Nazli TURAN, Yavuz Emre KAMIS, Murat CELIK STUDY OF MAGNETIC FIELD CONFIGURATION EFFECTS ON COUPLING BETWEEN HALL EFFECT THRUSTER AND HOLLOW CATHODE Nazli TURAN, Yavuz Emre KAMIS, Murat CELIK Bogazici University Istanbul, Turkey Speaker: Nazli TURAN

Outline Introduction The Coupling Problem between Thruster and Cathode Numerical Results Test Setup Experimental Measurements Comparison between the Results Discussion Future Work References

Introduction Spacecrafts moving in an orbit or in interplanetary space use propulsion system to provide thrust. Electric propulsion systems electrically expelling propellant at high speed using less propellant than chemical rockets providing a small thrust for a long time Ref: http://sec353ext.jpl.nasa.gov/ep/

Introduction Applications: orbit maintenance, orbit raising and deep space missions Advantages: reducing required propellant mass and resulting cost savings Ref: http://phys.org/news/2015-04-image-solar-electric-propulsion-ionizing.html

Introduction Hall effect thrusters (HET): use electric and magnetic fields to extract ions from plasma discharge. Ref: http://www.reliableplant.com/Read/4932/new-engine-helps-satellites-blast-off-with-less-fuel

Introduction Hollow cathode: emits electrons to ionize neutral atoms in the discharge channel and prevents the spacecraft from charging.

Introduction BUSTLab HK40 Hall effect thruster and LaB6 hollow cathode operation in vacuum chamber

The Coupling Problem between Thruster and Cathode A large distance between the cathode and discharge plasma causes higher magnetic obstacle for the electrons to overcome. Plasma potential increases due to magnetic field line restriction on electron motion from the cathode to ion beam and anode.

The Coupling Problem between Thruster and Cathode Magnetic field separatrix: signifies the surface which forms the boundary between closed magnetic surfaces and open field lines. Ref: Sommerville, J. D.(2009), Hall-Effect Thruster Cathode Coupling: The Effect of Cathode Position and Magnetic Field Topology, Ph.D. Thesis, Michigan Technological University, Houghton, MI,USA, 2009.

The Coupling Problem between Thruster and Cathode If plasma potential (Vp) increases, cathode coupling voltage (Vcg) decreases, thus becoming more negative. 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.

Numerical Results The colored contour values are vector potential and very close to zero. The dark blue region with minimum magnetic flux density shows the separatrix region.

Numerical Results The minimum magnetic flux density is detected on 70-80 mm axial distance from the center of the thruster exit.

Test Setup to map the magnetic field topology to determine the location of the separatrix region

Experimental Measurements Magnetic flux density decreases as the probe moves away from the thruster.

Experimental Measurements The region investigated starts at the center of the thruster exit. There are four outer permanent magnets those are assembled 90 degrees apart.

Comparison between the Results Magnetic flux density has been measured with the Hall probe, and the experimental measurement results are compared with the COMSOL modeling.

Discussion Depending on the external magnetic field topology of the thruster, there could be an optimum position for the cathode considering the separatrix region. The location of the separatrix region could be determined as the minimum magnetic flux density region on the thruster axis away from thruster exit. almost 10 mm difference between the numerical and experimental results while finding the separatrix region the differences caused by actual and tabulated material properties information entered into the COMSOL model

Future Work conducting experiments with different cathode positions to observe changes in cathode coupling voltage investigating magnetic field effects on the cathode coupling process with simulation including an electron emitting cathode comparing the results with those of the numerical simulations

References Goebel, D. M. and Katz, I.(2008), Fundamentals of Electric Propulsion: Hall Thrusters, JPL Space Science and Technology Series, New York, USA, 2008. Hutchinson, I. H. (2005), Principles of Plasma Diagnostics, Cambridge University Press, 2005. 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. Sommerville, J. D.(2009), Hall-Effect Thruster Cathode Coupling: The Effect of Cathode Position and Magnetic Field Topology, Ph.D. Thesis, Michigan Technological University, Houghton, MI,USA, 2009.

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BUSTLab Vacuum Chamber

HK40 Hall Effect Thruster

LaB6 Hollow Cathode

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