Non-invasive Hall current distribution measurement in a Hall effect thruster.
A means is presented to determine the Hall current density distribution in a closed drift thruster by remotely measuring the magnetic field and solving the inverse problem for the current density. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW Hall thruster equipped with a center-mounted hollow cathode. In the sensor array location, the static magnetic field is approximately 30 G, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide the current density distributions. These distributions are shown as a function of time in contour plots. The measured ratios between the average Hall current and the average discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode frequency of 24 kHz, which was in agreement with temporal measurements of the discharge current.
Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
Carl R
CR
Mullins
Plasma Controls LLC, 1180 La Eda Lane, Fort Collins, Colorado 80526, USA.
Casey C
CC
Farnell
Plasma Controls LLC, 1180 La Eda Lane, Fort Collins, Colorado 80526, USA.
Cody C
CC
Farnell
Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
Rafael A
RA
Martinez
Air Force Institute of Technology, Wright-Patterson AFB, Ohio 45433, USA.
David
D
Liu
University of Alabama, Tuscaloosa, Alabama 35487, USA.
Richard D
RD
Branam
Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
John D
JD
Williams