Yukihiro Tomita

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.

Direct observation of the decay of beauty particles into charm particles

Abstract The associated production of a pair of beauty particles B− and B 0 by a 350 GeV π− interaction has been observed in an emulsion target inserted in an array of silicon microstrip detectors. Both beauty particles decay into charm particles, both of which are also observed to decay in the emulsion. Two negative muons were identified and their momenta measured in a large muon spectrometer. One muon has a pT of 1.9 GeV/c and is associated with a beauty particle decay. The other, with a pT of 0.45 GeV/c is associated with a charm particle decay. The flight times of the two beauty particles are respectively (0.8 ± 0.1) × 10−13 s and (5+2−1) × 10−13 s. Alternative interpretations of this event have negligible probability.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

Some properties of charmed particles produced in π−-nucleus interactions

Abstract The azimuthal correlation distribution of 102 charmed-particle pairs observed in the hybrid emulsion experiment WA75 is compared with theoretical predictions. The various pairs - (D − D 0 ), (D − D + ), (D 0 D 0 ) and (D + D 0 )-all s how, within statistical error, the same azimuthal correlation distribution, demonstrating its independence from the specific nature of the production channel. Among the decays of 150 charged charmed particles and 138 neutral ones seen, higher multiplicities are favoured for hadronic as opposed to semileptonic decays. The data are consistent with the muonic decays of charged D mesons proceeding through the channels (μ ± , v, K 0 ) and [μ ± , v, K ∗0 (892)] , the fraction through K 0 being 0.76±0.06.

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.

Use of polarized helium-3 for the energy production

Abstract After the discovery of plentiful of minable helium-3 on the lunar surface, fusion scientists have tried to find out the methods for utilizing this attractive fuel for fusion reactors. Among various approaches, a field-reversed configuration (FRC) for confinement of fusion plasma appears the most promising candidate for a D- 3 He fueled fusion reactor. A conceptual design of D- 3 He fueled FRC reactor “ARTEMIS” (Momota et al., in: Proc. 7th Int. Conf. on Emerging Nuclear Energy Systems, Chiba, Japan, 1993) has been carried out showing that bases of engineering needed for achieving a commercial reactor are conventional and the cost of electricity from “ARTEMIS” is estimated as cheap as approximately 30 mills/(kWh). A low neutron yield allows us large freedom of reactor materials and reduces the problem of disposal of radioactive waste. In this paper, we will examine the use of polarized D- 3 He fuels. A favorable characteristic of polarized fuels lies on the reduction of neutron yield and the compactness of the fusion core. Because of the enhancement of reactivity of D- 3 He reaction by applying polarization, the neutron fraction in the total fusion power decreases to 1.3% with the same volume of “ARTEMIS” and consequently neutron wall loading is 72 kW/m 2 . The wall loading should be compared with 180 kW/m 2 from “ARTEMIS” or 10 000 kW/m 2 from a D-T fueled reactor. Consequently, this low neutron mode gives us large freedom in choosing reactor materials. The fusion reactor using polarized fuels with the same neutron yields as “ARTEMIS” decreases its size from 196 to 33 m 3 . This operation mode gives us the possibility of developing an economic fusion reactor.

A System for Long-Pulse REB Generation

A high-voltage pulse generator system producing intense relativistic electron beams (REB)(1.5 µs pulse width, 30 kA peak current, 1 MeV energy) was developed for the use of REB ring formation. This system consists of a Marx generator, 7-m-long transmission lines with plastics-water hybrid insulators and a magnetically insulated transmission line connected with a cathode. Plastics of the hybrid insulators mainly withstand electric breakdown, whereas local electric field concentration is degraded by water having a high permittivity. A high vacuum in the REB formation vessel is realized by the use of an interface of ultrahigh-molecular polyethylene between the line and the vessel. The system has been operated more than twenty thousand shots without encountering a breakdown.

Conducting Liquid Conveyer of Plasma Rings

Current-carrying plasma rings can be conveyed in a cylindrical channel with a conducting liquid flow to which the outer poloidal fields of the rings freeze. Fast tilting motion of the ring is stabilized when the liquid surface is set close to the ring within a critical distance. The effects of a resistive tube duct installed for the liquid are also examined.

High-Current Runaway Electron Beam in a Tokamak Plasma

An equilibrium of toroidal plasma with a large electron-beam current has been realized using the runaway effect in a tokamak. Reproducible runaway-mode discharges are obtained with pure hydrogen gas by the help of intense titanium flashing which results in a low electron density. The beam current is estimated to be more than a half of the total toroidal current. The equilibrium of this discharge is maintained by a strong vertical field because the beam pressure gives rise to an additional increase in Shafranov Λ. The beam pressure is estimated to be more than 80% of the total pressure. The kinetic energy and the spatial distributions of beam electrons are studied by seeing X-ray emission from a tungsten wire inserted into the plasma. The increase of Shafranov Λ due to beam pressure is enhanced by puffing gas into the discharge.

Experiment on Current Decay of Intense REB Ring with a Large Self-Magnetic Energy

Experiment on intense REB rings carried out in the toroidal device SPAC-VII demonstrated that the time dependent self magnetic flux plays a fundamental role on the current decay of the ring under the collisions with the plasma and/or neutral particles. The momentum distribution of the beam electrons evolves self-consistently under the influence of the electric field induced by the decay of REB ring current as well as the collisions. This mechanism was clearly observed by puffing hydrogen or argon gas on REB rings. Some examinations of experimental results are also given.