1. Supported by Office of Science NSTX S.M. Kaye, PPPL For the NSTX Research Team T&C ITPA Mtg. Naka, Japan 31 March – 2 April 2009 Electron Scale Turbulence and Transport in NSTX Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin

2. NSTX NSTX Transport – UCSDFeb. 12, 2009 2 NSTX is Unique in its Ability to Address Critical Transport Issues NSTX features –Strong rotational shear that can influence ion and electron transport –Anomalous electron transport can be isolated: ions often close to neoclassical –Large range of  T spanning e-s to e-m turbulence regimes: assess impact of electromagnetic contribution to transport –Localized measurements of electron-scale turbulence (  e ~0.1 mm)

3. NSTX NSTX Transport – UCSDFeb. 12, 2009 3 Results of the Scaling Experiments Have Revealed Some Surprises Strong dependence of  E on B T  E,98y,2 ~ B T 0.15  E,98y,2 ~ I p 0.93 Weaker dependence on I p

4. NSTX NSTX Transport – UCSDFeb. 12, 2009 4 Variation of Electron Transport Primarily Responsible for B T Scaling Ions near neoclassical Neoclassical Broadening of T e & reduction in  e outside r/a=0.5 with increasing B T

5. NSTX NSTX Transport – UCSDFeb. 12, 2009 5 We Are Attempting to Develop an Understanding Based on Both Turbulence Measurements and Theory Turbulent fluctuations are measured with coherent scattering of 280 GHz waves The scattering geometry takes advantage of the anisotropy of plasma fluctuations (k  >>k || ~1/qR) and the curvature of magnetic field lines to obtain a resolution of Scattering Geometry On NSTX, we can measure electron gyroradius scale turbulence locally

6. NSTX NSTX Transport – UCSDFeb. 12, 2009 6 Electron-Scale Turbulence is Observed on NSTX and is Consistent With Expectations for ETG Modes Dependence on scale of T e r/a~0.3 k   e =0.2-0.4 GS2 E. Mazzucato, D. Smith

7. NSTX NSTX Transport – UCSDFeb. 12, 2009 7 Negative Magnetic Shear Reduces Turbulence – Consistent with ETG  A strong negative magnetic shear was obtained with the RF heating (3 MW) starting early in the plasma pulse when current penetration was not complete  The suppression of turbulent fluctuations coincides with the formation of a very large temperature gradient at the location of measurement – transport barrier? E. Mazzucato

8. NSTX NSTX Transport – UCSDFeb. 12, 2009 8 Negative Magnetic Shear Reduces Turbulence – Consistent with ETG k ┴  e  0.2 H. Yuh

9. NSTX NSTX Transport – UCSDFeb. 12, 2009 9 Near ETG Marginal Stability, Fluctuation Amplitudes Decrease When the ExB Shear Rate Exceeds the ETG Growth Rate D. R. Smith et al, submitted to PRL

10. NSTX NSTX Transport – UCSDFeb. 12, 2009 10 The Connection Between the ETG Turbulence and Electron Transport is Not Fully Understood - There is Some Success, However - Electron transport anomalous: controls B T scaling Consistent with variation of high-k fluctuations 3.5 kG 5.5 kG Heat flux due to high-k electron modes (ETG) consistent with levels inferred from TRANSP in H-modes for r/a>0.5

11. NSTX NSTX Transport – UCSDFeb. 12, 2009 11 There is a Qualitative Agreement Between Inferred e - Transport and Theoretical Expectations Strongly reversed shear e-ITBs show low high-k fluctuation power despite strong  T e gradient drive –  T e well above ETG critical gradient for reversed shear cases Jenko and Dorland (2002) NSTX H. Yuh

12. NSTX NSTX Transport – UCSDFeb. 12, 2009 12 Non-Linear Gyrokinetic Calculations with GTS Have Been Completed k r -2.6 First global ETG simulation for actual plasmas High-k scattering measurement k r -4.4 W. Wang (r/a=0.3) GTS Electrostatic Adiabatic ions (k r + k  ) Calculated transport rates factor of ten low! More work has to be done on this - Sensitivity analyses (  T e, magnetic shear) - Synthetic diagnostic

13. NSTX NSTX Transport – UCSDFeb. 12, 2009 13 Electron Transport May be Controlled by Multiple Mechanisms (Including E-M) Low-k microtearing important in low shear/“Hybrid” discharges Driven by  T, damped by strongly reversed magnetic shear Collisionality predicted to be low enough in NSTX-U for suppression of microtearing K.L. Wong

14. NSTX NSTX Transport – UCSDFeb. 12, 2009 14 Recent Observations Indicate High-Frequency Core E-M Fluctuations May Also Cause Electron Transport 2 MW4 MW6 MW D. Stutman Global Alfvén Eigenmodes

15. NSTX NSTX Transport – UCSDFeb. 12, 2009 15 Measured Turbulence Amplitudes Can Lead to High Electron Transport Rates  n/n ~10 -4 from high-k interferometry Multiple modes Assume ~15 modes  B/B~10 -2 (summed) GAEs found to affect trapped electrons primarily These amplitudes can give  e ’s up to 10 m 2 /s (ORBIT – N. Gorelenkov)

16. NSTX NSTX Transport – UCSDFeb. 12, 2009 16 Conclusions Electron transport always anomalous in NSTX, and often is primary energy loss channel –Ions neoclassical in standard H-modes (though neoclassical can be high in NSTX) Localized electron-scale turbulence measurements indicate the presence of ETG modes –Sensitive to  T e, magnetic shear and rotation shear –Non-linear gyrokinetic simulations and comparison to experiment have found mixed results Other mechanisms operative –Microtearing in “hybrid-like” (low magnetic shear) discharges –High-frequency electromagnetic modes (GAEs) potentially important Would like to develop JEX for both microtearing and GAE