Experiments on the Polytron, a toroidal Hall accelerator employing cusp containment

The Polytron is a toroidal plasma configuration, using 36 magnetic cusps joined point-to-point. This paper presents observations of the acceleration and containment of the plasma. Measurement of the force on the plasma shows that the initial acceleration is given by a particle equation mi(dvphi /dt)=ZeEphi and occurs in thin sheaths in the ring cusp planes. The concept of a non-magnetic effective inductance is experimentally verified. However rapid, although not complete loss of plasma occurs after 1 mu sec for argon, limiting the electron temperature to 30 eV at an electron density of 1020 m-3. This loss is expected and an energy balance at this time implies that electron thermal conduction causes the principal loss of energy. After this loss, the rest of the plasma drifts to the outer wall of the vacuum vessel after about 3 mu sec.