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Oct 13 – 18, 2014
Hotel Park Inn Pribaltiyskaya
Europe/Moscow timezone

Cross-Polarization Doppler Backscattering Measurements and Microtearing at the Top of the MAST H-Mode Pedestal

Oct 15, 2014, 2:00 PM
4h 45m
Green 8-9 (Hotel Park Inn Pribaltiyskaya)

Green 8-9

Hotel Park Inn Pribaltiyskaya

Saint Petersburg, Russian Federation
Poster Poster 4

Speaker

Dr Jon Hillesheim (Culham Centre for Fusion Energy)

Description

Microtearing modes (MTMs) have been predicted to be unstable at the top of the H-mode pedestal in MAST plasmas [1], playing a role in determining pedestal transport between Edge Localized Modes (ELMs), and therefore of pedestal structure and ELM stability. This is a deepening of the understanding embodied by the widely applied model EPED [2], which relies only on Kinetic Ballooning Mode (KBM) stability to account for inter-ELM transport. We present a novel diagnostic technique, combining Doppler Backscattering (DBS) and cross-polarization scattering. This has enabled measurements sensitive to local, internal magnetic field fluctuations at the radial location and wavenumber range where MTMs have been predicted to be unstable in MAST. Doppler backscattering is a diagnostic technique, which is typically used to measure intermediate and high wavenumber density fluctuations and their lab frame propagation velocity. Two 8-channel DBS systems and a flexible quasi-optical system with 2D steering and a rotatable polarizer were installed at MAST in 2013, which enabled either standard or cross-polarization scattering. Results show a significant level of magnetic field fluctuations at the top of the pedestal, with a different temporal evolution than density fluctuations, at locations and wavenumbers where microtearing modes are predicted to be unstable. [1] Dickinson et al., Phys. Rev. Lett. 108, 135002 (2012) [2] Snyder et al., Nucl. Fusion 51, 103016 (2011) This work was part-funded by the RCUK Energy Programme [grant number EP/I501045], the European Union’s Horizon 2020 programme, and the US Department of Energy under DE-FG02-99ER54527. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Paper Number EX/P4-35
Country or International Organisation UK

Primary author

Dr Jon Hillesheim (Culham Centre for Fusion Energy)

Co-authors

Dr Andrew Kirk (Culham Centre for Fusion Energy) Colin Roach (Culham Centre for Fusion Energy) Dr David Dickinson (Culham Centre for Fusion Energy) Dr Hendrik Meyer (EURATOM/CCFE Fusion Association) Dr Neal Crocker (University of California Los Angeles) Dr Rory Scannell (Association CCFE/Euratom) Dr Samuli Saarelma (CCFE) Dr William Peebles (University of California, Los Angeles)

Presentation materials