Improved Hall thruster performance via tailored external magnetic field Lyon B. King Department of...
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Transcript of Improved Hall thruster performance via tailored external magnetic field Lyon B. King Department of...
Improved Hall thruster performance via tailored external
magnetic field
Lyon B. KingDepartment of Mechanical Engineering
Michigan Technological University
Tailored external magnetic fields
Background and Motivation
• Much interest of late in high thrust-to-power• Cathode coupling losses are significant at low
discharge voltage• Cathode position has been shown to affect
plume divergence, coupling voltage, and thruster efficiency
• Center-mount cathodes are superior to external, but impractical for small thrusters
Tailored external magnetic fields
Background and Motivation
Typical HET Magnetic Field Prior research has focused
primarily on the internal B-field
Examination of the external field reveals a separatrix
Recent research at Tech suggests the separatrix plays an important role in the coupling process
Tailored external magnetic fields
Background and Motivation
Typical HET Magnetic Field Prior research has focused
primarily on the internal B-field
Examination of the external field reveals a separatrix
Recent research at Tech suggests the separatrix plays an important role in the coupling process
Typical cathodelocations
Tailored external magnetic fieldsBackground and Motivation
Performance vs. Cathode PositionVd = 250 V, Mass Flow = 2.553 mg/s Kr (equiv. 4 mg/s Xe), I
mag = 2.5 A
Tailored external magnetic fieldsBackground and Motivation
Plasma Parameters Te (eV)
r = 200 mm
r = 120 mm
r = 100 mm
r = 80 mm
r = 60 mm
r = 50 mm
Tailored external magnetic fieldsBackground and Motivation
Plasma Parameters ne (x 1017 m-3)
r = 200 mm
r = 120 mm
r = 100 mm
r = 80 mm
r = 60 mm
r = 50 mm
Tailored external magnetic fieldsBackground and Motivation
Problem for Small (0.250 – 2-kW) Thrusters
Performance better with cathode inside separatrix
Separatrix too close to ion beam for external cathode
Cathode will sputter, decreasing lifetime
Thruster too small for center mount cathode
Tailored external magnetic fieldsBackground and Motivation
Orig
inal
Out
er P
ole
Ext
ende
d O
uter
Pol
e
Solution: Move the SeparatrixThe Extended Outer Pole
U.S. Patent applicationNumber 61/118,306
Tailored external magnetic fieldsBackground and Motivation
B-Field Comparison
Original Outer Pole At z=30 mm, r=60 mm
Extended Outer Pole At z=30 mm, r=78 mm
Tailored external magnetic fieldsBackground and Motivation
Vd = 250 V, Mass Flow = 2.553 mg/s Kr (equiv. 4 mg/s Xe)
Performance Comparison
Tailored external magnetic fields
• Understand physics of electron mobility across the external magnetic field / separatrix
• Determine how performance gains seen in preliminary work extend to flight-like conditions
• Explore tailored magnetic fields in search for “optimal” configuration(s)
Objective of Research
Tailored external magnetic fields
• Performance studies with Xe at range of operating conditions
• Numerical modeling of magnetic fields to explore means of controlling separatrix position
• Continued probe maps of plasma parameters• Numerical modeling of cathode / plume coupling
Technical Approach
Tailored external magnetic fields
• Design criteria for low-power Hall thrusters having improved efficiency over SOA
• Better understanding of cathode coupling voltage and loss mechanisms
• Possible implications for clustered Hall thrusters
Anticipated Results