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 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)

**30-50% increase with 2D FP

FIRE Auxiliary Systems

1250

160 300Current straps

Faraday shield

Coax feeds

First wall Ant front-side 7/30/03

Adjustablecapacitorstructure

Shielding

.32

.71

2.56

.65

FIRE Antenna Plan

4/24/01

Dimensions in m

1999 version of Vacuum vessel Port outline

Each block =8 waveguides+ cooling

1250

720

Array of 768 waveguides in midplane port

536

EC Launcher

EC Launcher

Blow-up of one square

60

67

ICRF

div. pumping

Pellet injection

LH & EC

FIRE Diagnostics Layout

FIRE Diagnostics Layout

FIRE H-mode: Parameters and Profiles

total

bootstrap

GLF23 core transport

FIRE H-mode: Parameters and Profiles

GLF23 core transport

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: m=1 Stability no sawtooth

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

PEST3 analysis needed

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 StabilitySelf consistent bootstrap/ohmic equilibria

No wallN(n=1) = 3.25, external kinkN(n=∞) 4.5**except in pedestal

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 calcs 3) pulse length limitations from

TF or VV nuclear heating4) FW and divertor power

handling limitations

identify operating points to pursue with more detailed analysis

Q = 5

FIRE AT-mode: Parameters and Profiles

Ip = 4.5 MA, BT = 6.5 T

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

qmin(3,1)

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 so close to plasma edge?

170 GHz may be adequate, but 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 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 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

Examine other pedestal prescriptions and wall locations

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

HBT-EPDIII-D

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 ≈ 3o(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• 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: Other

TF Coil

CS1

CS2

CS3

PF1,2,3PF4

PF5

Error correction coils

Fast vertical and radial position control coil RWM feedback coil

Fe shims

FIRE H-mode and AT-mode: OtherdIP/dt(max) = 1-3 MA/msquench = 0.1 msIhalo/IP TPF = 0.5-0.75

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

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 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

• 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

PF Coils

Fast PF Coils

RWM Coils

Error Correction Coils

FWCDLHCD

Bootstrap

EC/OKCD

Magnetic diagnostics

Non-magnetic diagnostics

Pellet/gas injection

Particle pumping

Impurity injection

Safety Factor

Transport

-heating

Pressure

Internal plasma physics is as Important as the External Tools