Thrust and efficiency model for electron-driven magnetic nozzles

A performance model is presented for magnetic nozzle plasmas driven by electron thermal expansion to investigate how the thrust coefficient and beam divergence efficiency scale with the incoming plasma flow and magnetic field geometry. Using a transformation from cylindrical to magnetic coordinates,...

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Bibliographic Details
Published in:Physics of plasmas 2013-10, Vol.20 (10)
Main Authors: Little, Justin M., Choueiri, Edgar Y.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANALYTICAL SOLUTION
APPROXIMATIONS
COLLISIONLESS PLASMA
EFFICIENCY
ELECTRONS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MAGNETS
NOZZLES
PLASMA DENSITY
PLASMA EXPANSION
PLASMA FLUID EQUATIONS
PLASMA SIMULATION
THERMAL EXPANSION
TRANSFORMATIONS
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Summary:A performance model is presented for magnetic nozzle plasmas driven by electron thermal expansion to investigate how the thrust coefficient and beam divergence efficiency scale with the incoming plasma flow and magnetic field geometry. Using a transformation from cylindrical to magnetic coordinates, an approximate analytical solution is derived to the axisymmetric two-fluid equations for a collisionless plasma flow along an applied magnetic field. This solution yields an expression for the half-width at half-maximum of the plasma density profile in the far-downstream region, from which simple scaling relations for the thrust coefficient and beam divergence efficiency are derived. It is found that the beam divergence efficiency is most sensitive to the density profile of the flow into the nozzle throat, with the highest efficiencies occurring for plasmas concentrated along the nozzle axis. Increasing the expansion ratio of the magnetic field leads to efficiency improvements that are more pronounced for incoming plasmas that are not concentrated along the axis. This implies that the additional magnet required to increase the expansion ratio may be worth the added complexity for plasma sources that exhibit poor confinement.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4824613