  A rotating plasma spoke is shown to develop in two-dimensional full-sized
kinetic simulations of a Penning discharge cross-section. Electron cross-field
transport within the discharge is highly anomalous and correlates strongly with
the spoke phase. Similarity between collisional and collisionless simulations
demonstrates that ionization is not necessary for spoke formation. Parameter
scans with discharge current $I_d$, applied magnetic field strength $B$ and ion
mass $m_i$ show that spoke frequency scales with $\sqrt{e E_r L_n / m_i}$,
where $E_r$ is the radial electric field, $L_n$ is the gradient length scale
and $e$ is the fundamental charge. This scaling suggests that the spoke may
develop as a non-linear phase of the collisionless Simon-Hoh instability.
