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Toroidal effects on propagation, damping, and linear mode conversion of lower hybrid waves

Description: A common simplifying assumption made in the consideration of radio-frequency heating of tokamaks near the lower hybrid frequency is that the wave-length imposed by the coupling device parallel to the magnetic field is not modified by gradients along the field. In the present calculation, the parallel wave-length is allowed to vary, and important effects are found on wave penetration and damping if the toroidal aspect ratio (R/sub major//r/sub minor/) is less than approx. 5. The calculation shows that heating at the center of a small aspect ratio torus is inhibited by a decrease of k/sub parallel/ if waves are launched at the outside, and that it may be possible to change the plasma current via electron Landau damping with a coupler of symmetric power spectrum by placing the coupler at the top (or bottom) of the torus.
Date: September 1, 1980
Creator: Ignat, D.W.
Partner: UNT Libraries Government Documents Department

Consequences of toroidal effects in lower hybrid heating of tokamaks

Description: The lower hybrid slow wave tends to follow magnetic field lines. Therefore, a generalization of Snell's Law modifies the wave length along the magnetic field as the wave moves inward from an exciter through regions of varying magnetic field strength. Predicting the consequences requires a numerical treatment, which has been developed in recent years by several authors. This paper searches for some general statements on the problem by analyzing many particular cases, without allowing for scattering, multiple traverses of the plasma radius, and non-linear effects. We find that the range of parameter suitable for ion heating varies from that predicted by simple estimates, and is dependent on launch position; and that electron heating including current drive is best pursued with unidirectional launching from a coupler at the top (or bottom) of the torus if the wave frequency is close to linear mode conversion condition.
Date: January 19, 1982
Creator: Bernabei, S. & Ignat, D.W.
Partner: UNT Libraries Government Documents Department

Heating the Compact Ignition Tokamak (CIT)

Description: The proposed CIT starts operation in the late 1990's with 20 MW of rf heating power. The tokamak and facility are to be designed to accommodate 50 MW auxiliary heating. The heating methods new being considered are ion cyclotron heating (ICH) and electron cyclotron heating (ECH). Aspects of these systems are described, and the choice of power level and type is discussed. 18 refs.
Date: November 1, 1989
Creator: Ignat, D.W.
Partner: UNT Libraries Government Documents Department

Feedback stabilization of magnetic islands by rf heating and current drive

Description: Feedback stabilization of the m = 2 mode in tokamaks would be advantageous for disruption-free operation at low q-values. Stabilization of the m = 1 mode and resulting ''sawteeth'' could lead to substantial increases in the stable ..beta..-value, as well as indirect stabilization of the m = 2 mode, by permitting q(0)-values below unity. Stabilization of these modes at acceptable amplitudes appears possible by feedback-modulated heating or current drive applied to the region within the mode-induced magnetic islands. Current drive offers by far the more efficient mechanism, and it can be accomplished using lower-hybrid or electron-cyclotron radio-frequency (rf) techniques. For the lower-hybrid case, ray-tracing calculations demonstrate the needed localization of the rf power, despite long ray paths in the toroidal direction. Top-launched lower-hybrid waves are favored for localized absorption.
Date: November 1, 1985
Creator: Ignat, D.W.; Rutherford, P.H. & Hsuan, H.
Partner: UNT Libraries Government Documents Department

Spreading of wave-driven currents in a tokamak

Description: Lower hybrid current drive (LHCD) in the tokamak Princeton Beta Experiment-Modification (PBX-M) is computed with a dynamic model in order to understand an actual discharge aimed at raising the central q above unity. Such configurations offer advantages for steady-state operation and plasma stability. For the particular parameters of this PBX-M experiment, the calculation found singular profiles of plasma current density J and safety factor q developing soon after LHCD begins. Smoothing the lower hybrid-driven current and power using a diffusion-Eke equation and a velocity-independent diffusivity for fast-electron current brought the model into reasonable agreement with the measurements if D{sub fast} {approx} 1.0 m{sup 2}/s. Such a value for D{sub fast} is in the range suggested by other work.
Date: January 1996
Creator: Ignat, D. W.; Kaita, R.; Jardin, S. C. & Okabayashi, M.
Partner: UNT Libraries Government Documents Department

LCS Users Manual

Description: The Lower Hybrid Simulation Code (LSC) is a computational model of lower hybrid current drive in the presence of an electric field. Details of geometry, plasma profiles, and circuit equations are treated. Two-dimensional velocity space effects are approximated in a one-dimensional Fokker-Planck treatment. The LSC was originally written to be a module for lower hybrid current drive called by the Tokamak Simulation Code (TSC), which is a numerical model of an axisymmetric tokamak plasma and the associated control systems. The TSC simulates the time evolution of a free boundary plasma by solving the MHD equations on a rectangular computational grid. The MHD equations are coupled to the external circuits (representing poloidal field coils) through the boundary conditions. The code includes provisions for modeling the control system, external heating, and fusion heating. The LSC module can also be called by the TRANSP code. TRANSP represents the plasma with an axisymmetric, fixed-boundary model and focuses on calculation of plasma transport to determine transport coefficients from data on power inputs and parameters reached. This manual covers the basic material needed to use the LSC. If run in conjunction with TSC, the "TSC Users Manual" should be consulted. If run in conjunction with TRANSP, on-line documentation will be helpful. A theoretical background of the governing equations and numerical methods is given. Information on obtaining, compiling, and running the code is also provided.
Date: February 1, 1998
Creator: Redd, A.J. & Ignat, D.W.
Partner: UNT Libraries Government Documents Department