NazlI TURAN, Ugur KOKAL, Murat CELIK EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF CATHODE CURRENT ON HK40 HALL THRUSTER OPERATION   NazlI TURAN, Ugur KOKAL, Murat CELIK BogazIcI UnIversIty Istanbul, Turkey Speaker: NazlI TURAN 5th International Conference on Space Propulsion, Space Propulsion 2016, 2nd to 6th May 2016, Roma, Italy

Outline Introduction The current schematic Cathode with continuous heating Cathode without heating Cathode with HK40 Hall thruster Magnetic field structure Efficiency analysis Conclusion References

Introduction electrons are extracted from LaB6 insert surface by thermionic emission the ionization of the propellant and the neutralization of the ion beam electric and magnetic fields to extract ions

Planar, 0.5 mm diameter wire inside an alumina tube Introduction HK40 Hall effect thruster Vd = 220 V Id = 1.2 A flow rate = 18 sccm BUSTLab hollow cathode flow rate = 1.5 sccm Langmuir probe Planar, 0.5 mm diameter wire inside an alumina tube

Introduction Cathode voltage (Vcg) Discharge voltage (Vd) Plasma potential (Vp) Cathode coupling voltage (Vc) Beam voltage (Vb) Ref: Jameson, K.(2008), Investigation of Hollow Cathode Effects on Total Thruster Efficiency in a 6 kW Hall Thruster, Ph.D. Thesis, University of California, Los Angeles, CA, USA, 2008.

The current schematic The source of the electrons that leave the cathode, thus providing the cathode current, is the LaB6 insert located inside the cathode tube.

The current schematic Icathode = Iec + Ieb Icathode = Iec + Ieb Id = Iec + Iei Id = Iib + Iec Icathode = Iec + Ieb Iib = Ieb Iground = Ikeeper + Icathode Ref: Goebel, D. M. and Katz, I.(2008), Fundamentals of Electric Propulsion: Hall Thrusters, JPL Space Science and Technology Series, New York, USA, 2008.

The current schematic Rb magnetic field topology in the discharge channel Rc the placement of the cathode as well as the external magnetic field of the thruster Rk the resistance between the cathode insert and the keeper

Cathode with continous heating Higher temperature increased thermionic emission increases the magnitude of cathode voltage keeper voltage arranges itself to a lower value to attract the same keeper current

Cathode without heating Vkeeper sheath shields the keeper voltage, keeper voltage increases. If keeper current is increased, electrons in sheath layer contribute to the keeper current. The cathode voltage becomes more negative.

Cathode with HK40 Hall thruster

Cathode with HK40 Hall thruster B increases anode voltage increases more electrons from ionization constant discharge current ground current decreases plasma potential increases ion beam current (Iib) > the electron current in the plume (Ieb) full neutralization is not achieved

Cathode with HK40 Hall thruster Id = Iib + Iec Pb = Ib (Va – Vp)

Magnetic field structure The neutralizing electron current is small. divergent plume magnetic contour lines taken from COMSOL modelling of the thruster magnetic topology magnetization of the electrons near the cathode

Magnetic field structure electron magnetization near the anode electrons fail to reach the anode accumulate on magnetic lines the discharge channel of HK40 would not be long enough for electrons magnetic field lines cross the anode

Efficiency analysis

Conclusion Measuring ground current Investigating cathode operation with heater and keeper characteristics Explaining the current schematic Using resistance analogy for the thruster-cathode system Operating HK40 with different magnetic coil currents Discussing the magnetic field topology of HK40 Calculating efficiency analytically

References Goebel, D. M. and Katz, I., Fundamentals of Electric Propulsion: Hall Thrusters, JPL Space Science and Technology Series, New York, USA, 2008. Jameson, K., Investigation of Hollow Cathode Effects on Total Thruster Efficiency in a 6 kW Hall Thruster, Ph.D. Thesis, University of California, Los Angeles, CA, USA, 2008. Guerrini, G., Michaut, C., Dudeck, M., Vesselovzorov, A., and Bacal, M., Characterization of Plasma Inside the SPT-50 Channel by Electrostatic Probes, Proceedings of the 25th International Electric Propulsion Conference, 1997, pp. 1997-053 Courtney, D.G., “Development and Characterization of a Diverging Cusped Field Thruster and a Lanthanum Hexaboride Hollow Cathode,” M.S. Thesis, Massachusetts Institute of Technology, Cambridge, MA, USA, May 2008. Kunning G Xu and Mitchell LR Walker. Effect of External Cathode Azimuthal Position on Hall-effect Thruster Plume and Diagnostics. Journal of Propulsion and Power, Vol.30, No.2, 2014. Martinez-Sanchez, M. and Pollard, J.E., Spacecraft Electric Propulsion-An Overview, Journal of Propulsion and Power, Vol. 14, No. 5, 1998, pp. 688699. E. Ahedo and J.M. Gallardo. Low Power Hall Thrusters: Physics, Technical Limitations and Design. Micro-Propulsion Workshop, Lerici, Italy, May 2002. Jameson, K. K., Goebel, D. M., Hofer, R. R. and Watkins, R. M., Cathode Coupling in Hall Thrusters. 30th International Electric Propulsion Conference, Florence, Italy September 2007. IEPC-2007-278.

THANKS FOR LISTENING

BUSTLab Vacuum Chamber

HK40 Hall Effect Thruster

LaB6 Hollow Cathode

Experimental Measurements

Experimental Measurements

Experimental Measurements