1 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Global MHD Mode Stabilization and Control for Disruption Avoidance 18 th International ST Workshop Princeton University 11/4/15 V1.4 S.A. Sabbagh 1, J.W. Berkery 1, J.M. Bialek 1, J.M. Hanson 1, C. Holcomb 2, M. Austin 3, D. Battaglia 4, R.E. Bell 4, K. Burrell 3, R. Buttery 3, N. Eidietis 3,D.A. Gates 4, S.P. Gerhardt 4, B. Grierson 4, I. Goumiri 5, G. Jackson 3, R. La Haye 3, J. King 3, E. Kolemen 4, M.J. Lanctot 2, M. Okabayashi 4, T. Osborne 3, Y.S. Park 1, C. Rowley 5, E. Strait 3 1 Department of Applied Physics, Columbia University, New York, NY, 2 Lawrence Livermore National Laboratory, Livermore, CA, 3 General, Atomics, San Diego, CA, 4 Princeton Plasma Physics Laboratory, Princeton, NJ, 5 Princeton University, Princeton, NJ

2 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Talk Outline  Prediction, stabilization, and control of global MHD instabilities – synergizing elements in NSTX-U  Kinetic resistive wall mode stabilization – unification of understanding  Plasma rotation control in NSTX-U for disruption avoidance  Active RWM control capabilities and expansion plans

3 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Disruption avoidance is a critical need for future tokamaks; NSTX-U is focusing stability research on this  The new “grand challenge” in tokamak stability research  Can be done! (JET: < 4% disruptions w/C wall, < 10% w/ITER-like wall) ITER disruption rate: < 1 - 2% (energy load, halo current); << 1% (runaways)  Strategic plan: utilize/expand stability/control research success  Disruption prediction, avoidance, and mitigation (DPAM) is multi-faceted, best addressed by a focused, (inter)national effort (multiple devices/institutions)  FESAC 2014 Strategic Planning report defined “Control of Deleterious Transient Events” highest priority (Tier 1) initiative  NSTX-U will allow focused research on disruption avoidance with quantitative measures of progress  Builds on success in MHD stability and control research

4 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Sensor/predictor (CY available) Control/Actuator (CY available) Low frequency MHD (n=1,2,3): 2003Dual-component RWM sensor control (closed loop: 2008) Low frequency MHD spectroscopy (open loop: 2005) Control of β N (closed loop: 2007) r/t RWM state-space controller observer (2010) Physics model-based RWM state-space control (2010) Real-time rotation measurement (2016)Plasma rotation control (NTV rotation control open loop: 2003) (+NBI closed loop ~ 2017) Kinetic RWM stabilization initial real-time model ( ) Safety factor control (closed loop ~ ) MHD spectroscopy (real-time) (in NSTX-U 5 Year Plan) Upgraded 3D coils (NCC) (in NSTX-U 5 Year Plan) Research in today’s presentation is part of NSTX-U’s evolving capabilities for disruption prediction/avoidance  +New Disruption Event Characterization and Forecasting code, initial results

5 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Joint NSTX / DIII-D experiments and analysis gives unified kinetic RWM physics understanding for disruption avoidance  RWM Dynamics  RWM rotation and mode growth observed  No strong NTM activity  Some weak bursting MHD in DIII-D plasma Alters RWM phase  No bursting MHD in NSTX plasma DIII-D (  N = 3.5)NSTX (  N = 4.4)  B p n=1 (G)  Bp n=1 (deg) (arb) Frequency (kHz) t (s) amplitude phase DD toroidal magnetics rotationgrowthrotationgrowth amplitude phase DD toroidal magnetics S. Sabbagh et al., DIII-D/NSTX experiments S. Sabbagh et al., APS Invited talk 2014

6 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015  Initially used for NSTX since simple critical scalar   threshold stability models did not describe RWM stability  Kinetic modification to ideal MHD growth rate  Trapped / circulating ions, trapped electrons, etc.  Energetic particle (EP) stabilization  Stability depends on  Integrated   profile: resonances in  W K (e.g. ion precession drift)  Particle collisionality, EP fraction Trapped ion component of  W K (plasma integral over energy) collisionality   profile (enters through ExB frequency) Hu and Betti, Phys. Rev. Lett 93 (2004) Sontag, et al., Nucl. Fusion 47 (2007) 1005 precession driftbounce Modification of Ideal Stability by Kinetic theory (MISK code) is used to determine proximity of plasmas to stability boundary J. Berkery et al., PRL 104, (2010) S. Sabbagh, et al., NF 50, (2010) J. Berkery et al., PRL 106, (2011) J. Berkery et al., PoP 21, (2014) J. Berkery et al., PoP 21, (2014) (benchmarking paper) Some NSTX / MISK analysis references

7 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Evolution of plasma rotation profile leads to linear kinetic RWM instability as disruption is approached DIII-D (minor disruption) NSTX (major disruption) MISK unstable stable unstable stable increasing time  wall S. Sabbagh et al., APS Invited talk 2014 Also see J.W. Berkery et al., ISTW 2015 poster for NSTX

8 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Kinetic RWM stability evaluated for DIII-D and NSTX plasmas, reproduces experiments over wide rotation range  Summary of results  Plasmas free of other MHD modes can reach or exceed linear kinetic RWM marginal stability  Bursting MHD modes can lead to non-linear destabilization before linear stability limits are reached  Extrapolations of DIII-D plasmas to different V  show marginal stability is bounded by 1.6 < q min < 2.8 Kinetic RWM stability analysis for experiments (MISK) Plasma rotation [krad/s] (  N = 0.5) Normalized growth rate (  w ) major disruption minor disruption DIII-D NSTX stable unstable extrapolation q min = 2.8 q min = 1.6 “weak stability” region  Reduced models of kinetic RWM stability now being investigated to support real- time disruption avoidance (e.g. by rotation profile control) (J.W. Berkery et al., ISTW 2015) J.W. Berkery, J.M. Hanson, S.A. Sabbagh (Columbia U.)

9 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Bounce resonance stabilization dominates for DIII-D vs. precession drift resonance for NSTX at similar, high rotation DIII-D experimental rotation profileNSTX experimental rotation profile |δW K | for trapped resonant ions vs. scaled experimental rotation (MISK) s stable plasma s stable plasma precession resonance bounce / circulating resonance precession resonance bounce / circulating resonance DIII-DNSTX

10 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Increased RWM stability measured in DIII-D plasmas as q min is reduced is consistent with kinetic RWM theory |δW K | for trapped resonant ions vs. scaled experimental rotation (MISK) Measured plasma response to 20 Hz, n = 1 field vs q min n = 1 |  B p | (G/kA) q min DIII-D experimental rotation profile precession drift resonance bounce / circulating resonance DIII-D (q min = 1.2) DIII-D (q min = 1.6) DIII-D (q min = 2.8)  Bounce resonance dominates precession drift resonance for all q min examined at the experimental rotation less stable

11 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Rotation feedback controller designed for NSTX-U using non-resonant NTV and NBI used as actuators 3D coil current and NBI power (actuators) t (s) 3D Coil Current (kA) feedback on NBI power (MW) NN NBI, -NTV torque density (N/m 2 ) Plasma rotation (rad/s) -NTV torque desired   t1t1 t4t4 4 2 NBI torque t 1 = 0.00  m t 2 = 0.68  m t 3 = 1.99  m t 4 = 4.78  m Rotation evolution and NBI and NTV torque profiles I. Goumiri (Princeton student), S.A. Sabbagh (Columbia U.), C. Rowley (P.U.), D.A. Gates, S.P. Gerhardt (PPPL)  Momentum force balance –    decomposed into Bessel function states  NTV torque: (non-linear)

12 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 NTV physics studies for rotation control: measured NTV torque density profiles quantitatively compare well to theory  T NTV (theory) scaled to match peak value of measured -dL/dt  Scale factor ((dL/dt)/T NTV ) = 1.7 and 0.6 for cases shown above – O(1) agreement n = 2 coil configuration Experimental -dL/dt NN NSTX NTVTOK x1.7 n = 3 coil configuration Experimental -dL/dt NTVTOK NN NSTX x0.6 S. Sabbagh et al., IAEA FEC 2014 (EX/1-4)

13 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Rotation feedback controller designed for NSTX-U can evolve plasma rotation profile toward global mode stability I. Goumiri (Princeton student), S.A. Sabbagh (Columbia U.), C. Rowley (P.U.), D.A. Gates, S.P. Gerhardt (PPPL) Recall: NSTX (major disruption) MISK unstable stable  wall Plasma rotation (kHz) NN NSTX-U (6 NBI sources and n = 3 NTV) marginally stable marginally stable  Steady-state reached in ~ 3  m

14 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 With NCC coil upgrade, rotation feedback controller can reach desired rotation profile faster, with greater fidelity I. Goumiri (Princeton student), S.A. Sabbagh (Columbia U.), C. Rowley (P.U.), D.A. Gates, S.P. Gerhardt (PPPL) Plasma rotation (kHz) NN marginally stable  NSTX-U   control with  6 NBI sources  NTV possible from planned NCC upgrade  Better performance  Faster to target t ~ 0.5  m  Matches target   better Planned NCC upgrade

15 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Disruption Event Characterization And Forecasting Code (DECAF) yielding initial results (pressure peaking example) PRP warnings PRP VDEIPRSCL Detected at: s0.4380s0.4522s0.4732s NSTX Disruption J.W. Berkery, S.A. Sabbagh, Y.S. Park (Columbia U.)  35 physical disruption chain events identified; 12 technical/human error events  10 physical events are presently defined in code with quantitative warning points  Code written to be easily expandable and portable to other tokamaks  This example: Pressure peaking (PRP) disruption event chain identified by code before disruption 1.(PRP) Pressure peaking warnings identified first 2.(VDE) VDE condition subsequently found 19 ms after last PRP warning 3.(IPR) Plasma current request not met 4.(SCL) Shape control warning issued Event chain and the NSTX-U Disruption PAM Working Group

16 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Active RWM control: dual B r + B p sensor feedback gain and phase scans produce significantly reduced n = 1 field  Favorable B p + B r feedback (FB) settings found (low l i plasmas)  Time-evolved theory simulation of B r +B p feedback follows experiment  t (s) (model) Radial field n = 1 (G) 180 deg FB phase 90 deg FB phase 0 deg FB phase Vacuum error field + RFA Simulation of B r + B p control (VALEN) Feedback on B r Gain = No B r feedback t (s) NN lili B r Gain = 1.50 B r n = 1 (G) NN lili B r gain scan B r FB phase scan S. Sabbagh et al., Nucl. Fusion 53 (2013)

17 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015  Controller model can compensate for wall currents  Includes plasma mode-induced current  Potential to allow more flexible control coil positioning  May allow control coils to be moved further from plasma, and be shielded (e.g. for ITER)  Straightforward inclusion of multiple modes (with n = 1, or n > 1) in feedback Model-based RWM state space controller including 3D model of plasma and wall currents used at high  N Balancing transformation ~ states Full 3-D model … RWM eigenfunction (2 phases, 2 states) State reduction (< 20 states) Katsuro-Hopkins, et al., NF 47 (2007) 1157 Controller reproduction of n = 1 field in NSTX Sensor Difference (G) t (s) Sensor Difference (G) Measurement Controller (observer) 5 states used 10 states used (only wall states used)

18 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 NSTX RWM state space controller sustains high  N, low l i plasma – available for NSTX-U with independent coil control RWM state space feedback (12 states)  n = 1 applied field suppression  Suppressed disruption due to n = 1 field  Feedback phase scan  Best feedback phase produced long pulse,  N = 6.4,  N /l i = 13 NSTX Experiments I p (MA) (A) S. Sabbagh et al., Nucl. Fusion 53 (2013)  Run time has been allocated for continued experiments on NSTX-U in 2016

19 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 NCC 2x12 with favorable sensors, optimal gain NCC 2x6 odd parity, with favorable sensors  Full NCC coil set allows control close to ideal wall limit  NCC 2x6 odd parity coils: active control to  N /  N no-wall = 1.58  NCC 2x12 coils, optimal sensors: active control to  N /  N no-wall = 1.67 Active RWM control design study for proposed NSTX-U 3D coil upgrade (NCC coils) shows superior capability NCC (plasma facing side)

20 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015  Physics Understanding  Unification of DIII-D / NSTX experiments and analysis gives improved RWM understanding for disruption avoidance  Linear kinetic RWM marginal stability limits can describe disruptive limits in plasmas free of other MHD modes  Complementarity found: at similar high rotation, kinetic RWM stabilization physics is dominated by bounce orbit resonance in DIII-D, and by ion precession drift resonance in NSTX  New Disruption Event Characterization and Forecasting code (initial results)  Stability Control  Rotation profile control has potential to steer away from unstable profiles  Model-based RWM state-space controller, and dual field component PID control available; development to further improve performance  Further improvements to rotation profile, active mode control possible with planned NCC 3D coil upgrade Global MHD mode stabilization understanding and control will synergize in NSTX-U for disruption avoidance

21 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Supporting slides follow

22 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Disruption event chain characterization capability started for NSTX-U as next step in disruption avoidance plan  Approach to disruption prevention  Identify disruption event chains and elements  Predict events in disruption chains Attack events at several places Give priority to early events  Provide cues to avoidance system to break the chain  Provide cue to mitigation system if avoidance deemed untenable t S.A. Sabbagh (for Disruption Prediction panel) Disruption prediction framework from upcoming DOE “Transient Events” report

23 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 JET disruption event characterization provides framework to follow for understanding / quantifying DPAM progress P.C. de Vries et al., Nucl. Fusion 51 (2011) JET disruption event chainsRelated disruption event statistics  JET disruption event chain analysis performed by hand, desire to automate  General code written (DECAF) to address the first step – test runs started using NSTX data

24 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 (Although thresholds are not at all optimized yet) what did DECAF show when applied to this 44 shot NSTX database?  These events found for all shots  DIS: Disruption occurred  RWM: RWM event warning Note: this module is not smart enough yet to distinguish RWM from locked TM  VDE: VDE warning (42 shots)  IPR: Plasma current request not met  LOQ: Low edge q warning  Very simple RWM event criteria  RWM B P n=1 lower sensor amplitude used  Simple criterion + no threshold optimization at all  “false positive” rate is high; adjust criteria to reduce it  Code already sees common disruption event chains  (event)  VDE  SCL  IPR occurs in 52% of the shots  “false positives” on VDE affecting this % J.W. Berkery, S.A. Sabbagh (Columbia U.) “RWM event” warning timing (simple criterion, no optimization) Within 100 ms of DIS (64%) Before 100 ms of DIS (36%) VDESCLIPR Common event chain (event)

25 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 Disruption Characterization Code now yielding initial results: disruption event chains, with related quantitative warnings (2) J.W. Berkery, S.A. Sabbagh, Y.S. Park  This example: Greenwald limit warning during I p rampdown 1.(GWL) Greenwald limit warning issued 2.(VDE) VDE condition then found 0.6 ms after GWL warning 3.(IPR) Plasma current request not met GWL warnings NSTX GWLVDEIPR Detected at: s0.7448s0.7502s Disruption during I p ramp-down Event chain

26 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015  Improved agreement with sufficient number of states (wall detail) Open-loop comparisons between measurements and RWM state space controller show importance of states and model A) Effect of Number of States Used  B p RWM Sensor Differences (G) t (s) t (s)  B p 180  B p t (s) t (s) States B) Effect of 3D Model Used No NBI Port With NBI Port 2 States RWM  3D detail of model important to improve agreement Measurement Controller (observer)

27 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 When T i is included in NTV rotation controller model, 3D field current and NBI power can compensate for T i variations t (s) 3D coil current and NBI power (actuators) NN NBI, NTV torque density (N/m 2 ) Plasma rotation (rad/s) NTV torque 10 4 desired   t1t1 t3t3 NBI torque t 1 = 0.59s t 2 = 0.69s t 3 = 0.79s  NTV torque profile model for feedback dependent on ion temperature Rotation evolution and NBI and NTV torque profiles K1 = 0, K2 = 2.5 3D Coil Current (kA) T i (keV) t (s) NBI power (MW) t2t2 t1t1 t3t3 t2t2 t1t1 t2t2 t3t t1t1 t3t3 t2t2

28 ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance ISTW 2015: Global MHD Mode Stabilization and Control for Disruption Avoidance (S.A. Sabbagh, et al.) Nov 4 th, 2015 NSTX-U: RWM active control capability increases as proposed 3D coils upgrade (NCC coils) are added  Partial 1x12 NCC coil set significantly enhances control  Present RWM coils: active control to  N /  N no-wall = 1.25  NCC 1x12 coils: active control to  N /  N no-wall = 1.52 Existing RWM coils NCC upper (1x12) (plasma facing side) Using present midplane RWM coilsPartial NCC 1x12 (upper), favorable sensors