Incoherent Thomson scattering measurements of electron properties in a conventional and magnetically-shielded Hall thruster

Abstract

Reliable measurements of electron properties are key for the validation of simulations of Hall thrusters and similar plasma sources. In this paper, a recently-developed incoherent Thomson scattering diagnostic is successfully applied to electron property measurement in a low-power Hall thruster discharge. Investigations of electron properties along radial and azimuthal directions in both conventional and magnetically-shielded architectures are performed. The high diagnostic sensitivity gives access to electron property measurements in a plasma environment with densities as low as 10 16 m −3 . Electron temperatures reaching several tens of eV and drift velocities on the order of 10 6 m s −1 are measured in the exit plane region. The impact of the magnetic field (intensity and direction) and discharge voltage are investigated.

Inertial and anisotropic pressure effects on cross-field electron transport in low-temperature magnetized plasmas

“…As shown in figure 2(f), the azimuthal electron bulk velocity near the channel exit is in good agreement overall between the PIC-MCC and FFM results, particularly at x ⩾ 1.8 cm. The azimuthal electron velocity at the channel exit is in a good agreement with the experimental data obtained from the LTS measurement [23]. A discrepancy can be seen toward the anode at x < 1.8 cm, indicating the effects of selective electrons colliding with and being absorbed by the anode.…”

“…However, a recent study suggests that DD approximations may not be valid in case the Hall parameter is large [6], leading to the development of a five-moment full fluid moment (FFM) model that accounts for the inertial terms [8]. Advanced incoherent laser Thomson scattering (LTS) indicates that the electron bulk velocity due to the ⃗ E × ⃗ B drift can be comparable to the electron thermal velocity [23,24], in which case the inertia (e.g. velocity shear) in the azimuthal direction cannot be neglected.…”

Physics of E × B discharges relevant to plasma propulsion and similar technologies

“…The recent development of a sensitive incoherent Thomson scattering (ITS) platform [137] allowing investigations of cathode [161], thruster [162], and magnetron plasmas [164] gives access to information that has long been lacking regarding background electron properties (temperature and drift) in these sources. This provides crucial information that can impact the predicted growth and density fluctuations in the measured waves.…”

Electrical characteristics of a Hall effect thruster body in a vacuum facility testing environment

“…The plasma environment surrounding the thruster body is divided into two regions: (1) Thruster face (TP1) and (2) Thruster circumference (TP2 and TP3). Figure 13 shows that the electric field of the anode, thruster magnetic field, and cathode position maintain electron number densities at the thruster face on the order of 10 15 -10 18 m − 3 [8,[28][29][30]. The electron Hall parameter in this region is significantly larger than unity [8], and electron motion is parallel to magnetic field lines.…”