Lyman-[alpha] radiation of a probe atomic beam to explore the electric field in plasma sheaths

• Published in: Europhysics letters Vol. 104; no. 3; p. 1
• Main Authors: Lejeune, Aurélien, Chérigier-Kovacic, Laurence, Doveil, Fabrice
• Format: Journal Article
• Language: English
• Published: Les Ulis IOP Publishing 01-11-2013
• EISSN: 1286-4854
• ISSN: 0295-5075

An innovative way to non-intrusively measure weak electric fields in plasmas is presented. The electric field is produced between two planar plates which can be immersed in a thermionic plasma. An atomic probe beam, obtained from the conversion of H^sup +^ ions into H(2s) in a resonant charge exchange cesium vapor cell, is sent between the two plates. Emission of the Lyman-α line is induced by the external electric field. It originates in the Stark mixing of the two 2s^sub 1/2^ and 2p^sub 1/2^ levels that are separated in energy by the so-called Lamb shift. The light is collected in a direction perpendicular to the probe beam. Theory predicts that its intensity is proportional to the square modulus of the electric field below a critical value. With a proper calibration through measurements in vacuum, the amplitude of the electric field is obtained. Creating an electric field within a plasma, Debye shielding is thus clearly observed. Such measurement can also be done in transparent diluted media.