Influence of the channel width on hall thruster instabilities by 2D radial-azimuthal particle-in-cell simulations

The discharge channel width is a critical design parameter for Hall effect thrusters, yet its influence on the cross-field electron transport governed by plasma instabilities remains inadequately understood, especially when wall absorption is included. The influence of the discharge channel width is investigated using 2D radial-azimuthal particle-in-cell (PIC) simulations with absorbing wall boundaries and an analytic ionization model. The channel width L_r is varied from 3.2 mm to 25.6 mm. We find a non-monotonic dependence of linear instability growth rate on L_r. The ECDI-1st linear growth rate increases, then decreases (notably at L_r=12.8 and 19.2 mm), and rises again at 25.6 mm. The MTSI exhibits a similar L_r-dependence with a pronounced reduction at L_r=19.2mm. Wider channels enhance nonlinear activity, inducing spectrum broadening and a transition from discrete ECDI-dominated oscillations to a broadband state where MTSI becomes dominant. Consequently, the radial electron temperature T_er increases from ∼ 10 eV (L_r=3.2mm) to ∼ 47 eV (L_r=25.6mm), reversing the temperature anisotropy (from T_eθ > T_er in narrow channels to T_eθ < T_er in wide channels). The time-averaged electron mobility in the plasma bulk is suppressed as L_r increases (reduction > 25% in the present parameter set). These results suggest that, with the plasma source fixed, the increase of L_r due to the wall-induced particle losses and enhanced nonlinear coupling substantially modifies instability development and anomalous transport.