Global modes of gradient drift instability in Hall plasma thruster

摘要

Plasma in coaxial Hall thrusters is subject to a lot of instabilities driven by azimuthal E × B electron flow [1, 2]. Such instabilities directly affect the operational capabilities of plasma thrusters due to their impact on anomalous electron mobility across the external magnetic field [1, 3, 4]. In this paper the instability analysis of global electrostatic modes in inhomogeneous partially magnetized plasmas (unmagnetized ions and magnetized electrons) is performed in the framework of two fluid model. Assuming that plasma is inhomogeneous along the axial direction of ions acceleration, x, such modes can be described by the following eigenvalue equation {formula} Here Ψ is the eigenfunction of the perturbed electrostatic potential, {formula} ; ω and k_y are the frequency and azimuthal wave-number of oscillations, respectively;{formula},B(x))/dx are the parameters characterizing axial gradients of plasma density and magnetic field;{formula} is the lower-hybrid frequency, ωB(e,i) ~(are) the electron and ion cyclotron frequencies; {formula} is the velocity of the azimuthal E x B-electron flow and {formula} Equation (1) describes electrostatic oscillations in the frequency range {formula} propagating strictly across the external radial magnetic field B= B(x)e_z and includes the effects of electron inertia and shear of equilibrium electron flow. For the derivation of the Eq. (1) see, e. g., Ref. [5].