Table of contents

The recent experimentally inferred values of multiplicity of deuterium-tritium fusion catalysed by muons have increased the interest in muon catalysed fusion reactors. Since the main energy expended is in pion (and consequent muon) production, it is tried to minimize the pion loss by magnetically confining pions where they are created. At the present time, it does not appear possible to achieve an energy gain by pure fusion, but it is possible to gain energy by combining catalysed fusion with fission blankets. Two new ideas for improvement of the muon fusion reactor concept are presented. The first idea is to combine the target which creates pions, the converter of pions to muons, and the synthesizer in one vessel (synergetic concept). This is accomplished by injecting a tritium or deuterium beam of 1 GeV per nucleon into DT fuel contained in a magnetic mirror. The confined pions slow down and decay to muons which are confined in the fuel whereby muon loss is kept small. The quantity of tritium necessary to keep the reactor viable has been derived. The second idea is to collect the beam passing through the target for reuse and to recirculate it, while directing the strongly interacting portion of the beam to electronuclear blankets. The present concepts are at the margin of known technologies and are based on known physical processes and data.

A global analysis of current drive in tokamaks by using waves in the ion cyclotron range of frequencies (ICRF), considering the entire antenna-plasma system, is presented. A phase shifted antenna array is used to inject toroidal momentum into the electrons. Within the context of quasi-linear theory, a Fokker-Planck calculation is combined with an ICRF wave propagation-absorption analysis which includes kinetic effects and realistic boundary conditions. The radial profile of the current induced by the mode converted ion Bernstein wave and by the magnetosonic fast wave is obtained, together with the global current drive efficiency (total induced current/total emitted power from the antennas) in the high density and temperature plasma regime. The phase dependence of the global efficiency is investigated by changing the launching conditions such as the total antenna number and the antenna spacing. – In medium size tokamaks, the electron power absorption and the associated driven current are found to be affected considerably by the plasma cavity resonance. It is also found that the global efficiency is sensitive to the antenna spacing. When the antenna spacing is increased, the global efficiency is reduced by counter current generation.

The free-boundary, axisymmetric tokamak simulation code TSC is used to model the transport time-scale evolution and positional stability of the Princeton Beta Experiment (PBX). A disruptive thermal quench will cause the plasma column to move inwards in major radius. It is shown that the plasma can then lose axisymmetric stability, causing it to displace exponentially off the midplane, terminating the discharge. The accuracy of the code is verified by modelling several controlled experimental shots in PBX.

Electron cyclotron resonance current drive in tokamak plasmas in the presence of a lower hybrid tail is investigated using a two-dimensional Fokker-Planck code. For an extraordinary mode at oblique propagation and down-shifted frequency it is shown that the efficiency of electron cyclotron current drive becomes (i) substantially greater than the corresponding efficiency of a Maxwellian plasma at the same bulk temperature, (ii) equal to or greater than that of lower hybrid waves, and (iii) comparable to the efficiency of a Maxwellian plasma at much higher temperatures. This enhancement of the efficiency results from a beneficial cross-effect of the two waves on the formation of the current carrying electron tail. The use of the ordinary mode for outside launching in the equatorial plane is also discussed and it is shown that the O-mode is generally not suited for current drive via the lower hybrid tail and that in a hot Maxwellian plasma the efficiency at down-shifted frequencies is comparable to that at up-shifted frequencies.

Bum simulations have been carried out for the DT ignitor/DD fuel pellet model by using a hydrodynamic code including neutron transport. The results showed that neutron heating has large effects on the bum performance, for instance the fusion yield and the internal tritium breeding ratio. The DD burning could be sustained by neutron heating and thus sufficient tritium could be bred by using one of the branches of the DD reaction, D + D → p + T. Furthermore, several treatments for neutron transport were compared. It was found that the treatment of the anisotropy of neutron scattering has a larger influence on the bum performance than the treatment of the time dependence of neutron transport. Finally a compressed state of the pellet was proposed as a candidate for the advanced fuel ICF reactor TAKANAWA-I.

The mechanism of convective losses in the phase preceding the formation of rotational transform is studied on the CASTOR tokamak. It is shown that convection is caused by × drift associated with a strong perpendicular electrostatic field. This field is generated by charge separation as a result of a directed flow of electrons along non-toroidal magnetic field lines intersecting the wall. Convection exceeds Bohm diffusion by a factor of 700 for a perpendicular magnetic field of 10⁻³ T.

Stable and clean AC tokamak discharges have been achieved in the STOR-1M device. The plasma current is reversed from +4.1 kA to −4.0 kA within 1.9 ms. During the reversal, no disruptive behaviour is observed, the loop voltage changes smoothly from +1 V to −5 V without any spike, and impurities are not released. An electron density of (2–4) × 10¹² cm⁻³ is maintained during current reversal. The possibility of continuous tokamak operation with a low frequency alternating plasma current is discussed.

Using data from two vertical charge exchange detectors on the Poloidal Divertor Experiment (PDX), a set of conditions have been identified for which loss of beam ions inwards in major radius is observed during a fishbone instability. Previously, it was reported that beam ions were lost only to the outside of the PDX tokamak. The losses to the inside are two orders of magnitude smaller than the losses to the outside and are consistent with numerical predictions based on the mode particle pumping theory.

The Grad-Shafranov equation for axisymmetric plasma equilibria has been solved in the ellipsoidal co-ordinate system (ρ, ζ, ϕ) with quasi-uniform current density profile up to the sixth order in ζ. Bean shaped and elongated elliptic equilibria and dee shaped equilibria can be described in this co-ordinate system. The basic characteristics of these equilibria are determined by the size, aspect ratio, elongation, poloidal beta, triangularity, and separatrix location.

The technical issues, development problems and required experiments and facilities for fusion nuclear technology have been investigated. The results have been used to develop a technical framework for a test plan that identifies the role, timing, characteristics and costs of major experiments and facilities. A major feature of this framework is the utilization of non-fusion facilities over the next 15 years, followed by testing in fusion devices beyond about the year 2000. Basic, separate effect and multiple interaction experiments in non-fusion facilities will provide property data, explore phenomena and provide input to theory and analytic modelling. Experiments in fusion facilities can proceed in two phases: (1) concept verification and (2) component reliability growth. Integrated testing imposes certain requirements on fusion testing device parameters; these requirements have been quantified. The nuclear subsystems addressed in the study are: (a) blanket and first wall; (b) tritium processing system; (c) plasma interactive components; and (d) radiation shield. The two generic classes of liquid and solid breeder blankets have significant engineering feasibility issues, and new experimental data must be obtained before selection of an attractive design concept. Liquid metal blanket issues are dominated by problems related to momentum, heat and mass transfer, which can be addressed in non-neutron test facilities. Solid breeder blanket issues are, however, dominated by the effects of radiation, including heating, transmutation and damage, which can be reasonably addressed in fission reactors. The tritium processing uncertainties are primarily related to the control and recovery systems, and most can be addressed in existing and planned non-neutron facilities. A dominant feature of plasma interactive components is the strong interrelation to both plasma physics and nuclear technology. Required facilities include thermomechanical test stands and confinement devices with sufficiently long plasma burn. The radiation shield poses no feasibility issues, but improved accuracy of predictions will reduce design conservatism and lower costs.

Continuing a 26-year history, the 14th Symposium on Fusion Technology, hosted by the Euratom-CEA Association, was held in the Palais des Papes at Avignon from 8 to 12 September 1986. This papal palace, dating back to 1335, is one of France's most impressive historical monuments. It provided an imposing and stimulating setting for the conference, which was attended by almost 500 scientists from 18 countries and four continents. About 275 invited and reviewed contributed papers were presented, covering the conference topics as shown in Table I. The number of papers was 11% greater than that for the 13th SOFT. The greatest increase occurred in topics relating to reactor technology; in keeping with the state of the art, however, contributions on plasma technology continued to dominate.

In 1986, after three years of additional research progress, the international community devoted to the generation and application of ultrahigh magnetic fields and currents, it reconvened at Santa Fe, New Mexico. The Conference had been announced at the previous meeting (Megagauss III) held at Novosibirsk, USSR, in 1983 under the auspices of the Lavrentyev Institute of Hydrodynamics and the Siberian Branch of the Soviet Academy of Sciences. The present meeting (Megagauss IIII) was hosted by Los Alamos National Laboratory (LANL) with active assistance by scientists from Lawrence Livermore National Laboratory (LLNL), the Air Force Weapons Laboratory (AFWL) and Sandia National Laboratories, Albuquerque, NM (SNLA). Over 220 scientists and engineers from eight countries (including, for the first time, the People's Republic of China) participated in the technical sessions of the Conference, which included more than one hundred papers, and in the subsequent tours of local laboratories (LANL, SNLA, AFWL).