ACCELERATION OF PLASMAS BY INDUCTIVELY GENERATED ELECTROMAGNETIC FIELDS. Final Report

Technical Report · Sat Apr 01 00:00:00 EST 1961

OSTI ID:4026441

Miller, D B

A discussion is given of the theory and experimental behavior of an induction electromagnetic accelerator, which employs a time-varying current in a coil to generate the force-prcducing electric and magnetic fields. Some aspects of the induction accelerator which can be derived theoretically are first brought out. These begin with a study of isolated particle behavior within a cylindrical coil. Charges gain energy from tue azimuthally directed electric field; their paths are turned in the radial and axial directions by the magnetic field, and they eventually are ejected out the end of the coil. The exact paths of electrons and helium and argon ions under various field conditions of magnitude and frequency are calculated by analog computer techniques, and from these calculations are obtained the velocity and angle which the ejected particles ultimately obtain. One important result which comes out of this particle analysis is the quantitative dependence of ejection characteristics on initial position of the particle. Another significant item is the marked difference in behavior when the field period is much less than and much more than the time taken for the particle to be ejected from the accelerator. Induction acceleration of plasmas is theoretically considered first under the simplifying assumption that the coil is very long. This eliminates radial magnetic field components and thrust in the axial direction, but it realistically treats the radial motion, an important energytransferring process in the experimental device. The effect of self-fields, electric caused by charge separation and magnetic caused by the gas current, on the radial motion is extensively studied; this reveals that even at quite low densities the particles are bound to one another by these fields, and it leads to the calculation of the radial motion of such low density plasmas. The radial dependences of magnetic field and current density within the ionized gas are shown to be approximated by Bessel functions. At high densities a skin current is shown to form and to prevent penetration of the magnetic field into the interior of tue plasma. For these high densities a "snowplow" analysis is used to calculate the radial motion of the plasma. The axial motion of plasma within a finite sized coil is considered. Qualitatively, it is argued that the majority of energy in axial motion arises from energy which is transmitted to the plasma by radial compression and then is converted to axial motion in the diverging magnetic nozzle. Characteristics of the flowing gas which can be obtained from observation of the advancing shock wave are brought out. Experiments using an induction accelerator are described. The accelerator is a 10-cm long by 10-cm diameter, single turn, cylindrical coil driven by a 37.5- mu fd capacitor bank. Capacitor voltages in the 5- to 10-kv range were used. Ionization of the gas within the coil was accomplished partly by a high frequency preionization circuit and partly by the accelerator field. Data on helium and argon over the general pressure range of 0.010 to 1.00 mm of Hg are reported. Specifically, Kinetic characteristics of radial and axial motion, and momentum and energy and internal structure of current and charge of the accelerating ionized gas were studied. The separate measurements are discussed and correlated whenever possible with each other and with the theory. Axial velocity of the gas as it emerges from the coil is typically 0.5 to 10 cm per microsecond. Energy in the amount of approximately 10 to 50 joules is transferred from the circuit to the gas; this represents up to 10% of the energy available in the magnetic field of the coil, and about half this transferred energy goes into directed motion of the gas. Ion temperatures, calculated from observations of the radial compression and axial shock, are in the 25,000 to 100,000 deg K range; electron temperature, measured for one pressure by an electric probe, is about one-third the concurrent ion temperature. (auth)

• Research Organization: Michigan. Univ., Ann Arbor. Coll. of Engineering
• DOE Contract Number: AF19(604)-4557
• NSA Number: NSA-15-024408
• OSTI ID: 4026441
• Report Number(s): AFCRL-462; UMRI-02836-10-F
• Resource Relation: Other Information: Orig. Receipt Date: 31-DEC-61
• Country of Publication: United States
• Language: English

Related Subjects

PHYSICS
ACCELERATORS
ANALOG SYSTEMS
ANGULAR DISTRIBUTION
ARGON
BESSEL FUNCTIONS
CAPACITORS
COILS
COMPUTERS
DENSITY
ELECTRIC CHARGES
ELECTRIC FIELDS
ELECTRONS
ENERGY
FREQUENCY
GASES
HELIUM
IONIZATION
IONS
MAGNETIC FIELDS
MATHEMATICS
MEASURED VALUES
MOMENTUM
MOTION
NOZZLES
PLASMA
PRESSURE
SNOW PLOW MODEL
TEMPERATURE
USES
VELOCITY