Tokamak Simulation Code modeling of NSTX

Abstract

The Tokamak Simulation Code [TSC] is widely used for the design of new axisymmetric toroidal experiments. In particular, TSC was used extensively in the design of the National Spherical Torus eXperiment [NSTX]. We have now benchmarked TSC with initial NSTX results and find excellent agreement for plasma and vessel currents and magnetic flux loops when the experimental coil currents are used in the simulations. TSC has also been coupled with a ballooning stability code and with DCON to provide stability predictions for NSTX operation. TSC has also been used to model initial CHI experiments where a large poloidal voltage is applied to the NSTX vacuum vessel, causing a force-free current to appear in the plasma. This is a phenomenon that is similar to the "plasma halo current" that sometimes develops during a plasma disruption.TSC models the evolution of free-boundary axisymmetric toroidal plasma on the resistive and energy confinement time scales. The plasma equilibrium and field evolution equations are solved on a two-dimensional Cartesian grid. Boundary conditions between plasma/vacuum/conductors are based on the fact that the poloidal flux is continuous across interfaces. The surface-averaged transport equations for the pressures and densities are solved in magnetic flux coordinates using matrix implicit methods. An arbitrary transport model can be used. Neoclassical-resistivity, bootstrap-current, auxiliary-heating, current-drive, alpha-heating, radiation, pelletinjection, sawtooth, and ballooning-mode transport models are all available. As an option, circuit equations are solved for all the poloidal field coil systems with the effects of induced currents in passive conductors included. Realistic feedback systems can be defined to control the time evolution of the plasma current, position, and shape. Open field lines can be included, and the halo current is computed as part of the calculation.TSC can be run in several operating modes. The time dependent one-dimensional functions for the pressure p(ψ,t), the density n(ψ,t), and the effective charge state Z(ψ,t) can either be specified as input or be calculated from transport equations, density evolution equations, or impurity transport and ionization physics. The plasma current is calculated self-consistently from the changing external coil currents, with or without feedback systems included. There is also an option to impose symmetry about the midplane or to model the full device with no up/down symmetry.TSC development has been project driven. Capabilities were added as needed. TSC had its origins in the S-1 spheromak in modeling the inductive formation using a flux core [1]. It was used on the PBX experiment to calculate the effect of strong shaping on plasma axisymmetric stability, disruption forces on the passive stabilizers, voltsecond benchmarking, and in modeling the current-drive experiments [2]. It was used on the TCV experiment for the design of a tokamak with a flexible shaping system, and to study doublet formation [3]. For CIT and Ignitor, it has ...

Plans for Electron Bernstein Wave and Electron Cyclotron Heating in NSTX

“…n e (R) and T e (R) were assumed to be flat, with n e = 3.5x10 18 m -3 and T e = 25 eV. ECH electron power deposition profile will be used in the Tokamak Simulation Code (TSC) [13] to simulate the evolution of the startup plasma in the presence of 28 GHz ECH. A bundle of 30 rays were launched in a cone with a half angle of 3 degrees to simulate the divergence of a diffraction limited 28 GHz antenna pattern.…”

Double-null divertor configuration discharge and disruptive heat flux simulation using TSC on EAST

“…TSC advances in time the magnetohydrodynamics equations with the inclusion of the axisymmetric transport and heating packages. These packages include the neoclassical-resistivity, anomalous transport, bootstrap-current, auxiliary-heating, current-drive, alpha-heating, radiation, pellet-injection, sawtooth, and ballooning-mode induced transport models [14][15][16]. Details of the computational methods with the description of these packages of TSC are given in [11,14,16].…”