Improved Hall thruster performance via tailored external magnetic field Lyon B. King Department of Mechanical Engineering Michigan Technological University

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



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 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


Plasma Parameters Te (eV)

r = 200 mm

r = 120 mm

r = 100 mm

r = 80 mm

r = 60 mm

r = 50 mm


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


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


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


B-Field Comparison

Original Outer Pole At z=30 mm, r=60 mm

Extended Outer Pole At z=30 mm, r=78 mm


Vd = 250 V, Mass Flow = 2.553 mg/s Kr (equiv. 4 mg/s Xe)

Performance Comparison


• 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


• 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


• 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

Documents

Improved Hall thruster performance via tailored external magnetic field Lyon B. King Department of Mechanical Engineering Michigan Technological University