Positive Ion Beam Research Articles

Development of hydrogen ionic plasma source with superimposed positive-ion beam

A hydrogen ionic plasma source has been developed that is with a low residual electron presence (<0.01) using an aluminum plasma grid for negative hydrogen ion production and a control grid for electron removal. The ionic plasma density increases when a positive-ion beam is superimposed on a hydrogen plasma and irradiated onto the Al plasma grid. Even though the ionic plasma is formed in a region with high-deflection magnetic flux density, a collapse phenomenon can occur downstream of the region under certain electrode voltage conditions, causing electrons to appear and forming an electron plasma. Under electrode voltage conditions that prevent the collapse, the nine ionic plasmas, each passing through extraction apertures with a diameter of 1.3 cm, are combined to form the ionic plasma with a diameter of approximately 6 cm and a density on the order of 109 cm−3.

Design, development and test of single beamlet microwave ion source with spot-dense plasma system

In this paper, an efficient ion source with unique characteristics is introduced and proposed. It outlines the generation of a spot-dense plasma just below the plasma electrode aperture of the extractor system through the utilization of a 2.45 GHz microwave plasma source with a power of 1000 W, in the absence of a magnetic field. This source utilizes a 2.45 GHz microwave plasma generator operating at 1000 W, resulting in the generation of a spot-dense plasma just below the plasma electrode aperture of the extractor system, all achieved without the need for a magnetic field.The spot-dense plasma results in the extraction of an ion beam with high current density. Furthermore, the suggested ion source can be utilized in a smaller size using a higher frequency. Therefore, our findings indicate that the proposed method not only substantially enhances the extracted positive ion beam current but also significantly reduces the size of the ion beam source system. Based on the design and simulation results, an experimental model of the ion beam source is constructed. The diagnostic tools provided the beam current density and system efficiency values of 99mA/cm2 and 7×10−6A/W, respectively.

Development of a negative helium ion source with non-metallic charge exchange

Negative helium ion (He−) beams are required for tandem accelerators used at research centers and implanter facilities. The common production method of such beams involves charge exchange between a positive helium ion (He+) source or beam, with a low pressure alkali metal vapour. However, the efficiency of this reaction is poor (only a small percentage) and the alkali metal vapour increases the potential flammability of the interior surfaces of the reaction chamber, as well as contributing to unwanted electrostatic discharge and target contamination downstream. In this paper we describe initial results from experiments using a focused He+ ion microscope (HIM) to measure charge uptake efficiencies after transmission through carbon membranes. The He+ beam (15 keV to 30 keV, 50 fA to 10 pA) collides with a non-metallic foil, and transmitted particles (He+, He0, and He−) are separated electrostatically into discrete beam spots and detected using a radiation camera (AdvaCam MiniPIX). A He− percentage uptake of 0.05 was observed using a 20 nm exfoliated graphite membrane consistent with previous reports. Future work will investigate the efficiency of charge exchange through other suitable membrane materials.

Development and Testing of a High-Frequency Driver for a Charge-Exchange Source of Negative Hydrogen Ions

A source of negative hydrogen ions based on the recharging of a beam of positive ions in a gas target is being developed at the Institute of Nuclear Physics. G.I. Budker SB RAS. The charge exchange source can be used to inject into the tandem accelerator a neutron source intended for boron neutron capture therapy. One of the important elements of the source is the plasma emitter, which creates positive ions for primary acceleration. As an emitter, a high-frequency driver based on an induction discharge and designed for a multi-second operating mode was chosen. In this work, we measured the emission characteristics of a high-frequency driver using a moving grid probe. As a result, the parameters necessary for the use of the driver in a rechargeable source of negative ions have been achieved. The analysis of experimentally measured thermal loads in the multisecond mode is carried out.

Fast and cold negative ion and neutral atom beams from a water spray

High-power lasers are routinely used to generate energetic positively charged ions, and this paper reports on the observation of negative ions in these experiments. A large number of negative ions and neutral atoms at MeV energies was obtained from the interaction of a high intensity laser pulse with a water spray along with positive ions [Abicht et al., Appl. Phys. Lett. 103, 253501 (2013)]. Beams of negative ions and neutral atoms have the same properties as beams of positive ions. However, the mechanism of negative ion formation and acceleration is still under discussion. In order to gain more information about physics of generation negative ions and neutrals, we present a new experiment where all species, positive, negative ions, and neutrals, are spatially separated, and the electron capture and loss of each in water spray is evaluated. The formation of negative ions and neutral atoms of hydrogen and carbon with energies up to 140 keV and 1.2 MeV, respectively, is confirmed. It is suggested that the electrification of spray droplets plays a decisive role in these charge-exchange processes.

Optimal Interplanetary Transfer of Solar Wind Ion Focusing Thruster-Based Spacecraft

The Solar Wind Ion Focusing Thruster (SWIFT) is a highly-innovative propellantless propulsion concept, recently proposed by Gemmer and Mazzoleni. In its nominal configuration, a SWIFT consists of a conically-shaped mesh of positively-charged conducting tethers, with its vertex linked to the spacecraft and its axis oriented towards the Sun. The SWIFT collects and filters the solar wind plasma and suitably directs the positive ions, which are then accelerated by an ion thruster. Such a device is theoretically able to generate a deep-space propulsive acceleration that comes, in part, from the solar wind dynamic pressure impinging on the conical grid and, in part, from the positive ion beam. In particular, the orientation of the ion beam may be chosen in such a way as to set the resultant propulsive acceleration and steer the spacecraft. The aim of this paper is to analyze the performance of a SWIFT-propelled spacecraft in an orbit-to-orbit two-dimensional interplanetary transfer. To that end, some mission scenarios are studied, in an optimal framework, by minimizing the total flight time necessary for the spacecraft to complete the transfer as a function of the propulsion system performance parameters. Numerical simulations are used to compare the optimal flight times calculated in simplified Earth–Venus and Earth–Mars transfers with those obtained by considering other propellantless propulsion systems.

Design and optimization of an adjustable RF positive hydrogen ion source

An adjustable radio frequency (RF) positive hydrogen ion source is designed in Huazhong University of Science and Technology (HUST) to provide ion beam with adaptive beam current and beam energy for neutral beam injection (NBI) related material research. The ion source aims to produce 10–20 keV positive hydrogen ion beam with total current of 50–125 mA. This paper investigates the design of the RF ion source including RF driver via inductively discharge mechanism and the extractor which is designed and optimized, including ion beam optics simulation, thermal analysis and power supply analysis. The vacuum analysis of the source is carried out as well.

Design and simulation of the high efficiency ion source for Damavand NBI heating system

Neutral beam injection (NBI) is known as one of the important methods of plasma auxiliary heating and current drive in fusion reactors. Optimization of the ion sources, as one of the main components of NBI systems, with high current and minimum divergence, can be very effective in order to reach more optimal dimensions of NBI systems. A high efficiency ion source designed using a helicon plasma source for neutral beam injection system (NBI) of Damavand Tokamak. The extraction system has the ability to extract a positive hydrogen ion beam with the current and voltage of 7A and 4.5 kV, respectively. In this paper, an ion source with optimized helicon plasma and optimized beam extraction system is developed using the COMSOL software. All parameters, including RF power, magnetic field, gas pressure, antenna length, and RF frequency, for the production of helicon plasma and ion beam extraction system with optimal geometry are investigated in the most effective way, in order to reduce the beam divergence and beam current increment. Finally, the helicon plasma with density of 4.12×1018m−3, electron temperature of 2.8eV and hydrogen beam extraction system consists of three Accel-Decel grid, each grid with 280 apertures of 3.5mm diameter, has been designed for neutral beam injection system of Damavand Tokamak. This ion production system has an extractor grid with very large transparency (60%) and the minimum single beamlet divergence of 27 mrad.

Negative ion beam bombardment of a protic ionic liquid: Alleviating surface charging and damage and analyzing the surface of organic insulating materials

Positive ion beams are widely used in surface processing and analysis; however, serious surface charging can occur in the case of insulating materials. To address this issue, we investigate bombardment effects of ionic liquid negative ions emitted from the tip of a sharp needle wetted with the protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate. Experimental results show that the potential of an electrically floating metal target bombarded with the ionic liquid negative ions is slightly higher (about 1 V) than that of a front electrode, indicating that the target potential can be controlled by adjusting the potential of a nearby electrode. We also investigate the application of the negative ion bombardment in secondary ion mass spectrometry. Two types of insulating materials, polytetrafluoroethylene and polyethylene glycol, are analyzed. Experimental results show that the negative ion bombardment allows one to analyze organic insulating materials by adjusting sample bias potential, without charge neutralization such as electron flooding. Results obtained show that the ionic liquid negative ion beam is a useful tool for alleviating sample charging and damage because tens of negatively charged low-energy constituent atoms hit a surface locally and simultaneously. The ionic liquid negative ion bombardment is shown to have the advantages of both negative and polyatomic ion bombardment.

Experimental Verification of Anode-Induced Phenomena During Prebreakdown Conduction in Vacuum Gaps Under Alternating Voltages With Special Electrode System

The results presented in this article relate to the work conducted to verify the existence of anode-induced phenomena, predominantly anode vaporization and consequent prebreakdown (PBD) current enhancement due to the impact of positive ions and microparticles over a relatively larger area at the cathode (presumably ion-assisted field (I-F) emission like). The verification of this hypothesis is attempted using a three-electrode arrangement. One electrode is comprised of a needle insulated from and projecting through a plane electrode (collector) of 40-mm diameter. It was surmised that if the positive ion beam from the anode spot (due to electron beam impact) were to be macroscopically diffuse, at least the collector would gather a part of it. However, no currents could be detected in the collector circuit even at voltages close to breakdown. The needle currents continued to display the typical characteristics of PBD currents under alternating voltages. The needle currents depended on the spacing between the needle tip and the plane of the collector and the polytetrafluoroethylene (PTFE) insulation used to prevent emission from the immediate vicinity of the needle evaporated significantly. Typical broad-area electrode behavior displayed by needle currents indicated that I-F emission, if any, is limited to the needle itself, which is certainly broad compared to the positive ion beam. Dependence of the PBD currents and breakdown voltages on the melting point of the anode material lend support to such anode-triggered electrode phenomena.

Space charge compensation of positive ion beams used in magnetic fusion applications

A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120 kV, 60 A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Space charge compensation of positive ion beams used in magnetic fusion applications

Abstract A model is presented for space charge neutralisation of positive ion beams. The model is used for the particular case of the beams used for magnetic based fusion applications. The beams consist, after a gas neutraliser, of ions and atoms at different energies. Account is taken of the contribution of all beam components to ionization of the background gas. Consideration is also given to not only beam heating of the plasma generated by the beam, due to Coulomb collisions, but also to Coulomb heating by fast electrons produced in ionization by all beam particles and stripping of the neutral components. Two approximations are considered for the motion of the secondary ions out of the beam potential; a drift approximation and a freefall approximation. All the beam plasma parameters can be calculated. The model is applied to a typical extracted beam of deuterium ions of 120kV,60A. It is found that these beams are very highly compensated and that beam plasma heating by the electrons produced is generally greater than that due to the beam ions.

Plume neutralization of an ionic liquid electrospray thruster: better insights from particle-in-cell modelling

Ionic liquid electrospray thrusters with high specific impulse, high thrust accuracy and low thrust noise are very promising for space gravitational wave detection missions. The plume, which may lead to surface charging of solar panels and sensitive spacecraft components is a great concern for the applications of electrospray thruster. Therefore, this paper investigates the plume neutralization process of the ionic liquid electrospray thruster through fully kinetic particle-in-cell simulations. The unipolarity operation mode is firstly simulated and compared with the experimental measurements. The bipolar operation mode is analyzed by considering the premixing and the separation of positive and negative ion beams. At the same time, the effect of beam spacing on the plume characteristics is investigated. The results show that the plume neutralization of the ionic liquid electrospray thruster is achieved by the spatial and temporal oscillations of the ion beams. In the horizontal direction, the spatial oscillations are caused by the different mass and hence velocities of positive and negative ions. In the vertical direction, the spatial oscillations are mainly because of the non-zero beam spacing. The temporal oscillations may be related to the tradition plasma oscillation. As the beam spacing increases, the oscillation amplitude of the horizontal electric potential curve changes scarcely; however, in the vertical direction, the oscillation amplitude of the curve increases. The ion temperature goes up with the beam spacing and the deviation of the temperature of beam ions does not exceed 15 eV in the horizontal direction but exceeds 100 eV in the vertical direction. Moreover, the plume divergence half angle and the beam spacing are positively correlated, suggesting that the ionic electrospray thrusters with positive and negative polarity need to be placed as close as possible in the spacecraft.

Energy properties and spatial plume profile of ionic liquid ion sources based on an array of porous metal strips

An ionic liquid ion source (ILIS) is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams. This paper presents a miniaturized ILIS based on an array of porous metal strips. The porous emitter array, integrated with seven 10 mm long strips, is fabricated using wire electrical discharge machining (WEDM) combined with electrochemical etching. The assembled ILIS is 30 mm × 30 mm × 17.5 mm in size and weighs less than 25 g. A series of experiments, including an I–V characteristic test, a retarding potential analyzer (RPA) test, and a spatial plume distribution test, have been conducted in vacuo to characterize the performance of the ILIS. Results show that the emitted current is up to about 800 μA and ion transparency is as high as 94%. Besides, RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8% in positive mode and 59.8% in negative mode. Further, with the increase in applied acceleration voltage, the voltage loss rises while the energy efficiency decreases. It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips. A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.

Neutral beam injection for fusion reactors: technological constraints versus functional requirements

In this paper we look at the technological constraints of neutral beam injection (NBI) systems and compare them with the functional requirements that NBI has in the various envisaged plasma scenarios for tokamak fusion reactors of the DEMO and fusion power plant (FPP) class. We show in particular that there is an intermediate beam energy range in which beamlines are unattractive because of size. Furthermore, for scenarios that consider NBI only for ion heating during the ramp-up and heat-to-burn phase we show that the use of beam energies in the range of 100 to 200 keV, which could be produced from positive ion beams with a much simpler system, could be an attractive option that should be further investigated.

RF and Microwave Ion Sources Study at Institute of Modern Physics

Intense ion beam production is of high importance for various versatile applications from accelerator injectors to secondary ion mass spectrometry (SIMS). For these purposes, different types of ion beams are needed and, accordingly, the optimum plasma to produce the desired ion beams. RF-type plasma features a simple structure, high plasma density and low plasma temperature, which is essential for negative ion beam production. A very compact RF-type ion source using a planar coil antenna has been developed at IMP for negative molecular oxygen ion beam production. In terms of high-intensity positive ion beam production, 2.45 GHz microwave power-excited plasma has been widely used. At IMP, we developed a 2.45 GHz plasma source with both ridged waveguide and coaxial antenna coupling schemes, tested successfully with intense beam production. Thanks to the plasma built with an external planar coil antenna, high O2− production efficiency has been achieved, i.e., up to 43%. With 2.45 GHz microwave plasma, the ridged waveguide can support a higher power coupling of high efficiency that leads to the production of intense hydrogen beams up to 90 emA, whereas the coaxial antenna is less efficient in power coupling to plasma but can lead to attractive ion source compactness, with a reasonable beam extraction of several emA.

Highly Efficient Small Anode Ion Source

We describe some modifications to a Bernas-type ion source that improve the ion beam production efficiency and source operating lifetime. The ionization efficiency of a Bernas type ion source has been improved by using a small anode that is a thin rod, oriented along the magnetic field. The transverse electric field of the small anode causes the plasma to drift in the crossed ExB field to the emission slit. The cathode material recycling was optimized to increase the operating lifetime, and the wall potential optimized to suppress deposition of material and subsequent flake formation. A three-electrode extraction system was optimized for low energy ion beam production and efficient space charge neutralization. An ion beam with emission current density up to 60 mA/cm2 has been extracted from the modified source running on BF3 gas. Space charge neutralization of positive ion beams was improved by injecting electronegative gases.

Electrochemical Reactions of Ionic Liquid in Vacuum and Their Influence on Ion-Beam Production by Electrospray

Electrochemical reactions at interfaces between metal and ionic liquid are of great practical importance in ionic liquid ion sources, which can produce negative and positive ion beams by electrospray in vacuum. This is because electrochemical reactions involved in ion beam production can cause emitter degradation, leading to beam instabilities. Here we investigate ion beam production using a tungsten needle wetted with ionic liquid. We also investigate electrochemical reactions of ionic liquid at tungsten electrodes in vacuum with a quadrupole mass spectrometer, which allows us to measure volatile products formed via electrochemical reactions. Two types of ionic liquids were tested: propylammonium nitrate (PAN), which is protic and hydrophilic, and 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)amide ([EMIM][TFSA]), which is aprotic and hydrophobic. Beam measurements show that a negative ion beam containing large cluster ions can be produced continuously using each ionic liquid. Electrochemical measurements with PAN show that volatile products are formed via electrochemical oxidation and reduction, thereby indicating that ion beams of PAN can be produced continuously in both negative and positive ion modes. Experiments with [EMIM][TFSA] show that the electrochemical reductions of both [EMIM]+ and [TFSA]− occur and thus form volatile products, indicating that such reactions enable its continuous negative ion beam production.

Preliminary design of the RF driven positive deuterium ion source at HUST

Huazhong University of Science and Technology (HUST) plans to develop a radio frequency (RF) ion source experimental setup for a high intensity neutron source which is at the conceptual design stage. The positive deuterium ion beam with the current of ∼14.5 A, the energy of 20 keV and the pulse length of ∼2 s is required. This paper introduces the RF driven deuterium ion source, and focuses on the design of the extraction systems. A triode extraction system is optimized to deliver the beam well inside the required divergence by means of ion beam optics simulation. Finite element calculations have been carried out to analyze the temperature and deformation of the electrode under heat power loads.

Key issues for the filament-arc ion source of EAST neutral beam injector toward high-power and long-pulse operation

Neutral beam injection is an effective plasma heating and current drive method for magnetic confinement devices. For supporting the high-confinement plasma operation of the fully superconducting tokamak EAST, a high-power and long-pulse neutral beam is foreseen to be injected into EAST. To achieve such a mission, the most important task is to develop a qualified ion source which can launch a positive ion beam for pulse length up to 100 s with the beam power larger than 2 MW. During the research and development on the EAST positive ion source, several key issues have been studied, including the heat load on electrode grids, the backstreaming electrons deposition, and the gas discharge efficiency. The capability of heat removal of the electrode grids has been demonstrated via a series of simulations and experiments. However, the backstreaming electrons deposition was extremely dense on the electron dump of the ion source, leading to its serious melting damage. According to the simulation of the trajectories of backstreaming electrons, the central magnets on the electron dump were removed as a preliminary solution. The melting damage was successfully avoided without the central magnets and the modified ion source has been operated without malfunction until now. But the total deposition of backstreaming electrons on the electron dump was increased and the magnetic confinement of primary electrons was reduced. Consequently, the arc efficiency was lower and the fraction of the neutral atoms with half beam energy was higher for the modified ion source.