Magnetic Mirror Field Research Articles

Sheath and presheath in a collisionless plasma containing negative ions with an open magnetic field

The effects of an axisymmetric magnetic mirror field with diverging field lines on the plasma presheath and sheath are numerically investigated by solving the plasma–sheath equation for a collision...

Neutron disappearance and regeneration from a mirror state

The purpose of this paper is to demonstrate that if the transformation of a neutron to a mirror neutron exists with an oscillation time of the order of ten seconds, it can be detected in a rather simple disappearance and/or regeneration type experiment with an intense beam of cold neutrons. In the presence of a conjectural mirror magnetic field of unknown magnitude and direction, the resonance transformation conditions can be found by scanning the magnitude of the ordinary magnetic field in the range e.g. $\pm 100 \mu$T. Magnetic field is assumed to be uniform along the path of neutron beam. If the transformation effect exists within this range, the direction and possible time variation of the mirror magnetic field can be determined with additional dedicated measurements.

Calculation of Lorentz force in planar EMAT for thickness measurement of steel plate

PurposeThe aim of this paper is to better understand the generation and transmission mechanism of the electromagnetic acoustic transducer (EMAT).Design/methodology/approachA semi-analytical method was used to calculate the Lorentz force. Both the hypothetical magnetic field mirror method and the diffusion equation were adopted to solve the eddy current distribution by variables separation method in time domain. A three-dimension magnetostatic finite element model was used to calculate the static magnetic field and the relative permeability. And an experimental platform with a piezoelectric probe to generate and an EMAT to receive, the ultrasonic wave was set up to verify the distribution of the Lorentz force.FindingsThe Lorentz force at different time and in different positions of the steel plate can be easily calculated. The experimental results show a good agreement with the analytical results.Originality/valueThe accurate prediction of the Lorentz force provides an insight into the physical phenomenon of EMAT and a powerful tool to design optimum EMAT.

Mirror-field confined compact plasma source using permanent magnet for plasma processings

A mirror-field confined compact electron cyclotron resonance (ECR) plasma source using permanent magnets was developed, aiming for the realization of high-quality plasma processings where high-density reactive species are supplied to a substrate with minimizing the ion bombardment damages. The ECR position was located between a microwave transmissive window and a quartz limiter, and plasmas were transported from the ECR position to a midplane of the magnetic mirror field through the quartz limiter. Thus, a radius of core plasma could be determined by the limiter, which was 15 mm in this study. Plasma parameters were investigated by the Langmuir probe measurement. High-density plasma larger than 1011 cm-3 could be produced by applying 5.85-GHz microwave power of 10 W or more. For the outside region of the core plasma where a wafer for plasma processings will be set at, the ion current density was decreased dramatically with distance from the core plasma and became smaller by approximately two orders of magnitude that in the core plasma region for the radial position of 40 mm, suggesting the realization of reduction in ion bombardment damages.

Hot plasma dielectric response to radio-frequency fields in inhomogeneous magnetic field

Hot plasma dielectric response models, which are now used in most linear full wave codes, are formulated in Fourier space assuming that particle's Larmor radius is much smaller than the scale of spatial nonuniformity of magnetic field. Such approximation assumes that the spatial scale of plasma dielectric response to the RF field is limited to a few Larmor radii, which is accurate for a limited range of wave frequencies ω. The scale of plasma dielectric response along the magnetic field line could be comparable to the scale of the magnetic field nonuniformity when ω is close to the particle's cyclotron frequency ωc or when ω is much smaller than ωc, which requires the use of a more accurate model. In the present approach, the hot plasma dielectric response is formulated in configuration space without limiting approximations by numerically calculating the plasma conductivity kernel based on the solution of the linearized Vlasov equation in nonuniform magnetic field. Results of the conductivity kernel calculation in hot collisionless plasma are presented for 1-D mirror and 2-D tokamak magnetic field configurations for ω∼ωc. Self-consistent simulation of RF fields using the calculated conductivity kernel of 1-D mirror magnetic field is made. A new parallel full wave RF code, based on the presented approach of accurate self-consistent modeling of plasma dielectric response in configuration space, is under development.

The oxygen-deficient TiO2 films deposited by a dual magnetron sputtering

This paper describes the deposition of the oxygen-deficient TiO2 films by the dual magnetron sputtering with different magnetic field configurations. The XRD survey and calculations of optical band gap demonstrate that the TiO2 films are polycrystalline with a mixture of anatase and rutile phases and have a low content of unbound Ti atoms. SEM and AFM investigations result in a columnar structure of the TiO2 films in the case of the mirror magnetic field configuration sputtering. For the closed configuration magnetic field, more intense ion bombardment of the growing films leads to the films densification. Optical and photocatalytic properties of the TiO2 films are strongly depended on the magnetic field configuration and determined by the films structure. The obtained results are interesting to modify the deposition technology of low-e coatings and solar materials.

Electron Escaping in the Magnetically Confined Electron Cloud

The morphology of magnetic equipotential lines in axisymmetric magnetic mirror field was analyzed. Based on the magnetic fluid theory of electrons, an electron cloud model formed by magnetic mirror field confined electrons was built in this paper. And twodimension differential potential equations were solved by using Runge-Kutta method. The calculation gave the Boltzmann distribution and potential distribution of electron density. The principle of both electron escape and confinement were analyzed in magnetic mirror field environment, the runaway electron current situation of the electronic cloud boundary was analyzed. Based on the leakage current of electron boundary, the balance of ionization electrons and escape electrons was used to deprive the confined region leakage current factor relationship equation in magnetic mirror environment. The relationship between the runaway electron current and the runaway factor, the effects electron temperature, electron velocity, and magnetic field lines on runaway factor were given. Furthermore, the minimum confined magnetic field needed to build electron cloud in magnetic mirror field was also given in this paper.

Helical mirrors for active plasma flow suppression in linear magnetic traps

A novel concept of helical mirror confinement with active axial and radial plasma flow control is discussed. The idea relies on the retarding force that appears when biased plasma experiences rotation in crossed electrical and helical mirror magnetic fields. Preparations for its experimental study started in Budker Institute of Nuclear Physics, Novosibirsk. Possible parameter space for a concept-exploration-class device SMOLA is identified. Details of numerical optimization of the magnetic structure of the device are presented. The main physical task for the SMOLA experiment will be direct demonstration of the helical mirror performance in simple experimental conditions at reasonably low plasma parameters.

Coherence imaging for ion temperature and flow measurements in a low-temperature helicon plasma source

This paper describes a coherence imaging system designed for spectroscopic Doppler measurements of ion light in a low-temperature (Te < 10 eV) helicon-produced argon plasma. Observation of the very small Doppler broadening of the Ar II 488 nm emission line requires very high spectral resolution, or equivalently, very large interferometric optical path delay (comparable with the coherence length of the emission line). For these polarization interferometers, this can only be achieved using large thicknesses (100 mm) of birefringent crystal. This poses special design challenges including the application of field-widening techniques and the development of passive thermal stabilization of the optical phase offset. We discuss the measurement principles and the optical design of these systems and present measurements of the line-integrated emissivity, and ion flow and ion temperatures along with tomographic reconstructions of the local values, for a cylindrical low temperature helicon discharge in a linear magnetized device with downstream magnetic mirror. Key results reveal a hollow edge-peaked temperature profile (central temperature ∼0.1 eV) and sheared rigid-body rotational flows and axial flows which are comparable with the ion thermal speed. The emission line brightness, ion temperature and azimuthal ion flows are all found to increase with increased mirror magnetic field strength.

Antifriction coatings based on a-C for biomedicine applications

This article reports on the investigation of mechanical properties of carbon films deposited by dual magnetron sputtering system with closed and mirror magnetic field. There is shown that a-C films with predominantly sp2-phase have relatively high hardness (up to 20 GPa) and low friction index (∼0.01). The influence of magnetic field on friction index is determined. The analysis of experimental data shows the obtained a-C samples can be used for biomedicine applications.

Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, two-color above-threshold ionization (ATI) experiment is conducted for measurement of the X-ray laser pulse duration, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IR laser probe. The correlation in the intensity of the sideband spectra of the 4d inner-shell photoelectrons and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.

Accessibility condition of wave propagation and multicharged ion production in electron cyclotron resonance ion source plasma.

A new tandem type source of electron cyclotron resonance (ECR) plasmas has been constructing for producing synthesized ion beams in Osaka University. Magnetic mirror field configuration with octupole magnets can be controlled to various shape of ECR zones, namely, in the 2nd stage plasma to be available by a pair mirror and a supplemental coil. Noteworthy correlations between these magnetic configurations and production of multicharged ions are investigated in detail, as well as their optimum conditions. We have been considering accessibility condition of electromagnetic and electrostatic waves propagating in ECR ion source plasma, and then investigated their correspondence relationships with production of multicharged ions. It has been clarified that there exits efficient configuration of ECR zones for producing multicharged ion beams experimentally, and then has been suggested from detail accessibility conditions on the ECR plasma that new resonance, i.e., upper hybrid resonance, must have occurred.

Electromagnetic characteristics of the superconducting magnets for the 28-GHz ECR ion source

Many laboratories have been involved in the development of electron cyclotron resonance (ECR) ion source for linear accelerators all over the world. The superconducting magnets for the 28-GHz ECR ion source consist of a Hexapole Coil and four Solenoid Coils. The Solenoid Coils produce an axial mirror magnetic field, and the Hexapole Coil produces a radial magnetic field. In this paper, the specifications of the superconducting magnets for the 28-GHz ECR ion source are deduced by using the finite-element method (FEM) to perform simulations. The research presents the result of analyses on the magnetic field and the electromagnetic force of the superconducting magnets for the ECR ion source for different the conditions of the Inner Yokes. The design of the Inner Yokes for a Hexapole Coil is performed to enhance the characteristics of the radial magnetic field and to lower the operating current level.

Three-dimensional particle-in-cell simulation of a miniature plasma source for a microwave discharge ion thruster

We have developed a three-dimensional particle model for a miniature microwave discharge ion thruster to elucidate the mechanism of ECR discharges confined in a small space. The model consists of a particle-in-cell simulation with a Monte Carlo collision algorithm (PIC-MCC) for the kinetics of charged particles, a finite-difference time-domain method for the electromagnetic fields of 4.2 GHz microwaves, and a finite element analysis for the magnetostatic fields of permanent magnets. The PIC-MCC results have shown that the electrons are well confined owing to the mirror magnetic fields and can be effectively heated in the ECR layer downstream of a ring-shaped antenna. The confinement results in the ring-shaped profiles of the plasma density along the antenna. The visual appearance of the plasma discharge of the thruster in operation was also ring-shaped. Moreover, the ions are expected to be accelerated effectively through the grid electrode without a large loss of ions toward side walls, that is, the plasma source developed here would be desirable in ion thrusters.

Radial constant of motion for particles in magnetic mirror fields

It is crucial for magnetic fusion devices that particle confinement occurs for long periods in a magnetic flux tube, and radial loss from the flux tube by a collision-free radial drift needs to be eliminated. Longitudinal, as well as radial, confinement is required. Two standard constants of motion, the energy and the magnetic moment of the gyrating particle, provide longitudinal confinement. A third constant of motion, which implies bounded radial motion, would be sufficient for radial confinement, but it is often impossible to identify such an invariant. A closed form expression for a radial invariant is derived for magnetic mirrors with a stabilizing quadrupolar field. A weak radial electric field, controlled by electrically biased endplates, is a tool for making a collision-free motion radially bounded in open systems. Experimental results in such magnetic confinement schemes indicate a qualitative agreement with our predictions for the existence of a radial invariant. Voltage and power requirements for the biased endplates are vanishingly small if the magnetic drifts are minimized in the magnetic field design. The power requirements to sustain the biased potentials are expected to be vanishingly small for a gross stable plasma.

An algorithm for approximating the L * invariant coordinate from the real‐time tracing of one magnetic field line between mirror points

AbstractThe L * invariant coordinate depends on the global electromagnetic field topology at a given instance, and the standard method for its determination requires a computationally expensive drift contour tracing. This fact makes L * a cumbersome parameter to handle. In this paper, we provide new insights on the L * parameter, and we introduce an algorithm for an L * approximation that only requires the real‐time tracing of one magnetic field line between mirrors points. This approximation is based on the description of the variation of the magnetic field mirror intensity after an adiabatic dipolarization, i.e., after the nondipolar components of a magnetic field have been turned off with a characteristic time very long in comparison with the particles' drift periods. The corresponding magnetic field topological variations are deduced, assuming that the field line foot points remain rooted in the Earth's surface, and the drift average operator is replaced with a computationally cheaper circular average operator. The algorithm results in a relative difference of a maximum of 12% between the approximate L * and the output obtained using the International Radiation Belt Environment Modeling library, in the case of the Tsyganenko 89 model for the external magnetic field (T89). This margin of error is similar to the margin of error due to small deviations between different magnetic field models at geostationary orbit. This approximate L * algorithm represents therefore a reasonable compromise between computational speed and accuracy of particular interest for real‐time space weather forecast purposes.

An inverted cylindrical sputter magnetron as metal vapor supply for electron cyclotron resonance ion sources.

An inverted cylindrical sputter magnetron device has been developed. The magnetron is acting as a metal vapor supply for an electron cyclotron resonance (ECR) ion source. FEM simulation of magnetic flux density was used to ensure that there is no critical interaction between both magnetic fields of magnetron and ECR ion source. Spatially resolved double Langmuir probe and optical emission spectroscopy measurements show an increase in electron density by one order of magnitude from 1 × 10(10) cm(-3) to 1 × 10(11) cm(-3), when the magnetron plasma is exposed to the magnetic mirror field of the ECR ion source. Electron density enhancement is also indicated by magnetron plasma emission photography with a CCD camera. Furthermore, photographs visualize the formation of a localized loss-cone - area, when the magnetron is operated at magnetic mirror field conditions. The inverted cylindrical magnetron supplies a metal atom load rate of R > 1 × 10(18) atoms/s for aluminum, which meets the demand for the production of a milliampere Al(+) ion beam.

Tandem Mirror Experiment for Basic Fusion Science

Research on controlled nuclear fusion has been largely concentrated on plasma confinement using toroidal magnetic fields. Toroidal systems are complex. A simpler magnetic confinement system may provide a valuable platform for understanding fusion plasmas. The linear mirror machine has delivered good performance with the potential of giving a direct conversion of nuclear energy into electric power. The GAMMA-10 (G-10) linear mirror confinement system at Tsukuba University demonstrated the principle of the direct conversion of plasma energy into electric power on a small scale from the exhaust plasma in the exterior divertor chamber. The tokamak fusion system has to prove that the 10 to 15 MA of plasma current can be sustained continuously with acceptable efficiency. Plasma confinement is due to the magnetic field from the plasma current in tokamaks. There is room for creative new solutions in the magnetic confinement of fusion plasmas, and consideration is given for the alternative approach of using a linear machine with high magnetic mirror fields and the direct conversion of the high temperature escaping plasma to electric power.

Etching of CVD diamond films using oxygen ions in ECR plasma

Etching with oxygen ions produced by ECR plasma with an asymmetric magnetic mirror field was investigated as a potential technique for polishing CVD diamond. The morphology, structure and roughness of the diamond film surface before and after etching were analyzed respectively using scanning electron microscope (SEM), Raman spectroscopy and surface roughness measuring instrument. It was found that the ridges on diamond surface had been preferentially etched away and thereby the surface roughness decreased from 3.061 to 1.083μm after 4h etching. Meanwhile, non-diamond phase appeared on surface and dramatically increased with the extending of etching time. In order to fundamentally understand the etching mechanism, an etching model of diamond film was reasonably proposed on the ground of the experimental results and the theory of plasma physics. The as-generated ions taking screw movement are firstly accelerated along the magnetic field lines in the plasma and collisional presheath, and then deflected from their route towards the diamond film in the MP. When coming into Debye sheath, the motion of ions will be deflected further and strongly accelerated by electric field in the direction normal to the (111) crystal facets. This process gave rise to energetic ion bombardment towards every (111) crystal face, and thereby caused preferential etching of pyramidal crystallites.

Modeling multiple-frequency electron cyclotron resonance heating

Electron cyclotron resonance (ECR) heating influences two of the main parameters (electron temperature and, indirectly, density) that determine the charge state of the ions produced in an ECR ion source (ECRIS). Therefore, various schemes to optimize ECR heating in the ECRIS have been pursued such as multiple-frequency heating, the radio-frequency tuning effect, volume heating, or wide-band heating. We investigate two-frequency ECR heating of electrons in a simple magnetic mirror field by right handed circularly polarized waves with infinite phase velocity. The study shows a heating barrier different from the well-know adiabatic barrier. Study also revealed a mechanism whereby multiple frequencies give improved heating. A preliminary interpretation of the study is presented.