Ion Beam Transport Research Articles

Electric field driven focusing and transport of plasma ion beams by micro-glass capillaries beyond the self-focusing limit

Micro-glass capillaries emerge as an important tool for the lossless guiding and focusing of ion beams (Kojima 2018 J. Phys. B: At. Mol. Opt. Phys. 51 042001). The self-focusing mechanism of the capillaries is primarily governed by charged patches induced on their inner walls by the incident beam (Stolterfoht et al 2002 Phys. Rev. Lett. 88 133201). However, the dominance of space charge forces over self-focusing forces in intense (J ≈ 1 A m−2) ion beams establishes a self-focusing limit (Maurya et al 2019 J. Phys. D: Appl. Phys. 52 055205), posing challenges to beam focusing beyond this limit. In this work, a novel method is introduced, demonstrating electrical control over the charge patch dynamics through an externally applied bias voltage, thereby enabling the focusing of Ar ion beams beyond the self-focusing limit. Experimental results reveal that adjusting the biasing voltage allows overcoming the self-focusing limit, resulting in the generation of a high-intensity ( Jout≈3.05×105 A m−2) nano-beam (∼160 nm). Furthermore, electrical control is shown to enhance the performance of both straight and tapered capillaries (SC/TC), with the TC being more effective for nano-beam generation. A Particle-In-Cell (PIC) simulation code has been developed to explain the experimental results. The implications of high-intensity nano ion beams in advancing nanopatterning, nanoscale material analysis, and matter wave interferometry, underscore significant contributions to research and innovation within electronics, materials science, nanotechnology, and emerging quantum technologies.

Numerical analysis of fast ions transport induced by magnetic islands in HL-2A

The transport of beam ions in the presence of single/multiple tearing modes (TMs) under HL-2A geometry has been investigated by test particle method. Simulation results show that there exists a threshold behavior in the number of lost beam ions in the plasma under perturbation of a (2,1) TM with amplitude α0 : when the amplitude α0 is over a critical value, the number of lost beam ions increases linearly with α0 at a much faster pace. Further analysis finds that the lost beam ions have relatively higher percentage of high energy at α0 around the critical value. It also finds that the distribution of lost beam ions which is initially concentrated on the high field side expands gradually toward the low field side as the perturbation amplitude α0 increases. From the phase space analysis, it shows that the enhanced outward transport of fast ions in the presence of magnetic islands results from orbit stochasticity, which is due to the overlap of the drift islands in the interaction of fast ions with TMs. When two TMs are simultaneously present, the stochastic threshold of fast ion orbit is found to be lower than that in their individual TM case. The phase space analysis shows that in the presence of two modes with the same toroidal mode number, the modes increase the loss of fast ions when they are out of phase; however, such the effect of strengthening transport of fast ions turns to weaken when they are in phase. In contrast, when two modes each with a different toroidal mode number, their phase difference phase hardly has any effect on the transport of fast ions.

Design of the beam transport optics of TRIUMF’s new 300 keV H− ion source terminal

An ion beam transport system has been designed to transport a highly intense and bright beam extracted from the H− ion source. This new system will be installed at the new injection terminal for the TRIUMF’s 500 MeV H− cyclotron. The low energy part of the transport section (25 keV) in the injection terminal has been designed with magnetic optical elements in order to maintain space charge neutralization. The injection terminal includes a permanent magnet lens, magnetic steerers, a pulser, a beam dump, and a 300 kV acceleration column with electron and positive ion suppressor rings. Beam optics calculations have been performed, including space charge effects up to 1 mA. The simulation results of the beam optics design are presented in this paper.

Recent progress in the construction of KoBRA for low-energy nuclear physics experiments

A multi-purpose experimental instrument, called as KoBRA (Korea Broad acceptance Recoil spectrometer and Apparatus), has been constructed for low-energy nuclear physics experiments at RAON (Rare Isotope Accelerator complex for ON-line experiments), and is being prepared in order to produce rare isotope beams at an energy of about 20 MeV/nucleon during the first beam commissioning phase. A test was performed to measure the positions of 4He ions at the dispersive and achromatic foci of KoBRA using an 241Am α-source placed at the production target position, so as to examine the momentum dispersion and ion beam transport. We report on the results of the test and the detailed design of KoBRA including ion optics, together with the status of detectors for particle identification of rare isotopes.

Progress in the development of a collinear resonance ionisation laser spectroscopy setup

A collinear resonance ionisation spectroscopy setup has been developed with the aim to study the nuclear properties of more exotic isotopes. It is developed on the basis of a recently-commissioned collinear laser spectroscopy, and could in principle measure the hyperfine structure spectra of studied isotopes using both laser-induced fluorescence and laser resonance ionisation approaches. In this paper, the latest technique development, the progress on the test of the vacuum system and the ion beam transportation, and the near-term offline experimental plans are presented.

Intense laser-generated ion beams in plasmas: the rapid heating regime

Previous work (Robinson 2022 Plasma Phys. Control. Fusion 64 105014) has shown that there is a regime of ion beam transport in plasmas where the electron–ion drag becomes so intense that the electron temperature rapidly rises to temperatures at which the electron–ion drag is strongly reduced. This regime is mainly thought to pertain to short-pulse laser-generated ion beams, because of the ion energy fluences required to enter this regime. The regime for was thought to be determined by a dimensionless number, . Here it is shown that there is another dimensionless number that needs to be considered. Numerical simulations show that this dimensionless number, χ h , does not affect the half-energy range of the ion beam, but does determine how strong stopping is at the ion beam front, and thus how rapidly the beam energy falls past the half-energy range.

Experimental setup for Weak Interaction Studies with Radioactive ion-beams WISArD

The article describes the commissioning and technical development of the Weak Interaction Studies with 32Ar Decay (WISArD) experiment, installed at the radioactive ion-beam facility ISOLDE/CERN. The experiment aims to extend the present limits on scalar and tensor currents in the weak interaction and hence search for physics beyond the Standard Model. The evaluation of these limits relies on measuring the proton energy in beta-delayed proton emission, sensitive to both the beta-neutrino angular correlation coefficient aβν and the Fierz interference term b. The method tries to improve previous studies by considering the positron-proton coincidences when determining the kinematic shift in the energy of the emitted protons. Using this coincidence technique, the aβν and b coefficients will be measured at the per mil level. Simulations were employed to optimize the ion beam transport efficiency and validate proof-of-principle results obtained in November 2018 (Nov2018). Upgrades are ongoing, and we are looking into improvements to the overall performance of the setup.

Study of the characteristics of the system: Ion source-ion decelerator.

The features of the method for the formation of dense low-energy ion beams in the system consisting of ion source-ion decelerator are considered. According to this method, a wide ion beam is formed using an ion source with an ion energy of 500eV and higher, and then the ions are decelerated just before landing on the substrate surface by an electric field created in the ion decelerator. In the considered ion decelerator, the electric field that slows down the ions is created in a gas discharge in E × B fields due to the Hall effect. The decelerated electrode imitating the substrate is located in the field of action of a magnetic field with an induction of 0.45T. The ion decelerator is characterized as a Hall magnetohydrodynamic converter of the ion beam kinetic energy into electrical energy. The analysis of plasma processes in the converter has been carried out on the basis of the model of the ion-vacuum regime of a discharge in E × B fields for estimating the expected properties of the converter and their verification based on experimental results. In experiments, an ion source of the Kaufman type formed an argon ion beam with a density of 0.5-2 mA/cm2 and ion energy of 300-1500eV was used. The voltage-current characteristics of the converter are given. The ratio of electron and ion components of the current in the circuit of the decelerated electrode was determined when the beam space charge neutralizer in the form of a heated filament was switched on and off. Using a Langmuir probe and a thermionic probe, the distributions of the ion beam current density and the potential of the plasma surrounding the ion beam in the beam transport space has been studied. A significant influence of the potential of the decelerator electrode on the plasma potential in the region of ion beam transport is shown. The features of the discharge in a specific design of the ion decelerator for a deceleration degree of ions to an energy of 50-75eV are revealed.

Simulation and experimental studies on the formation of high-power titanium ion beams for the synergy of ion implantation and energy impact on the surface

The development of a material modification method based on synergy of high-intensity ion implantation and simultaneous energy impact on the surface is aimed at creating deep ion-doped layers. To implement this method, the high power density of pulsed and repetitively-pulsed beams of metal and gas ions with micro-submillisecond duration are required. The paper presents the results of numerical simulation and experimental studies on the formation of pulsed high-intensity metal ion beams from vacuum arc plasma. The ballistic focusing of heavy ions at injection currents from 0.1 to 1 A has been studied. The influence of the ion current density, accelerating voltage, and conditions for neutralizing the beam space charge on the transport and focusing of a high power density ion beam has been studied. The possibility of ballistic formation of submillisecond titanium ion beams with a pulse power density of a hundred kilowatts per square centimeter has been experimentally shown.

Ion beam stopping power effects on nuclear fusion reactions

Fusion reactions in a plasma environment are fundamental issues with general interest in high energy density sciences. The reaction rate in an astro-system, which may differ from cold matter, is an important subject in the ambiguous problems of elemental abundance. In addition, the stopping of charged particle in plasma has a considerable impact on the design of nuclear fusion reactors as it is related to the α-particle heating process and ion-driven fast ignition, but still needs better understanding. In this research, an experiment on laser-driven D–D fusion reactions (D + D → 3He + n) has been carried out to investigate the effects of ion stopping power in plasma on fusion reactivities. The neutron yields, plasma density, and deuteron energy loss in the plasma have been measured simultaneously, and the plasma temperature has been analyzed from simulations. It is experimentally demonstrated that the fusion reaction yield is closely correlated with ion beam transportation in the plasma. As a cold target heated to plasma, the reaction probabilities from a deuteron beam and deuterated target interactions can be enhanced or suppressed, which is ascribed to the deuteron stopping power variation in the plasma. The results show the importance of considering the temperature adjusted ion stopping power to correctly model the fusion reaction yields. This work has an impact on understanding the fusion reactions in plasma environment, which is also likely to help achieve higher neutron yields.

Numerical study of stripping and stray particles for the one-RF-driver NBI negative ion source prototype of CFETR

The prototype for a negative hydrogen ion source for neutral beam injection of China Fusion Engineering Test Reactor is being developed at the Southwest Institute of Physics. To study the physics of negative ion beam transport and to optimize the design of the source, the stripping loss and the stray particles’ impacts on the one-RF-driver prototype are analyzed. Collision simulation, including both the beam-gas collisions and the particle-grid collisions, is carried out basing on the results of gas flow evaluation and particle tracing. The stripping loss, the distribution of stray particles and the heat loads are calculated, comparing two configurations of grounded grid (GG) (multiaperture or multislot). At the source filling pressure of 0.3 Pa and the vessel pressure 0.05 Pa, the extraction voltage being 8 kV and the acceleration voltage 200 kV and the extraction grid (EG) magnet peak of ±45 mT, the stripping loss of the 200 A m−2 H− beam can be reduced from 25% to 20% by changing GG from multiapertures to multislots. The H− proportion in the total current at 40 mm after GG, however, shows smaller change than the reduction of the stripping loss possibly because the multislot GG’s larger transparency increases the chance for the stray particles to pass through GG. The total heat load on EG in the two cases with different GG configurations are both around 66 kW, while the GG heat load is reduced from 45 kW for multiapertures to 17 kW for multislots. The study provides good comprehension of the transport process and useful guidance for practical operations.

Space Charge Compensation Study of High Intensity Ion Beams

The space charge effect is one of the key factors affecting ion beam transport and ion beam quality, especially for low-energy high-intensity ion beams. It can be partially compensated by the secondary electrons produced from the ionization of residual gas molecules in the beam pipe, and we are interested in the accurate value of this compensation degree. In this paper, we use a Three-grid Energy Analyzer (TEA) to measure the secondary ion energy distribution of the beam, which corresponds to the compensated beam potential distribution. To have accurate evaluation of the compensation degree, it is essential to adopt a proper transverse distribution of the ion beam, other than using the Gaussian theorem for uniform beams. The results of a space charge compensation degree study for singly charged ion beams with a 2.45GHz microwave ion source and for multiply charged ion beams with a high charge state ECR ion source are presented.

Characterization of a Multicusp Ion Source With Two-Grid Extraction System for Studying Extraction and Transport of Ion Beam

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.75\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> AV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3/2</sup> . The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode.

Features of the Formation of Ultralow Energy High-Intensity Metal and Gaseous Ion Beams

This article studies the features and patterns of the formation of high-intensity beams of metal and gaseous ions of low and ultralow energy from dc vacuum arc and gas-discharge plasma. It presents the results of repetitively pulsed plasma immersion extraction of aluminum, titanium, and nitrogen ions from the plasma followed by the formation and transport of ion beam under conditions of its ballistic focusing. This article presents the experimental data on the influence of the grid focusing electrode cell sizes of 150 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500~\mu \text{m}$ </tex-math></inline-formula> , the bias potential amplitude from 0.1 to 2 kV, the conditions for neutralizing the space charge of the beam during preliminary plasma injection into drift space and when using an additional thermoelectron source on the transport and focusing of ion beams. Here, it discusses the effect of the characteristic dimensions of the fine-structured grid and plasma parameters at ultralow bias potential amplitudes and the presence of significant initial energy in ions on the ion beam focusing. It was found that at bias potential amplitudes of 0.6 kV, it is possible to form repetitively pulsed ion beams with high current density reaching 170 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The obtaining of such beams opens up the possibility of implementing the method of high-intensity ion implantation under conditions of multiple decreases in the irradiated surface sputtering.

A study of beam ion and deuterium–deuterium fusion-born triton transports due to energetic particle-driven magnetohydrodynamic instability in the large helical device deuterium plasmas

Understanding energetic particle transport due to magnetohydrodynamic instabilities excited by energetic particles is essential to apprehend alpha particle confinement in a fusion burning plasma. In the large helical device (LHD), beam ion and deuterium–deuterium fusion-born triton transport due to resistive interchange mode destabilized by helically-trapped energetic ions (EIC) are studied employing comprehensive neutron diagnostics, such as the neutron flux monitor and a newly developed scintillating fiber detector characterized by high detection efficiency. Beam ion transport due to EIC is studied in deuterium plasmas with full deuterium or hydrogen/deuterium beam injections. The total neutron emission rate (S n) measurement indicates that EIC induces about a 6% loss of passing transit beam ions and a 60% loss of helically-trapped ions. The loss rate of helically-trapped ions, which drive EIC, is larger than the loss rate of passing transit beam ions. Furthermore, the drop of S n increasing linearly with the EIC amplitude shows that barely confined beam ions existing near the confinement-loss boundary are lost due to EIC. In full deuterium conditions, a study of deuterium–deuterium fusion-born triton transport due to EIC is performed by time-resolved measurement of total secondary deuterium–tritium neutron emission rate (S n_DT). Drop of S n_DT increases substantially with EIC amplitude to the third power and reaches up to 30%. The relation shows that not only tritons confined in confined-loss boundary, but also tritons confined in the inner region of a plasma, are substantially transported.

Transport of a Low-Energy Ion Beam with Ballistic Focusing

Transport of a Low-Energy Ion Beam with Ballistic Focusing

Electron cyclotron resonance charge breeder plasma parameters from the modeling of 1+ beam stopping

As a part of SPIRAL1 upgrade, several experiments were carried out to understand the transport of $1+$ (monocharged) ion beam through the SP1 ECR charge breeder ion source and to investigate the physical processes involved in charge breeding. Ion beam transport simulations were performed to reproduce the trends of the experimental results (charge breeding efficiency versus $1+$ beam injection energy $\mathrm{\ensuremath{\Delta}}\mathrm{V}$) by transporting the $1+$ beam through a potential map that reflects the presence of the ECR (electron cyclotron resonance) plasma. The role of Coulomb collisions in the capture of $1+$ beam leads to a necessary detailed analysis for an accurate description of the charge breeding process. This was done by using a full six-dimensional (6D) phase space Monte Carlo charge breeding (MCBC) code. MCBC models Coulomb collisions of the injected $1+$ beam in an ECR plasma and atomic processes (ionization and charge exchange). A simplified background ECR plasma model is implemented in the code to reproduce the trends of three different experiments (interaction of ${\mathrm{Na}}^{1+}$ with He plasma, ${\mathrm{K}}^{1+}$ with He plasma and ${\mathrm{K}}^{1+}$ with ${\mathrm{O}}_{2}$ plasma). The model is able to reproduce the low charge state ($1+$ and $2+$) experimental trends by tuning each plasma parameter (plasma density, plasma ion temperature and electron temperature) independently. The estimated plasma parameters obtained from each case are presented and their contribution in charge breeding process are discussed.

Collective energy-spectrum broadening of a proton beam in a gas-discharge plasma

An accurate understanding of ion-beam transport in plasmas is crucial for applications in inertial fusion energy and high-energy-density physics. We present an experimental measurement on the energy spectrum of a proton beam at 270 keV propagating through a gas-discharge hydrogen plasma. We observe the energies of the beam protons changing as a function of the plasma density and spectrum broadening due to a collective beam-plasma interaction. Supported by linear theory and three-dimensional particle-in-cell simulations, we attribute this energy modulation to a two-stream instability excitation and further saturation by beam ion trapping in the wave. The widths of the energy spectrum from both experiment and simulation agree with the theory.

Fuel costs estimation for ion beam assisted space debris removal mission with and without attitude control

Contactless space debris removal systems are the promising direction for solving the space debris problem. An ion beam transportation method is based on blowing the space debris with a high-speed plasma flow generated by the engine of an active spacecraft. The aim of the work is to evaluate the effect of controlling the attitude motion of space debris on the amount of fuel consumption during the contactless transportation. Four control strategies for an active spacecraft are proposed and compared. The first strategy involves transporting the object without considering its attitude motion. The second strategy involves stabilizing the object in a stable angular equilibrium position. The third strategy assumes transportation the space debris in the oscillation mode with the maximum average force. The fourth strategy involves stabilizing the object in an angular position corresponding to the maximum ion force. The control laws for the spacecraft's thrusters and for the direction of the ion beam axis, implementing these strategies, are proposed. The simulation of the transportation of the rocket stage is carried out and the fuel costs for various strategies are calculated. The most preferable from the point of view of minimizing fuel consumption is the second strategy. The fourth strategy is ineffective. The results obtained in this work can be used in the preparation of contactless space debris removal missions.

A review of diagnostic techniques for high-intensity negative ion sources

Plasma and beam diagnostic methods for high-current-density negative ion sources are reviewed. The pulse laser–induced photodetachment method was widely used to measure negative ion density in the ion source plasma. The method was used to understand fundamental processes of negative hydrogen (H−) ion formation and destruction in hydrogen plasmas. Species composition and plasma parameters in H− ion sources can be estimated from optical emission spectroscopy data, while electrostatic probes are utilized to obtain local plasma parameters in the ion source. Plasma transport toward the extractor is studied by combining a laser beam for photodetachment and a structured electrostatic probe to visualize a flow pattern of H− ions. Spatial distributions of large-area H− ion beams are monitored by infrared thermography images, showing interactions among multiple beamlets. These diagnostic methods deepen the understanding of how H− ions are produced and extracted through beam-forming apertures. The acquired knowledge on ion source plasma and beam transport improves the ion source design of the next-generation H− ion sources for fusion experiments and accelerators. The essence of research and development for negative ion source study is summarized through briefly tracing the history.