Thermal Waves in an Inhomogeneous Magnetized Plasma Pressure Filament

Results are presented from basic heat transport experiments using driven thermal waves in a magnetized plasma pressure filament. Using a small cathode source, low energy electrons are injected along the magnetic field into the afterglow of a pre-existing plasma forming a hot electron filament embedded in a colder plasma. A series of low amplitude, sinusoidal perturbations are added to the cathode discharge bias that creates an oscillating heat source capable of driving large amplitude electron temperature oscillations [1]. Langmuir probes are used to measure the amplitude and phase of the thermal wave field over a wide range of driver frequencies. The results are used to verify the excitation of thermal waves, confirm the presence of thermal resonances, and demonstrate the diagnostic potential of thermal waves through measurement of the parallel thermal diffusivity [2].

More recent experiments have significantly improved the measurement technique and allowed access to the previously unstudied cross-field regime. The results reveal a complex cross-field structure that is shown to be due to thermal wave interference effects from the inhomogeneous structure of the filament. A classical mechanics approach is used to model the inhomogeneous thermal conductivity profile to accurately predict the observed thermal wave interference patterns and extract thermal conductivities. A comparison of the observations in quiescent and turbulent conditions demonstrates thermal waves may be used to distinguish between classical and anomalous transport regimes.