Magnetic field distribution estimations with Zeeman splitting spectroscopy at the radial phase of the PF-400J device*

Discharge current measurements in Plasma Focus discharges are usually made with inductive probes such as Rogowskii coils, which present the disadvantage that it cannot determine the current circulating through the plasma column. This indetermination makes it more difficult to estimate plasma characteristics such as the temperature inside the column through the Bennett relation.  

Zeeman splitting, based on the spectral separation of optical emission lines, enables the estimation of the magnetic field in the plasma column when a high current is present. The emitted photons have a distinct polarization identified as σ⁺ and σ^-, possible to be separated by a λ/4 polarizing plate.

This work presents preliminary measurements of the magnetic field present at the plasma column of the PF-400J discharge in a high current density configuration (Φ_anode = 4.5 - 6.0 mm and Z_eff = 10 - 20 mm), by using the Zeeman splitting spectroscopic technique of the Ar III emission at 330.18 nm. The measurements are spatially resolved in the radial direction, with the use of the combination of a polarizing crystal and λ/4 polarizing plate, and a bifurcated fiber optic bundle focused on the entrance of a 0.5m spectrometer with a 2400 l/mm grating.

With this experimental configuration a magnetic field of around 2T is estimated at the pinch volume, when the maximum current (~100kA) is achieved.