REBOUND COEFFICIENT OF COLLISIONLESS GAS IN A RIGID VESSEL - A MODEL OF REFLECTION OF FIELD-REVERSED CONFIGURATION

A system of collisionless neutral gas contained in a rigid vessel is c onsidered as a simple model of reflection of field-reversed configurat ion (FRC) plasma by a magnetic minor. The rebound coefficient of the s ystem is calculated as a function of the incident speed of the vessel normalized by the thermal velocity of the gas before reflection. The c oefficient is compared with experimental data of FIX (Osaka U.) and FR X-C/T(Los Alamos N.L.). Agreement is good for this simple model. Inter esting is that the rebound coefficient takes the smallest value (simil ar to 0.365) as the incident speed tends to zero and approaches unity as it tends to infinity. This behavior is reverse to that expected for a system with collision dominated fluid instead of collisionless gas. By examining the rebound coefficient, therefore, it could be successf ully infered whether the ion mean free path in each expeiment was long er or shorter than the plasma length.