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Global Stability Issues for a Next Step Burning Plasma Experiment

Global Stability Issues for a Next Step Burning Plasma Experiment. S. C. Jardin with input from C.Kessel, J.Manickam, D.Meade, P.Rutherford. UFA Burning Plasma Workshop Austin, Texas December 11, 2000. Workshop charge boils down to two questions in each area:.

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Global Stability Issues for a Next Step Burning Plasma Experiment

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  1. Global Stability Issues for a Next Step Burning Plasma Experiment S. C. Jardin with input from C.Kessel, J.Manickam, D.Meade, P.Rutherford UFA Burning Plasma Workshop Austin, Texas December 11, 2000

  2. Workshop charge boils down to two questions in each area: • Are we ready to design a burning plasma experiment with confidence that it will succeed ? • What will we learn from it if we do build it? Note the trap we can fall into if the answer to either of these is too positive: the key is the right balance

  3. Let us consider FIRE, as it is being proposed as a next step burning plasma experiment • A major step in the study of alpha-heating dominated plasmas, and in simultaneous (*, *) values • Provides critical data point in a new parameter regime for benchmarking of advanced MHD+-particle simulation codes • Will demonstrate self-organization in core and edge in a way that cannot be totally predicted 100 4 AIRES designs 3 FIRE B R5/4 2 JET, JET-U 1 10 10 100 0 I A (MA)

  4. FIRE operating modes IP(MA) BT T(s) N fBS Standard operating mode (LF) 6.5 10 21 2.7 0.3 High-field (shorter pulse mode) 7.7 12 12 1.9 0.2 -------------------------------------------------------------------------------------------- Advanced Tokamak 1st stability 5.6 9 30 2.9 0.5 Reversed Shear Wall stabilized 4.5 6.7 60 4.5 0.8

  5. Guidelines for Predicting Plasma Performance Confinement (Elmy H-mode) ITER98(y,2): E = 0.144 I0.93 R1.39 a0.58 n200.41 B0.15 Ai0.19 0.78 P heat-0.69 H(y,2) Density Limit: n20 < 0.75 nGW = 0.75 IP/a2 H-Mode Power Threshold: Pth > (2.84/Ai) n200.58 B0.82 R a0.81

  6. High Field: H = 1.0 (12 T, 7.7 MA) Low Field: H = 1.2 (10 T, 6.5 MA) total total a-heating a-heating ICRF ICRF Time (sec) Time (sec) Q > 10 for 9 sec Q > 10 for 18 sec

  7. S = (1+2)/2  = a/R

  8. High Field li/2 q95 Low Field li/2 q95

  9. Physics Question: Role of the m=1 mode • Ideal MHD theory predicts m=1,n=1 mode unstable at design  for q0 < 1 • High-n ballooning modes also predicted to be unstable in the vicinity of and interior to the q=1 surface • Proper physics description must take into account: • energetic particle drive, • kinetic stabilization, • 2-fluid effects, and • non-linear saturation mechanism • This should be [and is] one of the major thrusts of the 3D macroscopic simulations communities • FIRE will provide critical data point for code benchmarking and hence for extrapolations

  10. Low Field: 10 T, 6.5 MA Balloon and Mercier stability edge q = 3 q = 2 surface number q = 1 PEST unstable eigenfunction at t=12.5 sec axis time (sec)

  11. High Field: 12 T, 7.7 MA Balloon and Mercier stability q = 3 edge q = 2 surface number q = 1 PEST unstable eigenfunction at t=12.5 sec axis time (sec)

  12. Comparison of unstable Eigenvalues Low Field g2 = -.0083 High Field g2 = -.0039

  13. FIRE nominal operating point is stable to kink modes. Relation of stability boundary and ELMs being studied I90 …(edge current) UNSTABLE STABLE Stability boundary for plasmas with the FIRE , and A, and with q95=3.1 • = 3.3% N= 2.61 q'….(edge shear) Manickam

  14. Physics question: NTM • neoclassical tearing mode sets  limits in many long-pulse discharges • scaling of this to new devices largely result of empirical fitting of quasi-linear formula • this is another major thrust of 3D macroscopic modeling effort • active feedback looks feasible • FIRE will provide critical data point (From LaHaye, Butter, Guenter, Huysmans, Marashek, and Wilson)

  15. Other Physics Issues for FIRE • conventional operating modes • the effect of H-mode profiles on MHD stability (Manickam, Chu,…) • relation to ELMS, n ~ 5-10 peeling modes, bootstrap currents • error fields and locked modes (LaHaye, et al) • need to assess disruption effects • reversed shear operating modes • characterization of no-wall advanced mode for entire discharge (Ramos) • wall stabilized advanced modes (GA/PPPL/Columbia experiments on DIII) • other advanced modes • off axis CD to raise q0 (Kessel) • edge current drive to improve stability (?)

  16. Example of Perturbation Study that can be done on FIRE: ICRF heating power increased by 5 or 10MW for 6 sec Other suggestions for XPs welcome !

  17. Summary • Overall, MHD stability looks favorable. Primary uncertainty is in non-catastrophic areas. • MHD activity associated with q=1 surface • edge currents due to H-mode pedestals (ELMs) • neoclassical tearing modes . Active feedback requirements • error fields and locked modes • What will we learn? • How does core self-organize with ’s and m=1 mode? • How does edge self-organize with bootstrap and ELMs • How does interior self-organize with NTM, at new (*,*) • How well can our codes predict these nonlinear events ?

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