Fundamental difference between the two variants of hall thmsters: SPT and TAL

The fundamental difference between the two variants of Hall thrusters, the stationary plasma thruster (SPT) and the thruster with anode layer (TAL), is illustrated quantitatively using an analytical model that accounts for the effects of secondary electron emission (SEE) from the walls. The model includes a prescription for the quenching of the temperature of the electrons on their way to the anode. This quenching results from the enhanced electron energy losses to the wall that occur at, and upstream of, an axial location where the wall potential reverses from electron-attracting to electron-repellent. For the higher SEE coefficient of an insulator wall (cornpared to that of a metallic one) this sign reversal occurs at a lower electron temperature and is shown to lead to a more extended acceleration region. By replacing the boron nitride walls (SPT) of an idealized Hall thruster with stainless steel (TAL), the acceleration zone is shown analytically to collapse to a region near the anode having an extent that is about eight times smaller than that for the SPT. The results are used to construct a detailed phenornenological picture of the fundamental difference between the two Hall thruster variants.