Multicusp Magnetic Field Research Articles

Effect of multi-cusp magnetic fields to generate a high-density hydrogen plasma inside a low pressure H2 cylindrical hollow cathode discharge

Based on probe measurements, the plasma density in a low pressure H2 radio-frequency (RF) magnetized cylindrical hollow-cathode capacitively coupled plasma (CCP) is demonstrated to be enhanced by applying a multi-cusp magnetic field (MCMF). CCPs can be used for fabricating functional thin-films, but are currently limited by low plasma densities of less than or about 1016 m−3. It is found that a maximum plasma density of 2.51, 2.88, and 3.14 × 1016 m−3 is obtained at 3, 4 and 5 Pa, respectively. The employed MCMF arrangement contributes to achieving superior plasma uniformity, both in axial and radial direction, at an RF power of 50 W.

Acceleration of particle-in-cell simulations using sparse grid algorithms. II. Application to partially magnetized low temperature plasmas

In Paper I [Garrigues et al., Phys. Plasmas 31, 073907 (2024)], we have extended the sparse PIC approach already used in the literature with the offset scheme to reduce the grid-based error. In this study, we demonstrate the ability of the offset sparse PIC algorithm to model partially magnetized low-temperature plasmas by reducing the grid-based error. In the context of multi-cusp magnetic field configurations, the offset scheme reduces the error of the current collected at the walls to less than 5% for more of the plasma conditions encountered in ion source applications. The formation of a double layer in the sheath region is also captured. In the context of the electron drift instability that occurs in the Hall thruster, the plasma properties as well as the ion velocity distribution function can be retrieved with a high enough precision without considering an initial regular grid with a smaller mesh resolution. The results also highlight the advantage of combining the electric potential at the nodes of the regular grid instead of directly combining the electric field from the component grids. Compared to the regular PIC algorithm, the typical speed-up factor is about three for a number of mesh nodes of 2562 and five for 5122.

Development of a planar ICP ion source for fusion based neutron generator

In this paper preliminary results of a new planar ICP ion source for neutron generator is investigated. This ion source has a cylindrical planar Aluminum plasma chamber. Set of Niobium permanent magnets have been arranged as multicusp geometry around the chamber to improve the plasma density and reduce the operational pressure. A copper made helical antenna has been used which is connected to the 2 kW 13.56 MHz radiofrequency power source including matching network. Preliminary results of ion beam measurements using 1 and 3 mm diameter apertures on plasma electrodes, represents improvement of ion current from μA range to mA with Helium operational gas. A primary result with Deuterium gas indicates that the ion current improves up to 7 mA by applying multicusp magnetic field around the plasma chamber at similar operational parameters with 1 kW of RF power. Theoretical and experiments are performed to regulate the optimum distance between plasma and the accelerating electrodes to have parallel deuteron ion beam at around 65 kV electrical potential between them. Accelerating electrode configuration which suppresses the secondary electron generated on the target surface is designed and fabricated based on the simulation results.

Spatial Distribution Analyses of Axially Long Plasmas under a Multi-Cusp Magnetic Field Using a Kinetic Particle Simulation Code KEIO-MARC

To realize the development of a long plasma source with a uniform electron density distribution in the axial direction, the spatial distribution of plasma under a multi-cusp magnetic field was analyzed using a KEIO-MARC code. Considering a cylindrical plasma source with an axial length of 3000 mm and a cross-sectional diameter of 100 mm, in which the filament electrode was the electron source, the electron density distribution was calculated using the residual magnetic flux density, Bres, and the number of permanent magnets installed at different locations surrounding the device, Nmag, as design parameters. The results show that both Bres and Nmag improved the uniformity of the electron density distribution in the axial direction. The maximum axial electron density decreased with increasing Nmag and increased with increasing Bres. These trends can be explained by considering the nature of the multi-cusp field, where particles are mainly confined to the field-free region (FFR) near the center of the plasma column, and the loss of particles due to radial particle transport. The use of multiple filaments at intervals shorter than the plasma decay length dramatically improved axial uniformity. To further improve axial uniformity, the filament length and FFR must be properly set so that electrons are emitted inside the FFR.

Моделирование мультикасповой магнитной системы источника ускоренных нейтральных частиц

The article considers the solution of an important technological problem of cleaning dielectric surfaces, during which the formation of a surface potential is eliminated, requiring the development of specialized sources of accelerated neutral particles integrated into ion-plasma installations. A significant disadvantage of these sources is the low density and poor uniformity of the output flow, which leads to an increase in the time of the technological operation and deterioration in the quality of surface treatment. To eliminate these disadvantages, a multicusp magnetic field system can be integrated into the device to reduce the plasma load on the anode, reduce the effective area of the anode and increase the density of the vapor-plasma flow. To optimize the design of the source, a simulation of the magnetic system was carried out and the calculation of the distribution of the magnetic field in the working area was conducted. For optimal operation of the source, it is necessary to achieve the largest possible magnitude of magnetic field induction at the walls of the working volume and as small as possible in the central region in which the vapor-plasma flow moves. The simulation results show that there is an optimal solution when choosing the number of permanent magnets holding the gas-discharge plasma. The retention effect increases with an increase in the number of permanent magnets, while the output of electrons from the loss cone becomes more frequent, which leads to a deterioration in the quality of the output flow. The optimal number of magnets is selected from the condition of balancing these two competitive effects.

A compact radio-frequency ion source for high brightness and low energy spread negative oxygen ion beam production.

A high brightness and low energy spread (∆E) ion source is essential to the production of a high-quality primary ion beam applied in secondary ion mass spectrometry (SIMS). A compact 13.56MHz radio-frequency (RF) ion source with an external planar spiral antenna has been developed as a candidate ion source for the production of negative oxygen ion beams for SIMS application. This ion source is designed with a three-and-a-half-turn water-cooled planar antenna for RF power coupling, a multi-cusp magnetic field for effective plasma confinement, and a three-electrode extraction system. The experimental results show that more than 50 µA negative oxygen ion beams have been extracted, which consist of 56% O-, 25% O2-, and 19% O3-. The ion energy distribution of the negative oxygen ion beam exhibits a Gaussian distribution with a minimum ∆E of 6.3eV. The brightness of the O- beam is estimated to be 82.4Am-2 Sr-1V-1. The simulation, design, and experimental study results of this RF ion source will be presented in this paper.

Development of Methods for Determining Near-Surface Plasma Parameters During Tests of Fusion Reactor First-Wall Prototypes Using the PLM Device

Plasma-surface interaction and high heat flux on plasma-facing materials in magnetic fusion devices cause surface ablation and degradation, while the influx of eroded materials into plasma can have a shielding effect. The reduction of the power load due to the plasma detachment effect over tungsten fuzz is an important phenomenon to be investigated for the ITER divertor problem. Measuring near-wall plasma parameters is a challenging task, requiring the development of improved and advanced techniques, including high-resolution spectroscopic methods. In this paper, we present study results of steady-state plasma over tungsten fuzz formed in plasma linear multicusp (PLM). The PLM device is a linear plasma trap composed of an eight-pole multicusp magnetic field with steady-state plasma discharge with parameters similar to the scrape-off layer and divertor plasma in a tokamak. We used spectroscopic measurements to estimate spatial distributions of plasma radiation in the vicinity of the sample surface exposed to the plasma column. Thus, we obtained information on the temperature and composition of the boundary layer plasma and the temperature of the sample surface. Helium plasma exhibits ionization-type nonequilibrium even at atmospheric pressure, necessitating the use of specific methods to estimate its electron temperature Te. When the helium ion spectral line He II 468.5 nm is present in the spectra, its intensity ratio to one of the atomic lines He I can be described by using coronal approximation. Spectrum analysis has shown that emitting helium ions are highly sensitive indicators of average electron energy = 3kTe/2. Therefore, utilizing intensity ratios of the strongest emitting lines in the ultraviolet-visible near-infrared range, He II 468.6 nm and several He I lines with well-known electron excitation functions were found to be a reliable Te measurement method in the case of magnetized low-pressure helium plasma. We also propose a method for determining the concentrations of the metallic admixture in the plasma on the data on relative intensities of its spectral lines.

Erosion of Fuzz Layers Formed in Steady-State Plasma Discharge

The erosion of nanostructured tungsten and titanium by high-heat plasma flux, laser, and arcing is investigated. To fabricate nanostructural fuzz layers and hierarchical granularity on the surfaces, samples were exposed to helium plasma in the steady-state plasma device PLM-M, which is a linear plasma trap of an eight-pole multicusp magnetic field with parameters similar to the scrape-off layer and divertor plasma in a tokamak. Arcing ignited with a Nd:YAG laser pulse on the target fuzzy surface in the helium plasma resulted in the melting of fibers and the creation of craters of several microns in depth and several tens of microns in diameter.

Extraction and transport of low-energy Ar ion beams with a broad cross-section

Low-energy argon (Ar) ion beams were accelerated from a quiescent discharge in a custom-designed ion reservoir. Around 100 eV Ar ion beams were extracted from an ion source with different multi-cusp magnetic field configurations through a 4-cm diameter two-electrode extraction system. Langmuir probe measurements correlated the source plasma characteristics to the extracted ion beam properties that were determined using a retarding potential analyzer and a moving Faraday cup. The ion extractor configuration allowed primary electrons from the ion reservoir to seep downstream to neutralize the space-charge of the Ar ions. The broad cross-section ion beam system is designed for material synthesis and surface modification.

Role of multi-cusp magnetic field on plasma containment

Two magnetic configurations of Multi-cusp Plasma Device (MPD) have been explored to obtain high quiescence level, large uniform plasma region with nearly flat mean density and temperature profiles. In particular, properties of plasma in a Six Pole Six Magnet (SPSM) and Twelve Pole Six Magnet (TPSM) cusp configurations are rigorously compared and reported here. It is found that more uniform plasma with nearly flat profiles is found in TPSM along with increased quiescence level. Findings are experimentally verified across various magnetic field strengths for both configurations.

Transverse Ion Current Density Profile of Laser Ablation Plasma Propagating through Multicusp Magnetic Field

Transverse Ion Current Density Profile of Laser Ablation Plasma Propagating through Multicusp Magnetic Field

Behavior of Laser Ablation Plasma During Transport in Multicusp Magnetic Field Using Different Targets for Laser Ion Source

To obtain laser ion sources with high current and long pulse, a method of applying multicusp magnetic fields to confine laser ablation plasmas has been proposed. The behaviors of the laser ablation plasmas during transporting in the multicusp magnetic fields are investigated by experiments using two types of multicusp magnetic field and the targets of aluminum, copper, and lead. To understand the behavior of the ablation plasma, numerical calculations for ion trajectory were also performed. The results indicate that the distance which a plasma proceeds until the appearance of the effect of the magnetic field on the plasma behavior at the center axis could be explained by ion motions affected by the azimuthal magnetic field.

The plasma device for the high-heat plasma testing of refractory metals and inventing of new highly porous materials

A unique plasma device has been constructed at the NRU “MPEI” for the study of plasma-surface interaction and the high-heat plasma testing of refractory metals, such as tungsten, molybdenum, steel and other plasma facing materials used in fusion reactor including the ITER. This plasma device is a multi-cusp linear stationary plasma confinement system. It has power-saving characteristics as well as compactness due to the employment of the 8-pole multicusp magnetic field configuration instead of a strong axial magnetic field. Experiments are planned to develop a novel technology for highly porous surface structure of the refractory metal with a pore size and nanofibers of 50 nanometers including tungsten “fuzz”.

Momentum transfer using variable gaseous plasma ion beams and creation of high aspect ratio microstructures

Intense gaseous ion beams are created from compact microwave plasmas confined in a multicusp magnetic field. The wave frequency (ω) is comparable to the electron plasma frequency (ωpe) and ⪢ the ion plasma frequency (ωpi); therefore, the heavier plasma (ions) are least disturbed by the high frequency electromagnetic waves. By changing the experimental gas, ion beams of different species are obtained, which expands the applicability of the ion beams. For the same applied accelerating potential, the controllability of the beam current owing to different velocities for different ionic species adds to the enhanced functionality. The ion beams are utilized to create a variety of microstructures by direct writing on metallic substrates, and microstructures of a high aspect ratio (ar = line width/depth) in the range of 100–1000 are created by varying the ion species and writing speed. For fixed species (Ga) and low current (1 pA) focused ion beam systems, typically ar ∼ 2.0 to 9.3 may be realized in a single beam scan. A parameter called current normalized force, defined as the momentum transfer per unit time, normalized with the beam current helps in understanding the different momentum transferred to the target sample upon impact by the ion beams of variable species. A mathematical formulation is developed to demonstrate this aspect.

Steady State Analysis of Vacuum Chamber

Plasma is a partially ionized gas in which a certain portion of electrons are free rather than being bound to an atom or molecule. The steady state plasma is produced by a machine named Q- Machine as the plasma is formed by Quiescent. In this device the Plasma source is a hot plate “heated to 2700K by electron bombardment. The vacuum chamber of Q-machine is a part of an experimental proposal for cesium plasma confined in a multi-cusp magnetic field at IPR. In this paper study the temperature distribution of a vacuum chamber by using ANSYS 13 software is to carried out steady state thermal analysis.

Simulation of RF power and multi-cusp magnetic field requirement for H− ion sources

A computer simulation study for multi-cusp RF based H− ion source has been carried out using energy and particle balance equation for inductively coupled uniformly dense plasma considering sheath formation near the boundary wall of the plasma chamber for RF ion source used as high current injector for 1 Gev H− Linac project for SNS applications. The average reaction rates for different reactions responsible for H− ion production and destruction have been considered in the simulation model. The RF power requirement for the caesium free H- ion source for a maximum possible H− ion beam current has been derived by evaluating the required current and RF voltage fed to the coil antenna using transformer model for Inductively Coupled Plasma (ICP). Different parameters of RF based H− ion source like excited hydrogen molecular density, H− ion density, RF voltage and current of RF antenna have been calculated through simulations in the presence and absence of multicusp magnetic field to distinctly observe the effect of multicusp field. The RF power evaluated for different H− ion current values have been compared with the experimental reported results showing reasonably good agreement considering the fact that some RF power will be reflected from the plasma medium. The results obtained have helped in understanding the optimum field strength and field free regions suitable for volume emission based H− ion sources. The compact RF ion source exhibits nearly 6 times better efficiency compare to large diameter ion source.

Ablation plasma transport using multicusp magnetic field for laser ion source

We propose a plasma guiding method using multicusp magnetic field to transport the ablation plasma keeping the density for developing laser ion sources. To investigate the effect of guiding using the magnetic field on the ablation plasma, we demonstrated the transport of the laser ablation plasma in the multicusp magnetic field. The magnetic field was formed with eight permanent magnets and arranged to limit the plasma expansion in the radial direction. We investigated the variation of the plasma ion current density and charge distribution during transport in the magnetic field. The results indicate that the plasma is confined in the radial direction during the transport in the multicusp magnetic field.

Development of a high-current ion source with slit beam extraction for neutral beam injector of VEST

A high-current pulsed ion source has been developed for the neutral beam injector of the VEST (Versatile Experiment Spherical Torus) to accommodate high-beta fusion plasma experiments. The ion source consists of two parts: an electron gun for supplying sufficient primary electrons by cold-cathode arc discharge and a hemi-cylindrical discharge chamber where uniform, high-density plasma generated by the primary electrons is confined by multi-cusp magnetic field. A pulse forming network is also developed to drive high current of ∼1kA to sustain the cold-cathode discharge in the electron gun up to 10ms. Diagnostics with a triple probe in the discharge chamber shows that a hydrogen plasma whose density is as high as 1×1018m−3 can be obtained near extraction slits at the gas pressure lower than 0.5Pa. This value is estimated to be sufficient to deposit a heating power of 90kW to the VEST plasma when the appropriate extraction through slits with 20cm2 in area and acceleration of ion beams up to 20kV are fulfilled.

Numerical Simulation of a Multi-Cusp Ion Source for High Current H- Cyclotron at RISP

The rare isotope science project (RISP) has been launched in 2011 to support a wide range science program in nuclear, material, and bio-medical sciences as well as interdisciplinary programs. The production of rare isotope beams at RISP is currently configured to include facilities for both an In-flight Fragmentation (IF) system and an Isotope Separator On-Line (ISOL) system, which will utilize a 70 MeV H− cyclotron. The cyclotron will deliver 70kW proton beam power to ISOL targets, where rare isotopes are generated and re-accelerated by a linear accelerator.A multi-cusp ion source used widely in H− cyclotrons is designed to have cusp geometries of magnetic field inside the ion source chamber, where ions are confined and enhanced plasma densities. Therefore the magnetic confinement fields produced by a number of permanent magnetic poles help to increase H− beam currents. In this work a numerical simulation is performed to understand the effect of multi-cusp magnetic fields when the number of magnetic poles is varied from 6 to 14. It is found that the larger number of magnetic poles provides a stronger ion confinement yielding higher extracted H− ion currents while the extracted electron current becomes lower.

Microwave remote plasma enhanced-atomic layer deposition system with multicusp confinement chamber.

A microwave remote Plasma Enhanced-Atomic Layer Deposition system with multicusp confinement chamber is established at the Plasma and Beam Physics research facilities, Chiang Mai, Thailand. The system produces highly-reactive plasma species in order to enhance the deposition process of thin films. The addition of the multicusp magnetic fields further improves the plasma density and uniformity in the reaction chamber. Thus, the system is more favorable to temperature-sensitive substrates when heating becomes unwanted. Furthermore, the remote-plasma feature, which is generated via microwave power source, offers tunability of the plasma properties separately from the process. As a result, the system provides high flexibility in choice of materials and design experiments, particularly for low-temperature applications. Performance evaluations of the system were carried on coating experiments of Al2O3 layers onto a silicon wafer. The plasma characteristics in the chamber will be described. The resulted Al2O3 films-analyzed by Rutherford Backscattering Spectrometry in channeling mode and by X-ray Photoelectron Spectroscopy techniques-will be discussed.