Magnetic field measurements in Z-pinches using polarization separation Zeeman techniques

Measurements of magnetic fields in current carrying plasmas using Zeeman splitting spectroscopic techniques are difficult when the splitting is much less than the line width of the transition. HY-Tech has employed a technique, developed by Jahoda et al, to record separately the spectrum of the right circularly polarized (RCP) σ(+) and left circularly polarized (LCP) σ(-) Zeeman components when viewing the plasma along the magnetic field direction (the π components are absent in this case). The Zeeman shift of the σ(±) components, corresponding to ΔM_J=±1 transitions, is larger than that of the π components (ΔM_J=0). The polarization separation is accomplished using a quarter wave retarder to convert the RCP and LCP components into orthogonal linearly polarized components which are spatially separated using a polarizing beam splitter. Linear optical fiber arrays select identical spatially resolved locations in the RCP and LCP images of the pinch which are focused onto the input slit of a spectrometer. An image intensified CCD camera records separately the spectra of the two polarization components at a number of spatial locations, from which the Zeeman splitting is inferred. Spectral measurements on the Hawk accelerator using annular gas puff neon loads containing 10% N₂ indicate that the splitting of the 4619 NV line to be 2 times the splitting of the 4603 NV transition. This is in reasonable agreement with the predicted splitting ratio of 1.36 for these lines. The technique conclusively demonstrates that the Zeeman splitting can be accurately inferred using this technique even when the splitting is one-tenth the line width and the signal is noisy.