Open AccessCharacterization of X‐ray gas attenuator plasmas by optical emission and tunable laser absorption spectroscopies
Author(s) -
Martín Ortega Álvaro,
Lacoste Ana,
Béchu Stéphane,
Bès Alexandre,
Sadeghi Nader
Publication year - 2017
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s1600577517012000
Subject(s) - plasma , argon , attenuator (electronics) , krypton , absorption (acoustics) , excited state , laser , atomic physics , absorption spectroscopy , spectroscopy , tunable diode laser absorption spectroscopy , materials science , chemistry , analytical chemistry (journal) , optics , tunable laser , physics , attenuation , quantum mechanics , chromatography
X‐ray gas attenuators are used in high‐energy synchrotron beamlines as high‐pass filters to reduce the incident power on downstream optical elements. The absorption of the X‐ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X‐ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X‐ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2 p excited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1 s 5 state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X‐ray transmission. The results showed a plasma confined around the X‐ray beam path, its size determined mainly by the spatial dimensions of the X‐ray beam and not by the absorbed power or the gas pressure. In addition, the X‐ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X‐ray beam plays an essential role in the X‐ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators.