Table of contents

Basic principles of heterodyne techniques are introduced and the various components of a heterodyne system are summarized. Special applications in ECE, interferometry and reflectometry are discussed after introducing the diagnostic principles. Realized systems as described in the literature are briefly outlined. Ordering principles are radiometer types in the case of ECE, mixing scheme and generation and stabilization of local oscillator and intermediate frequency signals in the case of interferometry and reflectometry. Special techniques and their impact on the performance of the diagnostic instruments are discussed.

An experimental overview on pumping and particle exhaust studies for deuterium as well as for helium and neon in the ASDEX Upgrade divertor tokamak is presented. Strong turbomolecular pumps connected to the divertor region allow effective pumping of all these gases.

Deuterium, however, is pumped effectively by the carbon walls in ASDEX Upgrade which dominate over the external pumping.

Noble gases are hardly pumped by the walls, and their pumping efficiency and exhaust rate depends strongly on their respective density in the divertor chamber, i.e. on the effectivity of scrape-off layer transport and divertor retention. Compression of helium and neon in the divertor chamber increases with the divertor neutral gas density, and in high-power, high-density discharges in H- or CDH-mode pumping is very efficient. Helium exhaust in these scenarios is sufficiently fast to fulfill the requirements for ITER or a fusion reactor.

The behaviour of large amplitude Langmuir waves is experimentally observed in a non-neutral electron plasma column with a cylindrical boundary. It is found that a Langmuir wave whose amplitude is above a threshold decays into lower frequency Langmuir waves. Since the dispersion relation is different from that of the unbounded neutral plasma, which is theoretically considered, the three-wave decay process of Langmuir waves becomes possible. In these processes, sidebands due to a large amplitude Langmuir wave satisfy the energy and momentum conservation relation. The threshold of this decay instability depends on the plasma temperature and becomes lower as the temperature becomes higher.

The Mercier stability of the plasmas carrying bootstrap currents with different plasma collisionality is studied in the Large Helical Device (LHD). In the LHD configuration, the direction of the bootstrap current depends on the collisionality of the plasma through the change in the sign of the geometrical factor. When the beta value is raised by increasing the density of the plasma with a fixed low temperature, the plasma becomes more collisional and the collisionality approaches the plateau regime. In this case, the bootstrap current can flow in the direction so as to decrease the rotational transform. Then, the large Shafranov shift enhances the magnetic well and the magnetic shear, and therefore, the Mercier stability is improved. On the other hand, when the beta value is raised by increasing the temperature of the plasma with a fixed low density, the plasma collisionality becomes reduced to enter the collisionality regime. In this case, the bootstrap current flows so that the rotational transform should be increased, which is unfavourable for the Mercier stability.

We present experimental evidence for the ion-cyclotron resonant-heating (ICRH) induced trapping of ions in the edge-mirror fields of a magnetically confined plasma. Relative changes in edge-plasma density have been monitored in an end cell of the Phaedrus-B Tandem Mirror (Breun R A et al 1981 Phys. Rev. Lett. 47 1833 - 6; Ferron J R et al 1983 Phys. Rev. Lett. 51 1955) via the use of electron cyclotron emission from a hot-edge population created by the application of electron cyclotron resonant heating. Edge-plasma density dependence upon the ICRH left-circularly-polarized electric field and on the edge-neutral density were found to be consistent with an edge rf-trapping model. A linear correlation is observed between the change in trapped edge density and the change in the applied ICRH . Furthermore, it is demonstrated that cold (less than 7 eV) ions born from atomic processes operating at or near the plasma edge are the dominant species participating in the trapping process. The results obtained are shown to be applicable to any device with mirror-like closed particle orbits at the plasma edge.

The possibility of using simple sets of planar coils to produce low-aspect-ratio stellarator (LARS) configurations is analysed. Various types of LARS with different planar coils of potential interest to fusion research are identified. It is found that these configurations possess rather attractive features including: compact design and coil simplicity; good access to the plasma; closed vacuum flux surfaces with large enclosed volume; a significant external rotational transform; strong magnetic well; and a natural divertor. Finite plasma-pressure and finite plasma-current effects are studied as well, and it is shown that the LARS configurations considered benefit from the plasma current.

A two-dimensional model describing the nonlinear evolution of pressure driven flute modes in an inhomogeneous magnetic field is derived. The model couples fluctuations in ion and electron temperatures and densities with the fluctuations in the electrostatic potential. The well known Rayleigh - Taylor instability is recovered by linear stability analysis based on a local approach in the long-wave limit. This mode is unstable when the pressure profile is more peaked than the profile of the square of the magnetic field. Using a quasi-linear approach it is revealed that the turbulent fluctuations driven by this instability may give rise to up-gradient transport, a `pinch flux', of either heat or particles.

The burning performance of the self-ignited steady-state plasma is investigated based on a point model. For the ITER-like parameters, the theoretical model scaling law , which could explain the characteristics of the L-mode and the high fairly well, and the effect of He-ash poisoning are introduced simultaneously. The solutions are obtained by solving the particle and energy balance equations in steady-state conditions, taking account of the effect of radiation loss due to He ash and fuel ions. Typically, there exist four solutions of the plasma current at fixed temperature. The divergence of the temperature, which is predicted by a previous study (Fukuyama et al 1995 Nucl. Fusion 35 1669) for the pure plasma in the high , disappears under the influence of He ash. In the low-density limit, the L-mode branches and the high branches are well separated on the plane of the current and the temperature. On the other hand, the merging of two branches occurs at higher densities due to the nonlinear effect contained in the scaling law. Examining the constraints imposed on the core plasma (the density limit, the limit and so on), we found that the self-ignited state of the high operation would be difficult.

The model equation for the electrostatic current diffusive interchange mode turbulence is extended for both electrostatic and electromagnetic turbulence. Not only convective nonlinearity but also the electromagnetic nonlinearity which is related to the parallel flow are incorporated into the model equation. The two-dimensional nonlinear simulation of the electromagnetic current diffusive interchange mode is performed based on the extended fluid model. Two cases are investigated. In the first case, we neglect the terms and in Ohm's law, but retain the electromagnetic nonlinearity. This case corresponds to a simple extension of previous work. It is found that the electromagnetic nonlinearity gives rise to the normal cascade and higher saturation of the fluctuating energy. In the second case, we retain and terms as well. In this case, the turbulent level develops higher than that in the electrostatic limit, and the strong oscillatory behaviour of the fluctuating energy is observed. The strong inverse cascade is observed, which overcomes the normal cascade due to the electromagnetic nonlinearity. The quasi-linear effect and the system size effect on the saturation level are also discussed in the context of the second model.

An electrostatic electron energy analyser has been inserted for the first time in the outer region of the RFX reversed-field pinch experiment, in order to investigate and characterize the presence of a superthermal electron population. It has been found that these electrons carry most of the current density parallel to the magnetic field. The time evolution during a single discharge of the superthermal electrons current density and parallel temperature indicates that the distortion of the electron distribution function is stationary during the plasma current flat-top phase. The dependence of the superthermal temperature on the plasma parameters has been investigated by varying the plasma density, and a relationship with the ratio of the on-axis applied electric field to the critical electric field for runaway generation has been identified.

The 4th EFPW was convened in December 1996 in Sollentuna near Stockholm. It was hosted by the Swedish Natural Science Research Council and was sponsored by the European Commission. The main theme of this meeting was the interplay between edge and core processes in fusion devices. Radiative scenarios, confinement modes, particle exhaust efficiencies, impurity transport, operational limits and control issues have been considered in contributions from almost all European EURATOM associations. This was divided into three sessions: (1) Confinement Modes and Exhaust, (2) Confinement Scalings and Transport and (3) Interplay Edge - Core. A fourth session was devoted to Recent Results from JET and a fifth one to the Status of ITER. This report provides a concise summary of the results presented and gives a survey of the critical issues discussed during the workshop.

8 - 12 December 1997 International Workshop on Plasma Diagnostics Calcutta, India Contact: IWPD, Saha Institute of Nuclear Physics, Calcutta 700 064, India. Tel +91-33-337-0397, Fax +91-33-337-4637, E-mail iwpd97@hp2.saha.ernet.in

22 May - 1 June 1998 Advanced Study Institute on Wave and Beam Generated Plasmas Sozopol, Bulgaria Contact: Professor H Schlüter, Ruhr-Universität Bochum, Department of Physics and Astronomy, NB 5/67, 44780 Bochum, Germany. Tel +49-234-7003670, Fax +49-234-7094643, E-mail hs@plasma.ep2.ruhr-uni-bochum.de

29 June - 3 July 1998 1998 International Congress on Plasma Physics (Joint Conference of the 12th Kiev International Conference on Plasma Theory and 12th International Congress on Waves and Instabilities in Plasmas) and 25th Conference on Controlled Fusion and Plasma Physics Prague, Czech Republic Contact: ICPP 98, Institute of Plasma Physics, Za Slovankou 3, PO Box 17, 182 00 Prague 8, Czech Republic. Tel +420-2-688-3028, Fax +420-2-858-6389, E-mail plasma98@ipp.cas.cz

30 June - 1 July International Conference on Fusion and Industry Oxfordshire, UK Contact: Ms Sue Frye, Thomas Telford Conferences, One Great George Street, London SW1P 3AA, UK. Tel +44-171-665-2315, Fax +44-171-233-1743.

7 - 11 September 20th International Symposium on Fusion Technology (SOFT) Marseille, France Contact: Mme V Poli - 20th SOFT, DRFC, CEA/Cadarache, F13108 Saint-Paul-lez-Durance Cedex, France. Tel +33-4-42-25-62-60, Fax +33-4-42-25-62-55.

18 - 24 October 17th International Conference on Fusion Energy Yokohama, Japan Contact: Conference Service Section, IAEA, PO Box 100, A-1400 Vienna, Austria. Tel +43-1-2060-21310, Fax +43-1-20607, E-mail official.mail@iaea.org