Abstract
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%.
Highlights
The measurement of the magnetic field in laboratory and astrophysical plasmas represents one of the most studied parameter in plasma physics, and at the same time is one of the most crucial parameters for steady-state plasma operation [1]
We demonstrate the first measurement of the magnetic field using tunable diode laser absorption spectroscopy (TDLAS) in the linear magnetized plasma of the PSI-2 device
We note that the obtained absorption spectra and results are line-integrated, and the magnetic field varies as a function of the position on the z-axis in the PSI-2
Summary
The measurement of the magnetic field in laboratory and astrophysical plasmas represents one of the most studied parameter in plasma physics, and at the same time is one of the most crucial parameters for steady-state plasma operation [1]. A variety of different techniques is used to determine the magnetic field. For laboratory plasmas the magnetic field can be obtained e.g., by optical emission spectroscopy (OES) by measuring the Zeeman splitting of an emission line [2,3], by Thomson scattering of laser light [4], by inductive sensors [5], or by accurate description of the line shapes of quasi-isotropic fields [6]. Only OES can be used to determine magnetic fields due to the distance between plasma source and observer [7,8,9]. TDLAS is a widely and commonly used technique in physics to measure the density and temperature of atomic or molecular species in the plasma [10,11,12,13]
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