Creation of large temperature anisotropies in a laboratory plasma

Abstract

Ion temperature anisotropy in an expanding magnetized plasma is investigated using laser induced fluorescence. Parallel and perpendicular ion velocity distribution functions (IVDFs) were measured simultaneously with high spatial resolution in the expanding plasma. Large ion temperature anisotropies (T⊥i/T∥i∼10) are observed in a conical region at the periphery of the expanding plasma plume. A simple 2D Boris stepper model that incorporates the measured electric field structure is able to reproduce the gross features of the measured perpendicular IVDFs. A Nyquist stability analysis of the measured IVDFs suggests that multiple instabilities with k⊥ρi∼1 and k||ρi∼0.2 are likely to be excited in these plasmas.