Helicon Core Formation: A Global Transport Bifurcation Leading to a Radial Transport Barrier and Spontaneous Axial Plasma Detachment

We report that helicon core formation in rf devices is accompanied by the formation of a radial transport barrier and simultaneous axial plasma detachment; via a self-organized global transition due to a transport bifurcation [1] . Evidence from both Langmuir probes and fast imaging show that the radial extent of the transport barrier is similar to the width of the helicon core. Using spectroscopy and neutral pressure measurements, we simultaneously observe axial plasma detachment, which follow the same hysteresis patterns associated with the radial transport bifurcation. We report dramatic changes in both mean and fluctuation profiles across this transition. This spontaneous self-organized global transition is universal, but the transition-threshold depends on the helicon source parameters. 2-D bifurcation diagrams elucidate various regimes of operation of rf plasma sources (Capacitively Coupled Plasmas, Inductively Coupled Plasmas, Helicon-detached, helicon-attached), allowing access to study basic plasma instabilities, turbulence and transport, as well as divertor-relevant plasma detachment in the same device. Spontaneous plasma detachment has serious implications on the relevance of similar rf devices [2] , [3] designed to study Plasma Material Interactions (PMI). In addition, this also gives us the opportunity to study instabilities, turbulence and transport associated with detached plasmas [4] , [5] .