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	299: Aspect ratio scaling of turbulence and transport: DIII-D and NSTX-U comparison
Name:	David Smith none	Affiliation:	ZZZ
Research Area:	Turbulence & Transport	Presentation time:	Not requested
Co-Author(s):	George McKee	ITPA Joint Experiment :	No
Description:	Measure the aspect ratio scaling of turbulence and transport in DIII-D and NSTX-U discharges with similar dimensionless parameters (q profile, Te/Ti, beta, rho*), and compare and contrast turbulence characteristics and behavior in tokamaks vs. spherical torus. Parameters that are unlikely to match, such as nu*, can provide additional scaling results.	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	An aspect ratio scaling experiment at ~1 T will require low field operation on DIII-D and high field operation on NSTX-U. In addition, neutral beam sources will be tuned to best match Te/Ti, beta, gradients, and rotation in the outer core region where temperature gradients are finite and turbulence amplitudes are adequate. Fueling, pumping, and wall conditioning are additional levers to control density and beta. Matching collision frequencies normalized to bounce frequencies (nu*) may not be feasible, but the challenge can be an opportunity to investigate nu* scalings. Target DIII-D H-mode plasmas will be similar to well-behaved NSTX plasmas scaled up to higher field, current and power as expected for NSTX-U plasmas. BES systems, available on both DIII-D and NSTX-U, will be the primary fluctuation diagnostics, along with a range of other high and low-k fluctuation systems. Rho* variations can establish a range of plasma conditions for future comparison to complimentary NSTX-U plasmas. Relatively high-rotation plasmas will be developed via co-current NB injection since NSTX-U will have full co-NBI systems.
Background:	The aspect ratio (A=R/a) is known to be a key dimensionless turbulence parameter along with rho*, nu*, Te/Ti, and beta. The aspect ratio can influence turbulence and transport through trapped particle fraction, curvature favorability, and zonal flow dynamics. While higher A reduces the trapped particle fraction that gives rise to TEM turbulence, higher A also expands bad curvature regions on flux surfaces. According to Rewolt et al (1996), the net result is higher micro-instability growth rates at higher A. On the other hand, other results point to reduced growth rates or transport coefficients at higher A (ITG: Kotschenreuther et al (1995), TEM: Lang et al (2007), ETG: Jenko et al (2001)). In addition, higher A reduces the zonal flow potential due to enhanced neoclassical polarization shielding (Diamond et al (2005)). An aspect ratio scaling experiment can provide insight into a key dimensionless parameter for turbulence, but such an experiment was previously not feasible on DIII-D and NSTX due to a large rho* discrepancy. The higher field and current capabilities on NSTX-U will make such an experiment feasible and exploit the similar minor radii and comparable fields/currents on DIII-D and NSTX-U.
Resource Requirements:	co-NBI
Diagnostic Requirements:	BES
Analysis Requirements:
Other Requirements: