Characterization of the W7-X scrape-off layer using reciprocating probes

Abstract

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Coherence imaging spectroscopy at Wendelstein 7-X for impurity flow measurements

“…The part outside this region (R>6.075 m) should not be considered since it is in the shadow of the divertor, featuring very short connection lengths (<10 m), so that field lines starting from the probe do not reach the CIS measurement region. Moreover, the electron temperature decay for R>6.075 m shows a tendency similar to the one obtained with no island chain [34]. In the highlighted region of interest, the flow velocity in the experiment with control coil operation is about 10 km/s higher, well agreeing with the CIS results.…”

“…On the other hand, the CIS measurements depend on where the carbon radiates. The C III photo-emission coefficient peaks for electron temperatures of 10-20 eV, values typically found in the SOL of W7-X [34,35]. Moreover, the magnetic islands are characterized, for standard plasma conditions, by strong pressure gradients along the field lines that enhance the parallel particles flows [17,36].…”

“…Additional comparisons with other flow diagnostics can further confirm the quality of the CIS measurements [25]. Suitable candidates are the Mach probes, mounted on the Multi-Purpose Manipulator (MPM) of W7-X [34,37,38]. Good agreement between CIS and Mach probes has already been observed in a recent investigation on the role of plasma currents for the SOL dynamics in W7-X, where similar changes of the plasma flow caused by increasing plasma currents has been found [39].…”

“…Fig.15(b) shows radial profiles of electron temperature (from a triple Langmuir probe) and parallel flow velocities (from the Mach probe) both along the MPM path. For clarity, the sign of the Mach probe flow has been chosen here in the same way as the CIS flows, on the contrary of the definition in previous publications on Mach probe flows [34,38,39]. The region which can be used for comparison with CIS is highlighted in yellow.…”

Turbulent transport in the scrape-off layer of Wendelstein 7-X

“…Γ r ∼ ∇p [8,18]. Here, this hypothesis is tested using reciprocating Langmuir probes mounted on the multi-purpose manipulator (MPM) [19,20] of W7-X. Exploiting spatially distributed arrangements of multiple probes, profiles of T e , n (and therefore the pressure gradient) as well as an estimate of radial fluctuating particle transport via Γ r = ñ ṽr = ñ Ẽ pol /B are obtained.…”