| One of the fundamental barriers to the use of electromagnetic launchers is the high power required to reach launch speed in a reasonable distance. It has been proposed that large external power supplies can be avoided by using superconducting persistent currents in the barrel of the launcher to store energy. This study examines the use of monolithic YBCO for these persistent current magnets.;Monolithic magnets, unlike wound magnets, can have a nonuniform current distribution, which causes energy transfer between the stationary energy storage magnets and the accelerated magnet to be inefficient. This problem can be overcome by optimization of the magnet shape. This requires a model for computation of current distribution, force vs. distance, and efficiency.;A model is presented for calculating the current distribution and magnetic force for two YBCO rings, each with a trapped field such that an attractive force is developed between them. Two different methods were used to find current as a function of time. The first is a system of differential equations for the time dependence of the current distribution, which is solved using the 4-step vector Runge-Kutta method. The second is a speed-independent approximation that is less computationally intensive. The integral equation for force at each time step is solved using the finite sum method.;After verifying the speed-dependent model by comparing computations to measured force vs. distance curves for twenty-eight pairs of YBCO magnets, the model was used to examine behavior at speeds up to 10,000 m/s. It was found that energy transfer is almost independent of speed for a properly designed launcher. Also, heating due to flux flow was found to be minimal.;The fact that energy transfer did not depend on speed allowed the speed-independent model to be used with an optimizer to find a more efficient shape for the accelerated YBCO magnet. A magnet of this shape was fabricated, and efficiency was measured to be 84%, compared to a maximum of 67% for the unoptimized, constant-radius magnet combinations. |
