Characterizing Structural Modifications from Large Amplitude Alfven Waves in the LArge Plasma Device (LAPD)

Structural modifications, such as density and temperature, from large amplitude Alfvén waves are seen in the ionosphere and have been explained by a combination of processes such as joule heating and ponderomotive forces. The LAPD, an 18 m long and 1 m diameter cylindrical device, produces a magnetized plasma (n = 10¹¹-10¹³ cm^-3, Te= 0.1-15 eV)¹ that sustains Alfvén waves. In recent large amplitude (𝛿b/B ~ 0.1%) Alfvén wave experiments in the LAPD, density and temperature modifications (up to 150% and 400% respectively) have been seen during the active phase of the discharge, in which the wave is in a kinetic regime. In the past, these modifications have been attributed to Landau and collisional heating and ionization, but have never been fully understood. It has been found that the antenna used to launch the waves has a significant effect on the modifications seen. In an effort to decouple the effects of the wave to those of the antenna, a new set of experiments will be designed to study the structural modifications from the wave alone. Results on the new experiments will be presented.



¹W. Gekelman, et al., Rev. Sci. Instr., 87, 025105 (2016)