Electrostatic Accelerator Research Articles

Strategy for Vacuum Insulation Tests of MITICA 1 MV Electrostatic Accelerator

The electrical insulation of the Megavolt ITER Injector and Concept Advancement (MITICA) beam source (BS) at 1 MV in vacuum is a challenging issue, which could not be fully addressed so far on the basis of experimental results and of theoretical models available in literature. A specific high-voltage (HV) test campaign is being prepared to validate and optimize the voltage holding capability of the BS insulation under realistic conditions, using full-size mockup electrodes reproducing in detail the geometry of the BS and accelerator. The proposed test strategy will address both the single-gap and the multistage insulation, so as to obtain a verification of voltage holding at 1 MV before the installation of the real components. This approach is intended to reduce the risk related to the HV insulation at 1 MV and, if necessary, to allow the development of effective corrections. In this article, the test motivations and requirements are defined, and the electrode implementation and diagnostic setup are described. Finally, the test configurations and the experimental procedure are discussed.

Optimal design of high-voltage DC power supply of 1.2 MV/45 mA applied to boron neutron capture therapy system.

To build a proton beam accelerator that can be applied to a boron neutron capture therapy system based on an electrostatic accelerator, a high-voltage direct-current (DC) power supply system equivalent to the generation of neutrons should be provided. The symmetrical Cockcroft-Walton voltage multiplier method is suitable for stable acceleration of the proton beam in the tandem electrostatic accelerator in this system. Before the second step-up with the Cockcroft-Walton circuit, the design of the inverter is prioritized by preponderantly considering the first voltage and resonance frequency. Moreover, the optimized stacking number is determined with consideration of the ripple voltage, voltage drop, average output voltage, and fundamental harmonics, and a design is performed to set related parameter values to be stable in the flat-top region of the voltage. A high-voltage DC power supply system of 1.2 MV/45 mA is needed for a stable terminal energy of 2.4 MeV/20 mA. Such a design can be optimized by securing reliable data using a simulation tool on the basis of theoretical calculations. This will become a formidable touchstone in manufacturing technology based on acquiring practical know-how for setting up a tandem electrostatic accelerator-based boron neutron capture therapy system in the future.

Development of Beam Optics Code LEADS-v5

To calculate nonlinear transport of space charge dominated beam in 6D phase spaces, a computer code package LEADS-v5 (Linear and Electrostatic Accelerator Dynamics Simulations) has been developed. The codes calculate particle motions in the beam transport systems consisting of electrostatic and magnetic focusing lenses, ion analyzers, multipoles and RF accelerating structures. The nonlinear forces of external electric/magnetic fields are analyzed by the Lie algebraic method, and the space charge forces are obtained by the particle in cell (PIC) scheme. In the codes, Uniform and Gaussian particle distributions can be chosen to generate randomly the particle initial coordinates. The optimization procedures are provided to make the beam optics designs reasonable and fast. Graphically displays of calculated results are provided.

Electrostatic–magnetic hybrid ion acceleration for high-thrust-density operation

To achieve high-thrust-density operation, we propose electrostatic–magnetic hybrid ion acceleration in which the empirical thrust density limit of the electrostatic acceleration is surpassed without violent plasma oscillation by combing the collisional momentum transfer mechanism, which is the ion acceleration mechanism of the electromagnetic acceleration. To achieve hybrid ion acceleration, we experimentally obtained two design criteria: one near anode propellant injection and another at the on-axis hollow cathode location. The thrust characteristics of three thrusters composed of a slowly diverging magnetic field between an on-axis hollow cathode and a coaxially set ring anode were examined. By injecting xenon propellant along the anode inner surface, the electron impact ionization process was enhanced, and generated ions are electrostatically accelerated through the radial-inward potential gradient perpendicular to the axial magnetic lines of force. The hybrid ion acceleration characteristics were obtained only if these two criteria were satisfied and the obtained thrust was consistent with the thrust formula derived for steady-state, quasi-neutral plasma flows. In addition to the criteria, strengthening the magnetic field and enhancing the propellant mass flux were effective for improving thrust density without deteriorating thrust efficiency. Among the experimental conditions in this study, the maximum thrust density was 70 N/m2 with an anode specific impulse of 1200 s, which cannot be achieved in a purely electrostatic thruster with thrust density 6.3 times than that of a typical Hall thruster.

High-performance alpha-voltaic cell based on a 4H-SiC PIN junction diode

Alpha-voltaic cells have great potential in military, biomedical, and infrastructure applications due to their characteristics of long operating life, small volume, and superior adaptability. However, improvements in power conversion efficiency (PCE), and the balance between power density and stability have been a challenge owing to the ‘poor-matching’ between energy conversion transducers and alpha-emitting isotope sources, as well as the radiation damage to semiconductor devices. In this study, we report the electrical properties of a high-performance alpha-voltaic cell based on a 4H-SiC PIN junction diode energy conversion transducer (active area of 1 cm2) that has been experimentally validated by a He ions electrostatic accelerator. Remarkably, the alpha-voltaic cell displayed an excellent PCE of 0.88%, exhibiting a nearly 7-fold enhancement compared to alpha-voltaic cells of previous studies, with a strikingly high open-circuit voltage of 1.99 V, a short-circuit current of 13.64 nA/cm2, and a maximum output power density of 16.78 nW/cm2.

In-orbit demonstration of an iodine electric propulsion system

Propulsion is a critical subsystem of many spacecraft1–4. For efficient propellant usage, electric propulsion systems based on the electrostatic acceleration of ions formed during electron impact ionization of a gas are particularly attractive5,6. At present, xenon is used almost exclusively as an ionizable propellant for space propulsion2–5. However, xenon is rare, it must be stored under high pressure and commercial production is expensive7–9. Here we demonstrate a propulsion system that uses iodine propellant and we present in-orbit results of this new technology. Diatomic iodine is stored as a solid and sublimated at low temperatures. A plasma is then produced with a radio-frequency inductive antenna, and we show that the ionization efficiency is enhanced compared with xenon. Both atomic and molecular iodine ions are accelerated by high-voltage grids to generate thrust, and a highly collimated beam can be produced with substantial iodine dissociation. The propulsion system has been successfully operated in space onboard a small satellite with manoeuvres confirmed using satellite tracking data. We anticipate that these results will accelerate the adoption of alternative propellants within the space industry and demonstrate the potential of iodine for a wide range of space missions. For example, iodine enables substantial system miniaturization and simplification, which provides small satellites and satellite constellations with new capabilities for deployment, collision avoidance, end-of-life disposal and space exploration10–14.

Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions

Abstract The solar wind escapes from the solar corona and is accelerated, over a short distance, to its terminal velocity. The energy balance associated with this acceleration remains poorly understood. To quantify the global electrostatic contribution to the solar wind dynamics, we empirically estimate the ambipolar electric field (E ∥) and potential (Φr,∞). We analyze electron velocity distribution functions (VDFs) measured in the near-Sun solar wind between 20.3 R S and 85.3 R S by the Parker Solar Probe. We test the predictions of two different solar wind models. Close to the Sun, the VDFs exhibit a suprathermal electron deficit in the sunward, magnetic-field-aligned part of phase space. We argue that the sunward deficit is a remnant of the electron cutoff predicted by collisionless exospheric models. This cutoff energy is directly linked to Φr,∞. Competing effects of E ∥ and Coulomb collisions in the solar wind are addressed by the Steady Electron Runaway Model (SERM). In this model, electron phase space is separated into collisionally overdamped and underdamped regions. We assume that this boundary velocity at small pitch angles coincides with the strahl break-point energy, which allows us to calculate E ∥. The obtained Φr,∞ and E ∥ agree well with theoretical expectations. They decrease with radial distance as power-law functions with indices α Φ = −0.66 and α E = −1.69. We finally estimate the velocity gained by protons from electrostatic acceleration, which equals 77% calculated from the exospheric models, and 44% from the SERM model.

Measurement of proton induced γ-ray emission cross sections on Cu for Ep < 3 MeV

Standardless PIGE analysis requires precise differential cross section values. In this research differential cross section data for proton-induced gamma-ray emission for 63Cu and 65Cu in the energy range 2000–3000 keV at 90◦ in the laboratory frame was measured. The research was carried out using the proton beam of the 3 MV Van de Graaff electrostatic accelerator of Nuclear Science and Technology Research Institute (NSTRI) in Tehran. The validity of present data was confirmed through thick target yield benchmarking procedure. The estimated systematic uncertainty is less than 9%.

Beam Scanning Controller for Proton-Beam Writing

A scanning control system of the ion beam of MeV energies has been developed for the nuclear scanning microprobe and proton-beam writing channel as a part of accelerator-analytical complex based on the Sokol electrostatic accelerator of the Institute of Applied Physics of the National Academy of Sciences of Ukraine. The system was put into operation to replace the obsolete one based on microcontrollers. The scanning control system is based on a National Instruments reconfigurable module with a Field Programmable Gate Array. The module operates in real time and is connected to a personal computer by a high-speed PCI-Express interface with data buffering. The system provides two main modes of operation: exposure of sample areas with a given profile and raster secondary electrons imaging of the sample or a calibration grid. Profile exposure is possible both in raster and functional scanning modes. Automatic calibration of the profile scale and scan raster is also implemented. Using of reconfigurable logic makes it possible to quickly adjust the system to the conditions of a particular experiment and the available equipment. The hardware capabilities of the scanning control system allows in the future to connect up to 4 spectrometric ADC for mapping the elemental composition of samples using Proton Induced X-ray Emission and Proton Backscattering. The first experiments on the irradiation of polymethylmethacrylate have been carried out; images of the obtained microstructures taken with a scanning electron microscope are shown. The aim of this work is to develop a control system for scanning a high-energy focused beam in proton beam writing technique to create small-sized structures for special purposes, as well as to demonstrate the efficiency of the developed system.

Design and simulation of a 500 kV acceleration tube for ‎Dynamitron accelerators

Due to their high efficiency and low ‎cost, electrostatic electron accelerators with a moderate energy, are used in the industry. In an electrostatic accelerator, the acceleration tube plays the role of dividing ‎the potential of the high-voltage terminal so that it accelerates the beam incrementally in a straight line. In this ‎paper, an acceleration tube for a Dynamitron accelerator with a voltage of 500 kV is designed by CST Studio ‎Suite software. In this design, an electron gun with flat cathode, and a current of 50 mA was used. In order to ‎extract the beam from the electron gun, two filters are used: electrodes and the lens electrode, with voltages of 495 and ‎‎481 kV, respectively; besides for electron acceleration, 13 electrodes with a potential step of 37 kV have been ‎designed. To hold the electrodes and prevent electrical discharges between the electrodes, insulating ‎sheets made of Pyrex are used. At the end of the acceleration tube, a 50mA beam current, a waist radius of less than 0.5 ‎mm, a 73nm radian emittance, and a 0.15μperv beam were obtained. The dimensions of the acceleration tube ‎and the results of investigating the change in the radius of the electrodes, the displacement and deviation of ‎the angles of the first electrode relative to the axis of the acceleration tube are presented in this paper‎.‎

Effect of structure and orientation of incident carbon-cluster ions Cn+(n≤4) on secondary-ion emission induced by electronic excitation

We present experimental results that show the secondary-ion yield depends on the structure and orientation of incident cluster ions. A beam of carbon-cluster ions ${{\mathrm{C}}_{n}}^{+}$ ($n\ensuremath{\le}4$) with an energy of 0.9 MeV per atom, which were obtained from a tandem electrostatic accelerator, was incident on a glycine target deposited on a carbon foil. The structure and orientation of the cluster ions after passing through the target were determined by the Coulomb explosion imaging method, and the positive secondary ions were simultaneously measured by time-of-flight mass spectrometry. When looking at the orientation dependence of linear structured ${{\mathrm{C}}_{2}}^{+}, {{\mathrm{C}}_{3}}^{+}$, and ${{\mathrm{C}}_{4}}^{+}$ projectiles, parallel orientations with respect to the beam direction were found to enhance the secondary-ion yield compared with perpendicular orientations. Additionally, comparison of the structure dependence of ${{\mathrm{C}}_{3}}^{+}$ and ${{\mathrm{C}}_{4}}^{+}$ projectiles with linear and ring structures showed that the secondary-ion yield was larger for linear structures. Interestingly, there was a clear correlation between the secondary-ion yield and the deposited energy density in the cluster-ion track. The energy density was calculated with electronic stopping power for incident cluster ions using linear-response dielectric theory and the cross section of the track of the incident cluster considering its geometrical structure and orientation. These results suggest that the deposited energy density in the cluster-ion track is a key parameter in the secondary-ion emission process induced by swift cluster-ion impacts.

Earth-bound millicharge relics

Dark sector particles with small electric charge, or millicharge, (mCPs) may lead to a variety of diverse phenomena in particle physics, astrophysics, and cosmology. Assuming their possible existence, we investigate the accumulation and propagation of mCPs in matter, specifically inside the Earth. Even small values of millicharge lead to sizeable scattering cross sections on atoms, resulting in complete thermalization, and as a consequence, considerable build-up of number densities of mCPs, especially for the values of masses of GeV and higher when the evaporation becomes inhibited. Enhancement of mCP densities compared to their galactic abundance, that can be as big as ${10}^{14}$, leads to the possibility of new experimental probes for this model. The annihilation of pairs of mCPs will result in new signatures for the large volume detectors (such as Super-Kamiokande). Formation of bound states of negatively charged mCPs with nuclei can be observed by direct dark matter detection experiments. A unique probe of mCP can be developed using underground electrostatic accelerators that can directly accelerate mCPs above the experimental thresholds of direct dark matter detection experiments.

Differential cross section measurement of the 107Ag (p,p′γ)107Ag and 109Ag(p,p′γ)109Ag for PIGE analysis

Differential cross sections for gamma-ray emission from the 107Ag (p, p′γ3-0)107Ag and 109Ag (p, p′γ3-0)109Ag reactions in the proton energy range 1200–2700 keV were measured at 90⁰ in the laboratory frame. In addition, differential cross sections for gamma-ray emission from the 107Ag(p, p′γ4-0)107Ag and 109Ag(p,p′γ4-0)109Ag reactions in the proton energy range 1310–2700 keV and 1330–2700 keV in the mentioned condition. The measurements were performed using the proton beam of the 3 MV Van de Graaff electrostatic accelerator of Nuclear Science and Technology Research Institute (NSTRI) in Tehran. Besides, the validity of the measured differential cross sections was verified through comparison between calculated thick target yields deduced from present work excitation curve and experimental thick target yield data available from literature. The overall systematic uncertainty of the measured values was estimated to be less than 8%.

Negative hydrogen ion dynamics inside the plasma volume of a linear device: Estimates from particle-in-cell calculations

Negative hydrogen or deuterium ions are the precursor particles used to generate a high power beam of neutrals in order to heat the tokamak plasma core of magnetic fusion devices, inject current, and to some extent control instabilities. In the case of ITER, for instance, the negative ions are produced inside a high power large volume low-pressure tandem type magnetized ion source and extracted toward an electrostatic accelerator which accelerates them to 1 MeV before entering a neutralizer converting the ions into a neutral beam. This so-called neutral beam injector relies on the production of negative ions on the surface facing the plasma of the ion source extraction electrode. The latter is covered by a cesium layer in order to increase the negative ion yield. The use of cesium is currently an issue as it may diffuse outside of the source and induce secondary particle production or voltage breakdowns inside the accelerator vessel requiring a regular maintenance in a nuclear environment. In this work, we analyze numerically with a 2.5D particle-in-cell model the production rate and transport of negative ions in a linear device used as an ion source. The negative ions are generated via a dissociative attachment process with a hydrogen molecule in the volume of a magnetized cesium-free plasma. The linear device in the model has a large aspect ratio with a radius of 5 and a length of 100 cm and the magnetic field strength ranges from 100 to 400 G. We show that the shape and depth of the plasma potential profile may be controlled by biasing the end-plates which in turn strongly influence the residence time of the electrons and hence the negative ion yield. We observe the formation of large-scale rotating structures when the positive ions become magnetized with a rotation velocity in the kHz range.

Bunching and chopping for tandem accelerators. Part I: Bunching

A pulsed system capable of delivering up to a few microamps with a mass range 1–100 u, and with pulse width of bursts of ions approximately 1–2 ns is described. Critical design limitations are discussed to show the overall approach to meet a number of experimental requirements. The system consists of a SNICS negative ion source, a low energy buncher which uses the entire tandem electrostatic accelerator as a drift path to produce bunched ion bursts at the targets or linac entry, and high energy choppers. The buncher consists of a single acceleration gap with aligned removable grids. A detailed analysis is presented of the factors limiting the system performance, with the aim to lessen their effect on the ultimate minimum longitudinal phase space of the ion burst.

Detection of Dust Particles Using Faraday Cup Instruments

Abstract Faraday cups can measure velocity distribution functions of space plasmas and are frequent instruments on heliophysics missions. A new version of a Faraday cup instrument is in development for the Luna 26 mission and will be used for fast monitoring of the solar wind plasma parameters. The prototype of this instrument is exposed to dust impacts in a velocity range of 0.2–60 km s−1 using an electrostatic dust accelerator. The collected data are used to evaluate the sensitivity and detection efficiency of dust particles on two different surfaces. The results indicate that the sensitivity is sufficient for detection of the interplanetary dust as well as for the registration of the dust lifted from the lunar surface. A simple modification of the FC electronics would increase the detection efficiency by an order of magnitude.

Neutron activation of Ga69 and Ga71 at kBT≈25keV

Background: About 50% of heavy elements are produced by the slow neutron capture process ($s$ process) in stars. The element gallium is mostly produced during the weak $s$ process in massive stars.Purpose: Our activation at ${k}_{\mathrm{B}}T\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}25$ keV is the first experiment in a series of activation and time-of-flight measurements on $^{69}\mathrm{Ga}$ and $^{71}\mathrm{Ga}$ relevant for astrophysics.Methods: We activated $^{69}\mathrm{Ga}$ and $^{71}\mathrm{Ga}$ with a neutron distribution that corresponds to a quasistellar distribution with ${k}_{\mathrm{B}}T=25\phantom{\rule{4pt}{0ex}}\mathrm{keV}$ at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction $^{7}\mathrm{Li}(\mathrm{p},\mathrm{n})$. The produced activity was measured via the $\ensuremath{\gamma}$ emission by the decaying product nuclei by high-purity germanium detectors.Results: We provide spectrum-averaged cross sections (SACS) and ratios of the cross sections ${\ensuremath{\sigma}}_{\text{Ga}}/{\ensuremath{\sigma}}_{\text{Au}}$ for the neutron spectrum of the activation. We obtain values of ${\ensuremath{\sigma}}_{69\mathrm{Ga},\mathrm{SACS}}=(186\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}12)\phantom{\rule{4pt}{0ex}}\mathrm{mb}$ and ${\ensuremath{\sigma}}_{71\mathrm{Ga},\mathrm{SACS}}=(112\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}7)\phantom{\rule{4pt}{0ex}}\mathrm{mb}$, and cross-section ratios of ${\ensuremath{\sigma}}_{\text{69Ga}}/{\ensuremath{\sigma}}_{\text{Au}}=0.29\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.02$ and ${\ensuremath{\sigma}}_{\text{71Ga}}/{\ensuremath{\sigma}}_{\text{Au}}=0.17\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.01$.Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for $^{69}\mathrm{Ga}$ and about 20% lower for $^{71}\mathrm{Ga}$.

Energy calibration of ion-beam accelerators with neutron and gamma nuclear reactions between 2 MeV and 4 MeV

The accurate knowledge of the beam energy is of first importance in most applications using ion beams delivered by electrostatic accelerators. Regular beam energy calibration is thus required. The standard procedure is to use neutron thresholds and well known gamma-ray resonances. However, only a few calibration points are available between 2 MeV and 4 MeV despite the need of such beam energies, for instance, for nuclear reaction analyses.In this work, the suitability of 27Al(p,γ)28Si and 45Sc(p,n)45Ti resonances has been studied in this specific energy range by comparison with well-established calibration energies. The methodology used for the experiments and data treatment is fully detailed.The usefulness of these resonances is shown through several calibration campaigns that led to a complete energy calibration of two accelerator based facilities from 500 keV up to 4 MeV.

Elemental characterization and risk assessment of indoor aerosols in an electrostatic particle accelerator laboratory

ABSTRACT Aerosol samples (PM10 and PM2.5) were collected during the 2018-2019 dry-cold season, inside an electrostatic particle accelerator laboratory at Instituto de Física, Universidad Nacional Autónoma de México, and on the rooftop. The goal was to measure gravimetric mass and elemental concentrations, to identify emitting sources, and to assess risks to human health due to inhalation, ingestion and dermal deposition, through Hazard Quotients. Concentrations of Mg, Al, Si, P, S, Cl, K, Ca, V, Mn, Fe, Ni, Cu, and Zn were measured with X-ray Fluorescence. Mass concentrations were lower indoors than outdoors. Elemental/gravimetric mass concentrations ratios showed that S, Ni, Cu, and Zn were more abundant in both indoors particle sizes, plus P in PM2.5. Possible sources, found through Cluster Analysis, were geogenic, SF6 subproducts, vacuum pump oil, and air conditioning, supported by Scanning Emission Microscopy and Electron Probe Microanalysis. Health risks due to enriched elements are not significant.

An explanation for 13 consecutive day activities of Mrk 421

It is surprising to find an instance of migration in the peak positions of synchrotron spectral energy distribution components during the activity epochs of Markarian 421 (Mrk 421), accompanying an orphan flare at the X-ray and GeV-TeV γ-ray bands. A geometric interpretation and standard shock or stochastic acceleration models of blazar emission have difficulty reproducing these observed behaviors. The present paper introduces a linear acceleration by integrating the reconnection electric field into the particle transport model for the observed behaviors of Mrk 421. We note that strong evidence for evolution in characteristic of multi-wavelength spectral energy distribution including shifting the peak frequency, accompanying an orphan flare at the X-ray and GeV-TeV γ-ray bands provides an important electrostatic acceleration diagnostic in a blazar jet. Assuming suitable model parameters, we apply the results of the simulation to the 13-day flaring event in March 2010 of Mrk 421, concentrating on the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency. It is clear that the ratio of the electric field and magnetic field strength plays an important role in temporal evolution of the peak frequency of synchrotron spectral energy distribution component. We suggest it is reasonable that the electrostatic acceleration is responsible for the evolution of multi-wavelength spectral energy distribution characteristic by shifting the peak frequency. Based on the model results, we assert that the peak frequency of the synchrotron spectral energy distribution component may signify a temporary characteristic of blazars, rather than a permanent one.