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Presented by J.E. Menard Princeton Plasma Physics Laboratory MHD SFG Meeting Thursday, May 19, 2005 nearly identical to my talk at: 2005 International Sherwood Fusion Theory Conference April 11-13, 2005 Stateline, Nevada, USA This work supported by the US DoE, UK EPSRC, and EURATOM Unique MHD Properties of Spherical Torus Plasmas Supported by

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J.E. Menard – MHD SFG – 5/19/2005 2 Special thanks to contributors to this talk: J. Bialek, S.A. Sabbagh, A. Sontag, W. Zhu (Columbia University) M.S. Chu, R.J. La Haye, P.B. Snyder (General Atomics) D. Stutman, K. Tritz (Johns Hopkins University) A.H. Glasser, X.Z. Tang (Los Alamos National Laboratory) H. Strauss (New York University) R. Maingi, Y.-K.M. Peng (Oak Ridge National Laboratory) E. Belova, J. Breslau, E.D. Fredrickson, G. Fu, D.A. Gates, J. Manickam, S.S. Medley, M. Ono, W. Park (PPPL) W. Heidbrink (University of California – Irvine) R. Betti, L. Guazzotto (University of Rochester) T. Jarboe, R. Raman (University of Washington) R. Fonck, C. Hegna (University of Wisconsin – Madison) R. Buttery, S. Saarelma, A. Sykes, H.R. Wilson (Culham Science Centre – United Kingdom) Y. Ono, Y. Takase (University of Tokyo - Japan) and the entire NSTX Research Team Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo JAERI Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec

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J.E. Menard – MHD SFG – 5/19/2005 3 World Spherical Torus (ST) Community Continues to Grow in Experiments and Research Goals Lowered cost, very high , and low-A physics attract high interest HIST LATE NUCTE-ST TS3,4 TST-2 UTST All Japan ST SUNIST MAST Globus-M GUTTA Proto-Sphera STPC-EX KTM HIT-SI Pegasus CDX-U/LTX NSTX ETE 19 ST research centers world-wide (M. Peng – ORNL)

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J.E. Menard – MHD SFG – 5/19/2005 4 NSTX (USA) and MAST (UK) are investigating low-collisionality toroidal plasmas at low aspect ratio NSTXMAST Close-fitting passive stabilizers: Wall stabilization of external kink Internal poloidal field coils: Plasma formation w/o solenoid Typical Parameters Aspect ratio A < 1.6 Elongation < 2.7 Triangularity < 0.8 Major radius R 0 0.85m Plasma Current I p < 1.5MA Toroidal Field B T0 < 0.6T Poloidal flux< 1Wb Pulse Length< 1.5s NBI Heating< 7MW T e, T i = 1-4keV n e = 10 19 -10 20 m -3 e, i 0.1, 1 S (Lundquist #) = 10 7 (core) Pr (Prandtl #) = 10-100 R0R0 a

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J.E. Menard – MHD SFG – 5/19/2005 5 Largest STs operate in unique MHD parameter regime Low–A configuration access to high –Configuration generates strong natural shaping –Higher stability limits with broad pressure and current profiles –Diamagnetic frequency comparable to ideal mode growth rates Neutral Beam Injection (NBI) heating dominant –Largest STs presently have uni-directional beam injection –Large toroidal rotation inseparable from high –n, p profiles decoupled from flux surfaces –Flow-shearing rates comparable to ideal growth rates –Large population of energetic ions produced Fast ions constitute 15-50% of total stored energy V fast / V Alfvén = 2-4 strong drive for energetic particle modes Parameters potentially relevant for ITER fast-ion physics The ST is an unique & important platform for testing MHD theory and simulation

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J.E. Menard – MHD SFG – 5/19/2005 6 ST configuration allows access to high plasmas Troyon scaling Max( T ) ~ N I P / aB T Low A higher I P / aB T at same q* (i.e. same kink stability) Low A also has higher N limit w.r.t. kink & ballooning modes P EGASUS : Explore plasma limits as A 1 Paramagnetic plasma: local 50%, diamagnetic: local 100%

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J.E. Menard – MHD SFG – 5/19/2005 7 STs can produce strongly-shaped plasmas Natural elongation increases rapidly with decreasing A and l i Low-l i plasma stability enhanced by large edge magnetic shear at low-A Elongation up to 2.6 at =0.5 achieved in NSTX at low l i = 0.5-0.6 – NSTX will increase from 0.5 0.8 at high this year Low A needs high and to maximize T at high P (i.e. bootstrap fraction) TRANSP Up to 60% non-inductive current fraction w/ f BS = 50% at T = 15-20% Internal Inductance Higher yields simultaneously higher T and f BS 0.5 1/2 P (elongation) 2004 2002-03 Control system upgrade higher (D. Gates - PPPL) T (%) 0.5 1/2 P

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J.E. Menard – MHD SFG – 5/19/2005 8 Unidirectional beam-heating drives large toroidal rotation Ne()Ne() Model n e ( ,R) w/ matches n e data Includes fast-ion p and nDnD 107540 at t=333ms Solid curves: Model n s ( ,R) w/ rotation Dashed curves: N s ( density w/o rotation M S = v / v sound = 0.4-0.8, M A = v / v A = 0.2-0.5 (higher in ST) Force balance + neutrality n e ( ,R) = N e ( ) exp(M 2 ( ) (R 2 –R 0 2 )/2T( )) Centrifugal effects evident in n e (R) profiles:

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J.E. Menard – MHD SFG – 5/19/2005 9 Presently studying role of flow in equilibrium reconstructions and effect of p-anisotropy FLOW code ( L. Guazzotto – U. Roch.) Density profile shift in a static plasma for varying anisotropy for an NSTX-like equilibrium EFIT w/ rotation + MSE (S. Sabbagh, CU) Phys. Plasmas, Vol. 11, No. 2, February 2004 -2 1 2 0 Z(m) 0.52.01.01.5 R(m) 0.0 114444 t=0.257s iso-surface p iso-surface (no p-anisotropy) Developing stability code for arbitrary flow and

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J.E. Menard – MHD SFG – 5/19/2005 10 ST configuration impacts full spectrum of MHD activity ST MHD areas treated in this presentation: Internal kink mode Resistive Wall Mode (RWM) Edge Localized Modes (ELM) Neoclassical Tearing Modes (NTM) Alfvén Eigenmodes (*AE) Solenoid-free ST plasma formation

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J.E. Menard – MHD SFG – 5/19/2005 11 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ Mode linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection and electron beam injection –Plasma merging/compression and PF-coil direct induction

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J.E. Menard – MHD SFG – 5/19/2005 12 Sawteeth are rare in NSTX at high- and with large rotation Neutron rate ½ expected value during mode activity, but sometimes recovers Instead, 1/1 mode saturates - Why? degrades fast-ion confinement flattens core rotation profile 108103 (Submitted for publication in Nuc. Fus. – J. Menard )

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J.E. Menard – MHD SFG – 5/19/2005 13 SXR data consistent w/ rapid growth saturation 227ms 228ms229ms 230ms240ms270ms (USXR data from Stutman & Tritz - JHU) Island model h fit to SXR SXR data (line-integrated)

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J.E. Menard – MHD SFG – 5/19/2005 14 Sheared rotation is stabilizing, but mode flattens profile M3D M3D resistive MHD code Sheared rotation slows mode growth by factor of 2-3 Core flattening observed in M3D and experiment even w/o complete reconnection Complete collapse of profile and island locking disruption W. Park - PPPL

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J.E. Menard – MHD SFG – 5/19/2005 15 Larger B P / B in ST enhances damping from modes Neoclassical Toroidal Viscosity (NTV) good candidate to explain core rotation flattening (K.C. Shaing et al., Phys. Fluids 29 (1986) 521, also Lazzaro, Sabbagh, Zhu…) Larger B P / B in ST larger ratio of b r m,n / B 1/1 mode NTV needed to match evolution diamonds measured lines calculated (Example shown: Coupled 1/1 + 2/1 modes at high- NTV apparently explains flattening from 1/1 Important to develop and include improved viscosity models in non-linear MHD simulations Torque balance Damping Without NTV With NTV W. Zhu – Columbia Univ.

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J.E. Menard – MHD SFG – 5/19/2005 16 Diamagnetic effects may contribute to saturation of the 1/1 mode at high 1/1 island displaces core enhanced p and q in reconnection region –Locally enhanced *i and *e stabilizing, higher shear destabilizing –Rogers and Zakharov: quasi-linear model with high-A, circular plasma, no rotation –Significant non-linear stabilization possible for ST parameters for range of q-shear High increased *i A i A i /a A = R 0 /a = aspect ratio i = ion skin depth a = minor radius Model predictions: -Mode stable for 0 < 0.5 *i -Low / high shear no saturation -Shear s 0.1-0.2 allows saturated 0 / r q=1 0.5 similar to measured displacement MSE will allow q measurement this year Preliminary M3D result * and may synergistically contribute to saturation (W. Park) B. Rogers and L. Zakharov Phys. Plasmas 2 (9), September 1995 0 / *i 0 / r q=1 108103

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J.E. Menard – MHD SFG – 5/19/2005 17 MHDCounter 2FuidsCo 2Fuids Saturation with hot spot pulled away from x-point Crash faster than MHD case M A =+-0.3 M A =-0.3M A =+0.3 Temperature

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J.E. Menard – MHD SFG – 5/19/2005 18 Saturated 1/1 modes observed late in longest-duration discharges this year Sawteeth (?) 400ms 1/1 mode

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J.E. Menard – MHD SFG – 5/19/2005 19 Rotation flattening from 1/1 observed, rotation decays gradually thereafter

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J.E. Menard – MHD SFG – 5/19/2005 20 Plasma J-profile appears nearly time-invariant late in saturation phase. Preliminary MSE EFITs consistent with q(0) < 1

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J.E. Menard – MHD SFG – 5/19/2005 21 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection and electron beam injection –Plasma merging/compression and PF-coil direct induction

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J.E. Menard – MHD SFG – 5/19/2005 22 Wall stabilization physics understanding is key to sustained plasma operation at maximum High t < 40%, N = 6.8 reached NN lili N /l i = 12 68 4 10 wall stabilized Global MHD modes can lead to rotation damping, collapse Physics of sustained stabilization is applicable to ITER Operation with N / N no-wall > 1.3 at highest N for pulse >> wall NN DCON WW 0 10 20 0.60.70.50.40.30.20.10.0 t(s) n=1 (no-wall) n=1 (wall) 112402 wall stabilized EFIT core plasma rotation (x10 kHz) (S. Sabbagh, CU)

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J.E. Menard – MHD SFG – 5/19/2005 23 ST research will improve our understanding of rotational stabilization of the RWM Drift Kinetic Theory: –Trapped-particle effects at finite significantly weaken ion Landau damping –Toroidal inertia enhancement modifies eigenfunction when / A > 1 / 4q 2 Experimental crit consistent with scaling / q 2 – why? ST has higher sound / A distinguish between s and A scaling? Is stabilizing dissipation localized to resonant surfaces, or more global? –Attempting to answer these questions w/ NSTX / DIII-D similarity experiments (R. La Haye – GA) (A. Sontag - CU)

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J.E. Menard – MHD SFG – 5/19/2005 24 Growth rate [ 1/s ] Active control of RWM in ST geometry will complement research at higher aspect ratio 2 0.0 0.20.40.60.81.0 1 0 N = 5.0 114024 R Z R 0 + aR 0 - a DCON R 0 + a R 0 - a B (arb) RWM eigenfunction strongly ballooning at high , low-A outboard coils effective Like (present) ITER design, NSTX feedback system must deal with external mid- plane coils and nearby (blanket-like) passive plates VALEN code J. Bialek – CU S. Sabbagh – CU, A. Glasser - LANL (Equilibria used have Nno-wall = 5.1; Nwall = 6.9) Feedback stabilize RWM at C = 68% without rotation

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J.E. Menard – MHD SFG – 5/19/2005 25 MARS code calculations for NSTX indicate plasma 0 destabilizing for RWM 0 increases WALL for large WALL Also apparent lowering of no-wall limit Ideal plasma Resistive Plasma = 0 0 required for benchmarking/comparison to M3D - Studying interplay between resistivity and dissipation Will test Bondeson/Chu kinetic damping model in MARS for NSTX - Kinetic damping model applicable to low-A needed No-wall limit Ideal-wall limit Chalmers, GA, PPPL

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J.E. Menard – MHD SFG – 5/19/2005 26 M3D simulations examining role of plasma and rotation Perturbed Poloidal flux at Saturates at w/ collisional viscosity Resistive plasma / resistive wall mode (RPRWM) growth rate scaling: (H. Strauss - NYU) 1.001 0.1.001 e e e WALL e RWM interacts w/ tearing / EM -ballooning mode Wall Plasma similar to analytic scaling Finn 1995; Betti 1998 Better dissipation models needed

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J.E. Menard – MHD SFG – 5/19/2005 27 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection and electron beam injection –Plasma merging/compression and PF-coil direct induction

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J.E. Menard – MHD SFG – 5/19/2005 28 (From P.B. Snyder - GA) ELITE code Coupled peeling-kink and ballooning modes explain many features of Edge-Localized-Modes (ELMs) in H-mode pedestal

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J.E. Menard – MHD SFG – 5/19/2005 29 54.23.3A=2.5 Collisionality, triangularity, and aspect ratio impact ELM stability Aspect ratio varied via R scan at fixed B T, I P, a, shape Need to extend stability scans to lower A, include 0, *, rotation… P.B. Snyder, et al., Plasma Phys. Control. Fusion 46 (2004) A131–A141

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J.E. Menard – MHD SFG – 5/19/2005 30 Sheared rotation predicted to enhance ELM stability in ST Experimental profiles analyzed w/ ELITE Expt. marginal p ped 2 kPa - consistent with analysis 10% variation in threshold with n and equilibrium q surf = m-nq surf Mode number n=6 p ped = 2kPa (From S. Saarelma, H.R. Wilson – Culham, UK) Sheared edge rotation stabilizing –High-n modes most easily stabilized –10-20% increase in stable p ped depending on n-number and rotation Expt. v ped

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J.E. Menard – MHD SFG – 5/19/2005 31 Model of ELM cycle including sheared rotation: 4. Hyper-exponential growth as dv/dr 0 ELM crash 1. p < sheared-velocity limit stable 2. p > sheared-velocity limit unstable 3. Instability reduces rotation shear Extension of Cowley / Wilson non-linear ballooning model to include rotation Filament-like structure A. Kirk, et al., PRL, June 2004

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J.E. Menard – MHD SFG – 5/19/2005 32 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection and electron beam injection –Plasma merging/compression and PF-coil direct induction

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3/2 NTM used to study stabilizing role of curvature From R. J. Buttery, et al. PRL 88, 25 March 2002, p. 125005-1 (Culham - UK) 2941 At higher p get 2/1 NTM: – earlier excitations do not grow – usually requires H mode and high p Sawteeth briefly reduce p high enough p 3/2 NTM 3/2 mode reduces energy confinement time: – W 3.0kJ (11%) Chang & Callen ‘belt’ model predicts: W 2.4kJ MAST Discharge

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incomplete pressure flattening w>~w d bootstrap term (drive) requires low collisionality ion polarisation effects w>w pol “classical” resistive tearing index (assumed stabilizing) Stabilization terms require minimum island size Evolution described by modified Rutherford Eqn. field curvature shape and aspect ratio dependence Ratio a GGJ / a bs 3/2 important as 1 Curvature term cancels 60% of BS drive for MAST case saturation dw dt w seed Glasser-Greene-Johnson term a GGJ D R Equation from O. Sauter Phys. Plasmas 4, May 1997

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Evolution can be well fit using modified Rutherford eqn. TM size responds to p step down, and fit is < 0 NTM Island width too large w/o GGJ term ( would be too negative) ion polarisationfinite island transportFit to decay requires either ion polarisation or finite island transport model (noise level) Island size (cm) / p x 15 models 3730 data pp NBI (800kW) sawtooth/ELM transients q-profile measurements needed for NSTX this year M.R. Eqn. derived for low-A & high- (C. Hegna – PoP 1999) will also be used

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Sawtooth seeding of TM strong in ST, not fully understood Sawtooth increases existing n=2 NTM width n=1 amplitude n=2 amplitude Sawtooth can excite n=2 on NSTX also… but, n=2 width can also decrease post-crash (R.J. Buttery) (E. Fredrickson) On MAST, sawtooth readily excites 3/2 NTM close to NTM marginal Large q=1 surface radius and stronger magnetic coupling likely important n=1

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J.E. Menard – MHD SFG – 5/19/2005 37 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection and electron beam injection –Plasma merging/compression and PF-coil direct induction

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J.E. Menard – MHD SFG – 5/19/2005 38 The ST inherently accesses unique region of parameter space for fast-ion-driven MHD Typical operational scenarios have: –Low B, high n e lower V A –High fast and high v fast /V A Strong drive for Alfvénic modes Excellent tests for theory/simulation Broad spectrum of modes often unstable simultaneously: –CAE: 1-3MHz (Compressional) –GAE: 0.3-1MHz (Global) –TAE: 50-150kHz (Toroidal) –Fishbone: 5-100kHz DIII-D

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J.E. Menard – MHD SFG – 5/19/2005 39 ST & standard tokamak can test A-dependence of fast-ion MHD by operating in similar (low B T ) parameter regime At B(0) 0.5-0.6T, NSTX & DIII-D observe: –EPM, TAE and CAE –Fast ion losses from EPM and TAE –Modes unstable when fast-ion β is high Differences: –NSTX TAE has lower n (from R scaling) –Rapidly chirping/bursting (100kHz 10kHz) EPM much more common on NSTX Also observed on START/MAST ST feature? NSTX 107335.0140 DIII-D 109855.1035 (Fredrickson - PPPL Heidbrink - UCI)

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J.E. Menard – MHD SFG – 5/19/2005 40 Non-linear TAE simulations reproduce many features observed in NSTX data M3D Nonlinear Hybrid simulations: –Mode growth and decay times are approximately 50 - 100 s –Bursting/chirping behavior results from: Non-linear modification of fast-ion distribution Change in mode structure Data Simulation t=0.0t=336 (G. Fu - PPPL) n=2 Simulations Mode moves radially outward during amplitude saturation phase

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J.E. Menard – MHD SFG – 5/19/2005 41 GAE/CAE unstable at higher k || and high v fast / v A > 2 HYM simulations of GAE and CAE –Nonlinear, global, fully kinetic ions –Beam ions treated with full-orbit f method GAE found to be most unstable ( < 10 -2 ci ) – = 0.3-0.5 ci just below the lower edge of the Alfven continuum < MIN( A ) –2 n 7, several m unstable for each n –Localized near magnetic axis – B || B / 3 Higher-n modes more compressional (CAE) – B || > B – = 0.4-0.7 ci –7 n 10, weakly unstable compared to GAE –Localized near outboard midplane Beam ion resonance condition: (Electron Landau and thermal ion cyclotron damping weak) VZVZ VRVR (E. Belova - PPPL)

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J.E. Menard – MHD SFG – 5/19/2005 42 Impact of fast-ion MHD on confinement can be significant Bursting/chirping EPMs correlate w/ large fast ion loss CAE bursts coincident w/ EPM onset suggest CAE-induced fast ion transport Are CAE modes large enough to stochastically heat thermal ions? (Gates, White - PPPL) Phys. Rev. Lett. 87, 205003 (2001) (Fredrickson - PPPL) Need internal measurement of CAE B to assess role in fast-ion transport & stochastic heating

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J.E. Menard – MHD SFG – 5/19/2005 43 ST configuration impacts full spectrum of MHD activity Internal kink mode –Flow-shearing rate ~ linear w/o rotation –Rotation + enhanced * possible saturation mechanism? Resistive Wall Mode (RWM) –Low A, high edge-q, and large v Sound / v Alfvén impact critical –Higher plasma (lower S) may impact RWM scaling Edge Localized Modes (ELM) –Strong intrinsic shaping enhances pedestal stability –Larger rotational shear may also enhance stability Neoclassical Tearing Modes (NTM) –Low-A enhances toroidal curvature effects –Toroidal mode coupling stronger, q=1 radius larger Alfvén Eigenmodes (*AE) and Energetic Particle Modes (EPM) –Intrinsically large v fast / v A and fast enhanced instability drive –Resonances at 1 st ci harmonic Solenoid-free ST plasma formation –Coaxial helicity injection (CHI) and electron beam injection –Merging/compression (MC) and PF-coil direct induction

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J.E. Menard – MHD SFG – 5/19/2005 44 Transient Coaxial Helicity Injection (CHI) Method attempts to force axisymmetric reconnection at injector to create equilibrium with closed flux surfaces (R. Raman – U. Washington) (Camera images – C. Bush)

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J.E. Menard – MHD SFG – 5/19/2005 45 Experiment (NSTX, Raman, et al) Fast camera view 3D Simulation (CHIP code, NESRC 256 CPUs) -averaged poloidal flux; n=1 helical kink CHI is helical instability cascading to relaxation Tang and Boozer, PoP, May 2004 Significant OH flux savings has been achieved on HIT-II using transient CHI Understanding from CHIP code (X. Tang - LANL) Line-tied kink driven unstable on open field lines Kink drives dynamo V LOOP in closed-flux region Closed-flux modes driven unstable by J-gradient relaxation and current penetration

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J.E. Menard – MHD SFG – 5/19/2005 46 Use MST-style gun current sources to inject helical current in divertor region Current amplification up to ~ 20 Merging / reconnection (?) above threshold power Closed flux surfaces requires field, gun optimization Noninductive ST Plasma Formation: Current Injectors in Divertor (R. Fonck – U. Wisconsin) 30ms

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J.E. Menard – MHD SFG – 5/19/2005 47 Merging/Compression: plasma rings formed on or near ‘induction’ coils, then merged together Recent scheme proposed by TS-3/4 team - ‘Double Null Merging’ (DNM) - produces plasma at X-point rather than coil surface to reduce impurities Coils ECH Small Tokamak Coils ST High- ST (TS-5 Proposal - Y. Takase, Y. Ono – U. Tokyo) Magnetic reconnection heats ions creating high- plasma M/C method w/o X-point already used on START and MAST in U.K. Small Tokamak

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J.E. Menard – MHD SFG – 5/19/2005 48 MAST recently produced 1 st example of 300kA DNM plasma Plasma is dense (9 10 19 m -3 ) and hot (~0.5keV) (From A. Sykes – Culham, UK) A B C D EF MAST benefits from internal coils; NSTX will test with external coils

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J.E. Menard – MHD SFG – 5/19/2005 49 20kA tokamak formed using outboard PF coil induction HHFW antenna used as ionization source in outboard field null B Z ramp supplies loop voltage and vertical field B Z and B R evolution will be optimized to keep plasma in high V LOOP region DINA modeling 8ms 9ms 10ms 114405 R 0 Low V LOOP (Camera images – C. Bush)

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J.E. Menard – MHD SFG – 5/19/2005 50 The ST is a unique & important platform for testing MHD theory and simulation Low–A high + strong intrinsic shaping NBI drives near-Alfvénic rotation + *AE modes Unique ST features highlight MHD theory needs: 1/1 mode Non-linear evolution with flow, 2-fluid, hot particles RWM Self-consistent kinetic damping in general geometry + ELM Rotation, , and * effects + non-linear evolution NTM 2-fluid treatment for high- , general geometry + seeding *AE, EPM Self-consistent non-linear treatment of multiple *AE I P creation Dynamo, relaxation, reconnection high I P w/ closed

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J.E. Menard – MHD SFG – 5/19/2005 51 I think we all agree that… From Horizon Casino

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J.E. Menard – MHD SFG – 5/19/2005 52 Backup Material

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Fitted parameters close to theoretical values ’ adjusted to match saturated island size field curvature fixed to theory - bootstrap allowed to vary Good match to predicted drive - confirms BS/GGJ physics Field curvature stabilises 60% of bootstrap drive r reduced - island affecting resistivity?

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