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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. R=2.14 m a=0.595 m  x =2.0  x =0.7 P fus =150 MW. PF4. PF1,2,3. H-mode Ip=7.7 MA B T =10 T  N =1.85

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Mhd issues and control in fire

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

Mhd issues and control in fire

Layout of FIRE Device

R=2.14 m

a=0.595 m



Pfus=150 MW




Ip=7.7 MA

BT=10 T



flat=20 s


Ip=4.5 MA

BT=6.5 T



flat=31 s

TF Coil


Cu stabilizers




Cu cladding


Fire description
FIRE Description

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

  • H-mode

  • IP = 7.7 MA

  • BT = 10 T

  • N = 1.80

  • = 2.4%

  • P = 0.85

  •  = 0.075%

  • q(0) < 1.0

  • q95 ≈ 3.1

  • li(1,3) = 0.85,0.66

  • Te,i(0) = 15 keV

  • n20(0) = 5.3

  • n(0)/n = 1.15

  • p(0)/p = 2.4

  • AT-Mode

  • IP = 4.5 MA

  • BT = 6.5 T

  • N = 4.2

  • = 4.7%

  • P = 2.35

  •  = 0.21%

  • q(0) ≈ 4.0

  • q95, qmin ≈ 4.0,2.7

  • li(1,3) = 0.52,0.45

  • Te,i(0) = 15 keV

  • n20(0) = 4.4

  • n(0)/n = 1.4

  • p(0)/p = 2.5

Cu passive plates



Cu cladding

Fire auxiliary systems

ICRF ion/electron heating

70-115 MHz

2 strap antennas

4 ports, 20 MW (10 MW additional reserved)

BT = 10 T, ion heating minority He3 and 2T for 100 MHz (also obtains a/2 heating)

BT = 6.5 T, ion heating minority H and 2D for 100 MHz (also obtains a/2 heating)

BT = 6.5 T electron heating/CD at 70-75 MHz

CD = 0.2 A/W-m2 (AT-mode)

PF coils, fast Z and R control coils, RWM feedback coils, error field correction coils

LH electron heating/CD

5 GHz

n|| ≈ 2, n||≈ 0.3

2 ports, 30 MW

CD = 0.16 A/W-m2 (BT = 6.5 T) and 0.25 A/W-m2 (BT = 8.5 T)**

EC electron heating/CD

170 GHz

in LH ports, top and bottom

20+ MW?

CD = 0.043 A/W-m2

Pellet/gas injection and divertor pumping

HFS, 125 m/s

LFS, vertical at higher speeds

16 cryo pumps (top&bottom)

FIRE Auxiliary Systems

**30-50% increase with 2D FP

Fire auxiliary systems1
FIRE Auxiliary Systems

Pellet injection



div. pumping

Fire h mode parameters and profiles
FIRE H-mode: Parameters and Profiles

GLF23 core transport



Fire h mode m 1 stability
FIRE H-mode: m=1 Stability

  • Sawteeth

    • Unstable, r/a(q=1) ≈ 0.35, Porcelli sawtooth model in TSC indicates weak influence on plasma burn due to pedestal/bootstrap broadening current profile, and rapid reheat of sawtooth volume

    • Alpha particles are providing stabilization, causing few crashes in flattop

    • To remove q=1 surface requires ≥ 1.2 MA of off-axis current at Ip = 7.7 MA, OR Ip ≈ 6.0 MA, ----> Improved H-mode/Hybrid Mode

    • RF stabilization/destabilization of sawteeth? To remove or weaken drive for low order NTM’s ----> FIRE’s high density does not produce high energy tail in minority species, implying some form of CD would be required

Fire h mode neo classical tearing modes
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 modes1
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

PEST3 analysis needed

Fire h mode ideal mhd stability
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

      • Ploss/PLH ≈ 1.0-1.6 in flattop, not > 2 like many present experiments

    • FIRE has high triangularity (x = 0.7) in Double Null and high density (n/nGr < 0.8)

    • What active methods should be considered?

Fire h mode ideal mhd stability1
FIRE H-mode: Ideal MHD Stability

Self consistent bootstrap/ohmic equilibria

No wall

N(n=1) = 3.25, external kink

N(n=∞)  4.5*

*except in pedestal

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

N ≤ 3

Fire at mode operating space
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 with

installed auxiliary powers

CD efficiencies from RF calcs

pulse length limitations from TF or VV nuclear heating

FW and divertor power handling limitations

identify operating points to pursue with more detailed analysis

Q = 5

Fire at mode parameters and profiles
FIRE AT-mode: Parameters and Profiles

Ip = 4.5 MA, BT = 6.5 T

Fire at mode neoclassical tearing modes
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 IPN2, 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 modes1
FIRE AT-mode: Neoclassical Tearing Modes

J. Decker, MIT

145≤≤155 GHz


midplane launch

10 kA of current for 5 MW of injected power

=149 GHz




Bt=6.5 T



170 GHz



Bt=7.5 T





200 GHz



Bt=8.5 T



Fire at mode neoclassical tearing modes2
FIRE AT-mode: Neoclassical Tearing Modes

=ce=170 GHz

r/a(qmin) ≈ 0.8

r/a(3,1) ≈ 0.87-0.93

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

Local *, *, Rem effects so close to plasma edge?

170 GHz may be adequate, but 200 GHz is better fit for FIRE parameters

Rays are launched with toroidal directionality for CD


Short pulse, MIT

Rays are bent as they approach =pe

Fire at mode ideal mhd stability
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 of H-mode edge plasmas, 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, actual wall location is 1.25a

    • 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? Are they becoming RWM’s or NTM’s

  • Intermediate n peeling/ballooning modes

    • Unstable under H-mode edge conditions

Fire at mode ideal mhd stability1
FIRE AT-mode: Ideal MHD Stability

H-mode edge

Ip = 4.8 MA

BT = 6.5 T

N = 4.5

 = 5.5%

p = 2.15

li(1) = 0.44

li(3) = 0.34

qmin = 2.75

p(0)/p = 1.9

n(0)/n = 1.2

N(n=1) = 5.4

N(n=2) = 4.7

N(n=3) = 4.0

N(bal) > 6.0*

Fire at mode ideal mhd stability2
FIRE AT-mode: Ideal MHD Stability

L-mode edge

Ip = 4.5 MA

BT = 6.5 T

N = 4.5

 = 5.4%

p = 2.33

li(1) = 0.54

li(3) = 0.41

qmin = 2.61

p(0)/p = 2.18

n(0)/n = 1.39

N(n=1) = 6.2

N(n=2) = 5.2

N(n=3) = 5.0

N(bal) > 6.0*

Mhd issues and control in fire

AT Equilibriumfrom TSC-LSC Dynamic Simulations

TSC-LSC equilibrium

Ip=4.5 MA

Bt=6.5 T

q(0)=3.5, qmin=2.8

N=4.2, =4.9%, p=2.3

li(1)=0.55, li(3)=0.42



Stable n=

Stable n=1,2,3 with no wall

L-mode edge


Fire at mode ideal mhd stability3
FIRE AT-mode: Ideal MHD Stability

Examine other pedestal prescriptions and wall locations

Growth Rate, /s


VALEN indicates 80-90% of n=1 with wall limit


RWM Feedback Coil



ICRF Port Plug

Mhd issues and control in fire

RWM Coils --- DIII-D Experience

  • Modes are detectable at the level of 1G

  • The C-coils can produce about 50 times this field

  • The necessary frequency depends on the wall time for the n=1 mode (which is 5 ms in DIII-D) and they have wall ≈ 3

  • FIRE has approximately 3-4 times the DIII-D plasma current, so we might be able to measure down to 3-4 G

  • If we try to guarantee at least 20 times this value from the feedback coils, we must produce 60-80 G at the plasma

  • These fields require approximately I = f(d,Z,)Br/o = 5-6.5 kA

  • Assume we also require wall ≈ 3

  • Required voltage would go as V ≈ 3o(2d+2Z)NI/wall ≈ 0.25 V/turn

  • Differences:

    • DIII-D’s C coils are outside the VV, far away, FIRE’s are very close

    • DIII-D has 6 coils, FIRE has 8 with smaller toroidal extent

    • DIII-D VV is made of Inconel, FIRE has Cu cladding on SS (wall)

    • FIRE has large ports providing smaller wall area (VALEN model is accurate)

Fire h mode and at mode other
FIRE H-mode and AT-Mode: Other

  • Alfven eigenmodes and energetic particle modes

    • Snowmass assessment indicated stable for H-mode, and AT-mode not analyzed

  • TF field ripple is low: H-mode losses 0.3%, AT-mode at 4.5 MA loses 7-8%, Fe shims are desired in between VV and TF

  • 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 (JT-60U, C-Mod)

    • Use of RWM feedback coils for ultra fast vertical control?

  • Vertical position control (n=0)

    • Cu passive stabilizers providing instability 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 other1
FIRE H-mode and AT-mode: Other



Error correction coils

TF Coil


Fe shims




Fast vertical and radial position control coil

RWM feedback coil

Fire h mode and at mode other2
FIRE H-mode and AT-mode: Other

HFS launch with 125 m/s, accesses core according to latest Parks modeling, and much higher speeds with LFS and vertical launch

dIP/dt(max) = 1-3 MA/ms

quench = 0.1 ms

Ihalo/IP  TPF = 0.5-0.75

Questions plasma rotation
Questions: Plasma Rotation

  • Externally driven plasma rotation

    • NBI for FIRE H-mode is prohibitive, > 1 MeV beams to access core

    • Off-axis NBI in FIRE-AT with conventional beams might be possible?

    • “Pinwheel” port configuration, if necessary for NBI, OK’d by engineers for FIRE

    • Can fusion reactor plasmas be rotated externally?

    • What MHD results are critically dependent on external rotation, what are implications in absense of strong external rotation?

    • Plasma self-rotation (C-Mod) is sufficient for transport, resistive stability, ideal/RWM stability? Sheared rotation versus bulk rotation

    • Error fields will still be present at some magnitude, causing a plasma response that amplifies them, affecting self-rotation

Questions ntm control by j bulk or j local in bp limit
Questions: NTM control by jbulk() or jlocal() in BP limit

  • NTM stabilization techniques

    • Does early detection remove the island or reduce it to a lower wsat

    • Bulk current profile control to make ’ more negative at rational surface with LHCD or ECCD

      • Positioning requirements less stringent?

      • Needs larger driven current

    • Local current drive to replace bootstrap current with ECCD

      • From DIII-D experience, searching and dwelling, and tracking after suppression

      • Smaller total current requirement, however, scaling with Ip*N2 to burning devices can lead to high currents

    • Do we need to do this at all??

      • Stationary plasmas with NTM (saturated) at sufficiently high N (T. Luce at APS2003)

      • Strategy might be to control profiles to avoid excessive confinement loss in presence of NTM, rather than trying to stabilize the NTM

Questions rwm s and error fields
Questions: RWM’s and Error Fields

  • When error fields are present, we are feeding back on a mode that is different than a pure kink mode (in absense of error field), which is what we are doing analysis on?

  • The higher n kink modes are linearly ideal unstable at a lower N than n=1, with a wall

    • Are they becoming RWM’s

    • Are they becoming tearing modes, as the ideal MHD limit is approached, ultimately becoming NTM’s

    • Are they edge localized modes, peeling modes

    • n=2 and 3 limits may be closer to n=1 limit at higher pressure peaking, and depend on wall location

Mhd control in burning plasmas
MHD Control in Burning Plasmas

Internal plasma physics is as Important as the External Tools

Non-magnetic diagnostics

RWM Coils

PF Coils

Error Correction Coils

Magnetic diagnostics

Fast PF Coils



Safety Factor




Pellet/gas injection


Impurity injection


Particle pumping