Abstract
In September of 2017 the Wendelstein 7-X experiment (major radius 5.5m, minor radius 0.5m, 30m3 volume, 2.5 T magnetic field) began operation with an inertially cooled island divertor. This island divertor consists of ten graphite modules which intersect an n/m=5/5 magnetic island chain, located at the plasma edge. Operation with such a divertor allowed regular plasma operation in excess of 25 s, reaching densities greater than 1. $2\mathrm{x}10^{20}\mathrm{m}^{-3}$ with 7 MW ECRH only. Glow discharge and ECRH discharge cleaning in He was found to be an effective tool for wall conditioning. Pellet injection and ECRH allowed achievement of a record plasma stored energy of 1.1 MJ at a density of $8\mathrm{x}10^{19}\mathrm{m}^{-3}$ and ion/electron temperature equilibration around 3.5 keV. It was observed that during these pellet-fueled discharges, a reduction in divertor heat flux by a factor of ten was possible, suggesting detachment. Long pulse operation with 75 MJ of injected ERCH energy at densities of $4\mathrm{x}10^{19}\mathrm{m}^{-3}$ were routinely run. It was found that even at this level of injected energy the divertor was not yet near operational temperature limits. Operation above 1. $2\mathrm{x}10^{20}\mathrm{m}^{-3}$ in Helium was made possible through successful X2 to 02 switchover. Error fields in the experiment were confirmed to be small and the n/m= 1/1 error field (critical to divertor operation) was compensated. Electron Cyclotron Current Drive (ECCD) experiments demonstrated co-ECCD currents up to 13 kA. Associated with these experiments were core temperature crashes suggesting sawtooth-like mode activity. Fast camera and Langmuir probe measurements detected evidence of edge and scrap-off layer turbulence. While phase contrast imaging detected varying levels of broad-band turbulence along with coherent mode activity. This presentation will cover these high-level results along with expectations for the upcoming NBI heated experimental program.
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