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Electric Field Induced Lyman-α Emission (EFILE) Diagnostic For Electric Field Measurements

Abstract : When a metastable hydrogen test beam is exposed to a constant or oscillating electric field, Lyman-α (121.6 nm) emission occurs. This results from the Stark quenching of the metastable 2s level, induced by the field. The intensity of the radiation is proportional to the square of the electric field amplitude and it is recorded by a lock-in technique, which gives an excellent signal to noise ratio. This provides us with a very sensitive and non intrusive method to measure the electric field value, called EFILE (Electric Field Induced Lyman-α emission). Sensitivity is as good as 0.1 V/cm in the case of an oscillatory field resonant with the Lamb shift frequency ≈ 1 GHz. Hydrogen ions are produced in a magnetic multicusp source by a thermo-electronic discharge. The ions are extracted from the source, focused by a series of electrostatic lenses and accelerated to 500 eV. The beam interacts with cesium vapor which produces atoms in the metastable 2s 1/2 state. In the diagnosed volume, the beam passes between a pair of plane electrodes separated by 5 cm. One of them is grounded, the other one is polarized to generate an electric field. The diagnosed volume can be kept under vacuum or exposed to an argon plasma. Lyman-α emission from the beam passing between the plates is measured as a function of the polarized plate voltage. A saturation of the signal is observed at large field amplitudes, which is explained through oscillatory and geometrical mechanisms. A function that takes this saturation into account is used as a calibration for the subsequent electric field profile measurements in the case of a constant voltage applied between the plates in vacuum. We find a good agreement between our results and a finite element method calculation of the profile.
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https://hal-amu.archives-ouvertes.fr/hal-01466174
Contributor : Laurence Chérigier-Kovacic <>
Submitted on : Monday, February 13, 2017 - 2:04:46 PM
Last modification on : Thursday, January 18, 2018 - 2:26:44 AM
Long-term archiving on: : Sunday, May 14, 2017 - 2:00:15 PM

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Laurence Chérigier-Kovacic, Petter Ström, Fabrice Doveil. Electric Field Induced Lyman-α Emission (EFILE) Diagnostic For Electric Field Measurements. PoS - Proceedings of Science, SISSA, 2015. ⟨hal-01466174⟩

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