Upper half: density and energy (in eV) distributions of electrons (a,c) and protons (b,d) at t = 140 Ω⁻¹ for m_i/m_e = 100, n₀ = 10¹² m⁻³. The magnetic field B₀ = 10⁻³ T, B_y/B₀ = 0.1, B_x/B₀ = 0.02, and electric field E₀ = 250 V m⁻¹. Lower half: V_z vs x distributions in the velocity phase space for (e) n₀ = 10⁸ m⁻³ and (f) 10¹² m⁻³. (g) and (h) compare the energy spectra and the polarisation electric field E_x vs x at among the simulations with different densities.