University of Alberta, Canada
Thursday, March 11, 2021
Thermal waves are fascinating because they are not actually waves, but they act and behave similar to a “standard wave”; they are a diffusive-type oscillation with propagation characteristics. Over the past few decades thermal waves have been used extensively to study the optical, thermal and electronic properties of solids, liquids and gases. This is mainly accomplished using a device known as a driven thermal wave resonator cavity (TWRC) where frequency and cavity length scanning are used to measure the thermal and other properties. Thermal waves are produced using sinusoidally time-varying heat sources and can be generated in magnetized plasmas through external wave sources, such as electron cyclotron heating in toroidal plasmas or through an oscillatory electron beam source, as is the case in the experiments I will describe carried out at the Large Plasma Device (LAPD) at UCLA. In order to make a TWRC in the large linear plasma device, we first inject an electron beam into a relatively cold background magnetized plasma (~0.25eV) which thermalizes and forms a finite-length, hot electron temperature filament aligned with the external magnetic field. Then an oscillating voltage is applied to modulate the electron beam energy, thus producing stimulated thermal waves within the filament which acts as a quarter-wave resonator. Using this Plasma-TWRC we can obtain the anisotropic thermal conductivity of the plasma. Results from our experiments on the LAPD as well as diffusion-wave theory and simulation will be presented.
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