Global Stability Issues for a Next Step Burning Plasma Experiment

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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

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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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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
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AIRES designs
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FIRE
B R5/4
2
JET, JET-U
1
10
10
100
0
I A (MA)
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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
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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 lt 0.75 nGW 0.75
IP/?a2 H-Mode Power Threshold Pth gt (2.84/Ai)
n200.58 B0.82 R a0.81
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High Field H 1.0 (12 T, 7.7 MA)
Low Field H 1.2 (10 T, 6.5 MA)
total
total
a-heating
a-heating
ICRF
ICRF
Time (sec)
Time (sec)
Q gt 10 for 9 sec
Q gt 10 for 18 sec
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S (1?2)/2 ? a/R
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High Field
li/2
q95
Low Field
li/2
q95
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Physics Question Role of the m1 mode

• Ideal MHD theory predicts m1,n1 mode unstable
  at design ? for q0 lt 1
• High-n ballooning modes also predicted to be
  unstable in the vicinity of and interior to the
  q1 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
Balloon and Mercier stability
edge
q 3
q 2
surface number
q 1
PEST unstable eigenfunction at t12.5 sec
axis
time (sec)
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High Field 12 T, 7.7 MA
Balloon and Mercier stability
q 3
edge
q 2
surface number
q 1
PEST unstable eigenfunction at t12.5 sec
axis
time (sec)
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Comparison of unstable Eigenvalues
Low Field g2 -.0083
High Field g2 -.0039
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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 q953.1

• 3.3
• ?N 2.61

q'.(edge shear)
Manickam
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• 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)
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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 (?)

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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 q1 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 m1
  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 ?