John Mandrekas

Comparisons and physics basis of tokamak transport models and turbulence simulations

The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the mo...

An impurity seeded radiative mantle for ITER

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 Fusion Transmutation of Waste Reactor

A design concept and the performance characteristics for a fusion transmutation of waste reactor (FTWR), a subcritical fast reactor driven by a tokamak fusion neutron source, are presented. The present design concept is based on nuclear, processing, and fusion technologies that either exist or are at an advanced stage of development and on the existing tokamak plasma physics database. An FTWR, operating with keff ≤ 0.95 at a thermal power output of ~3 GW and with a fusion neutron source operating at Qp = 1.5 to 2, could fission the transuranic content of ~100 metric tons of spent nuclear fuel per full-power year and would be self-sufficient in both electricity and tritium production. In equilibrium, a nuclear fleet consisting of light water reactors (LWRs) and FTWRs in the electrical power ratio of 3/1 would reduce by 99.4% the actinides discharged into the waste stream from the LWRs in a once-through fuel cycle that must be stored in high-level waste repositories.

A ``SUPERCODE`` for systems analysis of tokamak experiments and reactors

A new code, named SUPERCODE, has been developed to fill the gap between currently available zero dimensional systems codes and highly sophisticated, multidimensional plasma performance codes. The former are comprehensive in content, fast to execute, but rather simple in terms of the accuracy of their physics and engineering models. The latter contain state-of-the-art plasma physics modeling but are limited in engineering content and are time consuming to run. The SUPERCODE upgrades the reliability and accuracy of systems codes by calculating the self consistent 1 1/2-D plasma evolution in a realistic engineering environment. By a combination of variational techniques and careful formulation there is only a modest increase in CPU time over 0-D runs, thereby making the SUPERCODE suitable for use as a systems studies tool. In addition, we have expended considerable effort to make the code user- and programmer friendly, as well as operationally flexible, with the hope of encouraging wide usage throughout the fusion community.

A neoclassical calculation of toroidal rotation profiles and comparison with DIII-D measurements

Momentum and particle balance and neoclassical viscosity were applied to calculate the radial profile of toroidal rotation velocity in several DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] discharges in a variety of energy confinement regimes (low-mode, low-mode with internal transport barrier, high-mode, and high-mode with quiescentd double barrier). Calculated toroidal rotation velocities generally were found to (over) predict measured values to well within a factor of 2.

Evaluation of different control methods for the thermal stability of the International Thermonuclear Experimental Reactor

This paper reports on a zero-dimensional, time-dependent, particle and power balance code developed and used to evaluate the effectiveness of different burn control methods for the stabilization of unstable ignited and subignited operating points of the International Thermonuclear Experimental Reactor (ITER) physics phase machine. Based on the results of our calculations, we conclude that the operation of ITER at thermally unstable operating points is physically and technologically feasible. Control with auxiliary power modulation seems to be the method of choice for the control of subignited unstable points, while other methods such as modulation of the fueling rate and high-Z impurity injection can also be used, especially for the control of unstable ignited points where auxiliary power modulation cannot be used.

Neutral transport analysis of recent DIII-D neutral density experiments

Recent measurements of the neutral densities both inside and outside the separatrix near the X-point of the DIII-D tokamak, in both L- and H-mode plasmas, are analysed with the two-dimensional transmission/escape probability neutral transport code GTNEUT and with the two-dimensional Monte Carlo code DEGAS. The predictions of the two codes are in good agreement with each other and agree with the experiment to within the experimental error bars in most cases.

Impurity seeded radiative power exhaust solutions for ITER

The injection of impurities into the scrape-off layer (SOL) to stimulate radiative power exhaust from the mantle and SOL/divertor of the International Thermonuclear Experimental Reactor (ITER) is investigated. Intermediate Z impurities (e.g. argon to krypton) are able to radiate more than two thirds of the plasma heating power, without significant effect on the plasma power balance or the shear profile and without triggering an H to L mode transition

Comparision of neoclassical rotation theory with experiment under a variety of conditions in DIII-D

A neoclassical theory of gyroviscous radial momentum transport and poloidal and toroidal rotation has been compared with experiment in DIII-D [Luxon, Anderson, Batty et al., Plasma Physics and Controlled Nuclear Fusion Research 1986 (IAEA, Vienna, 1987), Vol. 1, p. 159] discharges in different confinement regimes, with a range of neutral beam powers and with co- and counter-injection, and with various types of dominant impurity species present. Calculated central toroidal rotation velocities and momentum confinement times agreed with experiment over a wide range of these conditions, with one notable exception in which a drift correction may be needed to reduce the gyroviscous toroidal force. Radial distributions of toroidal and poloidal rotation velocities and radial electric field, calculated using the radial distribution of toroidal angular momentum input density, agreed with measured distributions for the one time in an L-mode discharge that was examined in detail.

Sub-Critical Transmutation Reactors with Tokamak Fusion Neutron Sources

Abstract The principal results of a series of design scoping studies of sub-critical fast transmutation reactors (based on the nuclear and processing technology being developed in the USDoE Generation IV, Advanced Fuel Cycle and Next Generation Nuclear Plant programs) coupled with a tokamak fusion neutron source (based on the ITER design basis physics and technology) are presented.