Speaker
Dr
Laszlo Bardoczi
(UCLA, ORAU)
Description
We present the first localized measurements of ITG scale temperature and density fluctuations and TEM scale density fluctuations modified by m=2, n=1 magnetic islands. These islands are formed by a Neoclassical Tearing Mode (NTM) deep in the core plasma at the q=2 surface. NTMs are important as they often degrade confinement and lead to plasma termination. This is the first experimental confirmation of a long-standing theory prediction [1] of decreased local small-scale turbulence levels across large-scale magnetic islands. Our measurements capture a mean reduction of turbulence inside (and enhancement just outside) the island region during island evolution. Additionally, in the island saturated state the fluctuations at the O-point are reduced compared to the X-point [2]. A novel, non-perturbative measurement finds reduced cross-field electron thermal diffusivity (by 1-2 orders of magnitude) at the O-point, consistent with the local turbulence reduction. Initial comparisons to the GENE non-linear gyrokinetic code are promising with GENE predicting the observed turbulence reduction inside the island and increase just outside the island and replicating the observed scaling with island size [3]. These results are significant as they allow the validation of gyrokinetic simulations modeling the interaction of these multi-scale phenomena [4]. Improved understanding of NTM physics and interaction with turbulence can lead to improved control of NTMs and plasma performance, therefore has potential implications for future fusion devices such as ITER. Supported by USDOE under DEFG02-08ER54984, DE-FG02-08ER54999 and DE-FC02-04ER54698.
[1] C. J. McDevitt and P. H. Diamond, PoP, 13 032302 (2006);
[2] L. Bardoczi et al, PRL 116 215001 (2016);
[3] A. B. Navarro et al, 59 034004 PPCF (2017);
[4] L. Bardoczi et al, PoP 24 056106 (2017).
Primary author
Dr
Laszlo Bardoczi
(UCLA, ORAU)
Co-authors
Dr
A. Carter Troy
(UCLA)
Dr
Alejandro Banon-Navarro
(UCLA, IPP)
Dr
Colin Chrystal
(General Atomics)
Dr
Craig C. Petty
(General Atomics)
Dr
Frank Jenko
(UCLA, IPP)
Dr
George R. McKee
(UW-Madison)
Dr
Robert J. La Haye
(General Atomics)
Dr
Sung Choongki
(UCLA)
Dr
Terry L Rhodes
(UCLA)
