Hiromu Momota

Conceptual design of the D-3He reactor artemis

AbstractA comprehensive design study of the D-3He-fueled field-reversed configuration (FRC) reactor Artemis is carried out for the purpose of proving its attractive characteristics and clarifying the critical issues for a commercial fusion reactor. The FRC burning plasma is stabilized and sustained in a steady equilibrium by means of preferential trapping of D-3He fusion-produced energetic protons. A novel direct energy converter for 15-MeV protons is also presented. On the bases of consistent fusion plasma production and simple engineering, a compact and simple reactor concept is presented. The D-3He FRC power plant offers a most attractive prospect for energy development. It is environmentally acceptable in terms of radioactivity and fuel resources, and the estimated cost of electricity is low compared with a light water reactor. Critical physics and engineering issues in the development of the D-3He FRC reactor are clarified.

High‐energy tail formation by a monochromatic wave in the magnetized plasma

High‐energy tail formations due to the monochromatic wave in a magnetized plasma are studied numerically and analytically. By calculating the phase space trajectories of 10 000 particles, initially Maxwell‐velocity‐distributed, in the presence of a uniform magnetic field and a sinusoidal wave traveling closely in the perpendicular direction with the frequency of cyclotron harmonics, some properties of particle acceleration are clarified. The acceleration mechanism can be described by a modification of trapping theory and two types of stochastic acceleration. The behavior of the high‐energy tail formation depends on the magnitude of ω/Ω. For small ω/Ω (ω/Ω≲10), the cyclotron harmonics resonance is very important. The ratio of the perpendicular wavelength to the average Larmor radius and the wave amplitude play an important role in determining the ratio of tail to the bulk portion.

Positional Instabilities in a Tokamak with a Resistive Shell

The investigation of positional instabilities, that is, vertical displacement and horizontal expansion of the plasma loop, is extended to a tokamak with a resistive shell. The shell current induced by a small displacement of the current-carrying plasma column produces a restoring force, which contributes to the stabilization. The quantitative analysis of the effect due to the shell shows that the finiteness of the minor radius of the plasma column reduces the effective skin time of the shell τs from the intrinsic one. Consequently it is shown that although the stability condition is not altered, a resistive shell restrains the growth rate of the instability to the order of τs-1, in a wider region than the stable one.

Stochastic model of electron-cyclotron heating in a magnetic mirror

A heating mechanism of electron plasmas by high-power microwaves in a magnetic mirror is investigated theoretically, with reference to experiments in a device named TP-M. The heating is assumed to be due to a microwave mode propagating perpendicular to the magnetic field since higher harmonic resonances, the main features of the experiments, exist. The heating mechanism can be interpreted in terms of a stochastic process, a random walk in velocity space.It is confirmed numerically that localized resonance zones of finite width exist, the electrons are effectively heated only in the resonance zones, and that the presence of a randomization process of the relative phase relation between the wave and the electron gyration is essential for the heating process. On the basis of the numerical analysis, the heating process is treated analytically. The electrons are assumed to pass the resonance zones repeatedly in the course of oscillatory motions between turning points, and the relative phase relation is assumed to be random at each passage through the resonance zone. The heating rate is calculated and found to agree with the experimental value. The causes of phase randomization, the effects of the loss cone and the observed saturation of electron temperature are also discussed.

RF Ion Source-Driven IEC Design and Operation

Abstract The next step needed to achieve higher neutron yields and improved neutron production efficiency with Inertial Electrostatic Confinement (IEC) sources requires operation with an external ion source so that the reaction chamber pressure is controlled separately for the source pressure. This paper presents recent progress in IEC research at the UIUC using a unique external ion source ILLIBS (Illinois Ion Beam Source). When filled with deuterium, the IEC provides ~108 2.5-MeV D-D fusion neutrons/sec at steady-state. The design and operation of a radiofrequency (RF) ion gun designed for this purpose is also discussed.

Virtual Cathode in a Stationary Spherical Inertial Electrostatic Confinement

“Double-well” potential structure (virtual cathode formation) is studied in a stationary spherical inertial electrostatic confinement (SIEC) using the nonlinear Poisson’s equation and particle densities derived from kinetic theory. A novel method to obtain a spherically symmetric stationary distribution function is introduced and an integral-differential equation is simplified by applying a relevant approximated formula for an integral. Electron and ion beams are collision-free, and their velocities are roughly aligned toward the spherical center, but with a slight divergence. Analyses show that the angular momentum of ions and the smaller one of electrons create a virtual cathode, i.e., a double-well structure, of the electrostatic potential on a potential hill near the center. The density limit of an SIEC is exhibited, and the condition relevant to form a deep potential well is presented.

Destruction of Magnetic Surfaces in a Divertor Region Attributed to a Discrete Structure of Magnetic Coils

The destruction of magnetic surfaces near a separatrix of a divertor is analyzed. Unperturbed magnetic surfaces formed by a plasma current and a divertor current are assumed. Destruction of magnetic surfaces is attributed to perturbations of magnetic fields, which are assumed to be brought from discrete structure of magnetic coils. Analysis is based on “Stochasticity” and a spread of divertor region is calculated in terms of a ripple of the magnetic field.

A collimator-converter system for IEC propulsion

The collimator-converter system extracts fusion power from D-3He fueled IEC devices and provides electricity needed to operate ionic thrusters and other-power components. The whole system is linear and consists of a series of collimator units at the center, magnetic expander units at both sides of the fusion units, followed by direct energy converters at both ends. This system is enclosed in a vacuum chamber with a magnetic channel provided by magnetic solenoids out of respective chambers. The fusion unit consists of an IEC fusion core, a pair of coils anti-parallel to the solenoid coils, and a stabilization coil that stabilizes the position of coil pair coils. The IEC fusion core is installed at the center of the pair coils. After the magnetic expander, velocities of fusion particles from D-3He fueled IEC units are directed to the magnetic channel, which guides energetic fusion particles as well as leaking unburned fuel components to a high-efficiency traveling wave direct energy converter (TWDEC). Leaki...

Progress in Development of a Converging Beam Neutron Source for Driving a Sub-Critical Fission Reactor

Several laboratories are studying the possibility of a fission reactor system based on driving a sub-critical assembly using an accelerator-spallation target neutron source. The objective is to effectively eliminate possible criticality and meltdown accidents, increasing plant safety. However, one disadvantage is the large cost projected for the accelerator-driven source. In an ICONE-8 paper we proposed to overcome this problem by use of a Converging Beam Neutron Source (CBNS) to produce 14-MeV D-T fusion neutrons to drive the sub-critical core. [1] The CBNS is analogous to an accelerator-plasma target device with built-in re-circulation of the ions. It offers the unique advantage of being small enough to allow insertion of multiple “modular” units in fuel channel locations (cf. the large single target used in accelerator-drive designs). As proposed in an ICONE-9 paper, a first important step in development of such systems might be use in low power research reactors. [2] This reduces the neutron source strength requirement to a level only slightly above that obtained with present IEC experiments. Still, a key step for CBNS development is to increase the neutron production efficiency obtained in previous small-scale experiments. To do this we have recently developed a unique RF-driven ion source so that the ion production region can be separated from the main CBNS chamber. This has the combined advantages of allowing ion production at relatively high pressure, while the CBNS chamber can be pumped to ultra-low pressure. Initial experiments with this arrangement are presented here and it is shown that a very favorable scaling to the yields required for research reactor operation are predicted.Copyright

Ion cyclotron heating and energy confinement of plasma in a toroidal quadrupole

With the use of r.f. electric fields, the heating of the plasma and the improvement in the energy confinement are studied for an open-ended toroidal quadrupole. From an analysis of the loss mechanisms of the plasma and the heating rate, both theoretical and numerical, some optimizations have been made. The resulting heating and energy confinement are exhibited in computer experiments. The plasma can be heated easily and an improvement in the energy containment time of approximately 10% is obtained.