A New Plasma Confinement Geometry

Abstract

As is well known, the strong synchrotron radiation recently predicted by Trubnikov and Kudryavtsev¹ from a plasma containing a magnetic field at thermonuclear temperatures makes it harder to design a thermonuclear reactor using the deuterium–tritium reaction, and practically impossible to design a deuterium–deuterium reactor. One way to get around this difficulty is to have no magnetic field in the plasma, so that the radiation becomes only a surface phenomenon instead of a bulk one. Of all the magnetic confining geometries at present known, theoretically only one has enough stability to hold a pure (that is, β = 8πnkT/B² = 1) plasma. This is the picket fence or cusped geometry². Unfortunately, according to Grad³, the cusps will be very leaky. Attempts have been made to construct geometries to avoid these leaks by closing the cusps on themselves (compare the most interesting papers by Braginski and Kadomtsev⁴). The same idea was proposed independently by Longmire and me some years ago under the name ‘caulked picket fence’⁵ (Fig. 1). These geometries involved current-carrying rings, disposed inside a solenoid having a longitudinal magnetic field. Quite apart from the topological impossibility of connecting leads or cooling to these rings without making contact with the plasma, the systems were unstable in their toroidal form because there was no rotational transform⁶ in the torus axial field.