2D ExB vortex dynamics in pure electrons plasmas subject to time-dependent strain flows.*

The ExB drift dynamics of a pure electron plasma in a Penning-Malmberg trap closely mirror the vorticity dynamics in a 2D inviscid incompressible fluid, making it an excellent platform for studying fluidlike behavior in plasmas. Using a specially designed Penning-Malmberg trap, one can impose strain flows in 2D by biasing segmented electrodes surrounding the plasma [1,2]. Electron density, analogous to fluid vorticity, is directly measured with a CCD camera. Previous work has studied Kelvin-Helmholtz unstable modes with a constant strain [1] and breaking of an adiabatic invariant during ramped strain flows [2]. Here, we present experiments using a smooth waveform such as a half-sine pulse, which provides a more realistic representation of natural vortex behavior compared to the previously used square pulses. This smooth waveform can incorporate contributions from both Kelvin-Helmholtz instability and the breaking of diabatic invariants. The vortex response to this strain field is described as a function of both the amplitude and frequency of the applied strain. Comparison to the Kida vortex patch model [3] allows for the separation of these two competing processes. Repeated strain pulses as a possible route to turbulence will also be discussed.

[1] N. C. Hurst et al., Phys. Plasmas 27, 042101 (2020).

[2] N. C. Hurst et al., Phys. Rev. Fluids 6, 054703 (2021).

[3] S. Kida, J. Phys. Soc. Japan 50 10 3517-3520 (1981).

∗Work supported by U.S. DOE grant DE-SC0016532; DOE grant DOESC0018266

(for N. H.); and NSF grant PHY-2106332 (for D. D.).