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Overview of recent and current research on the TCV tokamak

Overview of recent and current research on the TCV tokamak. S. Coda. for the TCV team*. *including collaborating institutions:. S. Coda, 24 th IAEA Fusion Energy Conference, OV/4-4, San Diego, 9 October 2012. Outline. TCV parameters and capabilities Scientific mission of the TCV program

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Overview of recent and current research on the TCV tokamak

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  1. Overview of recent and current researchon the TCV tokamak S. Coda for the TCV team* *including collaborating institutions: S. Coda, 24th IAEA Fusion Energy Conference, OV/4-4, San Diego, 9 October 2012

  2. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t simulations • Integrated MHD instability control • Summary and outlook

  3. TCV 4.5 MW ECRH power, 7 steerable launchers R = 0.88 m, a = 0.25 m Ip < 1 MA, BT < 1.54 T k < 2.8, -0.6 < d < 0.9 ×4 ×2

  4. TCV mission • Study plasma and fusion science for ITER and next step • flexibility and proven ability to test new theories quickly • Develop and test techniques for reactor operation • strong emphasis on real-time control, particularly with event triggers

  5. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t simulations • Integrated MHD instability control • Summary and outlook

  6. Local ECRH in pedestal influences ELMs As power deposition moves towards plasma boundary, ELMs become smaller and more frequent (good!)… …even though less poweris absorbed  simple scaling of type-I ELMs(frequency increases with power)is incomplete:power deposition locationmust play a role too X3 r=0.97 r=0.93 X2 r=0.85 Resonances J.X. Rossel et al, NF 52, 032004 (2012)

  7. Pacing: r/t ECRH steadies ELM period • ELM detected  power cut for a set time  power restored to trigger next ELM • ELM period still governed by energy input(longer cut  less energy  longer period), but r/t control regularizes it standard deviation of period cw heating pacing

  8. ECRH triggers individual ELMsindependently of preceding ones For a given trigger sequence,the resulting ELM sequenceis highly reproducible see also B.P. Duval et al, EX/1-2(poster session P2, now)

  9. Shaping influences ELMs: smaller,more frequent at negative triangularity A. Pochelon et al, to be published in Plasma and Fusion Research (2012)

  10. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t simulations • Integrated MHD instability control • Summary and outlook

  11. The snowflake divertor: an advanced configuration proven to lessen wall loads • Merging of 2 X-points Bq=0  4 strike points • Benefits: doubling of strike points + flux expansion • On TCV, average ELM energy release reduced too s = (distance between X-points)  (minor radius)

  12. Extra snowflake strike points are activated well before X-points coalesce Infrared data Langmuir probe ion saturation current during ELM cycle Lower strike point activated for s<1.2 Lower strike point activated for s<1.2 in H-mode,for s<0.6 in L-mode s=1.6 s=1.2 s=0.8 s=0.4 Data qualitatively consistent with predictionof convection-dominated flux for bp > 1 t-tELM (ms) t-tELM (ms) t-tELM (ms) t-tELM (ms) see also W.A.J. Vijvers et al, EX/P5-22 (Thursday morning) see D. Ryutov et al, TH/P4-18 (Wednesday afternoon)

  13. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t simulations • Integrated MHD instability control • Summary and outlook

  14. L-mode confinement degradation:is it due to power deposition profile? PECRH POH Pa Vary ECRH deposition widthfrom peakedto Ohmic-like

  15. L-mode confinement degradationis not due to power deposition profile all profile widths: standard L-mode scaling further degradation with off-axis heating

  16. L-mode confinement is degraded further as power is deposited outside q=1 teE /tL-mode q=1 see also N. Kirneva et al,EX/P3-05 (Wednesday morning) N. Kirneva et al, PPCF 54, 015011 (2012)

  17. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t simulations • Integrated MHD instability control • Summary and outlook

  18. Adding live simulation to measurements: a new paradigm for r/t control • Use physics knowledge when measurements are inadequate (e.g. for q profile, bootstrap current) • State observer methodology incorporatesnew observers and new models seamlessly • Pilot TCV simulinkimplementation: raptor • Control of Te0 (measured)and li (simulated) 1 ms simulation cycle, ≪ current diffusion time see also F. Felici et al,EX/P3-12 (Wednesday morning) F. Felici et al, NF 51, 083052 (2011)

  19. Reactor economics: current profile control by Ohmic transformer in ramp-uplessens power demands later • Current profile best manipulated at low current (short skin time, less power needed) • Successful nonlinear control of li on TCV General formalism for optimization of tokamak pulse trajectories developed in parallel using offline version of raptor see alsoJ.A. Romero et al,EX/P4-35(Wednesday afternoon) F. Felici et al, PPCF 54, 025002 (2012) J.A. Romero et al, NF 52, 023019 (2012)

  20. Outline • TCV parameters and capabilities • Scientific mission of the TCV program • TCV science • ELM control by ECRH and by plasma shaping • Physics of the snowflake divertor • New insights into energy confinement • Pulse optimization by r/t control and r/t modeling • Integrated MHD instability control • Summary and outlook

  21. Sawtooth pacing by ECRH:complete control of individual crash times Crash occurs when stabilizing q=1 power is removed Pacing also achieved through destabilization (ECRH inside q=1) or locking to modulation frequency M. Lauret et al, NF 52, 062002 (2012) T.P. Goodman et al, PRL 106, 245002 (2012)

  22. Failsafe NTM prevention: sawtooth pacing+ preëmptive low-power ECRH on island + backup power for NTM stabilization • Long sawteeth cause large seed islands control them by pacing • Preëmptive ECRH only at knownsawtooth crash time: economical way to reduce seed island size • High-power ECRH stabilizes NTM directly if needed 320 kW:NTM-free shot 200 kW not enoughfor prevention see also B.P. Duval et al, EX/1-2(poster session P2, now) F. Felici et al, NF 52, 074001 (2012)

  23. Summary • ELM mitigation by local ECRH in pedestaland by shaping • Studies of edge physics at snowflake strike pointsfor varying X-point separation • Basic investigation of L-mode confinement • Demonstration of expanded r/t control schemeincluding live simulation • Pulse optimization by Ohmic transformer control • Deployment of integrated MHD(sawtooth + NTM) control

  24. Outlook: major upgradesand research opportunities • TCV science is built on unique versatilityin shaping and heating • Versatility to be strengthenedand operational domain to be expanded by MW-level NBI heating and additional X3 ECRH • The TCV program is flexible and • can quickly test new ideas • welcomes worldwide collaborators willing to work on TCV

  25. CRPP contributions • TCV • EX/1-2: B.P. Duval, “Real time control on TCV”, P2 poster session, Tue pm • EX/P3-05: N. Kirneva, “Confinement with ECRH”, Wed am • EX/P3-12: F. Felici, “Real-time model-based control”, Wed am • EX/P4-32: E. Lazzaro, “Triggerless onset and effect of rotation on NTMs”, Wed pm • EX/P4-35: J.A. Romero, “Current profile control using the Ohmic heating coil”, Wed pm • EX/P5-22: W.A.J. Vijvers, “Snowflake divertor in L- and H-mode”, Thu am • EX/P6-08: T.P. Goodman, “ECRH absorption measurement for real-time polarization optimization and studies of quasilinear effects”, Thu pm • Fusion technology • ITR/2-5: P. Bruzzone, “Test results of ITER conductors in the SULTAN facility”, Wed pm • FTP/4-5Ra: J. Fikar, “Optimization of nanostructuredferritic steel fabrication”, Fri am • FTP/P7-11: M. Battabyal, “Development of W based materials for fusion reactors”, Fri am • DIII-D • EX/P4-09: H. Reimerdes, “Rotation braking from test blanket module in ITER”, Wed pm • Basic plasma physics • EX/P6-28: A. Fasoli, “Turbulence and fast ions in magnetized toroidal plasmas”, Thu pm • Theory • TH/P4-14: P. Ricci, “Global validated simulation of edge plasma turbulence”, Wed pm • TH/7-1: W. Cooper, “Bifurcated helical core equilibrium states in tokamaks”, Fri am

  26. ELM frequency and sizesuccessfully r/t controlled by ECRH simply by varying the duration of the power cut based on a measurement of the ELM frequency see also B.P. Duval et al, EX/1-2(poster session P2, now)

  27. Extra snowflake strike points are activated well before X-points coalesce • Inverted quasi-bolometric tomography, at ELM crash s=0.8 s=0.4 s=1.2

  28. Measuring poloidal rotation:a new, more sensitive, indirect method • Incompressible flows: vf,HFS – vf,LFS≈ 4qvq • 4q≫ 1  toroidal speed asymmetry amplifies measurement ofpoloidal speed A. Bortolon et al, submitted to NF (2012)

  29. Poloidal rotation is neoclassical in TCV

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