G. Bateman

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...

Predicting temperature and density profiles in tokamaks

A fixed combination of theory-based transport models, called the Multi-Mode Model, is used in the BALDUR [C. E. Singer et al., Comput. Phys. Commun. 49, 275 (1988)] transport simulation code to predict the temperature and density profiles in tokamaks. The choice of the Multi-Mode Model has been guided by the philosophy of using the best transport theories available for the various modes of turbulence that dominate in different parts of the plasma. The Multi-Mode model has been found to provide a better match to temperature and density profiles than any of the other theory-based models currently available. A description and partial derivation of the Multi-Mode Model is presented, together with three new examples of simulations of the Tokamak Fusion Test Reactor (TFTR) [K. M. McGuire et al., Phys. Plasmas 2, 2176 (1995)]. The first simulation shows the strong effect of recycling on the ion temperature profile in TFTR supershot simulations. The second simulation explores the effect of a plasma current ramp—w...

Models for the pedestal temperature at the edge of H-mode tokamak plasmas

Predictive models are developed for the temperature at the top at the edge of type 1 ELMy (edge localized mode) H-mode (high-confinement mode) plasmas. Theory-motivated models are used for the pedestal width and pressure gradient, while the pedestal density is obtained from experimental data in this study. The pedestal pressure gradient is assumed to be limited by the ballooning mode instability and is expressed in terms of the magnetic shear and geometrical factors. The effect of the bootstrap current, which reduces the magnetic shear in the steep pressure gradient region at the edge of the H-mode plasma, is included in the determination of the magnetic shear. Approaches for calculating the magnetic shear, combined with proposed models for the pedestal width, are used to determine the pedestal temperature. The computed pedestal temperatures are compared with more than 500 measured pedestal temperatures for type 1 ELMy H-mode discharges in four tokamaks. Some of the uncertainties in these results are disc...

Predictions of H-mode performance in ITER

Time-dependent integrated predictive modelling is carried out using the PTRANSP code to predict fusion power and parameters such as alpha particle density and pressure in ITER H-mode plasmas. Auxiliary heating by negative ion neutralbeaminjectionandion-cyclotronheatingofHe 3 minorityionsaremodelled,andtheGLF23transportmodelis used in the prediction of the evolution of plasma temperature profiles. Effects of beam steering, beam torque, plasma rotation, beam current drive, pedestal temperatures, sawtooth oscillations, magnetic diffusion and accumulation of He ash are treated self-consistently. Variations in assumptions associated with physics uncertainties for standard base-line DT H-mode plasmas (with Ip = 15MA, BTF = 5.3T and Greenwald fraction = 0.86) lead to a range of predictions for DT fusion power PDT and quasi-steady state fusion QDT (≡PDT/Paux). Typical predictions assuming Paux = 50‐53MW yield PDT = 250‐720MW and QDT = 5‐14. In some cases where Paux is ramped down or shut off after initial flat-top conditions, quasi-steady QDT can be considerably higher, even infinite. Adverse physics assumptions such as the existence of an inward pinch of the helium ash and an ash recycling coefficient approaching unity lead to very low values for PDT. Alternative scenarios with different heating and reduced performance regimes are also considered including plasmas with only H or D isotopes, DT plasmas with toroidal field reduced 10% or 20% and discharges with reduced beam voltage. In full-performance D-only discharges, tritium burn up is predicted to generate central tritium densities up to 10 16 m −3 and DT neutron rates up to 5 ×10 16 s −1 , compared with the DD neutron rates of 6 × 10 17 s −1 . Predictions with the toroidal field reduced 10% or 20% below the planned 5.3T and keeping the same q98, Greenwald fraction and βn indicate that the fusion yield PDT and QDT will be lower by about a factor of two (scaling as B 3.5 ).

Theory‐based transport modeling of the gyro‐radius experiments

Self‐consistent predictive transport simulations of temperature and density profiles have been carried out for ten dimensionally similar low (L) mode discharges from the Tokamak Fusion Test Reactor (TFTR) [D. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)], Doublet III‐D Tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], and the Joint European Torus [P. H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)], where only the normalized Larmor radius was allowed to vary. It is found that a purely gyro‐Bohm transport model predicts temperature and density profiles that match the experimental data from these ρ* scans very well. In particular, a combination of theoretically derived transport models is used in these simulations, including the Weiland model for transport due to drift waves (ion temperature gradient and trapped electron modes) and the Guzdar–Drake model for transport due to resistive ballooning modes. These gyro‐Bohm transport models depend very sensitivel...

Burning plasma projections using drift-wave transport models and scalings for the H-mode pedestal

OAK-B135 The GLF23 and Multi-Mode (MM95) transport models are used along with a model for the H-mode pedestal to predict the fusion performance for the ITER, FIRE, and IGNITOR tokamak designs. The drift-wave predictive transport models reproduce the core profiles in a wide variety of tokamak discharges, yet they differ significantly in their response to temperature gradient (stiffness). Recent gyro-kinetic simulations of ITG/TEM and ETG modes motivate the renormalization of the GLF23 model. The normalizing coefficients for the ITG/TEM modes are reduced by a factor of 3.7 while the ETG mode coefficient is increased by a factor of 4.8 in comparison with the original model. A pedestal temperature model is developed for type I ELMy H-mode plasmas based on ballooning mode stability and a theory-motivated scaling for the pedestal width. In this pedestal model, the pedestal density is proportional to the line-averaged density and the pedestal temperature is inversely related to the pedestal density.

Physics of confinement improvement of plasmas with impurity injection in DIII-D

External impurity injection into L mode edge discharges in DIII-D has produced clear confinement improvement (a factor of 2 in energy confinement and neutron emission), reduction in all transport channels (particularly ion thermal diffusivity to the neoclassical level), and simultaneous reduction of long wavelength turbulence. Suppression of the long wavelength turbulence and transport reduction are attributed to synergistic effects of impurity induced enhancement of E × B shearing rate and reduction of toroidal drift wave turbulence growth rate. A prompt reduction of density fluctuations and local transport at the beginning of impurity injection appears to result from an increased gradient of toroidal rotation enhancing the E × B shearing. Transport simulations carried out using the National Transport Code Collaboration demonstration code with a gyro-Landau fluid model, GLF23, indicate that E × B shearing suppression is the dominant transport suppression mechanism.

Development of drift-resistive-inertial ballooning transport model for tokamak edge plasmas

A new model is developed for transport driven by drift-resistive-inertial ballooning modes (DRIBMs) in axisymmetric tokamak plasmas. The model is derived using two-fluid reduced Braginskii equations in a generalized s−α geometry. The unified theory includes diamagnetic effects, parallel electron and ion dynamics, electron inertia, magnetic perturbations, transverse particle diffusion, gyroviscous stress terms, electron and ion equilibrium temperature gradients, and temperature perturbations. A mixing length approximation is used to compute electron and ion thermal transport as well as particle fluxes from eigenvalues and eigenvectors of the linearized equations. The prediction for the saturation level is obtained by balancing the DRIBM growth rate against the nonlinear E×B convection. The parametric dependence of DRIBMs is investigated in systematic scans over density gradient, electron and ion temperature gradients, magnetic-q, collision frequency, magnetic shear, and Larmor radius. The DRIBM threshold ...

Comparison of high-mode predictive simulations using Mixed Bohm/gyro-Bohm and Multi-Mode (MMM95) transport models

Two different transport models—the Mixed Bohm/gyro-Bohm [Joint European Torus (JET)] model [Erba et al., Plasma Phys. Controlled Fusion 39, 261 (1997)] and the Multi-Mode model (MMM95) [Bateman et al., Phys. Plasmas 5, 1793 (1998)]—are used in predictive transport simulations of 22 high-mode discharges. Fourteen discharges that include systematic scans in normalized gyroradius (ρ*), plasma pressure (β), collisionality, and isotope mass in the JET tokamak [Rebut et al., Nucl. Fusion 25, 1011 (1985)] and eight discharges that include scans in ρ*, elongation (κ), power, and density in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] are considered. When simulation temperature and density profiles are compared with processed experimental data from the International Profile Database, it is found that the results with either the JET or MMM95 transport model match experimental data about equally well. With either model, the average normalized rms deviation is approximately 10%. In ...

Comparison of two resistive ballooning mode models in transport simulations

Predictive transport simulations of the temperature and density profiles have been carried out for Tokamak Fusion Test Reactor (TFTR) [K. Young et al., Plasma Phys. Controlled Fusion 26, 11 (1984)] current, density, and heating power scans. Two competing resistive ballooning mode theories are considered in order to examine their intrinsic magnetic‐q dependence. The theoretically derived transport model employed in this study includes drift wave contributions from the Weiland theory of trapped electron and ion temperature gradient modes, the Kwon–Biglari–Diamond neoclassical magnetohydrodynamic (MHD) theory, the Tang–Rewoldt kinetic ballooning mode theory, and either the previously used Carreras–Diamond or the recently developed Guzdar–Drake resistive ballooning mode theories. It is found that the Guzdar–Drake theory provides the correct scaling with plasma current while maintaining a scaling with density and auxiliary heating power that is consistent with experimental data from TFTR low confinement (L‐mod...