DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	106: Magnetic turbulence measurements in high beta H-mode discharges
Name:	Walter Guttenfelder wgutten@pppl.gov	Affiliation:	Princeton Plasma Physics Laboratory
Research Area:	Turbulence & Transport	Presentation time:	Requested
Co-Author(s):	J. Zhang, N.A. Crocker, E.J. Doyle, C.H. Holland, G.R. McKee, W.A. Peebles, C.C. Petty, T.L. Rhodes, C. Rost, G. Wang, Z. Yan	ITPA Joint Experiment :	No
Description:	The goal of this experiment is to document fluctuation characteristics in high beta H-mode discharges where magnetic (microtearing) turbulence is theoretically most likely to be present. Microtearing turbulence is predicted to have spatial characteristics that are distinctly different from ITG/TEM (outlined below). Data will be obtained with turbulence diagnostics in an attempt to cross-correlate between fluctuations in density (BES, DBS, PCI, mm backscattering), temperature (CECE), and magnetic field (recently commissioned UCLA polarimeter) to identify features that are, or are not, consistent with microtearing predictions.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:
Background:	Theoretical evidence suggests that microtearing modes (generally unstable at relatively high beta_e, nu_e, and a/LTe; and weak a/Ln~0) may sometimes be an important component of electron thermal transport in the core and near the pedestal top of of spherical tokamaks (NSTX, MAST), conventional aspect ratio tokamaks (AUG, DIII-D, JET), and RFPs (RFX). There is clear motivation to measure turbulence characteristics associated with microtearing modes. Non-linear simulations for both NSTX and AUG illustrate that microtearing turbulence is expected to be distinctly different from all other core-related micro-turbulence mechanisms (ITG, TEM, KBM, ETG). Most notably: (1) magnetic perturbations (k_theta*rho_s<0.2) are radially broad (compared to radially narrow for ITG/TEM), and (2) density and electron temperature perturbations exhibit narrow corrugations around rational surfaces (with spacing Drat=1/k_theta*s_hat). It is also expected that ne-Te cross phases should be different from other turbulence mechanisms. Based on the distinct spatial structures, cross-correlating turbulence measurements (ne, Te, Br) from multiple diagnostics may help identify features that are (or are not) consistent with microtearing turbulence. Previous calculations (based on NSTX simulations) using a synthetic diagnostic approach illustrate the broad magnetic perturbations of microtearing turbulence may be detectable by line-integrated polarimetry measurements [Zhang, APS 2011]. The UCLA polarimeter has now been successfully commissioned on DIII-D during the 2012 campaign, and both the hardware and synthetic diagnostic code have been validated. Chris Holland has previously identified a DIII-D discharge (128413) that exhibits unstable microtearing modes (k_theta*rho_s<0.2) between r/a=0.5-0.8. This provides one of the initial target discharges of the experiment. The second target would complement a similar experiment originally proposed for NSTX using polarimetry, BES, and high-k scattering. The UCLA 288 GHz polarimeter has recently been installed on DIII-D in this configuration, so DIII-D is in a unique position to obtain data on microtearing turbulence. The results would likely provide valuable information for, and comparison with, measurements and analysis on NSTX-U (beginning 2014 and beyond). These measurements will also contribute to Jie Zhang thesis data.
Resource Requirements:	Beams (heating, BES, MSE), ECH
Diagnostic Requirements:	BES, DBS, polarimetry, CECE, mm backscattering, PCI CER, TS, ECE, MSE
Analysis Requirements:	EFIT, ONETWO/TRANSP, TGLF, GYRO
Other Requirements: