Slanted Field Research Articles

Fast-Switching GaN-Based Lateral Power Schottky Barrier Diodes With Low Onset Voltage and Strong Reverse Blocking

GaN-based heterostructure lateral Schottky barrier diodes (SBDs) grown on n-SiC substrate are investigated in this letter. These SBDs own very low onset voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> = 0.43 V, high reverse blocking V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BR</sub> >; 1000 V, very low capacitive charge of 0.213 nC/A, and a very fast recovery time of 10 ps. These unique qualities are achieved by combining lateral topology, GaN:C back-barrier epitaxial structure, fully recessed Schottky anode (φ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> = 0.43 eV), and slanted anode field plate in a robust and innovative process. Diode operation at elevated temperature up to 200 °C was also characterized.

Studies on Density Dependence of Charge Separation in a Direct Energy Converter Using Slanted Cusp Magnetic Field

In an advanced fusion, fusion-produced charged particles must be separated from each other for efficient energy conversion to electricity. The CuspDEC performs this function of separation and direct energy conversion. Analysis of working characteristics of CuspDEC on plasma density is an important subject. This paper summarizes and discusses experimental and theoretical works for high density plasma by using a small scale experimental device employing a slanted cusp magnetic field. When the incident plasma is low-density, good separation of the charged particles can be accomplished and this is explained by the theory based on a single particle motion. In high density plasma, however, this theory cannot be always applied due to space charge effects. In the experiment, as gradient of the field line increases, separation capability of the charged particles becomes higher. As plasma density becomes higher, however, separation capability becomes lower. This can be

Correlation between magnetocapacitance effect and polarization flop direction in a slanted magnetic field in multiferroic helimagnets

The relationship between the magnetocapacitance effect and rotation direction of electric polarization (P) in a canted magnetic field has been investigated for multiferroic RMnO3 (R = Tb1−xDyx and Eu0.6Y0.4). We observed a clear correlation between the enhancement of the magnetocapacitance effect and the rotation direction of P in a P-flop transition. These results indicate that the mobility and the stability of the 90° domain wall in a P-flop transition are dominated by its thickness.

Suprathermal electron spectra in the Venus ionosphere

[1] In this study, a multistream kinetic model is used to derive the suprathermal electron intensity in the Venus ionosphere, to be compared with the observations made by the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) instrument onboard Venus Express (VEx) on 18 May 2006. Input parameters of the model are chosen to be consistent with the detailed ephemeris information. We consider two cases for the magnetic field line configuration. The first assumes vertical magnetic field lines, while in the second the configuration is consistent with the VEx Magnetometer (MAG) measurements for that particular orbit. The model calculations suggest that the energy spectrum of suprathermal electrons not only depends on the local photoelectron production but is also strongly influenced by transport as well as energy degradation. We confirm the postulation of Coates et al. (2008) that the spectral features seen in the ASPERA-4 ELS data are signatures of O+(4S0, 2P0, and 2D0) production by solar HeII 30.4 nm photons at altitudes where vertical transport is important. We also identify additional photoelectron peaks, in particular the peak associated with the ionization of atmospheric He by the solar HeII 30.4 nm photons. The combination of the identified photoelectron peaks provides a validation of the proposed spacecraft potential value of ∼−5 eV derived from the O+-related features by Coates et al. (2008). The model results indicate that the condition of local equilibrium is satisfied for suprathermal electrons below ∼155 km on Venus. However, transport becomes effective at higher altitudes, significantly altering the secondary electron production rate and leading to strongly anisotropic suprathermal electron flow. For the case with the MAG-derived, slanted magnetic field configuration, we make a data-model comparison in terms of both the absolute magnitude of the suprathermal electron intensity and the appearance of spectral peaks. The comparison suggests that the actual magnetic field lines are probably inclined more vertically than a simple extrapolation from the MAG measurements.

Plasma Direct Energy Converter for Thermal Ions Using a Slanted CUSP Magnetic Field and Two-Stage Deceleration

Plasma Direct Energy Converter for Thermal Ions Using a Slanted CUSP Magnetic Field and Two-Stage Deceleration

Control of the polarization flop direction by a tilted magnetic field in multiferroicTbMnO3

In spin-driven ferroelectrics, often referred to as magnetoelectric (ME) multiferroics, a domain wall separates two magnetic as well as ferroelectric domains. Therefore, it is expected that the control of such an ME domain wall could result in a large ME effect. Here, we show that the direction of a slanted magnetic field controls whether the electric polarization $(\mathbit{P})$ rotates by $+90$ or $\ensuremath{-}90\ifmmode^\circ\else\textdegree\fi{}$ upon the $\mathbit{P}$-flop transition in a prototypical spiral magnetic ferroelectric ${\text{TbMnO}}_{3}$. This behavior is discussed in terms of the domain-wall energy of a spiral magnet in a slanted magnetic field.

Plasma Direct Energy Converter for Thermal Ions Using a Slanted Cusp Magnetic Field and Two-Stage Deceleration

A direct energy converter (DEC) designed for thermal ions escaping from a fusion reactor consists of a cusp magnetic field and one-or two-stage decelerating electrodes. In this CUSPDEC, magnetized electrons are deflected along the field lines of the cusp magnetic field to the line cusp region and collected by an electron collector, while weakly magnetized ions can traverse the separatrix and enter into the point cusp region. Thus, ions are separated from electrons, and flow into an ion collector to produce DC power. A normal cusp magnetic field enables us to separate electrons and ions for low energy electrons from a test plasma source, but not for electrons with much higher energies from the tandem mirror GAMMA10. The reason for this is found that the high energy electrons do not follow the field lines due to a high potential applied to the ion collector for ion deceleration. Use of a slanted cusp field has resolved the difficulty resulting in good separation. The efficiency of energy conversion of separated ions with wide spread in energy is ~55 % for a one-stage decelerating electrode. An additional lateral electrode, together with the existing collector, constitutes a two-stage ion collector that provides distributed ion-decelerating fields. The system has revealed improvement in efficiency. From the measured voltage-current characteristics, the efficiency of this two-stage collector is estimated to have a value of 65-70 % at an optimum condition.

Influence of current ramp rate on voltage current measurement of a conduction-cooled HTS magnet

High-temperature superconductors (HTS) have notably different voltage current characteristic compared to the low-temperature superconductors (LTS). Due to the anisotropy and slanted electric field – current density characteristics the loss of stability in a Bi-2223/Ag magnet is viewed as a global temperature increase inside the coil rather than a local normal zone. Therefore, the quench current depends strongly on the cooling conditions. In this paper a finite element method based analysis method is presented and example runs are carried out in order to explain in detail the influence of the current ramp rate and cooling on the voltage current characteristics of a conduction-cooled Bi-2223/Ag coil at 20 and 45 K. The results show that in certain operation conditions the coil critical current has a maximum value with respect to the ramp rate used in the measurements.

Experiment on direct energy conversion from tandem mirror plasmas by using a slanted cusp magnetic field

A direct energy converter (DEC) designed for thermal ions escaping from a linear or near-linear device consists of a cusp magnetic field and decelerating electrodes. The electrons are deflected along the field lines and consequently separated from ions that are not fully magnetized. The ions are led to the decelerating electrodes to produce dc power. This type of DEC, the CUSPDEC, is applied to the GAMMA 10 tandem mirror in order to investigate the capability of separation of charged particles as well as to demonstrate energy conversion from ions. The separation of electrons and ions with energies of the order of kilo-electron Volt is achieved by using a slanted cusp magnetic field for the first time. It is also demonstrated that the separated ions are decelerated by the electric field in front of ion collectors and flow into the collectors at a high potential to produce electricity.

Study of Efficient Electron Cyclotron Wave Coupling with Grooved Mirror Polarizer in the GAMMA 10 Tandem Mirror

An improvement of electron cyclotron heating (ECH) system in the central cell of the GAMMA 10 tandem mirror is carried out by the use of two grooved mirrors. Two grooved mirrors consist of a twister and a circular polarizer. In case of the ECH system in the central cell region, fundamental ECH is examined and launched microwave beam from the antenna propagates through the two parabolic mirrors. The incident microwave is radiated from the second mirror at a position with magnetic field intensity B=2.0 T and with an incident angle of 35.1 degrees. Two grooved mirrors can generate suitable elliptical polarizations for both of ordinary mode (O-mode) and extraordinary mode (X-mode) in oblique launch with a slanted magnetic field line. The first results of the polarization control of the incident wave for high power ECH experiments are reported.

Research on Characteristics of Particle Discrimination and Direct Energy Conversion for Cusp Direct Energy Converter

In a D-3He fusion reactor, direct energy conversion is expected, and discrimination of charged particles from each other is needed to produce electric power. The authors have performed simulation experiments for discrimination and direct energy conversion in a CUSPDEC device with a slanted cusp magnetic field. This paper presents a scaling of particle discrimination with proposition of an appropriate scaling factor based on the consideration of the Störmer potential. Experimental results with the factor up to 0.7 for ions and 80 for electrons are presented. The paper also presents results of direct energy conversion of ions in higher energy region up to 5 keV. It is confirmed that the conversion efficiency does not depend on averaged energy, but depends on the broadness of energy distribution function.

Direct Energy Conversion Experiment on the GAMMA 10 Tandem Mirror

A direct energy converter (DEC) designed for thermal ions escaping from a fusion reactor consists of a cusp magnetic field and one or two stage decelerating electrodes. The electrons are deflected along the field lines and consequently separated from thermal ions that are not fully magnetized. The ions are led to the electrodes to produce DC power. For basic investigation of this type of DEC, the CUSPDEC, a small-scale experimental device is constructed and its characteristics have been investigated by using a low-energy plasma source. In this paper, the device is applied to the GAMMA 10 tandem mirror in order to investigate the capability of separation of charged particles as well as to demonstrate energy conversion from ions in much more reactor-relevant environment. The separation of electrons and ions with energies of the order of keV is achieved by using a slanted cusp magnetic field for the first time. It is also found that the separated ions are decelerated by the electric field in front of ion collectors and flow into the collectors at a high potential to produce DC power.

Optimization of HTS superconducting magnetic energy storage magnet volume

Nonlinear optimization problems in the field of electromagnetics have been successfully solved by means of sequential quadratic programming (SQP) and the finite element method (FEM). For example, the combination of SQP and FEM has been proven to be an efficient tool in the optimization of low temperature superconductors (LTS) superconducting magnetic energy storage (SMES) magnets. The procedure can also be applied for the optimization of HTS magnets. However, due to a strongly anisotropic material and a slanted electric field, current density characteristic high temperature superconductors HTS optimization is quite different from that of the LTS. In this paper the volumes of solenoidal conduction-cooled Bi-2223/Ag SMES magnets have been optimized at the operation temperature of 20 K. In addition to the electromagnetic constraints the stress caused by the tape bending has also been taken into account. Several optimization runs with different initial geometries were performed in order to find the best possible solution for a certain energy requirement. The optimization constraints describe the steady-state operation, thus the presented coil geometries are designed for slow ramping rates. Different energy requirements were investigated in order to find the energy dependence of the design parameters of optimized solenoidal HTS coils. According to the results, these dependences can be described with polynomial expressions.

PM—Power and Machinery: Development of a Slow Active Suspension for Stabilizing the Roll of Spray Booms, Part 2: Controller Design

To prevent local under- or over-application of chemicals, a spray boom must be kept parallel to the soil. On a slanted field, the operator, driving a sprayer equipped with a passive boom suspension, has to turn the boom manually in a skewed position. This paper presents the development of a slow active controller to do this automatically and to add damping to the suspension. A controller, designed for a cable suspension, captures the signals of two ultrasonic sensors, measuring the distance between the boom and the soil, and activates a low-power electrical DC motor which positions the boom automatically. Different control strategies have been tried out in simulation and in a laboratory experiment on a six-post electro-hydraulic shaking table. The best controller was implemented on a real spraying machine and validated under field conditions.

Basic Studies on Discrimination and Deceleration of Charged Particles in a Direct Energy Converter

Particle discrimination and deceleration are studied with employing experimental devices which simulate direct energy converters used for D–3He reactor. A Cusp-DEC simulator with a slanted cusp field is constructed, and the preparative numerical simulation about it shows the better discrimination is expected for ions with a small pitch angle. Experimental results in a TWDEC simulator are presented. Due to the measurements of energy distribution, the effectiveness of spatially varied wavelength structure is demonstrated. The simple 1-D orbit calculation shows that the efficiency of the same extent as that of the 2-D numerical simulation would be achieved in the experimental device.

The evaluation of mode purity for ECCD using single deep grooved polarizer

A new type single mirror polarizing system is proposed for Electron cyclotron current drive (ECCD) in toroidal plasma. A single deep grooved mirror (DGM) can generate suitable elliptical polarizations for both of ordinary mode (O-mode) and extraordinary mode (X-mode) in oblique launch with a slanted magnetic field line. Estimated mode purity of O and X modes on the plasma surface is higher than 90% for almost all ECCD experimental condition.

The atmospheric electric ring current in the higher atmosphere

The atmospheric electric current flow in the ionosphere was discussed in a qualitative way at the UGGI General Assembly at Berkeley, California in 1963. The following picture emerged: The atmospheric electric fair weather current leaves the earth in a radially outward direction. As it enters the higher regions of the atmosphere and the ionospheric it is increasingly influenced by the earth's magnetic field. Because the main part of the current is crowded into the polar regions, the current density over the equatorial belt is small. A circular movement around the earth's axis results in an overall flow pattern tentatively termed, ‘the atmospheric electric ring current’. An attempt to calculate this current flow soon made it clear that the generally used simplification of the one-dimensional case with slanted magnetic field lines is not adequate—not even as a first approximation. The same is true for the assumption usually made in magnetohydrodynamics that the current follows approximately the magnetic field lines. An essential feature of the atmospheric electric ring current is that in equatorial regions the flow is forced across the magnetic field lines, the component along the lines being zero. A calculation is discussed that treats the magnetic field lines as those of a true dipole field with the corresponding tensor character of conductivity. The results of the calculation are presented as graphs of the density distribution of the ring current, the space charge distribution, the current flow, and equipotential lines.

28. Positive column in a slanted magnetic field: E M Drobyshevskiy, Zh Tekh Fiz, 36(7), July 1966, 1175–1185 (in Russian).

28. Positive column in a slanted magnetic field: E M Drobyshevskiy, Zh Tekh Fiz, 36(7), July 1966, 1175–1185 (in Russian).