Session CP13: Poster Session: Fundamental Plasmas: Nonneutral Plasmas (2:00pm - 5:00pm)

An Elliptical Model for Inviscid Damping of a Smooth Vortex Under an Applied Strain Flow

The dynamics of a pure electron plasma in a Penning-Malmberg trap have been shown to be a good analog of the dynamics of vorticity in a 2D inviscid incompressible fluid in the presence of an external strain flow \footnote{N. C. Hurst, et al., {\it Phys. Rev. Lett.} {\bf 117}, 235001 (2016).}. Previously, vortices in the absence of strain were observed to undergo spatial Landau damping, when the vorticity profile is adequately non-flat. We present a model explaining experimental evidence of inviscid damping of the smooth vorticity under the influence of an applied strain flow, accompanied with vortex-in-cell simulations. An elliptical model, describing the dynamics of the smooth vortex as two embedded elliptical patches with preserved vorticity and area, is presented and compared to the experimental and simulation results. The model provides a time-dependent solution to simple coupled ordinary differential equations and analytical expressions for predicting the damping rate and stability of the vortex. Its connection to the strain-free spatial Landau damping is discussed. This work is the first theoretical approach to explain the inviscid damping of the smooth vortex under the presence of irrotational applied strain flow.   

Compression Regimes in a Kinetic Model of Rotating Wall Compression of Electron-Antiproton Plasma via Coupling to ExB Rotation Mode

Non-neutral plasma compression has applications ranging from maintaining trapped plasmas to antihydrogen synthesis. The theory of plasma compression via application of a rotating wall (RW) potential coupling to Trivelpiece-Gould modes is well-developed [1]. Here we continue our investigation of a kinetic model of RW compression coupling instead to ExB rotation [2] inspired by antiproton-electron multispecies compression used by the ALPHA collaboration for antihydrogen synthesis [3,4]. Using simulations we identify and explore three distinct regimes of compression: strong compression (also called strong drive [5]), weak compression, and cut-off, where the plasma rotation reaches the RW frequency, a fraction of the RW frequency, or remains relatively unchanged, respectively. We identify dimensionless parameters governing these regimes and discuss the implications of this model for effective plasma compression. [1]: Anderegg, F., et al. \textit{Physical Review Letters}~81.22 (1998): 4875. [2]: Zhmoginov, Andrey, et al.~\textit{APS}~2014 (2014): BP8-110. [3]: Gutierrez, A., et al.~\textit{TCP 2014}. Springer, Cham, 2017. 109-116. [4]: Andresen, G. B., et al.~\textit{Physical review letters}~100.20 (2008): 203401. [5]: Danielson, J. R., et al.~\textit{Physical review letters}~94.3 (2005): 035001.   

Poisson-Boltzmann equilibrium solutions for electron plasma trapped in a high field Penning-Malmberg trap

Thermal equilibrium for a non-neutral plasma in a finite-length Penning-Malmberg trap is governed by Poisson’s equation and the Boltzmann relation. We describe numerical solutions for such equilibria that are applicable to the PAX (Positron Accumulation eXperiment) high-field (3.1 T) trapped plasma. The PAX Experiment has the goal to accumulate positrons coming from the NEPOMUC source in Garching in order to provide the pair plasma experiment APEX with enough particles to observe collective plasma behavior. The experiment is currently being conducted with electrons in Greifswald to develop the key techniques needed for deployment at NEPOMUC. The equilibrium solution can be found numerically using an iterative finite-difference method for a given temperature (0.05 eV to 10 eV) and number of particles ($10^8$-$10^{11}$). For a unique solution it is also necessary to provide a fixed mean-squared radius of the plasma distribution. Alternatively the radial profile, which can be measured by dumping the plasma onto a phosphor screen, can be used. With such a profile a solution was found after 300 iterations that agrees with theoretical expectations.