Fast Electron Bremsstrahlung in Arbitrary Tokamak Configuration
During the last past years, the non-thermal plasma bremsstrahlung emission has proven to be a very powerful tool for investigating the build-up of a non-thermal electron tail in the range of energy 20-200 keV by resonant interaction between plasma and radiofrequency (RF) waves. Following the pioneering work done on the tokamak Tore Supra, tomographic systems with a large number of chords and refined spectrometric capabilities have therefore been installed on numerous toroidal devices. Most of them are dedicated to detailed observations of the hard x-ray (HXR) emission profile at different photon energies in a poloidal cross-section of the plasma, while few are concerned by angular dependence studies along the toroidal direction, and relativistic effect which is the signature of very energetic electrons. Despite numerous attempts, it has never been possible to invert the line-integrated HXR profile, and extract directly from measurements the shape of the electron momentum distribution function at different plasma locations. Since this problem is deeply illconditioned, HXR Abel inverted studies are only used to qualitative analysis, assuming that bremsstrahlung emission is a flux surface quantity, an assumption which is sometimes questionable when RF power absorption is well off-axis. Indeed, experimental observations have clearly shown lack of symmetry between high and low magnetic field side regions, a difference which may results not only from Shafranov shift, but also from the presence of trapped electrons, and also the complex combination between forward emission and helical field lines. A quantitative assessment of the consistency between line-integrated non-thermal bremsstrahlung emission and plasma current in fully non-inductive regimes requires therefore a complete description of the physical process at play, including the complexity that results from the interplay between momentum and radial spaces dynamics.
Bibliographic Reference: An oral paper given at: 32nd EPS Conference on Controlled Fusion and Plasma Physics Organised by: Asociación EURATOM-CIEMAT para Fusión Held at: Congress Palace of Tarragona, Tarragona (ES)
Availability: Available from Association EURATOM-CEA, Departement de Recherches sur la Fusion Controlee, CEA Cadarache, F-13108 St Paul-Lez-Durance, FranceL%Tel: (+33) 4 42 25 70 01; Fax: (+33) 4 42 25 64 21 E-mail: email@example.com
Record Number: 200518278 / Last updated on: 2005-07-26
Original language: en
Available languages: en