Direct measurement of the plasma loss width in an optimized, high ionization fraction, magnetic multi-dipole ring cusp

The loss width of plasma in the WiPAL multi-dipole magnetic ring cusp [Cooper et al., Phys. Plasmas 21, 13505 (2014); Forest et al., J. Plasma Phys. 81, 345810501 (2015)] has been directly measured using a novel array of probes embedded in the insulating plasma limiters. The large plasma volume ( ∼10 m3), small loss area associated with strong rare earth permanent magnets ( Bo∼2.23 kG at face), and large heating power ( ≤200 kW) produces a broad range of electron temperatures ( 2Debye length and electron gyroradius and comparable to the collision length. Plasma parameters measured at the surface of ceramic limiter tiles covering the magnets and along radial chords in the cusp m...