56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014;
New Orleans, Louisiana
Session NI1: Energy and Particle Transport
9:30 AM–12:30 PM,
Wednesday, October 29, 2014
Room: Acadia
Chair: Ron Waltz, General Atomics
Abstract ID: BAPS.2014.DPP.NI1.1
Abstract: NI1.00001 : Weimer Award: Reduction of core turbulence and transport in I-mode and comparisons with nonlinear gyrokinetic simulations*
9:30 AM–10:00 AM
Preview Abstract
Abstract
Author:
Anne White
(MIT)
Understanding transport in high performance ELM-suppressed tokamak plasmas
is of great interest for ITER and other future experiments. `I-mode' regime
on Alcator C-Mod, also known as `improved L-mode' on ASDEX Upgrade, has
several favorable characteristics: pedestals in electron and ion
temperature, with ITER98y2 H-factors similar to and exceeding H-mode
[Hubbard et al Phys. Plasmas 18, 056115 (2011)], but without a density
pedestal and without impurity accumulation and without ELMs. Most research
on I-mode focuses on changes in edge and pedestal turbulence/transport and
stability. In this work, transport in I-mode is probed by measuring changes
in \textit{core} turbulence across L-I transitions at Alcator C-Mod and comparing with
nonlinear gyrokinetic simulations. Long wavelength (k$_{\mathrm{\theta
}}\rho_{\mathrm{s}}$ \textless 0.5) density fluctuation levels decrease
from L-mode levels by up to 30{\%} in I-mode, and long wavelength
(k$_{\mathrm{\theta }}\rho_{\mathrm{s}}$ \textless 0.3) electron
temperature fluctuation levels decrease by up to 70{\%}, reaching the
instrumental sensitivity limit. Gyrokinetic simulation results suggest that
ExB shear in the core of these intrinsically rotating plasmas can reduce the
fluctuation amplitude in I-mode. As the pedestal temperature increases
across slow L-I transitions, core density fluctuations (0.40 \textless $\rho
$ \textless 0.95) are reduced prior to the onset of the edge-localized
(0.99\textless $\rho $ \textless 1.0) weakly coherent mode (WCM) and prior
to the reduction of low-frequency turbulence in the edge/pedestal region
(0.99\textless $\rho $ \textless 1.0), which suggests that effects of
profile stiffness across the radius can also lead to reduced core
turbulence. By comparing experimental measurements from Alcator C-Mod to
nonlinear gyrokinetic simulations and to different models of profile
stiffness, this talk will explore the impact of core turbulence and
transport on overall I-mode confinement and on the separation of particle
and heat transport in I-mode.
*This work was supported by U.S. Department of Energy contract DE-FC02-99ER54512-CMOD.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.DPP.NI1.1