Physics Basis for the Gasdynamic Mirror (gdm) Fusion Rocket

A detailed examination of the physics principles that underlie the operation of the GDM fusion confinement system is carried out in order to assess its transformation to a potential propulsion device. With an ion collision mean free path much shorter than its length, the plasma in GDM behaves like a fluid, and its escape from the chamber is analogous to the flow of a gas into vacuum from a vessel with a hole. A characteristic confinement time is shown to vary directly with the product of plasma mirror ratio and length, and inversely with the mean velocity of the plasma. Very efficient utilization of the confining magnetic field as reflected by a high beta (ratio of plasma pressure to magnetic field pressure) has been demonstrated analytically and experimentally. Presence of the plasma in the expansion region of the (mirror) magnetic nozzle leads to hydromagnetic stability for large mirror ratios that is further augmented by Finite Larmor Radius effects which are intrinsic to high aspect ratio devices. Confinement is also shown to be insensitive to "loss cone" microinstabilities and anisotropy-driven modes, while particles transport across the magnetic field is shown to be classical and negligible compared to axial transport under normal operating conditions. These and other considerations underscore the suitability of GDM as a propulsion device driven by fusion nuclear reactions. As such, it is further shown that it is capable of a propulsive performance that can lead to man's exploration of the solar system and beyond in relatively short times.