21 Search Results

Investigation of the plasma shaping effects on the Hmode pedestal structure using coupled kinetic neoclassical/MHD stability simulations
The effects of plasma shaping on the Hmode pedestal structure are investigated. High fidelity kinetic simulations of the neoclassical pedestal dynamics are combined with the magnetohydrodynamic (MHD) stability conditions for triggering edge localized mode (ELM) instabilities that limit the pedestal width and height in Hmode plasmas. We use the neoclassical kinetic XGC0 code [Chang et al., Phys. Plasmas 11, 2649 (2004)] to carry out a scan over plasma elongation and triangularity. As plasma profiles evolve, the MHD stability limits of these profiles are analyzed with the ideal MHD ELITE code [Snyder et al., Phys. Plasmas 9, 2037 (2002)]. In simulationsmore » 
The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code
The extendedMHD NIMROD code [C. R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)] is verified against the idealMHD ELITE code [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)] on a diverted tokamak discharge. When the NIMROD model complexity is increased incrementally, resistive and firstorder finiteLarmour radius effects are destabilizing and stabilizing, respectively. The full result is compared to local analytic calculations which are found to overpredict both the resistive destabilization and drift stabilization in comparison to the NIMROD computations. 
MHD modeling of a DIIID lowtorque QHmode discharge and comparison to observations
ExtendedMHD modeling of DIIID tokamak quiescent Hmode (QHmode) discharges with nonlinear NIMROD simulations saturates into a turbulent state but does not saturate when the steadystate flow inferred from measurements is not included. This is consistent with the experimental observations of the quiescent regime on DIIID. The simulation with flow develops into a saturated turbulent state where the n _{Φ} = 1 and 2 toroidal modes become dominant through an inverse cascade. Each mode in the range of n _{Φ} = 1–5 is dominant at a different time. Consistent with experimental observations during QHmode, the simulated state leads to large particlemore » 
The impact of collisionality, FLR, and parallel closure effects on instabilities in the tokamak pedestal: Numerical studies with the NIMROD code
The extendedMHD NIMROD code [C. R. Sovinec and J. R. King, J. Comput. Phys. 229, 5803 (2010)] is verified against the idealMHD ELITE code [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)] on a diverted tokamak discharge. When the NIMROD model complexity is increased incrementally, resistive and firstorder finiteLarmour radius effects are destabilizing and stabilizing, respectively. Lastly, the full result is compared to local analytic calculations which are found to overpredict both the resistive destabilization and drift stabilization in comparison to the NIMROD computations.Cited by 6 
Microtearing modes in tokamak discharges
Microtearing modes (MTMs) have been identified as a source of significant electron thermal transport in tokamak discharges. In order to describe the evolution of these discharges, it is necessary to improve the prediction of electron thermal transport. This can be accomplished by utilizing a model for transport driven by MTMs in whole device predictive modeling codes. The objective of this paper is to develop the dispersion relation that governs the MTM driven transport. A unified fluid/kinetic approach is used in the development of a nonlinear dispersion relation for MTMs. The derivation includes the effects of electrostatic and magnetic fluctuations, arbitrarymore » 
Fusion power production in International Thermonuclear Experimental Reactor baseline Hmode scenarios
Selfconsistent simulations of 15 MA ITER Hmode DT scenarios, from rampup through flattop, are carried out. Electron and ion temperatures, toroidal angular frequency, and currents are evolved, in simulations carried out using the predictive TRANSPort and integrated modeling code starting with initial profiles and equilibria obtained from tokamak simulation code studies. Studies are carried out examining the dependence and sensitivity of fusion power production on electron density, argon impurity concentration, choice of radio frequency heating, pedestal temperature without and with E × B flow shear effects included, and the degree of plasma rotation. The goal of these wholedevice ITER simulationsmore » 
Integrated modeling of temperature profiles in Lmode tokamak discharges
Simulations of doublet IIID, the joint European tokamak, and the tokamak fusion test reactor Lmode tokamak plasmas are carried out using the PTRANSP predictive integrated modeling code. The simulation and experimental temperature profiles are compared. The time evolved temperature profiles are computed utilizing the MultiMode anomalous transport model version 7.1 (MMM7.1) which includes transport associated with driftresistiveinertial ballooning modes (the DRIBM model [T. Rafiq et al., Phys. Plasmas 17, 082511 (2010)]). The tokamak discharges considered involved a broad range of conditions including scans over gyroradius, ITER like current rampup, with and without neon impurity injection, collisionality, and low and highmore » 
Kinetic modeling of divertor heat load fluxes in the Alcator CMod and DIIID tokamaks
The guidingcenter kinetic neoclassical transport code, XGC0 [Chang et al., Phys. Plasmas 11, 2649 (2004)], is used to compute the heat fluxes and the heatload width in the outer divertor plates of Alcator CMod and DIIID tokamaks. The dependence of the width of heatload fluxes on neoclassical effects, neutral collisions, and anomalous transport is investigated using the XGC0 code. The XGC0 code includes realistic Xpoint geometry, a neutral source model, the effects of collisions, and a diffusion model for anomalous transport. It is observed that the width of the XGC0 neoclassical heatload is approximately inversely proportional to the total plasmamore »