly for the wake field simulations of resonator cavities. Good agreement between simulations and measurements in terms of accelerating cavity parameters and impedances is illustrated.

Isotope production in thunderstorms

Thunderstorms and lightnings are natural particle accelerator systems. Terrestrial gamma-ray flashes, caused by relativistic runaway electron avalanches, produce bursts of X and γ rays, energetic enough to produce photo-nuclear reactions within the atmosphere. Such reactions cause the generation of new isotopes, which modify the air composition locally and produce new ways of detecting and characterizing this high-energy phenomena. In this work we explore, using the general purpose Monte Carlo transport code FLUKA, the production of secondaries after a Terrestrial gamma-ray flash and analyze the generation of new isotopes in detail. Their abundance, time and energy profiles are studied, which can be useful for establishing new measuring strategies.

High-voltage transformer

An original electric transformer was developed. The transformer generates a high AC voltage from a low-voltage AC. The input AC voltage generates an axial vibration in the electrodynamic actuator. The axial vibration is transmitted to piezoelectric crystals which are polarized in the axial direction and generates the output voltage. The transformer works at an axial mechanical resonance frequency of the system. Equations that describe the behaviour of the device were found. These equations were validated with measured data. The transformation ratio was obtained from these. Very high transformation ratio can reach this device, indicating the theoretical model. The proposed system is easy to build of reduced dimensions and low cost. Due to the high energy density of piezoelectric materials, high transformation ratio, the high electromechanical coupling factors and the high-quality factor of the mechanical resonance (low damping), it is lighter and more efficient than wire-wound transformers for high transformation ratio. This transformer could be used in devices, such as X‐ray machines, electron microscope, solid-state propulsion system, Ion thruster, small particle accelerator and accelerator-driven systems.

Machine learning for orders of magnitude speedup in multiobjective optimization of particle accelerator systems

High-fidelity physics simulations are powerful tools in the design and optimization of charged particle accelerators. However, the computational burden of these simulations often limits their use in practice for design optimization and experiment planning. It also precludes their use as online models tied directly to accelerator operation. We introduce an approach based on machine learning to create nonlinear, fast-executing surrogate models that are informed by a sparse sampling of the physics simulation. The models are 10^6 to 10^7 times more efficient to execute.We also demonstrate that these models can be reliably used with multi-objective optimization to obtain orders-of-magnitude speedup in initial design studies and experiment planning. For example, we required 132 times fewer simulation evaluations to obtain an equivalent solution for our main test case, and initial studies suggest that between 330 to 550 times fewer simulation evaluations are needed when using an iterative retraining process. Our approach enables new ways for high-fidelity particle accelerator simulations to be used, at comparatively little computational cost.

Cyberknife as a novel platform for targeted mouse tumor radiation studies

Cancer remains to be a leading cause of death worldwide, accounting for almost 10 million deaths in 2018. Radiation therapy (RT) is a common nonsurgical treatment in the management of patients with cancer that reduces disease recurrence and improves overall survival. However, preclinical RT modeling for accelerated bench‐to‐bedside transition of combination therapies is largely missing. While genetically engineered orthotopic murine tumor models can mimic human disease, conventional linear particle accelerator systems are not suited for targeted radiation of orthotopic tumors in mice. Although select institutions provide specialized mouse radiation systems overcoming these obstacles, most researchers are forced to use transplantable flank xenograft tumor models for targeted RT. We here report image‐guided, targeted radiation to mouse tumors using the Cyberknife (Accuray) radiation platform. The Cyberknife is a stereotactic radiosurgery system that utilizes real‐time image‐guidance to deliver high doses of radiation specifically to the tumor with minimal damage to the surrounding tissues using circular collimators as small as 5 mm. We applied targeted radiation of 2, 4, 6, and 8 Gy using field sizes of 7.5 to 12.5 mm to average gross tumor volumes (GTV) of volumes 0.87 cm3 (minimal 0.19 cm3) using Xsight (Accuray) spine‐based tumor localization. Treatment time lasted between 14 min (2 Gy), and 31 min (8 Gy), averaging at 20 min across all used doses. Doses were prescribed to 70% isodose, leading to a mean relative GTV dose of 92.1% (SD 1.6%), with a minimum dose of 80.3% (SD 3.8%). Coverage (volume of tumor that receive the prescription dose) was 99.4% (SD 0.8%) with a conformity (ratio of total tissue volume that receives the prescription isodose or more to tumor volume that receives the prescription isodose or more) of 1.10 (SD 0.03). To optimize the planning target volume (PTV), we examined 0, 1, 2, and 3 mm PTVs and analyzed the tumor tissue by immunohistochemistry staining of y‐H2AX. We found that 1 mm PTV is sufficient for target radiation of mouse tumors using the Cyberknife. Furthermore, we analyzed the impact of radiation on tumor infiltrating lymphocytes in a model of non‐small cell lung cancer (mutated for Kras and Trp35) by flow cytometry. We observed that higher radiation doses (6–8 Gy) decreased absolute cell numbers of lymphocytes and myeloid cells by approximately half compared to low doses (2–4 Gy) or non‐radiated. In summary, we here demonstrate that the Cyberknife system allows image‐guided targeted radiation of murine tumors with high precision and thus constitutes a novel promising platform for mouse radiation studies, and especially combination treatment studies.Support or Funding InformationThis study was supported by the DFG (HE 6810/3‐1 to J.M.H., HE 6897/2‐1 to G.H.S.) and the CMMC (CAP‐13 to J.M.H. and CAP‐16 to G.H.S. as well as B02 to G.H.S. and J.M.H.).

Innovative 20-MeV Superconducting Cyclotron for Medical Applications

The report contains a description of the conceptual design of a compact superconducting cyclotron, which can produce 20-MeV proton beam for isotopes production. The goal of the present project is to develop a machine that can be cost-effective, of small size and reliable in comparison with other particle accelerator systems aimed for producing proton beam of similar energy. Superconductivity is now a well established technology. Its application permits high magnetic field of the ultra-compact cyclotron that after careful system modeling and optimization can produce sufficiently good final beam parameters. The main parameters of the cyclotron, its design, and major stages of the development work are described in the report.

Propagation of modulated electron and X-ray beams through matter and interactions with radio-frequency structures

The generation and evolution of modulated particle beams and their interactions with resonant radiofrequency (RF) structures are of fundamental interest for both particle accelerator and vacuum electronic systems. When the constraint of propagation in a vacuum is removed, the evolution of such beams can be greatly affected by interactions with matter including scattering, absorption, generation of atmospheric plasma, and the production of multiple generations of secondary particles. Here, we study the propagation of 21 MeV and 25 MeV electron beams produced in S-band and L-band linear accelerators, and their interaction with resonant RF structures, under a number of combinations of geometry, including transmission through both air and metal. Both resonant and nonresonant interactions were observed, with the resonant interactions indicating that the RF modulation on the electron beam is at least partially preserved as the beam propagates through air and metal. When significant thicknesses of metal are placed upstream of a resonant structure, preventing any primary beam electrons from reaching the structure, RF signals could still be induced in the structures. This indicated that the RF modulation present on the electron beam was also impressed onto the x-rays generated when the primary electrons were stopped in the metal, and that this RF modulation was also present on the secondary electrons generated when the x-rays struck the resonant structures. The nature of these interactions and their sensitivities to changes in system configurations will be discussed.

Maintenance budget estimation for a particle accelerator system under its contextual conditions: a case study

Precise estimation of annual maintenance budget (AMB) drives appropriate maintenance actions. There appears to be a dearth of historical data to evaluate the AMB for a particle accelerator system as these are not many. This paper presents a case study on estimating the AMB of such a system for its contextual conditions using relational matrix of the budget variables. The diagonal elements of the matrix represent the variables while the off-diagonal elements signify the degree of influence among these. The maintenance budget function is evaluated from this matrix and is used to evaluate the AMB for the Pelletron system as a percentage of its asset replacement value. The actual maintenance expenditure on the Pelletron system was found to be within 2.07% of the estimated AMB. The approach is expected to aid the maintenance managers of similar systems, which operate under contextual conditions unique to their laboratory.

Recent developments and upgrades in ion source technology and ion beam systems at HVE

In this paper we discuss various ion sources used in particle accelerator systems dedicated to ion beam analysis techniques. Key performance and characteristics of some ion sources are discussed: emittance, brightness, gas consumption, sample consumption efficiency, lifetime, etc. For negative ion sources, we focus on the performance of volume H− ion sources (e.g. HVE model 358), the duoplasmatron negative ion source and the magnetically filtered multicusp volume sources (e.g. HVE model SO-120). The duoplasmatron ion source has been recently upgraded with a Ta filament to deliver up to 150μA H− ion beams and in conjunction with the Na charge exchange canal up to 20μA of He−. The available brightness from the duoplasmatron increased from 2 to 6Am−2rad−2eV−1. The ion source has been incorporated in a stand-alone light ion injector, well suited to deliver 20–30keV negative ion beams of H−, He−, C−, NHx− and O− to accelerate for most ion beam analysis techniques.

Circularly polarized carrier-envelope-phase stable attosecond pulse generation based on coherent undulator radiation.

In this Letter, we present a new method for generation of circularly polarized attosecond pulses. According to our calculations, shape-controlled, carrier-envelope-phase stable pulses of several hundred nanojoule energy could be produced by exploitation of the coherent undulator radiation of an electron bunch. Our calculations are based on an existing particle accelerator system (FLASH II in DESY, Germany). We investigated the energy dependence of the attosecond pulses on the energy of electrons and the parameters of the radiator undulator, which generate the electromagnetic radiation.

Tumor response parameters for head and neck cancer derived from tumor‐volume variation during radiation therapy

The main goal of this paper is to reconstruct a distribution of cell survival fractions from tumor-volume variation for a heterogeneous group of head and neck cancer patients and compare this distribution to the data from predictive assays. To characterize the tumor-volume variation during radiation therapy treatment, the authors use a two-level tumor-volume model of cell population that separates the entire tumor cell population into two subpopulations of viable cells and lethally damaged cells. This parameterized radiobiological model is integrated with a least squares objective function and a simulated annealing optimization algorithm to describe time-dependent tumor-volume variation rates in individual patients. Several constraints have been used in the optimization problem because tumor-volume variation during radiotherapy is described by a sum of exponentials; therefore, the problem of accurately fitting a model to measured data is ill-posed. The model was applied to measured tumor-volume variation curves from a clinical study on tumor-volume variation during radiotherapy for 14 head and neck cancer patients in which an integrated CT/linear particle accelerator (LINAC) system was used for tumor-volume measurements. The two-level cell population tumor-volume modeling is capable of describing tumor-volume variation throughout the entire treatment for 11 of the 14 patients. For three patients, the tumor-volume variation was described only during the initial part of treatment, a fact that may be related to the neglected hypoxia in the two-level approximation. The predicted probability density distribution for the survival fractions agrees with the data obtained using in vitro studies with predictive assays. The mean value 0.35 of survival fraction obtained in this study is larger than the value 0.32 from in vitro studies, which could be expected because of greater repair in vivo. The mean half-life obtained in this study for the head-and-neck squamous cell carcinoma (SCC) is equal to 3.8 mean potential doubling times, which agrees with 4.0 mean potential doubling times obtained previously for lung SCC. The distribution of cell survival fractions obtained in this study support the hypothesis that the tumor-volume variation during radiotherapy treatment for head and neck cancer can be described by the two-level cell population tumor-volume model. This model can be used for in vivo evaluation of patient-specific radiobiological parameters that are needed for tumor-control probability evaluation.

Beam dynamics simulation during final bunching and transport for heavy ion inertial fusion

In a particle accelerator system for heavy ion inertial fusion, space-charge-dominated beam dynamics is investigated during a final beam bunching. While the space charge effect undertakes an important role for the beam dynamics in the regime, the beam instability induced by space charge oscillation may occur, depending on the particle distribution of the beam. Particle simulations present that the instability due to the strong space charge effect may not be serious for realistic particle distributions during the final beam bunching.