Plasma Propulsion by a Rapidly Varying Magnetic Field

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Abstract
An investigation has been made of the motion of a plasma under the action of a rapidly varying magnetic field from a stationary coil. The analysis has been done for two cases: (1) the plasma is assumed completely diamagnetic so that the ionization history of the plasma may be ignored and (2) the nondiamagnetic case where the ionization process is considered in detail. For the diamagnetic case the analysis yields a coupled set of nonlinear ordinary differential equations which have been put in similarity form and solved for a wide range of the similarity parameters. An illustrative example is given to show how to use the results to obtain detailed information for a given physical system. The calculations indicate that, for field frequencies of about one megacycle, velocities of the order 107 cm/sec may be attained, but the efficiency of conversion of stored energy into kinetic energy is rather low (about 5–10%) and cannot be varied much by possible changes in the physical and geometrical parameters of the system. Because of the complexity of the analysis, a systematic series of solutions has not been made for the nondiamagnetic case. Instead, a typical example has been worked out to indicate the major differences to be expected. The results show that the nondiamagnetic plasma yields an efficiency slightly less than that obtained for the corresponding diamagnetic plasma. The ionization process inside the plasma levels off very rapidly so that the electron density increases by only a few percent during the motion of the plasma, but the amount of ionization has very little effect upon the efficiency of the system. The indications are that the efficiency of a plasma driven by a magnetic field from a stationary coil is probably too low for practical applications.

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