Hiromasa Takeno

Basic Experimental Simulation of a Traveling Wave Direct Energy Converter for a D?3He Fusion Reactor

We simulated a traveling wave direct energy converter for application in a D–3He fusion reactor. The deceleration of a simulated ion beam was studied, and the dependence of the efficiency of the decelerator on its length was examined. The effectiveness of spatial variation in the phase velocity of the traveling wave was demonstrated experimentally. Optimization of the structure of the decelerator is discussed with the aid of numerical simulations. By employing the proper decelerator structure, the efficiency per unit length of about 0.2 with the normalized decelerator length of about 2.5 is expected.

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.

Spatial structure of waves and plasma uniformity in planar microwave discharges

The spatial structure of waves and plasma uniformity in microwave discharges using a multi-slotted planar antenna are investigated experimentally and by calculation. The wave field amplitude and phase are measured in the axial and azimuthal directions, and are compared with three-dimensional finite-difference time-domain calculation result. The wave mode in the plasma does not change with various densities, and, as a consequence, spatially uniform plasmas are obtained for a wide range of parameters being free from abrupt changes associated with surface wave eigenmodes.

Studies on plasma direct energy converters for thermal and fusion-produced ions using slanted cusp magnetic and distributed electric fields

Two types of direct energy converters, cusp direct energy converter (CUSPDEC) and travelling-wave (TW) DEC, used to produce electricity from thermal ions and fusion products in an advanced fuelled fusion, are investigated using small-scale devices. In 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. Efficiencies of energy conversion of separated ions with large thermal spread of energy are measured to be ~55%. An additional lateral electrode, together with the existing collector, constitutes a two-stage ion collector that provides distributed ion-decelerating fields. From the measured voltage–current characteristics, the efficiency of this collector is estimated to be improved to 65–70%, which is consistent with the calculation. Fusion-produced fast ions enter into TWDEC and are velocity-modulated by RF fields, bunched and then decelerated by RF travelling-wave fields on the decelerator to produce RF power. The TWDEC device has shown that the energies of ions of 3–6 keV can be decreased by 10–15% for a one-wavelength decelerator. This would give a total efficiency of 60–70% for a full-length decelerator. A novel system is being investigated for further improvement, in which the incoming ions are deflected transversely, according to each energy, to form a fan-shaped beam and a distributed electrode array for modulation and deceleration generates travelling-waves appropriate to each ion path depending on the energy.

Experimental and Simulation Studies of Gas Phase Reaction in Planar Microwave Plasma

It is necessary to supply nitrogen radical fluxes in high uniformity to form high-quality nitrogen-incorporated films. An experiment on gas phase chemical reaction using a microwave discharge device with a multi-slotted planar antenna is performed. We use a three-dimensional simulation code, which calculates wave propagation in plasma obtained by the finite difference time domain method, power deposition, and plasma transport using a fluid model. The code can reproduce experimental results to a large extent. The code is capable of calculating several types of gas-phase reaction of neutral species. The results of both the experiment and the simulation show that the uniformity of the density distribution of nitrogen radicals strongly depends on the uniformity of the plasma.

Particle Discrimination Experiment for Direct Energy Conversion

Abstract A direct energy conversion system designed for D-3He fusion reactor based on a field reversed configuration employs a venetian-blind type converter for thermal ions to produce DC power and a traveling wave type converter for fusion protons to produce RF power. It is therefore necessary to separate, discriminate, and guide the particle species. For this purpose, a cusp magnetic field is proposed, in which the electrons are deflected and guided along the field line to the line cusp, while the ions pass through the point cusp. A small-scale experimental device was used to study the basic characteristics of discrimination of electrons and ions in the cusp magnetic field. Ions separated from electrons are guided to an ion collector, which is operated as a one-stage direct energy converter. The conversion efficiency was measured for cases with different values of mean and spread of ion energy. These experiments successfully demonstrate direct energy conversion from plasma beams using particle discrimination by a cusp magnetic field.

Enhanced Energy Recovery in a Secondary Electron Direct Energy Converter through Reduction of the Magnetic Mirror Effect

Abstract With an aim to improve the total efficiency of a D-3He nuclear fusion direct energy conversion system, a secondary electron direct energy converter (SEDEC) is proposed. The incident high-energy protons in an SEDEC penetrate a large number of foil electrodes aligned in the direction of the proton beam, and emitted secondary electrons are recovered. The results of the initial experiments showed that most of the secondary electrons flowed into anteroposterior electrodes and did not arrive at the electron collector located alongside and perpendicular to the direction of the proton beam. A magnetic field was introduced to push the electrons toward the electron collector, but it was not effective for energy recovery. This technical note analyzes the trajectories of electrons in the presence of the magnetic field and proposes and examines a revised arrangement of permanent magnets. The arrangement of the magnets along one side of the proton beam greatly improved the energy recovery; however, the recovery level was lower than that without magnets.

Basic Characteristics of Secondary Electron Emission from Foil Electrodes for New Energy Recovery Scheme of High Energy Ions in an Advanced Fusion

The new energy recovery method using secondary electron emission has been studied in order to improve energy recovery from high energy protons of fusion products in D-3He nuclear fusion generation. The model experiments were performed by using the tandem electrostatic accelerator and the basic characteristics were investigated. According to our results, for penetration aluminum is better as a target material than copper, H+ is better than He2+, and higher energy beam is better which agree with numerical calculations. A qualitative characteristic of secondary electron emission dependence on beam energy was also obtained.

Improvement of Structure of Traveling Wave Direct Energy Converter Simulator for Ion Flux with Wide Energy Spread

Abstract In D-3He fusion, most of fusion energy is carried by kinetic energy of created protons of 14.7 MeV. Concept of traveling wave direct energy converter (TWDEC) was proposed as an effective energy converter with less handling voltage. Although fundamental researches on TWDEC have been reported, the dependence on energy spread of flowing ions has not been investigated in spite of its significant effects against conversion efficiency. The paper treats this subject by an application of TWDEC simulator to GAMMA 10 tandem mirror whose end-loss flux has relatively wide energy spread. The energy distribution of the end-loss flux was measured, and a new structure of TWDEC simulator was designed according to the measured result. The conversion efficiency was estimated by one-dimensional numerical orbit calculations showing the designed structure had enough performance as TWDEC.

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

Abstract 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.