Field Asymmetry and Thrust Control in the GDM Fusion Propulsion System
[Abstract] One of the notable attributes of the Gasdynamic Mirror (GDM) fusion propulsion system is the fact that it lends itself readily to thrust control due to asymmetry in the magnetic field configuration. GDM is a magnetic plasma confinement device that has been proposed as a potential propulsion system. It differs from the standard “collisionless” mirror in that it operates at a much higher plasma density and is generally designed with a large aspect ratio to provide plasma stability. When a plasma is injected into such a device, the electrons tend to escape through the mirrors more readily due to their small mass, leaving behind an excess of ions and correspondingly a positive electrostatic potential. Such a potential accelerates the ions while slowing down the electrons until both species drift outward at equal rate. Of special importance to its value as a propulsion device is the effect of magnetic field asymmetry on such an electrostatic potential. Numerical simulations have been carried out to study this phenomenon and to quantify the role of asymmetry on the overall performance of the system. Experiments will be conducted in order to validate the theoretical and simulation models and to provide a basis for further assessment of GDM as a propulsion device with variable thrust capability.
Gasdynamic fusion propulsion system for space exploration
An open-ended fusion system in which a high-density plasma is confined and heated to thermonuclear temperatures is examined as a potential high specific power propulsion device that can be used for space exploration. With a collision mean free path much smaller than a characteristic dimension of the system, the plasma behaves much like a continuous medium (fluid) for which the confinement time is drastically different from that which characterizes a typical fusion power reactor. Noting that fact and using an appropriate set of balance equations we derive an expression for the length of the rocket in terms of the plasma parameters required for certain propulsive capabilities. We find that a moderately sized system can produce large values of specific impulse and thrust that would allow a massive rocket to make a round-trip to Mars in months instead of years. By carrying out a preliminary engineering design we also identify those technological areas that must be developed before such a system can become practical. Many of these technologies are surprisingly not out of reach today.
Flute instability of plasma in a gas-dynamic trap
The flute instability of a plasma confined in a gas-dynamic trap where the mean free path of the particles λ is small compared with the trap length L is examined. In analysing the instability the influence on the oscillations both of the energy and particle injection which maintains the system in steady state and also of the damping of perturbations which results from plasma flowing out through the mirrors is included. An expression is obtained for the growth rate of the flute instability which is used in formulating the necessary and sufficient criterion of stability. It is found that in certain conditions, even when the flute instability has been suppressed, an instability with a characteristic growth rate of the order of the reciprocal of the plasma life-time can still develop in the trap. The effects examined in the paper are also of interest for open traps with λ > L.