J.E. Kinsey

A theory-based transport model with comprehensive physics

A new theory-based transport model with comprehensive physics (trapping, general toroidal geometry, fully electromagnetic, electron-ion collisions, impurity ions) has been developed. The core of the model is the new trapped-gyro-Landau-fluid (TGLF) equations, which provide a fast and accurate approximation to the linear eigenmodes for gyrokinetic drift-wave instabilities (trapped ion and electron modes, ion and electron temperature gradient modes, and kinetic ballooning modes). The new TGLF transport model is more accurate, and has an extended range of validity, compared to its predecessor GLF23. The TGLF model unifies trapped and passing particles in a single set of gyro-Landau-fluid equations. A model for the averaging of the Landau resonance by the trapped particles makes the equations work seamlessly over the whole drift-wave wave-number range from trapped ion modes to electron temperature gradient modes. A fast eigenmode solution method enables unrestricted magnetic geometry. The transport model uses...

Non-dimensional scaling of turbulence characteristics and turbulent diffusivity

Plasma turbulence characteristics, including radial correlation lengths, decorrelation times, amplitude profile and flow velocity, have been measured during a ρ* scan on DIII-D while all other transport relevant dimensionless quantities (e.g., β, ν*, κ, q, Te/Ti) are held nearly constant. The turbulence is measured by examining the correlation properties of the local long wavelength (k⊥ρi ≤ 1) density fluctuations, measured with beam emission spectroscopy. The radial correlation length of the turbulence Lc,r is shown to scale with the local ion gyroradius, Lc,r ≈ 5ρi, while the decorrelation times scale with the local acoustic velocity as τc~a/cs. The turbulent diffusivity parameter, D~(Lc,r2/τc), scales in a roughly gyro-Bohm-like fashion, as predicted by the gyrokinetic equations governing turbulent transport. The experimental one fluid power balance heat diffusivity scaling and that from GLF23 modelling compare reasonably well.

Nonlinear gyrokinetic turbulence simulations of E×B shear quenching of transport

The effects of E×B velocity shear have been investigated in nonliner gyrokinetic turbulence simulations with and without kinetic electrons. The impact of E×B shear stabilization in electrostatic flux-tube simulations is well modeled by a simple quench rule with the turbulent diffusivity scaling like 1−αEγE∕γmax, where γE is the E×B shear rate, γmax is maximum linear growth rate without E×B shear, and αE is a multiplier. The quench rule was originally deduced from adiabatic electron ion temperature gradient (ITG) simulations where it was found that αE≈1. The results presented in this paper show that the quench rule also applies in the presence of kinetic electrons for long-wavelength transport down to the ion gyroradius scale. Without parallel velocity shear, the electron and ion transport is quenched near γE∕γmax≈2 (αE≈1∕2). When the destabilizing effect of parallel velocity shear is included in the simulations, consistent with purely toroidal rotation, the transport may not be completely quenched by any level of E×B shear because the Kelvin–Helmholtz drive increases γmax faster than γE increases. Both ITG turbulence with added trapped electron drive and electron-directed and curvature-driven trapped electron mode turbulence are considered.The effects of E×B velocity shear have been investigated in nonliner gyrokinetic turbulence simulations with and without kinetic electrons. The impact of E×B shear stabilization in electrostatic flux-tube simulations is well modeled by a simple quench rule with the turbulent diffusivity scaling like 1−αEγE∕γmax, where γE is the E×B shear rate, γmax is maximum linear growth rate without E×B shear, and αE is a multiplier. The quench rule was originally deduced from adiabatic electron ion temperature gradient (ITG) simulations where it was found that αE≈1. The results presented in this paper show that the quench rule also applies in the presence of kinetic electrons for long-wavelength transport down to the ion gyroradius scale. Without parallel velocity shear, the electron and ion transport is quenched near γE∕γmax≈2 (αE≈1∕2). When the destabilizing effect of parallel velocity shear is included in the simulations, consistent with purely toroidal rotation, the transport may not be completely quenched by any ...

Progress toward fully noninductive, high beta conditions in DIII-D

The DIII-D Advanced Tokamak (AT) program in the DIII-D tokamak [J. L. Luxon, Plasma Physics and Controlled Fusion Research, 1986, Vol. I (International Atomic Energy Agency, Vienna, 1987), p. 159] is aimed at developing a scientific basis for steady-state, high-performance operation in future devices. This requires simultaneously achieving 100% noninductive operation with high self-driven bootstrap current fraction and toroidal beta. Recent progress in this area includes demonstration of 100% noninductive conditions with toroidal beta, βT=3.6%, normalized beta, βN=3.5, and confinement factor, H89=2.4 with the plasma current driven completely by bootstrap, neutral beam current drive, and electron cyclotron current drive (ECCD). The equilibrium reconstructions indicate that the noninductive current profile is well aligned, with little inductively driven current remaining anywhere in the plasma. The current balance calculation improved with beam ion redistribution that was supported by recent fast ion diagno...

Predicting core and edge transport barriers in tokamaks using the GLF23 drift-wave transport model

The density and temperature profiles are predicted in core and edge transport barriers in the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] using the GLF23 drift-wave model. The GLF23 model has been retuned to yield a better fit to the linear gyrokinetic growth rates for reversed magnetic shear and H-mode pedestal parameters. The turbulent saturation levels are determined using nonlinear gyrokinetic simulations. Using a large profile database, it is found that the retuned and original GLF23 models yield comparable results for discharges with monotonic safety factor profiles and no discernable internal transport barriers (ITBs). Examples of using retuned GLF23 model to predict the temperature profiles in simulations of several DIII-D strongly reversed magnetic shear ITB discharges are provided. Particle transport simulations show that the model is successful in predicting the density profile in discharges without ITBs but that some additional background particle diffusivity is...

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.

Stationary high-performance discharges in the DIII-D tokamak

Discharges which can satisfy the high gain goals of burning plasma experiments have been demonstrated in the DIII-D tokamak under stationary conditions at relatively low plasma current (q95>4). A figure of merit for fusion gain (?NH89/q952) has been maintained at values corresponding to Q = 10 operation in a burning plasma for >6?s or 36?E and 2?R. The key element is the relaxation of the current profile to a stationary state with qmin>1. In the absence of sawteeth and fishbones, stable operation has been achieved up to the estimated no-wall ? limit. Feedback control of the energy content and particle inventory allow reproducible, stationary operation. The particle inventory is controlled by gas fuelling and active pumping; the wall plays only a small role in the particle balance. The reduced current lessens significantly the potential for structural damage in the event of a major disruption. In addition, the pulse length capability is greatly increased, which is essential for a technology testing phase of a burning plasma experiment where fluence (duty cycle) is important.

The effect of safety factor and magnetic shear on turbulent transport in nonlinear gyrokinetic simulations

This paper reports on over 100 nonlinear simulations used to systematically study the effects of safety factor q and magnetic shear s on turbulent energy and particle transport due to ion temperature gradient (ITG) modes and trapped electron modes (TEM) for several reference cases using the GYRO gyrokinetic code. All the simulations are collisionless, electrostatic, and utilize shifted circle geometry. The motivation is to create a database for benchmarking and testing of turbulent transport models. In simulations varying q, it is found that the ion and electron energy transport exhibit an offset linear dependence on q for 1⩽q⩽4. This result is valid for cases in which the spectrum is dominated by either TEM or ITG modes. The particle transport also follows a linear q dependence if the diffusivity D is positive (outward). If a particle pinch is predicted, however, then D is found to be insensitive to q. In kinetic electron simulations varying the magnetic shear s, the particle transport can exhibit a nu...

Core barrier formation near integer q surfaces in DIII-D

Recent DIII-D experiments have significantly improved the understanding of internal transport barriers (ITBs) that are triggered close to the time when an integer value of the minimum in q is crossed. While this phenomenon has been observed on many tokamaks, the extensive transport and fluctuation diagnostics on DIII-D have permitted a detailed study of the generation mechanisms of q-triggered ITBs as pertaining to turbulence suppression dynamics, shear flows, and energetic particle modes. In these discharges, the evolution of the q profile is measured using motional Stark effect polarimetry and the integer qmin crossings are further pinpointed in time by the observation of Alfven cascades. High time resolution measurements of the ion and electron temperatures and the toroidal rotation show that the start of improved confinement is simultaneous in all three channels, and that this event precedes the traversal of integer qmin by 5–20ms. There is no significant low-frequency magnetohydrodynamic activity pri...

Simulations of internal transport barrier formation in tokamak discharges using the GLF23 transport model

Results are presented for simulations of tokamak discharges exhibiting internal transport barriers (ITBs) with significant reductions in the core thermal transport using a comprehensive theory-based model for drift-wave transport. The predicted temperature and toroidal velocity profiles from the GLF23 model are compared against the experimental data for twenty-two L- and high-confinement mode (H-mode) ITB discharges from three large tokamaks including DIII-D [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)], and Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)]. The combined effects of E×B shear and Shafranov shift stabilization of the turbulent transport are essential in reproducing the barriers in the plasma core. Shafranov shift or α-stabilization is found to be an essential ingredient in suppressing the thermal transport due to ion and electron temperature gradient and tra...