A METASTABLE HYDROGEN PROBE BEAM TO MEASURE STATIC AND OSCILLATING ELECTRIC FIELDS
Résumé
A new diagnostic to measure directly an electric field in vacuum or in a plasma has been developed. It is based on the emission of the Lyman-α line by a hydrogen probe-beam in the 2s state when the beam passes through a region where an electric field is present (Electric Field Induced Lyman-α Emission). The electric field couples the Lamb-shift spaced 2s and 2p atomic hydrogen levels, the 2s lifetime is shortened and this level decays via 2p to the ground state. By measuring the intensity of the subsequent Lyman-α radiation, it is possible to determine the magnitude of the field in a defined region. The aim of this work is to study the performances of this diagnostic when measuring an oscillating electric field at frequencies around Lamb-shift frequency (1 GHz), where Lyman-α emission is enhanced by a factor of almost 400. We show a good agreement between measurements in vacuum and results of a simulation of both experimental device and diagnostic. A calibration of the diagnostic using abolute static field measurements is proposed.
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