The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium–tritium (D–T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D–T, deuterium-deuterium (D–D), and deuterium–helium-4 (D–4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne≳10%). Mode conversion current drive in D–T plasmas was simulated with experiments conducted in D–3He–4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing.
An expression for local power absorption for linear wave propagation in a nonuniform hot magnetoplasma is derived from fundamental principles. The power-absorption definition is used to obtain a local power-conservation relation for a one-dimensional configuration. The formalism is applied to wave propagation in the ion cyclotron range of frequencies where strong damping and mode-conversion processes are present.
Fast magnetosonic wave absorption by fast alpha particles at small concentrations during an approach to ignition in ITER-like fusion plasmas is examined for the fundamental deuterium heating scheme. Numerical results are obtained using a full-wave code which solves coupled second order differential equations for the wave fields in a slab geometry. The fast alpha particle velocity distribution is approximated by a Maxwellian, chosen so that its velocity space density of resonant particles equals that of a slowing down distribution when both are evaluated at the absorption peak. For the cases considered, the thermal gyroradius of the Maxwellian alpha distribution satisfies the condition (k⊥ραf)2/2 < 1. Significant absorption of the fast wave by the alphas can occur in a parameter window characteristic of startup conditions. This is because the Doppler broadened alpha particle resonance zone encompasses the deuterium-tritium hybrid resonance where the left hand circularly polarized component of the wave electric field peaks
The subject of linear wave propagation and its associated power conservation in a slab geometry for waves in the ion cyclotron range of frequencies is treated. The governing differential equations and conservation relation are obtained using a Taylor series representation of the field evaluated to third order in the parameter, gyroradius/wavelength, which is assumed to be small for the cases examined here. This approach correctly incorporates the effects of transverse nonuniformity and is valid for all values of k∥. The local power conservation relation follows from a definition of local power absorption and a new companion general expression for kinetic flux based on fundamental principles. These expressions are evaluated to second order in gyroradius/wavelength in a numerical code, and results are presented for 3He fundamental minority and majority second harmonic cases. For fundamental minority 3He absorption, substantial reflection and mode conversion is found for lower parts of the k∥ spectrum with strong absorption, especially for the ion-Bernstein wave for k∥ >5 m−1. For second harmonic heating at higher 3He concentrations, strong absorption is found for lower values of k∥ with reduced reflection and mode conversion. For plasmas with substantial ion tail formation, tail absorption is found to dominate the absorption process with negligible mode conversion or reflections.
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