Dartmouth Events

Abstract: The Large Plasma Device (LAPD) is modeled using a modified version of the
 3D Global Braginskii Solver code (GBS). Comparisons to experimental measurements
 are made in the low-bias regime showing strong qualitative agreement with the
 data, particularly the radial dependence of the density fluctuations, cross-correlation
 lengths, radial flux dependence outside of the cathode edge, and camera imagery.
 
Kelvin Helmholtz (KH) turbulence at relatively large scales is the dominant driver of cross-field
transport in these simulations with smaller-scale drift waves and sheath modes playing a secondary
role. Plasma holes and blobs arising from KH vortices in the simulations are consistent with the
scale sizes and overall appearance of those in LAPD camera images.
 
Sheath effects are proposed as a mechanism for the intrinsic $E\times B$ rotation seen
in LAPD in the unbiased regime with little effect from the nonlinear Reynolds stress.
Modification of this rotation through a biasable limiter near the cathode end of the device
is also explored for the first time in simulations showing a departure from the 2D sheath
approximation used to set the potential.

Strong biasing in the ion-diamagnetic direction shows the emergence of a coherent mode of
order m=6, a moderate density confinement, and a quiescence in the plasma turbulence of
the core. Biasing opposite of the intrinsic flow in the electron-diamagnetic direction reduces
the shear flow and leads to a stronger presence of drift modes that saturate in simulations seen
when the KH drive has been suppressed.