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Global Stability Issues for a Next Step Burning Plasma Experiment UFA Burning Plasma Workshop Austin, Texas December 11, 2000 S. C. Jardin with input from C.Kessel, J.Manickam, D.Meade, P.Rutherford
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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
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I A (MA) 10100 B R 5/4 10 100 Let us consider FIRE, as it is being proposed as a next step burning plasma experiment 0 1 2 3 4 JET, JET-U FIRE AIRES designs 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
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FIRE operating modes I P (MA)B T T(s) N f BS Standard operating mode (LF)6.510212.70.3 High-field (shorter pulse mode)7.712121.90.2 -------------------------------------------------------------------------------------------- Advanced Tokamak 1 st stability5.69302.90.5 Reversed Shear Wall stabilized4.56.7604.50.8
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Guidelines for Predicting Plasma Performance Confinement (Elmy H-mode) ITER98(y,2): E = 0.144 I 0.93 R 1.39 a 0.58 n 20 0.41 B 0.15 A i 0.19 0.78 P heat -0.69 H(y,2) Density Limit: n 20 < 0.75 n GW = 0.75 I P / a 2 H-Mode Power Threshold: P th > (2.84/A i ) n 20 0.58 B 0.82 R a 0.81
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High Field: H = 1.0 (12 T, 7.7 MA)Low Field: H = 1.2 (10 T, 6.5 MA) Time (sec) Q > 10 for 9 secQ > 10 for 18 sec -heating ICRF total
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S = (1+ 2 )/2 = a/R
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High Field Low Field i /2 q 95
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Physics Question: Role of the m=1 mode Ideal MHD theory predicts m=1,n=1 mode unstable at design for q 0 < 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
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Low Field: 10 T, 6.5 MA time (sec) surface number axis edge q = 1 q = 2 q = 3 PEST unstable eigenfunction at t=12.5 sec Balloon and Mercier stability
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High Field: 12 T, 7.7 MA time (sec) surface number edge q = 1 q = 2 q = 3 PEST unstable eigenfunction at t=12.5 sec axis Balloon and Mercier stability
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Comparison of unstable Eigenvalues Low Field 2 = -.0083 High Field 2 = -.0039
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UNSTABLE STABLE q'….(edge shear) I 90 …(edge current) Manickam FIRE nominal operating point is stable to kink modes. Relation of stability boundary and ELMs being studied = 3.3% N = 2.61 Stability boundary for plasmas with the FIRE , and A, and with q 95 =3.1
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(From LaHaye, Butter, Guenter, Huysmans, Marashek, and Wilson) 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
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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 q 0 (Kessel) edge current drive to improve stability (?) Other Physics Issues for FIRE
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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 !
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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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