Speaker
Laurence Cherigier-Kovacic
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P1.3009.pdf
A metastable hydrogen probe beam to measure
static and oscillating electric fields in plasma
L. Chérigier-Kovacic1, C. Poggi2, T. Guillaume1, F. Doveil1
1
Aix-Marseille Université, CNRS, PIIM UMR 7345,
FR-13397 Marseille Cedex 20, France
2
Consorzio RFX, Corso Stati Uniti, 35127 Padova, Italy
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- 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- Emission). The electric field couples 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- radiation, it is possible to determine the magnitude of the
field in a defined region.
Absolute measurements of a static electric field between two polarized metallic plates in
vacuum or in the sheath between a plasma and one of the plates have been successfully
performed1.
We now address the case of oscillating fields: measurements of a radiofrequency field (in
function of injected power and frequency in the range 800-1400 MHz) compare well to
simulations of our experimental device including the measurement method. We observe a
spectrum with very narrow peaks associated to resonant modes of the cavity. Signal intensity
at the measurement point depends on many unknown parameters such as the transmission
factor of the detection optics, the neutral beam density, and the electric field the beam
encountered all along its path. Thus calibration is not straightforward. However, we can draw
conclusions about possible ways to calibrate measurements in the RF case.
References:
1. L. Chérigier-Kovacic et al., Review of Scientific Instruments 86, 063504 (2015)
