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The radial profile of the neutron production rate in spherical inertial electrostatic confinement plasmas is investigated. The electrostatic potential is obtained by solving the Poisson equation, and by using the potential; the fuel ion velocity distribution function is determined at each radial point. From the velocity distribution function, the neutron production rate is accurately evaluated. Numerical results show that if it is assumed that fuel ions are confined keeping the total energy and angular momentum almost constant, the double radial peak in the neutron production rate can appear without creation of the deep double potential well.

An international multi-tokamak profile database has been assembled, constituting a representative set of reference tokamak discharges for the purpose of testing local transport models against well documented data. In particular, it will allow one to measure the accuracy with which the models can reproduce experiments and draw confidence intervals for the predictions of the models outside the range covered in the database. This database is now available to the fusion community and may be accessed by anonymous ftp to iterphys.naka.go.jp; the purpose of this article is to describe the structure of the database and the discharges contributing to it so that all can take full advantage of this resource. Thus, after an introductory general discussion of the database, there is a more detailed description of its structure, with listings of variables emphasized and how to access the database. There is then a brief description of each contributing tokamak and information on the type of discharges available from that tokamak. This is followed by a more quantitative description of the data, giving the ranges of dimensional and dimensionless variables available. Some typical modelling results to illustrate the use of the database are given in the conclusion.

The compatibility of the reversed field pinch configuration with a highly radiative mantle at the edge has been proven by injecting neon into high density RFX plasmas: with respect to ordinary non-seeded discharges, energy confinement only marginally deteriorates, and the convection losses onto the plasma facing wall are reduced. Injection of neon into low density plasmas entails instead a significant increase of the effective charge and an increment of the ohmic input higher than the radiated power increase. The associated degradation of energy confinement τ_E appears not to be peculiar to impurity injection but follows a more general scaling with the heating power P_heat of the type τ_E ∝ P_heat^-1. The radiation efficiency, defined as the ratio between radiated power and the impurity contribution to effective charge, is found to be 3 to 5 times higher than that in tokamaks. RITM simulations confirm the experimental findings.

A neural network technique has been used to predict disruptions in the ADITYA tokamak. A time series prediction method is employed whereby a series of past values of some time dependent quantity is used to predict its value in the future. The time varying observables used in the present work are the different diagnostic signals from four Mirnov probes, one soft X ray monitor and one H_α monitor. The predicted quantities are the same observables at some future time. The neural network is trained with the past values of the different diagnostic signals as inputs and the future values of the same quantities as targets. The trained neural network is used to forecast in a multistep sequence. This amounts to a prediction several time steps earlier. Very good prediction results have been obtained up to 8 ms earlier with little distortion of the signals and no appreciable time lag, a capability which is believed to be well suited to the task of on-line predictions of disruptions in ADITYA. As actual experimental signals are used, confidence regarding the performance of the neural network on hardware implementation is automatically ensured.

High Mach flows and their formation mechanism in tokamak divertor regions have been studied. Numerical calculations using a two dimensional edge plasma simulation code (the B2-EIRENE code) have been made for the JT-60U open divertor geometry with discharge parameter ranges of relatively low input power and L mode experiments. In the high density case, typical formation of an X point MARFE, which is accompanied by plasma detachment, has been observed. At the same time, high Mach flows appear near the ionization front, where the plasma static pressure rapidly drops and is far away from the target plates. Redistribution from static pressure to dynamic pressure without a large momentum loss is shown to be a possible cause of the high Mach flows observed in the simulation. In addition, a simple 1-D analytic model along the field lines has been applied and the results are compared with the B2-EIRENE results in order to identify the formation mechanism of high Mach flows.

Alternating current operation with one full cycle at a plasma current level of 2.5 kA has been achieved in the CT-6B tokamak. The poloidal magnetic field in the plasma is measured with two internal magnetic probes in repeated discharges. The plasma current distribution is reconstructed with an inversion algorithm. The reversed plasma current first appears on the low field side due to decreasing poloidal beta. Two plasma current components flow in opposite directions when the net current vanishes. The existence of the magnetic surfaces and rotational transform provides particle confinement in the current reversal phase.

Neoclassical tearing modes (NTMs) with different mode numbers have been observed in tokamak plasmas. These NTMs, however, never occur simultaneously in ASDEX Upgrade. As a mode with a different helicity starts to grow, this usually leads to suppression of the first NTM. Both analytical and numerical modelling have been carried out to investigate the interaction between NTMs of different helicities. It is found that once the two magnetic islands are close, the more unstable magnetic island survives and suppresses the less unstable one, in agreement with the experimental results. The mechanism responsible for this suppression is the decreased fundamental harmonic pressure perturbations of the NTM in the presence of magnetic perturbations of different helicities.

Cross-field particle transport increases sharply with distance into the SOL and plays a dominant role in the `main-chamber recycling' regime in Alcator C-Mod, a regime in which most of the plasma particle efflux recycles on the main-chamber walls rather than flows into the divertor volume. This observation has potentially important implications for a reactor: contrary to the ideal picture of divertor operation, a tightly baffled divertor may not offer control of the neutral density in the main-chamber such that charge exchange heat losses and sputtering of the main-chamber walls can be reduced. The conditions that give rise to the main-chamber recycling regime can be understood by considering the plasma-neutral particle balance: when the flux surface averaged neutral density exceeds a critical value, flows to the divertor can no longer compete with the ionization source and particle fluxes must increase with distance into the SOL. This critical neutral density condition can be recast into a critical cross-field plasma flux condition: particle fluxes must increase with distance into the SOL when the plasma flux crossing a given flux surface exceeds a critical value. Thus, the existence of the main-chamber recycling regime is intrinsically tied to the level of anomalous cross-field particle transport. Direct measurement of the effective cross-field particle diffusivities D_eff in a number of ohmic L mode discharges indicates that D_eff near the separatrix strongly increases as plasma collisionality increases. Convected heat fluxes correspondingly increase, implying that there exists a critical plasma density (or perhaps collisionality) beyond which no steady state plasma can be maintained, even in the absence of radiation.

The eigenfunctions for the transport of radiation between concentric spheres are proved to be the spherical harmonics and Legendre polynomials. The corresponding eigenvalues are then derived for the cases of both an outer emitting sphere and an inner absorbing sphere, and an inner emitting sphere and an outer absorbing sphere. Simple approximations to these eigenvalues are found and their various properties are derived. These results are then applied to the problem of ICF capsules inside hohlraums.