Simulation Model Type 1 & Type 2 Weak Double Layer Electrostatic Potential (Type 1) x-v Phase Space (Type 1) Dependence on the density of cold ions (Type 1) Dependence on the drift velocity of hot electrons (Type 1) Vd=-0.4 Vdi=0.2 (Type 2) Vd=-0.4 Vdi=0.3 (Type 2) Vd=-0.4 Vdi=0.4 (Type 2) Conclusions