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Influence of rapid rotation on high- b NSTX plasmas

Supported by. 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 New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U

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Influence of rapid rotation on high- b NSTX plasmas

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  1. Supported by 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 New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec Influence of rapid rotation on high-b NSTX plasmas J.E. Menard, for the NSTX Team With contributions from: R.E. Bell, A. Bondeson, M.S. Chu, J. Ferron, E.D. Fredrickson, D.A. Gates, A. Glasser, C. Greenfield, S.M. Kaye, L. Lao, B.P. LeBlanc, T. Luce, W. Park, S.A. Sabbagh, D. Stutman, K. Tritz, and M. Wade 45th Annual Meeting of the Division of Plasma Physics Monday, October 27, 2003 Albuquerque, New Mexico

  2. NSTX has achieved high-b and long-pulse bT 2m0p / BT02 bT = 30-35% bN= 5-6 at IP/aBT0= 5-6 Typical pulse-length = 0.3-0.4s All shots at peak WTOT fBS up to50% Pulse-length up to 1s bT = 15-20% bN= 5-6.2 at IP/aBT0 3 • High-b obtained with  7MW of tangential co-NBI • Drives toroidal flow velocities up to 40% of vAlfven • How does rapid rotation impact NSTXMHD? DPP2003 - BI1.002, J.E. Menard

  3. Rotation impacts several MHD areas • Equilibrium: Centrifugal force from rotation shifts particle density off flux surfaces • Complicates kinetic profile/transport interpretation • Rotation not typically included in equilibrium codes • NSTX beginning to use EFIT with rotation, FLOW code • Stability: Flow and flow-shear potentially stabilizing to a variety of MHD modes • At highest toroidal b, flow and flow-shear may aidsaturation of internal modes • At high poloidalb and elevated q, rotation + dissipation stabilize external modes (RWM) • Comparisons with DIII-D AT discharges DPP2003 - BI1.002, J.E. Menard

  4. Rotation effects evident in ne(R) profiles • Most easily seen in MHD-quiescent L-mode discharges Te =Te(y) Maximum ne off-axis • Single-fluid MHD force balance:J B = p + rv•v  • Near axis, J B small  R/p p/R = 2MA2 / b where MA vf / vA • NSTX total MA = 0.15-0.4 • 2 higher than typical DIII-D AT • b also 4-10 higher in NSTX • Similar p shift in DIII-D (?) ne(y=0)  0 107540 at t=330ms Te (keV) ne (m-3) 4x1019 local MA Magnetic axis DPP2003 - BI1.002, J.E. Menard

  5. MHD force balance model of density asymmetry: • Total force balance in multi-species plasma  J B = s (nsTs(y)) - smsnsWfs(y)2 (R2/2) B this equation = 0 has solution: ns(y,R) = Ns(y) exp( U(y)(R2/R02-1) ) U(y) =PW(y) / PT(y) PW(y) = smsNs(y) Wfs(y)2 R02 / 2 Centrifugal pressure PT(y) = sNs(y)Ts(y) Thermal pressure sNs(y)Zs = 0Charge neutrality • Charge neutrality  all species have same exponential form • Test consistency:can this model fit measured ne, Te, TC, WfC, nC ? • Use neoclassical WfD from TRANSP/NCLASS (  WfC ) • Treat fast ions as having Pfast = Pfast(y), Wffast = Wffast(y) • Then, compare to first EFIT reconstructions with rotation DPP2003 - BI1.002, J.E. Menard

  6. MHD model can predict density asymmetry Solid curves: MHD model ns(y,R) Dashed curves: Ns(y) density w/o rotation 107540 at t=333ms MHD model ne(y,R) can match ne data Ne(y) nD Model ne(y,R) without PW (fast) Cannot match nedata w/o fast ion PWincluded For this shot, PW (fast) 1.5PW (thermal) DPP2003 - BI1.002, J.E. Menard

  7. Density asymmetry from EFIT with rotation: p iso-surfaces clearly shift outward from flux surfaces when rotation high black – flux surfaces white – constant pressure surfaces Recall ns(y,R) = Ns(y) exp( U(y)(R2/R02-1) ) p(y,R) = P(y) exp( U(y)(R2/R02-1) ) ns(y,R) / Ns(y) should = EFIT p(y,R) / P(y) For cases studied so far, this works well For more info on NSTX EFITs w/ rotation, see contributed oral KO1.004 by S. Sabbagh Future: incorporate results into transport & MHD stability analysis 109070, 534ms DPP2003 - BI1.002, J.E. Menard

  8. Rotation impacts several MHD areas • Equilibrium: Centrifugal force from rotation shifts particle density off flux surfaces • Complicates kinetic profile/transport interpretation • Rotation not typically included in equilibrium codes • NSTX beginning to use EFIT with rotation, FLOW code • Stability: Flow and flow-shear potentially stabilizing to a variety of MHD modes • At highest toroidal b, flow and flow-shear may aidsaturation of internal modes • At high poloidal b and elevated q, rotation + dissipation stabilize external modes (RWM) • Comparisons with DIII-D AT discharges DPP2003 - BI1.002, J.E. Menard

  9. Highest b shots obtained despite large 1/1 modes 35% bT (%) 31% • Sawtooth activity rare at high b • Rotating 1/1, usually b roll-over • In highest b shots, b saturates or actually rises during 1/1 activity • 1/1 saturates or decays at high b • b 1.2-1.4  onset b • Onset bN = 4.2 - 4.5  n=1 ideal limit • These shots reach bN = 5.5 – 6 • Synergistic effects may aid high b • 1/1 mode flattens core p and J • Large fast ion diffusion or loss • H-mode onset broadens p and J • Broad p, J + rotation stabilizing • What is the role of rotation? 1.2MA,7MW 1.0MA, 5MW b=35% mode saturates Mode Bq (Gauss) b=31% mode decays Neutron Rate (1014/s) DPP2003 - BI1.002, J.E. Menard

  10. Initial state Island forms Island grows Reconnection continues Reconnection complete Core displaced Use nonlinear MHD code M3D to study 1/1 mode Nonlinear mode evolution: no rotationsawtooth-like crash W. Park PPPL B-field lines T iso-surface Density contours Hot core (a-c) is replaced by cold island (d-f) DPP2003 - BI1.002, J.E. Menard

  11. MA = 0.3 0 1 2 Time vf P Nonlinear evolution with peak rotation of MA=0.3 • Sheared-flow reduces growth rate by factor of 2-3 M3D simulations Simulated SXR signals MA = 0 0 1 Time • In experiment, the NBI power is held roughly fixed • In M3D, with a fixed momentum source rate, • the vf and pprofiles flatten inside the island, • and reconnection still occurs… DPP2003 - BI1.002, J.E. Menard

  12. Possible saturation mechanisms identified with M3D • Simulations  at least partial reconnection should occur •  saturation process will be acting on subsequent non-linear state Possible mechanisms: Saturated state with higher p in island • (1)Following reconnection, and with initial shear-flow,perturbedrandTcan spontaneously become anti-phase. • This state can saturate if phighest inside island • Mechanism is robust, not easily obtained • (2)Sufficient source rate and viscosity to maintain sheared flow with island • Robust, experimentally possible • Requires slow reconnection rate • (3) Fast particles, 2-fluid, being studied B-field lines T iso-surface Density contours • Are any of these mechanisms consistent with experiment? DPP2003 - BI1.002, J.E. Menard

  13. Saturated phase 108103 Mode growth phase Island 108103 Te flat spots t=243ms (saturated phase) t=260ms (saturated phase) Kinetic data shows higher island p unlikely Tihas minimum at island radius Carbon pstarts peaked, becomes hollow Impurity accumulation? 108103 Te flat-spots observed Before mode Mode saturated Island • Electron pressure lower in island • Bulk ion pressure lower in island • Only carbon pressure possibly higher nenot higher in island  Consider 2nd Mechanism: Favorable profiles and rotation itself slow mode growth & reconnection - enough rotation sustained to saturate mode DPP2003 - BI1.002, J.E. Menard

  14. SXR inversion aids analysis of mode evolution rs bT = 21% Island model fits data well • Perturb EFIT equilibrium helical flux with m/n = 1/1 dyh • Reconstruct total emission as function of total helical flux Z SXR Data Island Model Fit error < 6% rs = 0.43 w = 0.3 f = 15.4 kHz DPP2003 - BI1.002, J.E. Menard

  15. bT  31% island grows slowly (t1ms), saturates with rs 0.5 t=245ms t=227ms t=229ms t=230ms • Early growth: best-fit emission highest in displaced core • Later, during saturated phase, best-fit  higher emission from island • This may indicate impurity accumulation in island and/or cooling rs DPP2003 - BI1.002, J.E. Menard

  16. bT = 31% - Rotation flattens, then core recovers Rotation data  shear-flow mode saturation plausible bT  23% bT 31% NOTE: Carbon ff data is 20ms average tgrowth , 1/ff bT=23% - Rotation flattens, broadens, collapses IP (MA) PNBI/10 (MW) frot (R,t) (kHz) bT (%) 10kHz 230ms 230ms 250ms ff(0) (kHz) frot (R,t) (kHz) 14kHz Mode Bq (Gauss) Island q0 (w/o MSE) Favorable q or Wf profile slows mode growth? Enough rotation retained for later saturation? DPP2003 - BI1.002, J.E. Menard

  17. Rotation impacts several MHD areas • Equilibrium: Centrifugal force from rotation shifts particle density off flux surfaces • Complicates kinetic profile/transport interpretation • Rotation not typically included in equilibrium codes • NSTX beginning to use EFIT with rotation, FLOW code • Stability: Flow and flow-shear potentially stabilizing to a variety of MHD modes • At highest toroidal b, flow and flow-shear may aidsaturation of internal modes • At high poloidalb and elevated q, rotation + dissipation stabilize external modes (RWM) • Comparisons with DIII-D AT discharges DPP2003 - BI1.002, J.E. Menard

  18. 109070 computed conducting plates Expt. value of bN Plasma 109070 t=530ms Elevated q sustains operation above no-wall limit • Increase q the old-fashioned way: • Raise field from 0.3T to 0.5T + early H-mode • Decrease current to 0.8MA  fBS  50% • Operate with bN > 5 for Dt > tCR=0.25s • No rotation slow-down or evidence of RWM • Stabilization of RWM with rotation+dissipation demonstrated on DIII-D • Compare NSTX RWM predictions to DIII-D using MARS code DPP2003 - BI1.002, J.E. Menard

  19. NSTX DIII-D WftA (%) Similar RWM parameter regimes exist for NSTX & DIII-D Neither discharge exhibits n=1 RWM NSTX 109070: LSN, 0.8MA, 0.5T n=1 internal disruptions at bN 6 DIII-D 113850: DND, 1.2MA, 1.8T n  3 ELM-like bursts limit bN 4 NSTXDIII-D 109070, 429ms 113850, 2802ms q9575 q0 1.32.3 qmin 1.31.6 r/a(q=2) 0.770.68 WftA(r=0)15%7% WftA(q=2)4.1%3.2% li0.830.79 p(0)/p 2.2-2.72.8-2.9 NOTE: NSTX w/o MSE DPP2003 - BI1.002, J.E. Menard

  20. no-wall limit RWM stabilized for WftA(q=2)> 2% for both cases Uncertainty in form & magnitude of dissipation remains (theory & expt.) Use k||=0.2 for sound wave damping coefficient (h=0, twall = 104 tA ) (k|| 0.2used to match DIII-D, JET critical rotation data) MARS n=1 growth ratevs.bNand Wf Predict RWM critical WftA (q=2)= 2.1% for k|| = 0.2, 1.3% for k||=1 FUTURE: Compare predictions to experiments by varying Wf or q NSTX DIII-D gtWall gtWall unstable stable (i.e. at Wf=0) Both cases computed stable at experimental rotation value DPP2003 - BI1.002, J.E. Menard

  21. NSTX DIII-D k||=1 k||=1 no-wall limit no-wall limit Plasma mode stabilized at 20-30% of experimental Wf MARSn=1growth ratevs.bNand Wf • As Wf Wf(expt), marginal stability can vary with Wf, k|| • Example: k||=0.2 and Wf=Wf(expt) NSTX bN limit = 6.1 5.3,DIII-D 4.1  4.3 • Inconsistent with NSTX reaching bN =6 • May need to consider both RWM and plasma mode in AT optimization DPP2003 - BI1.002, J.E. Menard

  22. Summary • Density asymmetry result of high pCentrifugal / pThermal • Data consistent with MHD force balance model • Developing analysis tools to handle high flow velocities • 1/1 modes saturate or even decay in highest b shots • Rotation flattening observed in experiment and simulations • Consistent with at least partial reconnection during growth • Several non-linear saturation mechanisms being studied • Higher pressure in island robustly stable, but unlikely • Sustainment of shear-flow with slowed reconnection plausible • Higher q discharges operate above no-wall limit • MARS predicts rotational stabilization of RWM in NSTX • Predictions quantitatively similar to high-bN DIII-D AT • Good position to test RWM physics across devices Please visit NSTX oral (KO1) and poster (LP1) sessions on Wednesday DPP2003 - BI1.002, J.E. Menard

  23. EFIT w/ rotation important tool for high bP plasmas For diamagnetic H-mode plasmas, need EFIT w/ rotation for accurate Raxis EFIT p with rotation consistent with ne profile asymmetry: 109070 at t=470ms DRaxis = 5cm Ne(y)  p(y,R) / P(y) from EFIT For this shot, PW (fast)PW (thermal) Now working on including PW(fast) in reconstructions DPP2003 - BI1.002, J.E. Menard

  24. no-wall limit no-wall limit no-wall limit Plasma mode stability sensitive to Wf and k|| DIII-D k||=5 • k||>>1 unphysically destabilizes plasma mode for expt. Wf (y) • k||>>1 lowers growth rate when Wf=0 • g becomes independent of Wffor flat Wf • Future: compare to “kinetic damping” model in MARS, and across devices • aid understanding of dissipation k||=1 Wf(y) = Wf(q=2) DIII-D k||=1 DPP2003 - BI1.002, J.E. Menard

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