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Title: Innovative measurement of Debye shielding in plasmas by Lyman-α radiation of a probing metastable hydrogen beam

Answering to a long-standing challenge, a new way to non-intrusively measure weak electric fields in plasmas is presented. Here we show it using an H(2s) atomic probe beam, obtained from the conversion of H{sup +} ions into H(2s) either by collisions with H{sub 2} residual gas or in a resonant charge exchange cesium cell. The probe beam is sent between two polarized plates creating an electric field applied within a thermionic plasma. Indeed the interaction between a metastable H(2s) atomic hydrogen beam and an external electric field leads to the emission of the Lyman-alpha line owing to the Stark mixing of the 2s{sub 1/2} and 2p{sub 1/2} levels. When the field is weak, it can be treated as a perturbation of these two states separated by a small amount of energy called Lamb-shift. It induces a radiation with intensity proportional to the square modulus of the electric field which is measured in a direction perpendicular to the probe beam. Contrary to measurements in vacuum, the Debye sheath formation is clearly observed in the presence of plasma. This contribution reviews: presentation of Stark mixing of the 2s{sub 1/2} and 2p{sub 1/2} levels and of Lamb shift for hydrogen-like atoms, brief descriptionmore » of the experimental set-up, observation of the formation of a sheath between two polarized plane electrodes in a plasma, either with a probe ion beam, or atom beam.« less
Authors:
 [1] ; ;  [2]
  1. Turbulence Plasma, PIIM, UMR7345, CNRS, Aix Marseille Université, case 321, Centre universitaire de Saint Jérôme, FR-13397 Marseilles cedex 20, France and Cameca SAS, 29 Quai des Grésillons, 92622 Gennevilliers Cedex (France)
  2. Turbulence Plasma, PIIM, UMR7345, CNRS, Aix Marseille Université, case 321, Centre universitaire de Saint Jérôme, FR-13397 Marseilles cedex 20 (France)
Publication Date:
OSTI Identifier:
22263922
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1582; Journal Issue: 1; Conference: International conference on complex processes in plasmas and nonlinear dynamical systems, Gandhinagar (India), 6-9 Nov 2012; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CESIUM; CHARGE EXCHANGE; COLLISIONS; DISTURBANCES; ELECTRIC FIELDS; EMISSION; INTERACTIONS; ION BEAMS; LAMB SHIFT; PERTURBATION THEORY; PLASMA; PROBES