Electrostatic Accelerator Research Articles

AI-Based Electrode Optimisation for Small Satellite Ion Thrusters

Computing capacities for numerical modelling are available to an unprecedented extent today. The spread of various artificial intelligence (AI) -based solutions (which in many cases are also resource-intensive operations) is also facilitated by this increase in capacity, which offers several new opportunities in this area. On the one hand, optimization tasks can be done quickly, on the other hand, it is also possible to solve (estimate) problems where we cannot (for some reason) create a model for the initial problem. In our article, we investigate how to apply artificial intelligence-based solutions to electromagnetic field computing tasks as efficiently as possible. The required theoretical summary presents an implemented application: optimization of electrostatic ion engine accelerator electrodes for orbit correction operations. To solve each problem, we used methods from the supervised machine learning toolkit, usually along with LMS (least mean square method) update steps. All inputs required for AI were solved by numerical space calculation (primarily using the finite element method). The data input required to optimize the electrodes of an ion thruster can come from two sources: measurement data or simulation results. Given that the operating environment of a satellite can be modelled in a vacuum chamber, it is a particularly difficult issue to perform the measurement, but even more difficult in the case of optimisation. Therefore, an effective solution to the problem can only be achieved by simulation. The primary goal of this research is to optimise the fuel (in this case, the number of ions) during operation, with the stated aim of maximising the time of operation of the spacecraft.

AIFIRA: a light ion beam facility for ion beam analysis and irradiation

AIFIRA is a small-scale ion beam facility equipped with a single-stage electrostatic accelerator delivering bright beams of light ions (protons, deuterons and helium ions) in the MeV energy range. The facility provides ion beam irradiation, analysis, and imaging techniques to academic research groups and companies. These techniques cover a wide range of applications including materials research, life sciences, environment, geology and geochemistry, archeometry, and applied physics. About 200 days of beam time are allocated each year to internal and external users either coming from local, national, or international teams. AIFIRA is certified as a research platform by its two parent institutions: CNRS/IN2P3 and the university of Bordeaux. Therefore, beamtime allocation is opened to external teams that are accompanied by local experts to prepare, perform and analyze their experiments. This paper describes the facility and the developments performed in the last years. We highlight two original features of the facility: charge collection studies using a microbeam and the production of secondary neutron fields.

Hypervelocity impact flash expansion geometry under various spacecraft surface electrical conditions

A more congested space environment due to increasing space activities introduces new threats to spacecraft operators. Among these threats include hypervelocity impacts from microparticles (<1 µg) in the form of meteoroids and space debris. These microparticles travel at speeds between 11.2 and 72.8 km/s with respect to the Earth and can impact spacecraft forming a small (∼1 µm) and dense (∼1026 m−3) plasma. This plasma can generate a strong optical emission (impact flash) and a radio frequency (RF) emission. These emissions can lead to spacecraft electrical anomalies when the impacted spacecraft surface (target) carries high electrical potential due to various space weather effects.To understand the microparticle hypervelocity impact plasma and its associated threat to spacecraft electronics, we studied the hypervelocity impact flash expansion geometry under various spacecraft surface electrical conditions. Three high-speed broadband photomultiplier tubes (PMT) are used to capture the temporal evolution of the impact flash and the temporal evolution of the angular distribution of the impact flash expansion geometry in a 3 MV electrostatic dust accelerator during a ground-based experiment. Results indicate that the impact surface electrical condition has a statistically significant influence on the impact flash geometry, and a strong similarity between the impact plasma and flash expansion geometry. Thus, this paper provides new experimental support for the impact flash origin from and connection with the impact plasma, and serves as the first impact flash expansion geometry characterization under various impact surface electrical conditions in a collisionless environment (<10−5 Torr).

Experimental Transverse Beam Emittance Measurement Using Solenoid Magnet Strength Variation in AB-BNCT

Boron neutron capture therapy (BNCT) is a more efficient cancer treatment method compared to direct radiation therapy using charged particles such as protons or carbon beams. Particularly, accelerator-based BNCT (AB-BNCT) is attracting attention due to easy construction in a hospital. The Korea Institute of Radiological & Medical Sciences (KIRAMS) has constructed an injection system for an electrostatic AB-BNCT accelerator and commissioned 30 keV H− and 5 keV D− ion beam facilities. The beam characteristic parameters and Twiss parameters should be confirmed experimentally, and various methods have to be applied for the related measurements. In this study, the linear matrix formalism is used as a technique to measure the beam characteristic and Twiss parameters by varying the magnetic field strength of a solenoid in the beam line. To confirm the validity of this method, a multi-particle tracking code was executed. The simulation results confirm that the proposed method is effective for extracting Twiss parameters. After verification via the multi-particle tracking code, the method was applied to perform experimental measurements. Notably, the method accurately obtains the transverse beam emittance within reasonable uncertainty levels. Thus, our results show that the proposed method is a convenient technique for extracting the Twiss parameters indirectly. The results of the Twiss parameter measurement can potentially be more precise if other aspects, such as the quadrupole magnetic field strength, are incorporated.

Electrostatic shock acceleration of ions in near-critical-density plasma driven by a femtosecond petawatt laser

With the recent advances in ultrahigh intensity lasers, exotic astrophysical phenomena can be investigated in laboratory environments. Collisionless shock in a plasma, prevalent in astrophysical events, is produced when a strong electric or electromagnetic force induces a shock structure in a time scale shorter than the collision time of charged particles. A near-critical-density (NCD) plasma, generated with an intense femtosecond laser, can be utilized to excite a collisionless shock due to its efficient and rapid energy absorption. We present electrostatic shock acceleration (ESA) in experiments performed with a high-density helium gas jet, containing a small fraction of hydrogen, irradiated with a 30 fs, petawatt laser. The onset of ESA exhibited a strong dependence on plasma density, consistent with the result of particle-in-cell simulations on relativistic plasma dynamics. The mass-dependent ESA in the NCD plasma, confirmed by the preferential reflection of only protons with two times the shock velocity, opens a new possibility of selective acceleration of ions by electrostatic shock.

A time-dependent particle acceleration and emission model: understanding particle spectral evolution and blazar flares

ABSTRACT The jets of blazars are renowned for their multiwavelength flares and rapid extreme variability; however, there are still some important unanswered questions about the physical processes responsible for these spectral and temporal changes in emission properties. In this article, we develop a time-dependent particle evolution model for the time-varying emission spectrum of blazars. In the model, we introduce time-dependent electric and magnetic fields, which consistently include the variability of relevant physical quantities in the transport equation. The evolution of the electron distribution is solved numerically from a generalized transport equation that contains terms describing the electrostatic, first- and second-order Fermi acceleration, escape of particles due to both advection and spatial diffusion, and also energy losses due to synchrotron emission and inverse-Compton scattering of both synchrotron and external ambient photon fields. We find that the light-curve profiles of blazars are consistent with the particle spectral evolution resulting from time-dependent electric and magnetic fields, rather than the effects of acceleration or cooling processes. The proposed model is able to account simultaneously for the variability of both the energy spectrum and the light-curve profile of the BL Lac object Mrk 421, with reasonable assumptions about the physical parameters. The results indicate strongly that the magnetic field evolution in the dissipated region of a blazar jet can account for the variabilities.

Electrostatic ion acceleration in an inductive radio-frequency plasma thruster

Spatially and temporally resolved ion flow measurements are performed inside the plasma source of an inductive radio frequency plasma thruster. Using the resulting data, the pure effects of the inductive current drive on the ion flow are identified. The cross field ion acceleration and the establishment of the cross field electric field are found in the upstream region, where the azimuthal current is induced by the superimposition of a time-varying magnetic field. Analyzing the electron and ion dynamics with two-fluid equations, the magnetized electrons form the in-plane Hall electric field to satisfy the electron force balance, which results in the electrostatic acceleration of unmagnetized ions. The enhanced density gradient forms a stronger Boltzmann electric field along the magnetic field. It generates a supersonic ion group along the magnetic field line, which increases the field-aligned ion flow velocity and the momentum thrust.

Activation Measurements of the Integral Cross Sections of the 12C(d,X)13N, 14N(d,X)15O, 14N(d,X)13N, 14N(d,X)11C, and 16O(d,X)17F Reactions

Cross sections of the 12C(d,X)13N (β+, T1/2 = 9.965 min), 14N(d,X)15O (β+, T1/2 = 122 s), 14N(d,X)13N (β+, T1/2 = 9.965 min), 14N(d,X)11C (β+, T1/2 = 20.39 min), and 16O(d,X)17F (β+, T1/2 = 64.5 s) reactions are measured at the electrostatic tandem accelerator via activation method at deuteron energies of 1–12 MeV. (C5Н4О2) mylar films (5 ± 1%) μm thick and layers of atmospheric air of 2.1, 5.1, and 7.1 mm thick are used as targets.

Measurement of Møller scattering at 2.5 MeV

Moller scattering is one of the most fundamental processes in QED. Understanding it to high precision is necessary for a variety of modern nuclear and particle physics experiments. In a recent calculation, existing soft-photon radiative corrections were combined with new hard-photon bremsstrahlung calculations to take into account the effect of photon emission at any photon energy, where the electron mass was included at all steps. To test the calculation, an experiment was carried out using the 3 MV Van de Graaff electrostatic accelerator at the MIT High Voltage Research Laboratory. Momentum spectra at three scattering angles at an incident electron energy of 2.5 MeV are reported here, and compared to the simulated radiative Moller spectra, based on our previous calculation. Good agreement between the measurements and our calculation is observed in the momentum spectrum at the three angles.

Characterization of Southwestern Nigeria River Sand for foundry use

The greater number of castings produced globally are made by using sand casting techniques that utilize sand as major moulding material. This paper characterizes Isasa River sand based on its physical and chemical properties with the aid of Tandem pelletron electrostatic accelerator, trinocular microscope, mechanical sieve shaker, and box furnace, for Foundry application. Results obtained revealed that the River sand has moisture content of 4.30%, clay content of 2.22%, grain fineness number (GFN) of 49, Silica (SiO2) content of 93%, and sintering point of 1400oC. The River sand is a 4-screen sand, having angular grains with medium sphericity. Isasa River sand will be suitable for casting of gray iron and non-ferrous metals, with the addition of binding agent in suitable proportion.

Study of high DC voltage breakdown between stainless steel electrodes separated by long vacuum gaps

High voltage (HV) insulation across a single gap in vacuum and low-pressure gas is a critical issue in relation to the development and realization of the electrostatic accelerator for the ITER neutral beam injector (NBI) (Toigo et al 2017 New J. Phys. 19 085004). The present paper describes and analyzes the recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF), the laboratory aimed at supporting the development of the prototype for the ITER NBI (De Lorenzi et al 2011 Fusion Eng. Des. 86 742–5). A voltage up to 800kVDC was achieved in the HVPTF during the experimental campaigns with a sphere-plane configurations having variable gap length (from 30 to 150 mm) and pressure ranging from high vacuum (10–7 mbar) to 10–3 mbar in argon. Such an experimental campaign represents one of the few examples where voltages higher than 500–550 kV DC are sustained by a single vacuum gap between electrodes (Rohrbach 1971 CERN Report 71-5) and therefore constitutes additional experience to improve the knowledge of voltage holding across large vacuum gaps. The results in high vacuum indicate that at the beginning of voltage conditioning the breakdown events occur at the same cathodic electric field irrespective of the electrode geometry. However, after sufficient conditioning time, the breakdown voltage distribution seems to depend also on the electric field at the anode and on the total voltage between electrodes. A benchmark between a numerical tool previously developed to predict the voltage holding in high vacuum (voltage holding prediction model, VHPM (Pilan et al 2011 Fusion Eng. Des. 86 742–5)) and the experimental results is also reported and discussed.

Ionizing radiation in electronics from the Compton scattering of quasi-stationary particles generated by characteristic and Bremsstrahlung x rays

Characteristic x rays generated by a collision between a tungsten target and relativistic electron beams generated from a compact electrostatic accelerator based on a Marx generator and a Blumlein pulse-forming line can induce transient ionizing radiation in electronics. While the decelerated electron beam is close to a collector out of range of an external magnetic field, Bremsstrahlung x rays occur at the same time. Compton scattering also occurs through secondary reaction interactions with quasi-stationary particles such as ejected inner shell electrons or photons. During a simulation, a semiconductor process is used to analyze the effects and processes of photocurrents derived from the flow of the drain current when transient pulses generated from the compact electrostatic accelerator are incident in the pMOSFET-AD420-based detector. The photocurrent induced from the detector is also measured by experimental results in comparison with a computer simulation, and a photocurrent detection experiment was then conducted with a high-pulse-current compact electrostatic accelerator. In addition, data pertaining to the irradiation dose rate and photon emission rate were obtained. In order to confirm the radiation pattern in the situation of Compton scattering, the ionizing radiation effect in the photosensitive phosphor was identified using a fluorescent lamp. During the experiment, a relativistic electron beam operating at high energy and current levels at a maximum of 1MeV-10 kA was utilized.

Effect of Proton Irradiation on the Defect Evolution of Zr/Nb Nanoscale Multilayers

Nanoscale multilayer coatings (NMCs) with different crystal structures are considered as capable of self-healing after radiation damage due to the recombination of vacancies and interstitials. This work is focused on a defect distribution study of NMCs based on Zr/Nb layers (25/25 nm and 100/100 nm) after proton irradiation. Coatings with a total thickness of 1.05 ± 0.05 µm were irradiated by 900-keV protons using a pelletron-type electrostatic accelerator with an ion current of 2 µA for durations of 60 min to 120 min. The influence of the irradiation effect was studied by X-ray diffraction analysis (XRD), glow discharge optical emission spectrometry (GD–OES), and Doppler broadening spectroscopy using a variable energy positron beam. The results obtained by these methods are compatible and indicate that defect concentration of Zr/Nb NMCs remains unchanged or slightly decreases with increasing irradiation time.

Development of an MeV proton generator using a 3He ion source at the Research Center for Nuclear Physics.

For simple applications, such as the calibration of a charged particle detector, a multi-MeV proton generator may be preferable to cyclotrons or electrostatic accelerators such as Van de Graaff generator. Thus, a proton generating system, consisting of an 18 GHz superconducting (SC)-ECR ion source and a deuterated polyethylene target, was developed at the Research Center for Nuclear Physics at Osaka University. A 3He2+ beam of 400 eμA was generated by the SC-ECR ion source with the acceleration voltage of 20 kV in an experiment that utilized the fusion reaction 3He + deuteron (D) → proton(P) + 4He. Protons with energies of the order of several MeV were successfully generated at 3.67 Hz at the atmosphere side of the target in the experimental setup, using a novel target base with a thin aluminum window.

Experimental Demonstration of Hadron Beam Cooling Using Radio-Frequency Accelerated Electron Bunches.

Cooling of beams of gold ions using electron bunches accelerated with radio-frequency systems was recently experimentally demonstrated in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. Such an approach is new and opens the possibility of using this technique at higher energies than possible with electrostatic acceleration of electron beams. The challenges of this approach include generation of electron beams suitable for cooling, delivery of electron bunches of the required quality to the cooling sections without degradation of beam angular divergence and energy spread, achieving the required small angles between electron and ion trajectories in the cooling sections, precise velocity matching between the two beams, high-current operation of the electron accelerator, as well as several physics effects related to bunched-beam cooling. Here we report on the first demonstration of cooling hadron beams using this new approach.

Achievement of high power and long pulse negative ion beam acceleration for JT-60SA NBI.

Long pulse acceleration of hydrogen negative ion beams with the power density over 70 MW/m2 and the pulse length over 100 s has been demonstrated for the first time by using a multi-aperture 3-stage accelerator. Such long pulse acceleration was achieved by integrating the design of beam optics and voltage holding capability to meet the requirements of JT-60SA. By using the newly designed accelerator for JT-60SA, voltage holding at 500 kV with beam acceleration was stably sustained even after 5 g of cesium was seeded, and heat load on each acceleration grid was reduced below the allowable level for long pulse, less than 5% of total acceleration power. As a result, 500 keV, 154 A/m2 for 118 s beam acceleration was achieved, which satisfies the requirement of the negative ion source for JT-60SA. This pulse length of such high-power density beams is longest in the world. In addition, the result contributes to the long pulse acceleration of multi-stage electrostatic accelerators, such as 1 MeV negative ion accelerator for ITER.

High-Specific-Impulse Electrostatic Thruster with Argon Propellant

In this study, an electrostatic thruster was newly developed, in which a diverging magnetic field with a cusp around a cathode was applied by using two solenoid coils. The effects of the magnetic field strength on thrust performance under a similar applied-magnetic-field configuration were investigated. Because of its light weight and lower price, argon was used as a propellant. By increasing the magnetic field strength, the thrust efficiency was improved owing to the suppression of the discharge current while an almost constant thrust was maintained. A specific impulse of 3800 s with thrust efficiency greater than 30% was obtained; the corresponding mass-averaged exhaust velocity exceeded the value by full-potential electrostatic acceleration of singly charged ions. From the thrust performance, ion beam current, and ion energy distribution function that were experimentally measured under the representative operation condition, 32% of the ion beam current and 43% of the total thrust were evaluated as the contribution of doubly charged ions.

Design and Construction of an Imaging beamline at the Nagoya University Neutron Source

The Nagoya University Accelerator driven Neutron Source (NUANS) is constructed at the main campus of the Nagoya University. The electrostatic accelerator is used with the maximum proton energy and intensity of 2.8MeV, 15mA(42kW) respectively. Two neutron beamlines are designed at NUANS. The BL1 is dedicated to BNCT development. The BL2 is designed for research and development for neutron devices and neutron imaging. The neutrons used for the BL2 are generated by using the (p, n) reaction from a thin beryllium target. We constructed a compact target station for the BL2 and measured the neutron transmission image.

Autonomous Neutron Facility for Detecting Fissile Nuclear Materials

The prospect of creating an autonomous neutron facility for the detection of fissile nuclear materials in samples, including those in confined volume, is discussed. It is proposed to obtain a reference field of thermal neutrons on the basis of a polyethylene moderator ball and a portable fast neutrons source, developed at NRC “Accelerator” NSC KIPT based of a continuous electrostatic accelerator of deuterons. The developed source of thermal neutrons is planned to be used to activate small objects and goods in order to identify substances prohibited for movement containing to find 233U, 235U and 239Pu in their composition. The prompt finding of fissile elements will indicate about an attempt to transport them illegally. A more thorough inspection can be carried out using special equipment after the detention of suspicious goods, citizens or vehicles. The possibility of detecting prompt fission neutrons is considered not only in the traditional way using a polyethylene moderator and proportional 3He detector, but also without application of any moderator using oxide or semiconductor scintillators. For detection fissile materials the method based on using the high-energy part of the γ-spectrum of fission fragments (greater than 4900 keV), as well, as the approach applied in the passive non-destructive analysis by the γ-line with Eg = 185.7 keV from 235U, are substantiated. It is shown that the proposed facility for the detection of fissile nuclear materials is able to determine the presence of isotopes 233U, 235U and 239Pu in tested objects and goods with the using non-destructive testing method.

Measurement of a time dependent spatial beam profile of an RF-driven H- ion source.

The AC component of a beam current extracted from a negative hydrogen (H-) ion source was detected through a 0.1 mm wide, 66.5 mm long entrance slit to observe the spatial distribution. An internal antenna type multicusp source driven by a 2 MHz radio frequency (RF) power delivered beams to an electrostatic accelerator coupled to a pair of magnetic lenses. The local beam intensity measured by a Faraday cup after the entrance slit exhibited an oscillation showing two main frequency components: the RF power supply frequency and the frequency two times the driving RF. The frequency spectrum of the detected signal showed sharp peaks at 2 MHz, 4 MHz, and 6 MHz as well as at 3 MHz and 5 MHz. A 1 mm displacement of the Faraday cup slit position from the center of the beam axis increased the oscillation amplitude, corresponding to a larger amplitude of the AC component at the beam edge.