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Electric field measurement with the diagnostic EFILE (Electric Field Induced Lyman-alpha Emission)

par Elodie PICO - publié le , mis à jour le

Thesis advisor : Doveil Fabrice

Email and address : fabrice.doveil, 04 91 28, centre St Jérôme, service 362

Co-advisor : Kovacic Laurence

Subject description :

EFILE is a diagnostic which allows to directly measure an electric field in vacuum or in a plasma. When a beam of 2s (metastable state) hydrogen atoms is exposed to an electric field, Stark mixing between 2s and 2p levels induces the Lyman-α transition to the ground state which intensity is directly related to the amplitude of the electric field. Its absolute value is determined with a proper calibration.
The aim of this work is to study a radiofrequency electric field in vacuum and in a plasma, especially in the sheath between the plasma core and the surface of the polarized plate which serves as antenna. Theoretical descriptions and numerical simulations of RF sheaths are active research topics, but quantitative experimental verifications are missing since they require simple geometries, specific diagnostics and sufficient experimental time. The existing diagnostic EFILE will thus be used in a simple cylindrical configuration first, where the plasma is not magnetized and where the field is generated between two parallel plates. This will allow to study the physical problem of sheath and also test the diagnostic. Experimental results will be compared to theoretical models or numerical calculations. Then, this work might be completed by or compared to the study with EFILE of a RF sheath in front of an ICRF antenna in IShTAR (which is a test bench operating at tokamak edge-like conditions for density and temperature), thanks to a collaboration with Institute of Plasma Physics in Garching (Germany).

Bibliography :
L. Chérigier-Kovacic, P. Ström, A. Lejeune and F. Doveil, Review of Scientific Instruments 86, 063504 (2015) ; doi : 10.1063/1.4922856