Remote Broadcast: Shaun Haskey

Friday, March 13, 2020 at 3:00pm to 4:00pm

Building NW17, 218
175 ALBANY ST, Cambridge, MA 02139

PSFC Seminar: Active spectroscopy measurements of the Deuterium temperature, rotation, and density in the pedestal region of the DIII-D tokamak,
a seminar by Shaun Haskey,
Broadcast from Princeton Plasma Physics Laboratory

Main-ion charge exchange recombination spectroscopy (MICER) [1,2] uses the neutral beam induced D-alpha emission spectrum to determine the local deuterium ion (D+) temperature, rotation and density, as well as several beam and equilibrium properties from the neutral beam emission. An edge MICER system consisting of 16 densely packed sightlines was installed on DIII-D extending the MICER technique from the core to the pedestal and steep gradient region of H-mode plasmas where the D+ and commonly measured impurity ion properties can differ significantly. A combination of iterative collisional radiative modeling techniques and greatly accelerated spectral fitting algorithms allowed the extension of this diagnostic technique to the plasma edge where the steep gradients introduce significant diagnostic challenges that require employing direct synthetic diagnostic modeling. Data from a wide range of plasma conditions has been acquired uncovering sometimes large temperature differences between D+ and impurity ions near the separatrix, inwardly shifted C6+ density pedestals, and rapid co-Ip D+ edge rotation. These observations provide significantly better experimental data for testing models and improving understanding in areas such as ion thermal transport and intrinsic rotation. For example the D+ temperature measurements resolve inconsistencies such as negative ion heat fluxes near the plasma edge, which are sometimes inferred when using the historical assumption that the impurity ion temperature is a good proxy for the D+ temperature. The measurements and analysis demonstrate the state of the art in active spectroscopy and integrated modeling for diagnosing fusion plasmas and the importance, despite the difficulties, of direct D+ measurements at the plasma edge.
[1] B.A Grierson, RSI, 2012
[2] S.R Haskey, RSI, 2018

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