Modelling of Spatial and Velocity Distributions of Diffusive Fast Ion Loss in JET

Spatial and velocity distributions of Charged Fusion Products (CFPs) escaping from tokamak fusion plasmas provide important information about the loss mechanisms involved and the knowledge of these distributions is essential for predicting the heat loads associated with CFP's impinging on the tokamaks first wall. The present study aims at modelling the poloidal, toroidal and pitch-angle distributions of high energy ions diffusively lost to the first wall. We consider an inevitable and hence most important loss mechanism due to pitch-angle scattering of fast ions on the bulk plasma particles. Evidently, the diffusive loss of fast ions may be substantially enhanced by Toroidal Field (TF) ripples or MHD perturbations. We note that radial diffusion of fast ions is crucial for the CFP heat deposition on the first wall, since it results in a strong localization of the escaping ions in the vicinity of the mid-plane. Lastly it should be pointed out that modelling of the poloidal, toroidal and pitchangle distributions can help in the interpretation of anomalous loss of CFP's from D-D reactions observed on JET by a scintillator probe.
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EFDC110418 1.03 Mb