Ray-tracing analysis of ICRH power-deposition profiles in non-circular large Tokamaks

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Abstract
Using self-consistent initial conditions obtained from the full-wave solution of the field radiated by an ion-cyclotron resonance heating (ICRH) antenna, the ray-tracing technique is applied to generate r.f. power-deposition profiles in non-circular large Tokamaks such as JET and NET/INTOR. An analytic expression has been used to simulate the shape of the flux surfaces, which fit reasonably well to the numerical solutions of the Grad-Shafranov equation describing the Tokamak equilibrium, by adjusting three free parameters: the flux-surface shift Delta , the elongation ratio kappa and the triangularity parameter delta . For an elliptic INTOR plasma, it is found that the focussing of rays is much reduced and when the absorption layer is located in the center, the r.f. power density figures are lower approximately by a factor of 1.9 compared to that obtained in an equivalent circular case. This reduction in power density is not so significant when the power is deposited off-center, as demonstrated by an example treated for the JET D-shaped plasma.