Status of Advanced Tokamak Modes for FIRE

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Status of Advanced Tokamak Modes for FIRE

• C. Kessel, PPPL
• NSO/PAC Meeting, MIT, January 17-18, 2001

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Advanced Tokamak Modes for FIRE

• AT modes could be divided into 4 major areas
• Transient (significant inductive component)
• Quasi-stationary (small if any inductive
  component)
• Without external kink stabilization
• With external kink stabilization

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Advanced Tokamak Modes in FIRE

• Transient AT modes
• Current is all or mostly inductive, but could
  have insufficient non-inductive current component
  to fix q-profile
• Value of q(min) and r/a(qmin) will be changing
• These modes can only be maintained at desired
  parameters for approximately a few seconds
• Even FIREs shortest flattop (20 s) will allow
  these modes to evolve significantly

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Advanced Tokamak Modes in FIRE

• Quasi-stationary AT modes
• The safety factor profile is held by
  non-inductive current sources
• Values of q(min) and r/a(qmin) dont change much
  during the flattop
• Over the longest pulse lengths (about 45 seconds)
  only small variations in q profile occur

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TSC Simulation of FIRE Burning AT Discharge
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TSC Simulation of FIRE Burning AT Discharge
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Advanced Tokamak Modes in FIRE

• With no stabilization of the external kink mode
• To maximize b, q(min) is roughly limited to
  1.2ltq(min)lt1.5 and 2.1ltq(min)lt2.3
• Location of r/a(qmin) determines Ip achievable
• Lower aspect ratios give slightly higher bN
  values (over range of A 3.0-4.5)
• There is a pressure profile dependence to obtain
  the highest bN
• Take lesser of 4li or 1.15bN(no wall) (typical
  of DIII-D experimental observations)

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Reconstruction from TRANSP DIII-D AT Mode 98549
(t1.3 s)
Ip1.2 MA, Bt1.7 T, R1.6 m, a0.6 m, k1.93,
d0.65, q(0)1.9, q(min)1.63,q3.75,
li(1)0.94, li(3)0.71, bN3.25, b3.8, bN(no
wall)2.75, 4li3.76, 1.15bN3.16, fbs0.42,
stable with wall at 1.5
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Advanced Tokamak Modes in FIRE

• With stabilization of the external kink mode
• Only stabilization of n1 mode, so n2 determines
  beta-limit, bN will rise (typical of an n1
  feedback system)
• Stabilization of n1-3 or so, typical of ARIES-RS
  and ARIES-AT equilibria, leading to the highest
  possible bN and fbs values

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FIRE AT Modes Bt8.5 T, A3.8, k1.9, d0.65
n(0)/ltngt1.5 balloon limited n1,2,3 checked
for n1 stabilized
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FIRE AT Mode
r/a(qmin)0.8, qmin2.19, Ip5.4 MA, bN2.54,
I(LH)2.2 MA, fbs0.58
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FIRE AT Mode
r/a(qmin)0.65, qmin2.12, Ip4.54 MA bN2.8,
I(LH)1.7 MA, fbs0.58
more broad pressure
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FIRE AT Mode
r/a(qmin)0.65, qmin2.10, Ip4.5 MA, bN2.85,
I(LH)1.75 MA, fbs0.59
more peaked pressure
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FIRE AT Modes Bt8.5 T, A3.8, k1.9, d0.65
n(0)/ltngt1.5 balloon limited n1,2,3 checked
for n1 stabilized
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Advanced Tokamak Modes in FIRE

• Issues for AT modes in burning plasmas
• Ip must be high enough to avoid excessive ripple
  losses and AE losses
• Want maximum Ip to provide longest confinement
  time
• Want to avoid (3,2) and (2,1) NTMs (making
  qmingt2 more desirable than qminlt2)
• Want to operate at low temperature to weaken
  AEs, but need high temperature for CD
• Current profile shapes limited by CD sources
• Want to provide Q5, so relying on alpha heating
  and bootstrap current

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Conclusions

• For no external kink stabilization, qmingt2
  appears to be most viable for minimizing CD power
  and avoiding NTMs, however, need higher bN and
  fbs
• Approximately 2 MA of LHCD would be necessary
  which is about 30 MW (pending CD calculations)
• Stabilization of the n1 kink would yield
  attractive configurations (n1 feedback) for
  qmingt2, and allow greater flexibility in choosing
  qmin
• TSC simulations indicate we can create
  quasi-stationary plasmas for flattop burn

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Future Work

• Continue ideal MHD search for AT modes
• Pressure profile variations
• Finite edge densities, and H-mode edge conditions
• n1 stabilized b-limits vs. qmin
• Include LH profile from CD calculations
• Examine DIII-D AT modes for FIRE
• Observed edge and core conditions
• Are ITBs present
• Comparison of theory and observed b-limits
• RWM feedback

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Future Work

• CD analysis
• LH calculations to optimize frequency and n for
  penetration and efficiency
• Feasibiliy of making ICRF ion heating system
  tunable and with phasable antenna for FWCD
• Is another CD source necessary to drive current
  in the range 0.2 lt r/a lt 0.6 ECCD, HHFW
• Continue TSC calculations with identified stable
  target equilibria
• How to form quasi-stationary plasmas in the
  shortest time
• Do coupled TSC/LSC simulations