1 / 64

RFX/RFP mode control issues

RFX/RFP mode control issues. Piero Martin & Sergio Ortolani Consorzio RFX Associazione Euratom-ENEA sulla fusione Padova, Italy Presented by P. Martin at the 2003 workshop on “active control of MHD stability: extension to the burning plasma regime” University of Texas-Austin

gavan
Download Presentation

RFX/RFP mode control issues

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. RFX/RFP mode control issues Piero Martin & Sergio Ortolani Consorzio RFX Associazione Euratom-ENEA sulla fusione Padova, Italy Presented by P. Martin at the 2003 workshop on “active control of MHD stability: extension to the burning plasma regime” University of Texas-Austin Nov. 3-5, 2003

  2. CONTRIBUTORS • L. Marrelli, G. Spizzo, P. Franz, P. Piovesan, I. Predebon, T.Bolzonella, S.Cappello, A. Cravotta, D.F. Escande, L.Frassinetti, S. Martini, R. Paccagnella, D.Terranova and the RFX team And fruitful collaborations with the • MST team: B.E. Chapman, D. Craig, S.C. Prager, J.S. Sarff • EXTRAP T2R team: P. Brunsell, J.-A. Malmberg, J. Drake • TPE-RX team: Y. Yagi, H. Koguchi, Y. Hirano

  3. Hopefully this is the last workshop… • …. without RFX ! • …. RFX reconstruction is in the final phase and first plasmas are expected in Sept. 2004 • The new RFX will be a “state of the art” MHD MODE CONTROL FACILITY: • 192 ACTIVE COILS, INDEPENDENTLY DRIVEN, COVERING THE WHOLE PLASMA SURFACE

  4. Outline of the talk • Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  5. Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  6. The new RFX device Main new components: • 192 saddle coils, covering the whole plasma boundary, each independently powered and feedback controlled • a smoother and thinner shell • the first wall with higher power handling capabilities • an in-vessel system of magnetic and electrostatic probes • the toroidal field power supply R /a = 2.0 / 0.46 (m) - I up to 2 MA

  7. Overview of the magnetic boundary Active saddle coils vessel shell • - 4 coilsin the poloidal direction: 90° spaced • 48 coils in the toroidal direction: 7.5° spaced

  8. Saddle coil performance • each independently powered • 24 kAt: 400 A x 60 turns • Wide spectrum of Fourier components can be produced: • m=1,2 • n ≤ 24 • DC < f < 100 Hz • Significant amplitude available. For example: edge br for (1,8) mode: • 20 mT@10 Hz • 1.3 mT @100 Hz

  9. The new RFX shell • 3 mm Cu layer • 50 ms time constant (450 ms before) • High reduction of gap field error • 1 overlappedpoloidalgap • 1 toroidal gap on highfield side.

  10. Integrated System of the Internal Sensors (ISIS) • 97 Electrostatic (Langmuir) probes • 139 Magnetic pick up probes • 8 Calorimetric probes Langmuir probe Magnetic probe

  11. Test of RFX mode control equipment in T2R 16 coils Partial coverage • Some RFX digital controllers have been moved to Stockholm to be tested in an “intelligent shell” experiment, which will be done in the EXTRAP T2R device as a joint T2R-RFX collaboration. • Preliminary results with analog controllers developed by KTH positive! • MORE IN JIM DRAKE’S TALK WEDNESDAY!

  12. Outline of the talk • Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  13. What shall we use the new RFX for ? • To explore the RFP physics and to optimize the RFP confinement performance in a steady fashion in the MA current range • To contribute to the worldwide program on MHD modes control in fusion devices

  14. What do we use the new RFX for ? • To explore the RFP physics and to optimize the RFP confinement performance in a steady fashion in the MA current range • Control of MHD modes: • m=1 “dynamo” modes (resonant inside the Bt reversal surface) • m=0 non-linearly generated and/or linearly unstable The standard RFP has many of these modes with 1% B amplitude simultaneously present, and they spoil confinement! • RWM when the shell is resistive (reactor relevance)

  15. The modes we have to deal with • m=0 • various n: resonant at the Bt reversal surface • m=1 • |n| ≥ 2R/a, resonant inside the Bt reversal surface (resistive kink, “dynamo modes”) • |n| ≤ 2R/a,internally non resonant from above (RWM, with the same helicity as the “dynamo” modes and the same handedness as the core B) • |n| ≤ R/a,externally non resonant (RWM, with opposite helicity)

  16. The RFP dynamo issue • The electrical currents flowing in a RFP can not be directly driven by the inductive electric field Eo • ….but RFP plasmas last for times much longer than the resistive diffusion time ! (actually, as long as Eo is applied)

  17. The RFP dynamo: E + vxB = hJ • An additional electric field, besides that externally applied, is necessary to sustain and amplify the toroidal magnetic flux. • A Lorentz contribution vxB is necessary, which implies the existence of a self-organized velocity field in the plasma. • The origin of this contribution is the classical RFP dynamo problem

  18. Turbulent dynamo: remarkable self-organization • A wide experimental and numerical database supports the MHD turbulent dynamo theory: the dynamo electric field is produced by the coherent (and non-linear) interaction of a large number of MHD modes: Multiple Helicity (MH) dynamo

  19. The standard Multiple Helicity (MH) RFP … and severe plasma-wall interaction if the modes lock in phase and to the wall ! • m=1 “dynamo” modes (resonant inside the Bt reversal surface) • m=0 non-linearly generated and/or linearly unstable Magnetic stochasticity allover the plasma !

  20. The strategy towards dynamo modes • Keep them rotating in the lab frame • Reduces amplitude br • Optimizes the basic standard target plasma • Make their amplitude lower • …but you must provide dynamo electric field from outside • Run the plasma in a regime where resort to dynamo is reduced • Work in a regime where their spatial spectrum is monochromatic, i.e. dynamo is driven only by ONE INDIVIDUAL SATURATED MODE ALL THESE TOPICS MIGHT BE INFLUENCED BY ACTIVE CONTROL !

  21. Outline of the talk • Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  22. Mode dynamics in RFPs • Previous experimental evidence in several different devices shows that the evolution of MHD modes, including the dynamo modes, depends on the magnetic boundary, and in particular on the shell: • thickness • proximity • geometry

  23. The RFP synopsis

  24. TPE-RX spontaneous mode rotation b1/a = 1.08 thin shell, b2/a= 1.16 thick shell tshell =10 mstshell =330 ms

  25. Spontaneous Rotation in EXTRAP T2R RWM’s RWM’s • Tearing modes rotate From Malmberg Brunsell PoP 2002

  26. MST modes spontaneous rotation • ….listen Brett Chapman’s invited talk !

  27. Conclusions on mode rotations • Mode rotation is beneficial and depends on magnetic boundary • Modes were locked to the wall in the old RFX and this lead to a serious deterioration of performance • Slow rotation of modes was actively driven in RFX ( Bartiromo et al, PRL 99) • Dynamo modes are spontaneously rotating in RFP devices with boundary conditions similar to the new RFX. • There is a reasonable basis to hope for spontaneous mode rotation in the new RFX (even if a threshold in current might exist)

  28. Outline of the talk • Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  29. Magnetic chaos is not intrinsic to RFP DYNAMO CAN BE PRODUCED BY A SINGLE MHD MODE

  30. The Single Helicity (SH) dynamo • a theoretically predicted state with a unique m = 1 saturated resistive kink (a pure helix wound on a torus), • Stationary LAMINAR dynamo mechanism with good helical flux surfaces Escande et al., PRL 85 (2000)

  31. Magnetic order with SH dynamo Good magnetic flux surfaces in SH Overlapping of many modes ! SH Turbulent (MH)

  32. Helical states in the experiment • Quasi Single Helicity (QSH) spectra have been observed in all RFP devices, under a variety of boundary conditions (Martin, NF 2003). • The mode spectrum is dominated by one geometrical helicity • The other modes have still non-zero amplitude RFX MST TPE-RX T2R

  33. Stationary Quasi-Single Helicity • Stationary QSH spectra have been observed in the RFX device • with a helical coherent structure emerging from magnetic chaos in the plasma core. Toroidal mode number n spectrum vs. time RFX pulse length

  34. Flow velocities measurements in QSH plasmas Plasma flow velocity fluctuations measured in MST with Doppler spectroscopy (Den Hartog et al., Phys Plasmas 99) • In QSH not only the spectrum of magnetic fluctuation spectra become narrower in comparison with MH, but also that of flow velocity fluctuations Remember: Work due to D. Craig, L. Marrelli, P. Piovesan in MST

  35. Magnetic and Flow velocity fluctuations toroidal spectra QSH MH QSH MH

  36. Dynamo electric field in QSH • Dynamo in QSH becomes more concentrated in one mode than in standard MHD plasmas! QSH MH

  37. MH vs. QSH vs. SH

  38. QSH and mode wall locking • The access to QSH regime is beneficial for the problem of modes wall locking. • The dominant (big) mode might be more prone to lock to the wall (see Brett Chapman’s talk), but… • Non-linear interaction between modes decreases • The “strength” of mode locking decreases • Easier rotation for secondary modes

  39. Spontaneous mode rotation in RFX during QSH Dominant and Rotating Mode amplitude Phase of Rotating Mode From Bolzonella,Terranova, PPCF 2002 This is consistent with theoretical calculations (Guo-Chu, Fitzpartick,Chapman), which predict that modes rotate more easily if they are smaller

  40. PWI in QSH is milder anyway ! • Vertical displacement of the plasma column in RFX QSH MH • Edge fluctuating magnetic field Toroidal angle Toroidal angle

  41. Favorable conditions for QSH active control • There are already plasma regimes where monochromatic spectra are more easily obtained spontaneously • At higher plasma current • With shallower reversal • We can also “select” the toroidal mode number n we wish to be the dominant one.

  42. Mode selection • Note that the pre-programming the magnetic equilibrium allows to select efficiently the mode that will dominate the spectrum!

  43. Shallow reversal, m=0 modes and QSH • Shallow reversal brings outwards the reversal surface, where q=0. • Narrower stochastic region produced by m =0 when the reversal surface is closer to the plasma edge. • This provides a smoother plasma boundary, which helps the onset of QSH • In the new RFX m=0 modes are not any more LINEARLY unstable, as they were in the OLD device. • Positive feedback, since in QSH non-linear generation of m=0 modes is strongly reduced.

  44. Numerical studies on active control: successful drive and sustainment of m=1 n=7 SH state starting from MH conditions • Low dissipation conditions • Thin shell • Simoultaneous active control of RWMs ! t Remember we can apply with the saddle coils up to ~20 mT on a single m=1 mode Paccagnella, MHD workshop 2002

  45. Conclusions on Single Helicity • There is enough theoretical understanding and experimental evidence which support the idea that this regime might lead to significant improvement of RFP performance • We know how to produce a target plasma, which more easily could achieve a QSH spectrum. • From an active control point of view, QSH is a robust state: • One big mode, well identified, selectable in advance • RFX has more than enough power to deal with QSH

  46. Outline of the talk • Status of the RFX reconstruction • RFP mode control issues • Mode rotation • The monochromatic dynamo • Suppression of dynamo modes • RWMs • RFX operational scenarios

  47. Dynamo modes active reduction • Pulsed Poloidal Current Drive (PPCD): • the induction of a poloidal current at the plasma edge causes a dramatic reduction of the magnetic turbulence (MST + RFX PRLs) and STRONG PLASMA HEATING • ROBUST TECHNIQUE (recently performed in T2R at high aspect ratio-many modes to suppress!-Cecconello, PPCF 2003) It is TRANSIENT, but in RFX a quasi-stationary version has been implemented

  48. Oscillating Poloidal Current Drive (OPCD) • Periodic (oscillating) applied inductive variations of the poloidal electric field allows to extend the PPCD benefits in a stationary fashion stationary average improvement of confinement obtained with OPCD in RFX (Bolzonella et al., PRL 2001)

  49. PPCD action strongly affects MHD in the RFP • Though transient (but quasi stationary version is feasible), PPCD is an efficient tool to interact actively with MHD modes in the RFP. Why might be useful for future operation in the new RFX ? • “per se”: the new RFX coils system allow optimized, high power, quasi stationary PCD. This is a technique for improving confinement. • It can set-up an improved collisionless target plasma on which to work with feedback • Record reduction of magnetic stochasticity • Change the properties of broadband magnetic turbulence

  50. Active control issue: PPCD triggers QSH spectra • Evolution of m=1 modes in MST following the application of PPCD

More Related