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 PF1,2,3 PF4 PF5 VV R=2.14 m a=0.595 m  x =2.0  x =0.7 P fus =150 MW H-mode Ip=7.7 MA B T =10 T  N =1.85 li(3)=0.65  flat =20 s AT-mode Ip=4.5 MA B T =6.5 T  N =4.2 li(3)=0.40  flat =31 s Cu cladding Cu stabilizers

FIRE Description H-mode I P = 7.7 MA B T = 10 T  N = 1.80  = 2.4%  P = 0.85    = 0.075% q(0) < 1.0 q 95 ≈ 3.1 li(1,3) = 0.85,0.66 T e,i (0) = 15 keV n 20 (0) = 5.3 n(0)/  n  = 1.15 p(0)/  p  = 2.4 R = 2.14 m, a = m,  x = 2.0,  x = 0.7, P fus = 150 MW AT-Mode I P = 4.5 MA B T = 6.5 T  N = 4.2  = 4.7%  P = 2.35    = 0.21% q(0) ≈ 4.0 q 95, q min ≈ 4.0,2.7 li(1,3) = 0.52,0.45 T e,i (0) = 15 keV n 20 (0) = 4.4 n(0)/  n  = 1.4 p(0)/  p  = 2.5 Cu passive plates Cu cladding Port plasma

FIRE Auxiliary Systems ICRF ion/electron heating – MHz –2 strap antennas –4 ports, 20 MW (10 MW additional reserved) –B T = 10 T, ion heating minority He3 and 2T for 100 MHz (also obtains a/2 heating) –B T = 6.5 T, ion heating minority H and 2D for 100 MHz (also obtains a/2 heating) –B T = 6.5 T electron heating/CD at 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 (B T = 6.5 T) and 0.25 A/W-m2 (B T = 8.5 T)** EC electron heating/CD –170 GHz –in LH ports, top and bottom –20+ MW? –  CD = 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 ICRF div. pumping Pellet injection LH & EC

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 R o ) –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/n Gr = 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 P loss /P LH ≈ in flattop, not > 2 like many present experiments –FIRE has high triangularity (  x = 0.7) in Double Null and high density (n/n Gr < 0.8) –What active methods should be considered?

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 Database of operating points by scanning q 95, n(0)/  n , T(0)/  T , n/n Gr,  N, f Be, f Ar Constrain results with 1)installed auxiliary powers 2)CD efficiencies from RF calcs 3)pulse length limitations from TF or VV nuclear heating 4)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, B T = 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 I P  N 2, 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 q min ) and another contribution in the vicinity of rational surfaces outside q min to modify current profile and resist NTM’s ----> this requires splitting available power

FIRE AT-mode: Neoclassical Tearing Modes 145≤  ≤155 GHz -30 o ≤  L ≤-10 o midplane launch 10 kA of current for 5 MW of injected power  =149 GHz  L =-20 o Bt=6.5 T Bt=7.5 T Bt=8.5 T Ro Ro+a fce=182fce=142 fce=210fce=164 fce=190fce= GHz 200 GHz J. Decker, MIT q min (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(q min ) ≈ 0.8 r/a(3,1) ≈ Does (3,1) require less current than (3,2)? Local *,  *, Re m 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 < –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 p o /  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 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 Stability H-mode edge Ip = 4.8 MA B T = 6.5 T  N = 4.5  = 5.5%  p = 2.15 li(1) = 0.44 li(3) = 0.34 q min = 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 Stability L-mode edge Ip = 4.5 MA B T = 6.5 T  N = 4.5  = 5.4%  p = 2.33 li(1) = 0.54 li(3) = 0.41 q min = 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*

AT Equilibrium from TSC-LSC Dynamic Simulations TSC-LSC equilibrium Ip=4.5 MA Bt=6.5 T q(0)=3.5, q min =2.8  N =4.2,  =4.9%,  p=2.3 li(1)=0.55, li(3)=0.42 p(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 ICRF Port Plug RWM Feedback Coil Growth Rate, /s NN  N =4.2 Examine other pedestal prescriptions and wall locations VALEN indicates 80-90% of n=1 with wall limit HBT-EP DIII-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 G at the plasma These fields require approximately I = f(d,Z,  )B r /  o = 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 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 PF1,2,3 PF4 PF5 Error correction coils Fast vertical and radial position control coil RWM feedback coil Fe shims

FIRE H-mode and AT-mode: Other dI P /dt(max) = 1-3 MA/ms  quench = 0.1 ms I halo /I P  TPF = 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 j bulk (  ) or j local (  ) in BP limit NTM stabilization techniques –Does early detection remove the island or reduce it to a lower w sat –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*  N 2 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 FWCD LHCD 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