Laboratory Investigation of Nonlinear Sub-cyclotron Damping

A unique feature of whistler chorus wave observations is the power gap at frequencies near half the electron gyrofrequency, which is observed approximately 2/3 of the time. 1 Additionally, some of these observations have multiple power gaps, which are typically oblique chorus waves. 2 A variety of theories have been developed over the decades to explain these power gaps, including excitation by two separate electron populations, 3 damping due to nonlinear wave-particle interactions, 2 , 4 and lower band cascade generating the upper band through coupling between electrostatic and electromagnetic components of lower band waves. 5 Recently, Gao et al . 5 published a statistical survey of the whistler chorus power gap using seven years of chorus observations from THEMIS. The results of the survey are that the theories involving damping due to nonlinear wave-particle interactions are the most consistent with the observations, but that they do not each explain all the observations. This led the authors to conclude that the power gaps may be a result of a combination of mechanisms or may require new mechanisms. We are currently conducting laboratory experiments coupled with numerical simulations to test the theories most consistent with observations: nonlinear Landau damping and nonlinear sub-cyclotron damping.