Destabilization of Alfvenic fluctuations by a parallel-ion beam on the Large Plasma Device

An energetic (15KeV at 10 Amps) hydrogen ion beam was axially injected into a magnetized hydrogen plasma with a magnetizing field ranging from 300 to 1500 Gauss. This experiment was conducted on the Large Plasma Device (LAPD) using a barium oxide source. Excitations of shear Alfven waves by energetic ions through resonant processes such as Doppler-shifted ion-cyclotron-resonance (DCIR) and Landau resonance have been observed in the past on the LAPD¹. We have observed fluctuations at sub-cyclotron range of frequencies that cannot be explained by the above resonance processes. We will present results of our preliminary analysis exploring the possibility of these waves being generated by beam associated pressure and momentum gradients.

[1] S.K.P. Tripathi, B. Van Compernolle, W. Gekelman, P.Pribyl, and W. Heidbrink, PRL 119, 205002, APS (2016).