1. Supported by Office of Science NSTX S.M. Kaye, PPPL For the NSTX Research Team ITPA T&C Mtg. Naka, Japan 31 March – 2 April 2009 The Effect of Rotation and Rotation Shear on Confinement and Transport in NSTX H-mode Plasmas 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 NSTX Designed to Study High-Temperature Toroidal Plasmas at Low Aspect-Ratio Aspect ratio A1.27 – 1.6 Elongation  1.8 – 3.0 Triangularity  0.2 – 0.8 Major radius R 0 0.85m Plasma Current I p 1.5MA Toroidal Field B T0 0.4 – 0.55 T (Pulse Length~2 – ~1 s) Auxiliary heating: NBI (100kV)5 – 7 MW (Pulse Length5 – 2 s) RF (30MHz)6 MW (5 s) Central temperature1 – 5 keV Central density≤1.2  10 20 m -3 Flexible outer PF coils for shaping, control Insulated VV breaks for CHI Graphite/CFC PFCs + Lithium coating Slim center column with TF, OH coils Conducting plates for MHD stability Excellent diagnostic access

4. NSTX NSTX Transport – UCSDFeb. 12, 2009 4 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

5. NSTX NSTX Transport – UCSDFeb. 12, 2009 5 What is Causing the Global Confinement Trends? - Turn to Local Transport Analysis - Neoclassical ion transport typical and governs I p dependence  i,GTC-NEO (r/a=0.5-0.8) GTC-Neo neoclassical: includes finite banana width effects (non- local)

6. NSTX NSTX Transport – UCSDFeb. 12, 2009 6 Why is Ion Transport Neoclassical? Linear GS2 calculations indicate possible suppression of low-k turbulence by ExB shear during H-phase - Supported by non-linear GTC results -  i routinely anomalous in high density L-modes (  lin, ITB >  ExB ) Need BES to confirm conclusions - To be implemented for 2009 run

7. NSTX NSTX Transport – UCSDFeb. 12, 2009 7 External Control Coils Can Be Used to Study the Effect of Rotation on Confinement 6 External Control Coils 48 Internal B P, B R sensors Copper stabilizing plates External control coils used to actively compensate error fields, resistive wall modes (RWM) and for ELM pacing Applied n=3 fields used to change the plasma rotation (both steady-state and transiently) Max torque from braking near R=135 cm Note suppressed zero

8. NSTX NSTX Transport – UCSDFeb. 12, 2009 8 Minimal Effect of Rotation/Rotation Shear on Plasma Stored Energy Possibly some small effect on fast ions Higher shear Rotation shear is acting on a small part of plasma – Improvement may be limited to that region

9. NSTX NSTX Transport – UCSDFeb. 12, 2009 9 Observe Some Change in T i, T e With Magnetic Braking - Little Change in n e -

10. NSTX NSTX Transport – UCSDFeb. 12, 2009 10 Most Significant Local Transport Change is in Ions

11. NSTX NSTX Transport – UCSDFeb. 12, 2009 11 Ion Transport Tightly Coupled to Rotation, Rotation Shear Ion thermal diffusivity decreases with increasing rotation shear Decreasing shear Non-linear calculations needed to determine magnitude of turbulence reduction and resulting heat flux levels ExB shear may also be important for reducing high-k turbulence (Smith, submitted to PRL) Linear GS2 Region of maximum torque from applied n=3  i /  i,neo =1.2  i /  i,neo =2.3  i /  i,neo =3.9 Due to varying P bi (0)

12. NSTX NSTX Transport – UCSDFeb. 12, 2009 12 Is Change of  i With Applied Fields Due to ExB Shear or Ergodization of Edge? Expect region of stochasticity at edge (C>1) due to nRMP –Vacuum field calculations indicate C>1 beyond r/a~0.7 –IPEC (with plasma shielding currents on rational surfaces) indicates C>1 only beyond r/a~0.95  ExB shear dominant J.K. Park Vacuumw/plasma response

13. NSTX NSTX Transport – UCSDFeb. 12, 2009 13 Conclusions Used n=3 applied fields (and associated magnetic braking) as a tool to control rotation and rotation shear in NSTX Rotation plays a strong role in controlling ion transport –Rotational shear suppression of low-k turbulence –May also control electron-scale turbulence (Electron Transport session) More of a local, than a global effect Need to take into account how the applied fields affects the magnetic topology near the edge –Is stochastization of the flux surfaces responsible for the enhanced ion transport? –In NSTX, it appears not