  The performance gain of co-axial vacuum arc thruster in external axial
magnetic field is analyzed by power and direct thrust measurements. Thruster
geometry is actively controlled and inspected using laser profilometry. Peak
performance is shown to be obtained in magnetic induction of 0.1 - 0.2 T, with
measured thrust of 21 uN at arc power of 2.7 W, and thruster efficiency of ~ 4
%. The performance gain is attributed to ion beam focusing, increased erosion
rate, and ion acceleration due to the axial magnetic field.
