Experimental studies oe a seawater superconducting electromagnetic thruster: A continuing quest for higher magnetohydrodynamic propulsive efficiency

J. C. S. Meng - P. J. Hendricks - J. D. Hrubes - C. W. Henoch

Naval Undersea Warfare Center, Newport, Rhode Island, USA

Abstract
This paper describes the building of a high-field, 7-tesla, superconducting magnet, and it summarizes and compares experimental magnetohydrodynamic (MHD) efforts at the Naval Undersea Warfare Center (NUWC) and the Argonne National Laboratory (ANL). Experimental data and theoretical predictions are compared in terms of the MHD interaction parameter, load factor, Hartmann number (Ha), and Reynolds number (Re), with illuminating results. There is an optimal performance condition in terms of the interaction parameter-load factor map. A very sharp dropoffin efficiency is revealed in NUWC s experimental investigation with an independent control of test section velocity. Increasing the magnetic field to 6 testa in the NUWC facility brings the efficiency to nearly 10%, while the larger volume of the ANL facility provides an efficiency as high as 38%. From these comparisons, an ideal seawater electro-MHD facility is derived, so that any future effort will benefit from the past lessons learned, and duplication of existing capabilities will be avoided by promoting more direct international cooperative efforts. Future efforts should be directed toward addressing optimal thruster geometry to minimise the effects of loss mechanisms such as entrance and exit fringe fields, friction, and end losses. All future experimental efforts should be conducted in real seawater to avoid the ambiguity associated with artificial seawater solutions.