Effects of Magnetic Field Gradients on Inertial Alfvén Waves

We have performed laboratory experiments on the Large Plasma Device (LAPD) to measure the transmission and reflection of Inertial Alfvén waves (electron thermal speed << Alfvén speed) through a parallel magnetic field gradient. Alfvén waves are important in natural systems, such as the solar corona and the terrestrial magnetosphere, as well as in laboratory experiments. The reflection and transmission of Alfvén waves through inhomogeneities in the background plasma are important for understanding wave propagation, turbulence, and heating of thermonuclear plasmas. In a recent laboratory experiment, it was observed that Kinetic Alfvén waves (thermal speed >>Alfvén speed) lose energy after passing through a magnetic field gradient. Surprisingly, though, no reflection from the magnetic field gradient was observed. One possibility is that wave energy is dissipated rapidly in the gradient region. To better understand the effects of gradient, we are now carrying out an analysis of Alfvén wave propagation under similar conditions, but in the inertial regime. The propagation of these waves has been studied for different magnetic field gradients and for different wavelengths. We will present our measurements of the reflection and transmittance of Inertial Alfvén waves through a magnetic field gradient. This work is supported, in part, by grants from the NSF Solar-Terrestrial Program under grant AGS-1834822 and the U.S. Department of Energy, Office of Science, Office of Fusion Energy Science under Award Numbers DE-SC0016602 and DE-SC0021261. The experiments were performed at the Basic Plasma Science Facility (BaPSF), which is supported by the DOE and NSF, with major facility instrumentation developed via an NSF award AGS–9724366.