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Self-consistent, coupled transport/MHD/scrape-off layer (SOL) divertor calculations indicate that a stable, radiating mantle can be maintained just inside the separatrix by iron impurity injection into the SOL in an ITER EDA model. The power flux to the divertor plate is reduced thereby by an order of magnitude or more. This reduction of the power exhausted to the divertor is predicted to be achieved without significant deleterious effect on the core power balance, without producing significant changes in the current profile that might trigger a disruptive collapse of the current channel and without inducing an H to L mode transition. These results suggest that an impurity seeded radiative mantle should be considered as part of the solution to the divertor heat load problem in ITER and other future tokamaks

A new computational model for neutral particle transport in the outer regions of a diverted tokamak plasma chamber is presented. The model is based on the calculation of transmission and escape probabilities using first-flight integral transport theory and the balancing of fluxes across the surfaces bounding the various regions. Both long and short mean free path regions can be handled. The complex geometry of the outer regions of a diverted tokamak can be represented accurately and economically using precomputed probabilities which depend only on the mean free path of the region. Benchmark comparisons with Monte Carlo illustrate that quite accurate results may be expected with the method.

A 0-D time-dependent particle and power balance code has been developed and used to evaluate the effectiveness of different methods of controlling thermally unstable ignited and subignited operating points of the physics phase ITER machine. Based on the results of calculations, the authors conclude that operating the ITER at thermally unstable operating points is physically and technologically feasible. Auxiliary power modulation is recommended as the primary control method for high-Q subignited operation, and fueling modulation is recommended for the control of unstable ignited points, of edge-region phenomena on the dynamics and controllability of a burning plasma are also addressed. >

The effect of ion orbit loss on the poloidal distribution of ions, energy and momentum from the plasma edge into the tokamak scrape-off layer (SOL) is analysed for a representative DIII-D (Luxon 2002 Nucl. Fusion 42 614) high-mode discharge. Ion orbit loss is found to produce a significant concentration of the fluxes of particle, energy and momentum into the outboard SOL. An intrinsic co-current rotation in the edge pedestal due to the preferential loss of counter-current ions is also found.

This report presents a review of reflectometry with particular attention to eXtraordinary mode (X-mode) reflectometry using the novel technique of dual frequency differential phase. The advantage of using an X-mode wave is that it can probe the edge of the plasma with much higher resolution and using a much smaller frequency range than with the Ordinary mode (O-Mode). The general problem with previous full phase reflectometry techniques is that of keeping track of the phase (on the order of 1000 fringes) as the frequency is swept over the band. The dual frequency phase difference technique has the advantage that since it is keeping track of the phase difference of two frequencies with a constant frequency separation, the fringe counting is on the order of only 3 to 5 fringes. This fringe count, combined with the high resolution of the X-mode wave and the small plasma access requirements of reflectometry, make X-mode reflectometry a very attractive diagnostic for today`s experiments and future fusion devices.

A fluid representation of viscosity has been incorporated into a set of fluid equations that are maximally ordered in the ``short-radial-gradient-scale-length`` (srgsl) ordering that is appropriate for the edge of tokamak plasmas. The srgsl ordering raises viscous drifts and other viscous terms to leading order and fundamentally alters the character of the fluid equations. A leasing order viscous drift is identified. Viscous-driven radial particle and energy fluxes in the scrape-off layer and divertor channel are estimated to have an order unity effect in reducing radial peaking of energy fluxes transported along the field lines to divertor collector plates.

The results and analysis of a well-diagnosed, dedicated rotation experiment in TFTR are presented. Various neoclassical and anomalous theories for momentum transport are described and compared with the experimental data. The gyroviscocity theory is able to predict the measured central toroidal rotation speed, momentum confinement time and radial torque flow profile reasonably well when a poloidal asymmetry factor {tilde {Theta}} = 1.5 is used. The cold-ion-perpendicular-viscocity theory requires the assumption of an implausibly large number of cold ions in order to predict the magnitude of the experimental torque flow. The ion-temperature-gradient-mode theory, the untrapped-particle-electrostatic-mode theory and the stochastic-magnetic-perturbation theory all predict torque flows that differ greatly in magnitude, radial profile and parametric dependence from the experimental values.

Reference operating scenarios for the physics phase of the International Thermonuclear Experimental Reactor (ITER) rely on low temperature, high density operation for good divertor performance. Operating points in this region are usually thermally unstable and active burn control is required to maintain operation at the selected operating point. We present a series of transport simulations of ITER burn control scenarios with modulated neutral beam heating, using the 1-1/2D code WHIST. Our results indicate that control is possible, except at very high densities ({l angle}n{sub e}{r angle} {ge} 1.80{times}10{sup 20} m{sup {minus}3}) where off-axis heating due to the poor beam penetration makes control difficult, especially for negative perturbations 15 refs., 20 figs.

In a recent paper, I cited the work of Hsu and Sigmar as an illustration that the choice of collisionality ordering can affect the results of a calculation of poloidal density and velocity asymmetries. In their Comment, Connor et al. argue that the Hsu-Sigmar strong collisionality regime (Δ ~ 1) is irrelevant for JET and that, even if it were relevant, I ~ O() would not lead to significant gyroviscous momentum damping because Vθ ~ O(δVth).

A model is presented for the self-consistent interpretation of the global momentum and energy confinement times and the central rotation velocities measured in plasmas that are rotating at speeds comparable to their thermal speed. This model incorporates corrections for non-steady state and represents the effect of radial density, temperature and velocity profiles. The momentum transport model is based upon gyroviscosity theory, which remains controversial. Good agreement between measured and predicted rotation frequencies and momentum confinement times is obtained for a collection of JET data and for one TFTR beam power scan. The energy confinement is shown to be degraded by a viscous energy flux, which is predicted to account for up to one fourth of the total energy loss for the JET data and for one half of the energy confinement degradation measured in the TFTR beam power scan. This implies that the measured energy confinement times in strongly rotating plasmas are significantly shorter than the times of energy confinement against conductive and convective transport processes.

Current transport theory is extrapolated to predict the performance characteristics of future tokamak power reactors operating in a quasi-steady-state mode. Criteria for the suppression of macroscopic instabilities are used to delimit a stable reactor regime. Microscopic instabilities are accounted for by enhancement of the transport coefficients. The effect of variations in reactor size and aspect ratio, toroidal current, injected ion source strength, and toroidal magnetic field strength are evaluated. Results are presented in terms of engineering parameters such as fractional fuel burn-up and power output.

A theory is outlined for explaining the observed effects of neutral beam injection on impurities in tokamak plasmas. In the collisional regime, it is shown for a representative model problem that for sufficiently strong co-injection the outward impurity flux component produced by the radial electric field becomes larger than the inward flux components due to the density gradient, rotation and direct beam-impurity momentum exchange, thereby producing an outward impurity flux. In the mixed regime, a preliminary version of the theory provides a reasonable interpretation of the PLT impurity flow reversal experiments when the effective viscous drag coefficient that is observed experimentally is used in the model. This preliminary theory, when adjusted to match the PLT results, predicts significant impurity reversal in TFTR and in a plasma of the size of FED and INTOR.

Solutions of the radial particle and energy transport equations in a hypothetical tokamak reactor have been investigated. Sensitivity of the solutions to various physical processes was examined.

New techniques for inferring several reactor kinetic parameters from frequency-domain noise analysis measurements in coupled-core reactors are developed and utilized. These parameters are the eigen...

A point model of particle densities and temperatures within a CTR is formulated, and equilibrium solutions are obtained for different plausible operating regimes of a D-T reactor of commercial interest. The stability of these equilibrium points against excursions in the overall particle densities and temperatures is determined by linear analysis and confirmed by dynamic simulation – certain regimes are found to be unstable. Control of a CTR about an unstable equilibrium point by varying the injected ion intensity and D-T mixture is investigated and found to be difficult when the ion containment time is not large with respect to the delay time between consecutive changes in the injected ion beam.

The relationship among several approximate formutations—variational, adjoint difference, forward difference, perturbation—for the solution of deep penetration radiation transport problems is establ...

A scoping study for a Tokamak Engineering Technology Facility (TETF) is presented. The TETF is a tokamak with R = 3 m and I/sub p/ = 1.4 MA based on the counterstreaming-ion torus mode of operation. The primary purpose of TETF is to demonstrate fusion technologies for the Experimental Power Reactor (EPR), but it will also serve as an engineering and radiation test facility. TETF has several technological systems (e.g., superconducting toroidal-field coil, tritium fuel cycle, impurity control, first wall) that are prototypical of EPR.

A recently formulated theory about the effects of sources upon particle transport in the collisional regime is applied to estimate the magnitude of effects which would be expected in the ISX-A flow reversal experiment.

A new, preliminary design has been identified for the tokamak experimental power reactor (EPR). The revised EPR design is simpler, more compact, less expensive and has somewhat better performance characteristics than the previous design, yet retains many of the previously developed design concepts. This report summarizes the principle features of the new EPR design, including performance and cost.

The theory underlying the variational sensitivity formalism is reviewed. Some general characteristics of uncertainties in fast reactor parameters as a function of nuclear data uncertainties are discussed. Numerical studies based on the variational sensitivity theory and the statistical theory are reviewed.

An extended impurity transport theory, which includes NBI momentum input and radial momentum transfer effects, inertial strong-rotation (vø ∼ vth) effects and radial electric field effects, has been applied to analyse the impurity accumulation experiments in ISX-B and PLT. Theory and experiment are found to be in good agreement. Counter-injection causes a central impurity accumulation that is several times larger than for co-injection, and this difference can be understood in terms of differences in transport properties between co-injection and counter-injection.