Emission of fast non-Maxwellian hydrogen atoms in low-density laboratory plasma

Ertmer

et al. 2019

Atoms

Self Cite

In this work, we present a new application for the line shapes of emission induced by reflected hydrogen atoms. Optical properties of the solids in contact with the plasma could be effectively measured at the wavelength of Balmer lines: time-resolved measurements of reflectance and polarization properties of mirrors are performed using the wavelength separation of the direct and reflected signals. One uses the Doppler effect of emission of atoms excited by collisions with noble gases, primarily with Ar or with Kr. In spite of a new application of line shapes, the question of the source of the strong signal in the case of Ar exists: the emission observed in the case of the excitation of H or D atoms by Ar exceeds the signal induced by collisions with Kr atoms by a factor of five, and the only available experimental data for the ground state excitation show practically equal cross-sections for both gases in the energy range of 80–200 eV.

Section: Emission Of Fast Reflected Atoms and Measurements Of Reflectmentioning

confidence: 54%

Emission of Fast Hydrogen Atoms in a Low Density Gas Discharge—The Most “Natural” Mirror Laboratory

Ertmer

et al. 2019

Atoms

Self Cite

“…The knowledge of the magnetic field is also important to measure the behavior of metastable levels of argon (Ar) in the linear plasma of PSI-2 [15,16]. Metastable Ar has a potential role in the excitation channel [17] of the emission of reflected hydrogen atoms at the plasma-surface interface. The current application and further development of the Doppler-shifted reflectance measurements (DSRM) diagnostic [18] in plasma cleaning discharges with electron temperature on the order of a few eV or less depends crucially on the answer to the following question: Are the metastable levels of Ar, in comparison with Kr or other noble gases, responsible for the strong emission of Balmer lines [19]?…”

Section: Introductionmentioning

confidence: 99%

Measurement of the Magnetic Field in a Linear Magnetized Plasma by Tunable Diode Laser Absorption Spectroscopy

Tsankov

et al. 2019

Atoms

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Tunable diode laser absorption spectroscopy (TDLAS) is a commonly used technique to measure the temperature and density of atoms or molecules in a gas. In this work, we demonstrate that the TDLAS diagnostics could be effectively applied to measure the magnetic field in a low-density weakly magnetized plasma using the Zeeman splitting of the absorption spectrum of lines from noble gases. The laser wavelength is tailored to fit the 1 s 5 → 2 p 6 transition of atomic Ar with the wavelength λ = 763.51 nm . Two mechanisms of line broadening and splitting are observed: Doppler broadening and Zeeman effect. The latter is especially pronounced by applying polarization-selective observation of the absorption to the TDLAS measurements. By fitting the σ and π components of the absorption spectrum, the line-integrated magnetic field on the order of 30–50 mT is determined. The agreement between the measured values and the vacuum field (neglecting the impact of the plasma) calculations on the axis of the PSI-2 is found to be about 15–20%.

In situ measurements of the spectral reflectance of metallic mirrors at the H α line in a low density Ar–H plasma

Review of Scientific Instruments

Brandt

et al. 2018

The efficient and reliable control and monitoring of the quality of the optical properties of mirrors is an open problem in laboratory plasmas. Until now, the measurement of the reflectance of the first mirrors was based on the methods that require additional light calibration sources. We propose a new technique based on the ratio of the red- and blue-shifted emission signals of the reflected hydrogen atoms which enables the in situ measurement of the spectral reflectance of metallic mirrors in low-density Ar-H or Ar-D plasmas. The spectral reflectance coefficients were measured for C, Al, Ag, Fe, Pd, Ti, Sn, Rh, Mo, and W mirrors installed in the linear magnetized plasma device PSI-2 operating in the pressure range of 0.01-0.1 Pa. The results are obtained for the H line using the emission of fast atoms induced by excitation of H atoms through Ar at a plasma-solid interface by applying a negative potential U = -80, …, -220 V to the mirror. The agreement between the measured and theoretical data of reflectance is found to be within 10% for the investigated materials (except for C). The spectra also allow us to efficiently determine the material of the mirror.