MHD Issues and Control in FIRE

C. Kessel

Princeton Plasma Physics Laboratory

Workshop on Active Control of MHD Stability

Austin, TX 11/3-5/2003

Layout of FIRE Device

TF Coil

CS1

CS2

CS3

PF1,2,3PF4

PF5

VV

R=2.14 ma=0.595 mx=2.0x=0.7Pfus=150 MW

H-modeIp=7.7 MABT=10 TN=1.85li(3)=0.65flat=20 s

AT-modeIp=4.5 MABT=6.5 TN=4.2li(3)=0.40flat=31 s

Cu cladding

Cu stabilizers

FIRE Description

H-modeIP = 7.7 MABT = 10 TN = 1.80 = 2.4%P = 0.85 = 0.075%q(0) < 1.0q95 ≈ 3.1li(1,3) = 0.85,0.66Te,i(0) = 15 keVn20(0) = 5.3n(0)/n = 1.15p(0)/p = 2.4

R = 2.14 m, a = 0.595 m, x = 2.0, x = 0.7, Pfus = 150 MW

AT-ModeIP = 4.5 MABT = 6.5 TN = 4.2 = 4.7%P = 2.35 = 0.21%q(0) ≈ 4.0q95, qmin ≈ 4.0,2.7li(1,3) = 0.52,0.45Te,i(0) = 15 keVn20(0) = 4.4n(0)/n = 1.4p(0)/p = 2.5

Cu passive plates

Cu cladding

Portplasma

FIRE H-mode Parameters and Profiles

total

bootstrap

FIRE H-mode Parameters and Profiles

FIRE H-mode: m=1 Stability

• Sawteeth– Unstable, r/a(q=1) ≈ 0.33, Porcelli sawtooth model in TSC

indicates weak influence on plasma burn due to pedestal/bootstrap broadening current profile, and rapid reheat of sawtooth volume

– Requires ≥ 1 MA of off-axis current to remove q=1 surface

– RF stabilization/destabilization of sawteeth? To remove or weaken drive for low order NTM’s

FIRE H-mode: Neo-Classical Tearing Modes

• Neo-Classical Tearing Modes– Unstable or Stable?

– Flattop time (20 s) is 2 current diffusion times, j() and p() are relaxed

– Sawteeth and ELM’s as drivers are expected to be present

– Operating points are at low N and P, can they be lowered further and still provide burning plasmas ----> yes, lowering Q

– EC methods are difficult in FIRE H-mode due to high field and high density (280 GHz to access Ro)

– LH method of bulk current profile modification can probably work, but will involve significant power, affecting achievable Q ----> is there another LH method such as pulsing that needs less current?

FIRE H-mode: Neo-Classical Tearing Modes TSC-LSC simulation

POPCON shows access to lower N operating points

(3,2) surface

P(LH)=12.5 MW

I(LH) = 0.65 MA

n/nGr = 0.4

FIRE H-mode: Ideal MHD Stability

• n=1 external kink and n=∞ ballooning modes

– Stable without a wall/feedback

– Under various conditions; sawtooth flattened/not flattened current profiles, strong/weak pedestals, etc. N≈3

– EXCEPT in pedestal region, ballooning unstable depending on pedestal width and magnitude

• Intermediate n peeling/ballooning modes

– Unstable, primary candidate for ELM’s

– Type I ELM’s are divertor lifetime limiting, must access Type II, III, or other lower energy/higher frequency regimes

– FIRE has high triangularity (x = 0.7) and high density (n/nGr < 0.8), what active methods should be considered?

FIRE H-mode: Ideal MHD StabilitySelf consistent bootstrap/ohmic equilibria

No wallN(n=1) = 3.25N(n=∞) 4.5

Other cases with different edge and profile conditions yield various results ----->N ≈ 3

FIRE AT-mode: Operating Space

Database of operating points by scanning q95, n(0)/n, T(0)/T, n/nGr, N, fBe, fAr

Constrain results with1) installed auxiliary powers2) CD efficiencies from RF calcs3) pulse length limitations from

TF or VV nuclear heating4) FW and divertor power

handling limitations

identify operating points to pursue with more detailed analysis

FIRE AT-mode Parameters and Profiles

FIRE AT-mode Parameters and Profiles

FIRE AT-mode: Neoclassical Tearing Modes

• Neoclassical Tearing Modes– Stable or Unstable?– q() > 2 everywhere, are the (3,1), (5,2), (7,3), (7,2)….going to destabilize?

If they do will they significantly degrade confinement?– Examining EC stabilization at the lower toroidal fields of AT

• LFS launch, O-mode, 170 GHz, fundamental• 170 GHz accesses R+a/4, however, p e ≥ ce cutting off EC inside r/a ≈ 0.67• LFS deposition implies trapping degradation of CD efficiency, however, Ohkawa

current drive can compensate• Current required, based on (3,2) stabilization in ASDEX-U and DIII-D, and

scaling with IPN2, is about 200 kA ----> 100 MW of EC power! Early detection

is required

– Launch two spectra with LHCD system, to get regular bulk CD (that defines qmin) and another contribution in the vicinity of rational surfaces outside qmin to modify current profile and resist NTM’s ----> this requires splitting available power

FIRE AT-mode: Neoclassical Tearing Modes

145≤≤155 GHz-30o≤L≤-10o

midplane launch

10 kA of current for 5 MW of injected power

=149 GHzL=-20o

Bt=6.5 T

Bt=7.5 T

Bt=8.5 T

Ro

Ro

Ro

Ro+a

Ro+a

Ro+a

fce=182 fce=142

fce=210 fce=164

fce=190fce=238

170 GHz

200 GHz

J. Decker, MIT

FIRE AT-mode: Neoclassical Tearing Modes

=ce=170 GHz

pe=ce

Rays are launched with toroidal directionality for CD

Rays are bent as they approach =pe

Short pulse, MIT

r/a(qmin) ≈ 0.8r/a(3,1) ≈ 0.87-0.93

Does (3,1) require less current than (3,2)?

Local *, *, Rem effects?

200 GHz is better fit for FIRE parameters

FIRE AT-mode: Ideal MHD Stability

• n= 1, 2, and 3…external kink and n = ∞ ballooning modes– n = 1 stable without a wall/feedback for N < 2.5-2.8– n = 2 and 3 have higher limits without a wall/feedback– Ballooning stable up to N < 6.0, EXCEPT in pedestal region ballooning

instability associated with ELM’s– Specifics depend on po/p, H-mode or L-mode edge, pedestal

characteristics, level of LH versus bootstrap current, and Ip (q*)

– FIRE’s RWM stabilization with feedback coils located in ports very close to the plasma, VALEN analysis indicates 80-90% of ideal with wall limit for n=1

– n = 1 stable with wall/feedback to N’s around 5.0-6.0 depending on edge conditions, wall location, etc.

– n = 2 and 3 appear to have lower N limits in presence of wall, possibly blocking access to n = 1 limits ----> how are these modes manifesting themselves in the plasma when they are predicted to be linear ideal unstable?

• Intermediate n peeling/ballooning modes– Unstable under H-mode edge conditions

FIRE AT-mode: Ideal MHD StabilityH-mode edgeIp = 4.8 MABT = 6.5 TN = 4.5 = 5.5%p = 2.15li(1) = 0.44li(3) = 0.34qmin = 2.75p(0)/p = 1.9n(0)/n = 1.2

N(n=1) = 5.4N(n=2) = 4.7N(n=3) = 4.0N(bal) > 6.0*

FIRE AT-mode: Ideal MHD StabilityL-mode edgeIp = 4.5 MABT = 6.5 TN = 4.5 = 5.4%p = 2.33li(1) = 0.54li(3) = 0.41qmin = 2.61p(0)/p = 2.18n(0)/n = 1.39

N(n=1) = 6.2N(n=2) = 5.2N(n=3) = 5.0N(bal) > 6.0*

AT Equilibrium from TSC-LSC Dynamic Simulations

TSC-LSC equilibriumIp=4.5 MABt=6.5 Tq(0)=3.5, qmin=2.8N=4.2, =4.9%, p=2.3li(1)=0.55, li(3)=0.42p(0)/p=2.45 n(0)/n=1.4

Stable n=Stable n=1,2,3 with no wall

√V/Vo

L-mode edge

FIRE AT-mode: Ideal MHD Stability

Current strap, grounded at each end

Faraday shield(one side only)

Port flange

ICRF Port Plug

RWM Feedback Coil

Gro

wth

Rat

e, /s

N

N=4.2

FIRE H-mode and AT-Mode: Other

• Alfven eigenmodes and energetic particle modes

• Error fields from coil misalignments, etc. ----> install Cu window coils outside TF coil, stationary to slow response

• Disruptions ----> – Pellet and gas injectors will be all over the device, resulting radiative heat

load is high

– Up-down symmetry implies plasma is at or near the neutral point, not clear if this can be used to mitigate or avoid VDE’s

• Vertical position control– Cu passive stabilizers providing growth time of ≈ 30 ms, vertical feedback

coils located outside inner VV on outboard side

• Fast radial position control, antenna coupling, provided by same coils as vertical control

• Shape control provided by PF coils

FIRE H-mode and AT-mode: Other

TF Coil

CS1

CS2

CS3

PF1,2,3PF4

PF5

Error correction coils

Fast vertical and radial position control coil

FIRE H-mode and AT-mode: Other