Radial control of the electrostatic potential in a tandem mirror with quadrupole end cells

It is demonstrated that the radial electrostatic potential in the Phaedrus tandem mirror [Plasma Physics and Controlled Fusion Research, 1984 (International Atomic Energy Agency, Vienna, 1985), Vol. 2, p. 265] can be altered using plasma potential control rings (PPC rings) situated at each end of the device. With the PPC rings grounded, the radial electric field in the central cell was directed outward and peaked near the plasma edge. By externally controlling the potentials of the PPC rings, the peak value of the radial electric field was varied by over a factor of 2, obtaining plasmas with a maximum value of the radial electric field E(r)≤15 V/cm. A simple calculation to model the change in the central cell potential due to a bias voltage applied to the PPC rings is presented.