Multi-Dimensional Electron Velocity Distribution Functions Measured Via Incoherent Thomson Scattering System in PHASMA

For weakly collisional, magnetized plasmas, particle temperatures perpendicular and parallel to background magnetic field can be different. Such temperature anisotropy occurs in the expanding solar wind, during magnetic reconnection in the magnetosphere, and in laboratory plasmas. Electron temperature anisotropies are also believed to play an important role in laboratory magnetic mirror and terrella experiments. However, direct measurement of electron temperature anisotropies is quite challenging. Having demonstrated 1D electron velocity distribution functions (EVDFs) measurement via incoherent Thomson scattering system in the PHAse Space MApping (PHASMA) device [Shi et al., Rev. Sci. Instrum. 92, 033102 (2021)], we have now enhanced the Thomson scattering system in PHASMA to provide 3D EVDF measurements for the first time in a laboratory plasma. Our approach is to add one more injection path along the axial direction and one more collection path in the perpendicular plane. Four Thomson scattering spectra are measured along four different directions, defining an over-determined set of measurements of 3D . Preliminary 3D EVDF measurements for the pulsed gun plasmas and static helicon plasmas will be presented.