H. H. Woodson

Electromagnetic induction launchers

The electromagnetic launcher consists of a system of stator coils producing a traveling field which accelerates an armature carrying currents induced by the traveling field (induction accelerator [1,2]) or persistent currents supplied from otner sources (synchronous accelerator [2,10]). The fact that their armature has no electrical contact with the stator, essentially riding on the crest of a traveling magnetic wave, makes induction accelerators very attractive for a large number of applications. This paper is devoted exclusively to the accelerator of the induction type. Efficiency considerations require that the traveling wave should accelerate at approximately the same rate as the projectile. This can be achieved either using variable (increasing) winding pitch or a continuously increasing power supply frequency or a combination of both. A new dimension was added to the induction coaxial accelerator technology with the definition at the Center for Electromechanics at The University of Texas at Austin (CEM-UT) of a new electrical machine, the Rising Frequency Generator (RFG) representing a more attractive integrated power source for induction accelerators which had previously been forced to conform to constant frequency power supplies. This paper outlines the principles of design and shows two applications of induction coaxial launchers; a half-scale aircraft launcher in which the system also acts as an electromagnetic brake, stopping the shuttle and driving it in the opposite direction, and a high performance, 18-m long launcher capable of accelerating a 1-kg aluminum projectile to a velocity of 10 km/s at an average acceleration of 250,000 G.

Fabrication of a compact storage inductor for railguns

A liquid nitrogen-cooled, coaxial, energy storage inductor has been designed and built to be used in conjunction with a compact homopolar generator to form a high-energy-density power supply for use with electro-magnetic accelerators. The low-resistance, lightweight aluminum inductor stores 3.1 MJ at a peak current of 1.0 MA. Minimizing weight rather than size was emphasized in the design, resulting in a 1.23-m (48.5-in.) diameter by 0.91 m (36 in.) long inductor weighing 14.7 kN (3,300 lb). A coaxial design was chosen to eliminate high external magnetic fields without the necessity for shielding. External magnetic fields are undesirable because of effects on nearby components and the possibility of detection. Also, attention has been given to minimizing the partial flux linkages or internal inductance of the coil, thereby maximizing the overall transfer efficiency into a railgun. Details of the design, fabrication, and predicted performance will be presented.

The Design, Fabrication, and Testing of a Five Megajoule Homopolar Motor-Generator

The current and future generations of controlled thermonuclear fusion experiments require large amounts of pulsed energy for heating and confinement of plasma. Kinetic energy storage with direct conversion to electrical power (i.e. homopolar machines) seems to be the most economically attractive solution for meeting these requirements.

Improved energy density homopolar generator

The preliminary design of a self excited, air-core (SEAC) homopolar generator (HPG) which stores about 250 MJ inertially and is4 capable of delivering 3.2 MA current pulses is presented. In aiming for maximum energy density in an HPG and inductor power supply for electromagnetic (EM) accelerators, the improved energy density (IED) machine uses its self-excited field coils as energy storage inductors and a lightweight graphite reinforced flywheel for inertial energy storage. Weighing approximately 5,000 kg, the design represents a twenty-fold increase in mass energy density over the state of the art and addresses the problem of trapping flux in the rotor during discharge by separating the voltage generating and energy storage functions. Voltage is generated across a squirrel-cage rotor armature by an opposed pair of five-turn cryogenically cooled field Coils/inductors. Inertial energy is stored in a graphite-reinforced epoxy flywheel which will operate at a maximum tip speed of 1,100 m/s. Current collection is accomplished at the smaller radius of the squirrel-cage armature which implies brush slip speeds of no more than 300 m/s at the design speed. The machine is expected to develop about 500 V at half speed while charging the coils to 130 MJ at 3.2 MA. Peak output voltage during discharge of coils will be roughly 10 kV.

MAGNETIC FIELD DIFFUSION IN FAST DISCHARGING HOMOPOLAR MACHINES

ABSTRACT The unusually high mechanical and thermal stresses occuring in fast discharging homopolar machines require accurate prediction of high magnetic fields accompanying their operation. Linear methods and ideal configurations are no longer acceptable as simplifying assumptions in designing such devices used in controlled thermonuclear fusion experiments, laser applications, etc. A finite element method - Galerkin technique is used for solution of Maxwells equations for a moving medium. The transient skin effect in the system is described in terms of a magnetic vector potential and an electric scalar potential. Lagrange multipliers are used to impose the necessary constraint on the vector potential Ā. The formulation for the steady-state magnetic fields in nonlinear media results as a particular case of the method. This approach was used for predicting the parameters for the very fast discharging homopolar machine (FDX) designed by the Center for Electromechanics at The University of Texas at Austin. ...

Fundamental Limitations and Topological Considerations for Fast Discharge Homopolar Machines

Fusion research experiments require high energy short duration pulses. A homopolar machine, as an inertial energy storage system, offers an attractive source of energy meeting these requirements. The Energy Storage Group at The University of Texas at Austin has investigated the fundamental limitations to the discharge time of homopolar machines of various topological configurations. This paper presents a mathematical model for fast discharge homopolar machines. Based on this model, various machine configurations are analyzed. A new configuration - the spool type machine - is also discussed, criteria for the evaluation of different alternatives are presented, and it is concluded that highly efficient (¿ 95%), high energy (¿ gigajoules), fast-discharge (¿ 5 to 30 milliseconds) homopolar inertial energy storage systems are technically feasible. Brief reference is also made to some of the experimental results obtained from the existing laboratory models.

Simulation and predicted performance of the Balcones GEDI experiment

The guided electromagnetic defense interceptor (GEDI) railgun launcher system is powered by six Balcones homopolar generators (BHPG), each of which stores 10 MJ in kinetic energy. Each BHPG is connected to a coaxial inductor which stores about half of the BHPGs energy when charged to 1.2 MA. Six two-stage opening switches open in sequence or simultaneously after current peak, directing the current to the railgun armature. As much as 7.2 MA can be delivered to the railgun. A computer simulation code is developed to perform design parameter studies, sensitivity studies, and to predict GEDI system behaviors. The code is general enough for analyzing any railgun driven by multi-HPG inductors coupled with two-stage opening switches. A Gear type, multistep algorithm is used to overcome stiffness of the differential system caused by the way the switches are modeled. GEDI system performances are predicted with the code based on most updated component parameters.