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The Role of MHD in 3D Aspects of Massive Gas Injection

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1 The Role of MHD in 3D Aspects of Massive Gas Injection
V.A. Izzo,1 N. Commaux,2 N.W. Eidietis,3 R.S. Granetz,4 E. Hollmann,1 G. Huijsmans,7 D.A. Humphreys,3 C.J. Lasnier,3 M. Lehnen,7 A. Loarte,7 R.A. Moyer,1 P.B. Parks,3 C. Paz-Soldan,5 R. Raman,6 D. Shiraki,2 E.J. Strait3 1UCSD, 2ORNL, 3GA, 4MIT, 5ORISE, 6UW, 7ITER IO 25th IAEA Fusion Energy Conference 16 October 2014 TH/4-1

2 Massive Gas Injection is a leading candidate for disruption mitigation on ITER
In the event that a disruption is unavoidable, the goal of massive gas injection (MGI) shutdown is to radiate plasma stored energy in order to: Avoid conduction of large heat loads to the divertor during the thermal quench (TQ), and … Appropriately tailor the current quench (CQ) time to avoid large vessel forces

3 # of valves & location(s) Radiation toroidal peaking factor (TPF)
Goal of massive gas injection is to isotropically radiate plasma stored energy # of valves & location(s) MGI valve Radiation toroidal peaking factor (TPF)

4 # of valves & location(s) Radiation toroidal peaking factor (TPF)
NIMROD modeling finds a more complicated relationship # of valves & location(s) ? MGI valve ? MHD Impurity transport Heat flux Radiation toroidal peaking factor (TPF)

5 # of valves & location(s) Radiation toroidal peaking factor (TPF)
Outline PART I. Key 3D Physics of Massive Gas Injection PART II. DIII-D TPF Predictions & Comparison with Measurements PART III. ITER TPF Predictions # of valves & location(s) ? MGI valve ? MHD Impurity transport Heat flux Radiation toroidal peaking factor (TPF)

6 Ne plume expansion || to B
PART I. Key 3D Physics of Massive Gas Injection NIMROD 4-stage MGI shutdown Pre-TQ Early TQ Late TQ CQ Ne MGI at t=0 MHD None m/n >1 m=1/n=1 Particle Transport Ne plume expansion || to B Radial mixing Heat Transport Slow  conduction Fast || Br conduction V·T convection

7 PART I. Key 3D Physics of Massive Gas Injection
NIMROD 4-stage MGI shutdown NIMROD predictions concerning the role of the n=1 mode have been tested experimentally Pre-TQ Early TQ Late TQ CQ Ne MGI at t=0 NIMROD finds asymmetric impurity spreading for off-midplane injection MHD None m/n >1 m=1/n=1 Particle Transport Ne plume expansion || to B Radial mixing Heat Transport NIMROD multi-valve MGI simulations reveal implications of both effects for optimum valve positioning Slow  conduction Fast || Br conduction V·T convection

8 PART I. Key 3D Physics of Massive Gas Injection
NIMROD 4-stage MGI shutdown NIMROD predictions concerning the role of the n=1 mode have been tested experimentally Pre-TQ Early TQ Late TQ CQ Ne MGI at t=0 NIMROD finds asymmetric impurity spreading for off-midplane injection MHD None m/n >1 m=1/n=1 Particle Transport Ne plume expansion || to B Radial mixing Heat Transport NIMROD multi-valve MGI simulations reveal implications of both effects for optimum valve positioning Slow  conduction Fast || Br conduction V·T convection

9 NIMROD simulations produced two predictions regarding the role of the 1/1 in an MGI TQ*
1) 1/1 phase determines location of toroidal radiation peaking due to asymmetric convected heat flux 180º 2) Absent other asymmetries, 1/1 phase is anti-aligned with gas jet m/n=1/1 MGI 0º *IZZO, V.A., Phys. Plasmas 20 (2013)

10 NIMROD predicted n=1 phase
DIII-D experiments: Initial n=1 phase corresponds to NIMROD prediction NIMROD predicted n=1 phase MGI location

11 DIII-D experiments: n=1 phase at TQ influenced by rotation, error fields
Rotation and error field effects (not in simulations) also determine final mode phase at TQ

12 TQ Wrad asymmetry vs. applied n=1 phase
Experiments verify: the phase of the n=1 mode (relative to the gas jet) affects asymmetry TQ Wrad asymmetry vs. applied n=1 phase 0.1  DIII-D experiments: Changing phase of applied n=1 fields changes measured radiation asymmetry during TQ 0.0 Radiated energy asymmetry -0.1 -0.2 -0.3

13 PART I. Key 3D Physics of Massive Gas Injection
NIMROD 4-stage MGI shutdown NIMROD predictions concerning the role of the n=1 mode have been tested experimentally Pre-TQ Early TQ Late TQ CQ Ne MGI at t=0 NIMROD finds asymmetric impurity spreading for off-midplane injection MHD None m/n >1 m=1/n=1 Particle Transport Ne plume expansion || to B Radial mixing Heat Transport NIMROD multi-valve MGI simulations reveal implications of both effects for optimum valve positioning Slow  conduction Fast || Br conduction V·T convection

14 Contours/isosurface of ionized Ne density
Injected Ne plume spreads along B-field in one direction toroidally  toward HFS poloidally Contours/isosurface of ionized Ne density MGI15U 2.25 ms MGI135L 0.25 ms MGI135L MGI15U MGI15U

15 Contours/isosurface of ionized Ne density
Below midplane jet spreads in the opposite toroidal direction, also toward HFS Contours/isosurface of ionized Ne density MGI135L MGI15U 2.25 ms MGI15U 0.25 ms MGI135L MGI135L

16 PART I. Key 3D Physics of Massive Gas Injection
NIMROD 4-stage MGI shutdown NIMROD predictions concerning the role of the n=1 mode have been tested experimentally Pre-TQ Early TQ Late TQ CQ Ne MGI at t=0 NIMROD finds asymmetric impurity spreading for off-midplane injection MHD None m/n >1 m=1/n=1 Particle Transport Ne plume expansion || to B Radial mixing Heat Transport NIMROD multi-valve MGI simulations reveal implications of both effects for optimum valve positioning Slow  conduction Fast || Br conduction V·T convection

17 Ionized Ne density contours/isosurface
NIMROD: Ip direction affects direction of impurity spreading MGI15U NORMAL HELICITY MGI135L Ionized Ne density contours/isosurface MGI15U REVERSED HELICITY MGI135L

18 Radiated power and n=1 amplitude
Relative spacing of gas valves affects interaction with 1/1 mode 135º 15º MGI15U Temperature contours MGI35L Radiated power and n=1 amplitude Time (ms)

19 Radiated power and n=1 amplitude
MGI15U and MGI135L will tend to drive the same 1/1 mode phase 135º 15º MGI15U Temperature contours Gas jets are separated by 120º poloidally and toroidally MGI35L Radiated power and n=1 amplitude Time (ms)

20 Radiated power and n=1 amplitude
Simulation with both gas jets drives same mode phase as single jet 135º 15º Normal Helicity MGI15U Temperature contours MGI35L Radiated power and n=1 amplitude Time (ms)

21 Radiated power and n=1 amplitude
Heat flux due to 1/1 convection is simultaneously away from both jets 135º 15º MGI15U 1/1 convection also mixes impurities inward radially at both locations Temperature contours MGI35L Radiated power and n=1 amplitude Time (ms)

22 Radiated power and n=1 amplitude
In reversed helicity, spacing of two jets no longer coheres with 1/1 symmetry 135º 15º MGI15U Reversed Helicity Temperature contours MGI35L Radiated power and n=1 amplitude Time (ms)

23 Radiated power and n=1 amplitude
Interaction of 1/1 mode with each of the two impurity plumes is very different 135º 15º MGI15U No coherent 1/1 mode can interact with both jets in the same way Temperature contours MGI35L Radiated power and n=1 amplitude Time (ms)

24 PART II. NIMROD asymmetry predictions and comparison with DIII-D measurements
 DIII-D has two fast radiated power measurements Prad210  Both jets are closer to Prad90 MGI15U Diagnostic locations MGI135L Radiated Energy Prad90 TPF = Max(Wrad)/Mean(Wrad) Clearly, asymmetry calculated from 2 measurement locations is an approximation… Toroidal angle

25 All cases in normal helicity
NIMROD predicts improved symmetry when both DIII-D jets are used Pre-TQ TQ BOTH BOTH ONLY MGI135L ONLY MGI135L ONLY MGI15U ONLY MGI15U All cases in normal helicity

26 All cases in normal helicity
NIMROD predicts improved symmetry when both DIII-D jets are used Pre-TQ TQ BOTH BOTH ONLY MGI135L ONLY MGI135L ONLY MGI15U ONLY MGI15U All cases in normal helicity

27 DIII-D finds little or no variation in the asymmetry for one vs two gas jets
DIII-D measured asymmetry Pre-TQ Radiated energy asymmetry TQ CQ Asymmetry calculated from 90 and 210 degree detectors ONLY MGI15U ONLY MGI135L BOTH tMGI135L – t MGI15U (ms)

28 NIMROD synthetic asymmetry diagnostic largely reproduces missing trend in DIII-D data
NIMROD 2-point “TPF” DIII-D measured asymmetry Pre-TQ Radiated energy asymmetry Comparison of asymmetry using only information from 90 and 210 degrees TQ CQ ONLY MGI15U ONLY MGI135L BOTH tMGI135L – t MGI15U (ms)

29 NIMROD “synthetic 2-point TPF”
NIMROD: 2-point “TPF” does not capture real trend in TPF NIMROD real TPF Pre-TQ TQ ONLY MGI15U BOTH BOTH ONLY MGI135L ONLY MGI135L ONLY MGI15U NIMROD “synthetic 2-point TPF”

30 Reversed Helicity Case
NIMROD: reversing helicity increases TQ TPF with 2 jets Pre-TQ ONLY MGI15U TQ BOTH BOTH ONLY MGI135L ONLY MGI135L ONLY MGI15U Reversed Helicity Case

31 Part III. ITER simulations use three upper ports allocated for TQ mitigation part of DMS
Valve Normalized Ne injection rate Fraction of plenum injected Total particle injection rate vs. time based on FLUENT calculations  Assumes 1 m delivery tube: unrealistically short!

32 3-valves and 1-valve have same TPF, different TQ durations
Slight decrease in TPF during pre-TQ with 3 valves Virtually no change in TPF during TQ Single valve has higher maximum Prad Three valve has longer TQ duration TPF Number of valves Time (ms)

33 NIMROD modeling provides new physics insights into MGI with single or multiple gas valves
NIMROD predicts that DIII-D 2-valve configuration reduces TPF, but increased diagnostic resolution is needed to capture trend, validate model On ITER, 3 upper valve configuration is not found to reduce TPF compared to single upper valve during TQ  Single jet TPF during the thermal quench is not very severe in DIII-D or ITER

34 NIMROD modeling provides new physics insights into MGI with single or multiple gas valves
NIMROD predicts that DIII-D 2-valve configuration reduces TPF, but increased diagnostic resolution is needed to capture trend, validate model On ITER, 3 upper valve configuration is not found to reduce TPF compared to single upper valve during TQ  Single jet TPF during the thermal quench is not very severe in DIII-D or ITER THANK YOU!

35 # of valves  MHD Mode #  TQ duration?
1 valve  n=1 dominant 3 valves n=3 dominant <B/B> - - Prad (a.u.) <B/B> - - Prad (a.u.) n=1 n=3 n=3 n=1

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