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Description
Steep pressure gradients in a magnetized plasma can induce a variety of spontaneous low frequency excitations such as drift-Alfven waves and vortices. We present results from basic experiments on energy and particle transport in magnetized plasmas with multiple heat sources in close proximity [1]. The experiments were carried out at the upgraded Large Plasma Device (LAPD) operated by the Basic Plasma Science Facility at the University of California, Los Angeles. The setup consists of three biased probe-mounted cerium-hexaboride crystal cathodes that inject low energy electrons along a strong magnetic field into a pre-existing cold afterglow plasma forming localized regions of elevated temperature and density. A cross-field triangular spatial pattern is chosen for the sources and multiple axial and transverse probe measurements allow for determination of the mode patterns and axial filament length. When the three sources are placed within a few collisionless electron skin depths, a non-azimuthally symmetric wave pattern emerges due to the overlap of drift-Alfven modes forming around each filament. This leads to enhanced nonlinear convective (E×B) chaotic mixing and rapid density and temperature profile collapse in the inner triangular region of the filaments. Steepened thermal gradients form in the outer triangular region, which spontaneously generates quasi-symmetric, higher azimuthal mode number drift-Alfven fluctuations. A statistical study of the fluctuations reveals amplitude distributions that are skewed which is signature of intermittency in the transport dynamics. Nonlinear gyrokinetic simulations using seeded filaments confirm the presence of unstable drift-Alfven modes driven by the steep thermal gradient along with fluctuation spatial patterns that are comparable to the experiments.
[1] R.D. Sydora et al, “Drift-Alfven fluctuations and transport in multiple interacting magnetized electron temperature filaments”, Journal of Plasma Physics, 85 (6), 905850612 (2019).
[2] S. Karbashewski, et al, “Magnetized plasma pressure filaments: Analysis of chaotic and intermittent transport events driven by drift-Alfven modes”, Phys. Plasmas, 29 (11) 112309 (2022).
[3] R.D. Sydora, et al, “Experiments and gyrokinetic simulations of the nonlinear interaction between spinning magnetized plasma pressure filaments”, Phys. Plasmas, (in press, 2024).
