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Media type:
E-Article
Title:
A two photon absorption laser induced fluorescence diagnostic for fusion plasmas
Contributor:
Magee, R. M.;
Galante, M. E.;
McCarren, D.;
Scime, E. E.;
Boivin, R. L.;
Brooks, N. H.;
Groebner, R. J.;
Hill, D. N.;
Porter, G. D.
Published:
AIP Publishing, 2012
Published in:
Review of Scientific Instruments, 83 (2012) 10
Language:
English
DOI:
10.1063/1.4728092
ISSN:
1089-7623;
0034-6748
Origination:
Footnote:
Description:
The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm2), narrow bandwidth (0.1 cm−1) laser is injected into a hydrogen plasma to excite the Lyman β transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer α emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.