Radiation scattering back to the plasma by the tokamak inner wall in the energy range 50-500 keV during lower hybrid current drive
A study of the diffusion of X-rays in the energy range 50 keV - 500 keV, by the inner wall of a tokamak, is presented. In the first simple model, various emission profiles and plasma positions in the tokamak chamber are considered and the contribution of multiple reflections investigated. It is shown that the wall reflectivity can lead to spurious conclusions for a peaked radial profile in the vicinity of the plasma edge. The next step is the resolution of the radiation transport equation in solid matter. The reflectivity is shown to be greatly enhanced by a carbon layer between 50 keV and 150 keV, even for a thickness of one centimetre. The reflectivity is then nearly independent of the energy of the entering photons up to 500 keV. Finally, a full description of the X-ray reflectivity in the high energy range is presented taking account of the toroidal geometry and the exact solution of the radiation transport equation. Theoretical and experimental results obtained with the Tore Supra high energy X-ray spectrometer are compared. A strong reflectivity effect is observed for the more peripheral line of sight when the plasma emission profile is peaked. A procedure to determine the energy threshold above which the photon energy spectrum is free of the reflected contribution is proposed.
Bibliographic Reference: Report: EUR-CEA-FC-1410 EN (1990) 84 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199110109 / Last updated on: 1994-12-02
Original language: en
Available languages: en