Simultaneous measurement of the ELMs at both high and low field sides and ELM dynamics in crash-free period in KSTAR Hyeo eon K. Pa Park UN UNIST, Uls Ulsan, Korea at 25 th IAEA FEC Conference Oct. 12 -18 2014, St. Petersburg, ELMs at the ELMs in 3D Russian Federation high & low field sides [low field side) In collaboration with W. Lee (UNIST), M.J. Choi, M. Kim, J.H. Lee, J.E. Lee, G.S. Yun (POSTECH), X.Q. Xu (LLNL), S.A. Sabbagh, Y.S. Park (Columbia U.) ,C.W. Domier, N.C. Luhmann, Jr. (UC Davis), S.G. Lee (NFRI), KSTAR Team
Outline KSTAR 2D/3D ECE Imaging and MIR system 2D validation of the physics in modeling predictive capability of MHD and transport physics modeling Images of the ELMs in H-mode plasma Growth -> Saturation -> Crash Validate the measured ELMs with synthetic images ELMs at High field side Discrepancies with the current understanding ELM dynamics during the crash free period Underlying dynamics of suppression/mitigation of the ELMs?
KSTAR 2D/3D Imaging systems at 23 rd FEC Daejeon Korea H G Modified sawtooth Combined EX/P8-12, G. Yun with 2D MIR m/n=2/1 mode #8969 t=7.043442-7.197158s (ref.ch. ECEI G 1404) 1.5 1 -1 ] Poloidal wavenumber [cm 0.5 0 -0.5 -1 -1.5 0 50 100 150 200 250 Frequency [kHz] 2D T e T e fluctuation fluctuation (k vs. ω ) (30-50 kHz) Cold bubble Leads to disruption EX/P8-13, W. Lee EX/P8-15, Choi 2D Density fluctuation
KSTAR ECEI viewing windows (B 0 =2.0 T) High Field Side (HFS) Low Field Side (LFS) HFS LFS HFS O-mode Measurement with O-mode polarization is verified for Sawtooth crash J. Lee_JINST_(2011) Poloidal view of Characteristic frequencies of the KSTAR plasma the electron cyclotron emission
Dynamics of a single ELM in KSTAR H-mode plasmas (1) Initial growth (2) Saturation 4 1 2 3 400 µ s 0 µ s 100 µ s 200 µ s LCFS LCFS G.S. Yun et al., PRL 107 (2011)
Validation of the ELM structure BOUT++ Synthetic Image Synthetic Image Measured Simulation* with system noise (ideal) image δ T/<T <T> phantom Instrument Function Major radius (cm) • Observed structure = a faithful representation of ELM filaments - Phantom image outside the separatrix due to ECE downshift from inside (well known); masked by finite system noise and scattered emission - We ignore ECE signals contaminated by the downshifts M. Kim et al., NF 54 (2014)
Relationship between toroidal (n), poloidal (m) mode numbers & pitch angle ( α∗ ) Poloidal ECEI-1 spacing Pitch angle ECEI-2 Range of toroidal mode numbers Toroidal spacing 4 < n < 16 ECEI-2 (GFS) ECEI-1 (LFS) ch_15 ch_10 J.H. Lee, RSI, 85 (2014) J.E. Lee, 9th APFA conference (2013)
Simultaneous measurement of the ELMs at both HFS and LFS (2013) ECEI ~5.569s TV image with EFIT HFS i ima mage KSTAR #9380 ECEI ~5.569s LFS i image 0.5 AU 100 0 -1.4 V 50 -1.6 Frequency [kHz] ECEI LFS, 0902 20 z [cm] 0 10 LFS-0902 X 0 -1.8 -50 V -1.85 Frequency [kHz] ECEI HFS, 0306 20 HFS-0306 -100 X 10 0 5.5 5.52 5.54 5.56 5.58 5.6 Time [s] 140 160 180 200 220 240 R [cm]
Rotation direction and mode strength KSTAR #9380 ECEI ~5.569s HFS i image ge KSTAR #9380 ECEI ~5.569s LFS i ima mage LFS ECEI edge ge HFS S ECEI edge ge Rotation direction – Asymmetries in toroidal and/or poloidal velocity Comparable mode strength at HFS and LFS – No shear flow damping at HFS ?
Mode spacing based on Ballooning mode Refraction effect - the actual mode spacing in HFS should be larger than the observed one. ECEI ~6.840s HFS i ima mage ECEI ~6.840s LFS i image Z [m] Refractive index n e (max)~3x10 19 /m 3 R [m] In and out pressure asymmetry ? unlikely The structure of ELM filaments at the HFS is not consistent with the ballooning mode structure.
2-D correlation image of the HFS & LFS ELMs Correlation image for #9379 t=6.839249-6.843688s (ref.ch. GD 22-5) Correlation image 25 for #9379 t=6.839249-6.843688s HFS-2205 0.2 (ref.ch. LD 9-2) 0.8 X Pitch (mid-plane) 20 20 0.15 0.6 15 15 0.1 0.4 10 10 0.05 0.2 5 5 0 140 160 180 200 220 Z [cm] Z [cm] 0 0 R [cm] 0 LFS-0902 -5 -5 X -0.2 -10 -10 225 13 0.13 LFS -0.4 -15 -15 132 10 0.09 HFS -0.6 -20 -20 215 220 225 -0.8 R [cm] -25 130 135 140 ELM structure + strong shear flow in HFS R [cm] edge -> streamer like role ?
Burst process of the HFS & LFS ELMs (2013) Time evolution of a single global ELM crash
ELMs & crashes in crash free period (2011) B 0 =2T, I p =600kA, T e (0)~2.5 keV, <n e >~3 × 10 13 cm -3 A B C n =1 MP W tot ~250kJ 240kJ D α change from n=10 to n=5 mode 15 B A n e (m -2 ) 10 5 d B /dt 0 (T/s) -5 -10 f (kHz) -15 205 210 215 220 225 230 Major radius R(cm) rf ( 0.6 GHz ) No steady ELMs ELMs with tiny crashes Time (s) C ELM crash free period (No steady ELM) accompanied with rf bursts No large crash but occasional tiny crashes 205 210 215 220 225 230 No changes in Time (sec) background G.S .S.Y .Yun, , PoP 19 ( (2012)
ELMs & crashes in crash free period (2012) MP B 0 = 1.8 T, I p = 510 kA D α q 95 ~ 4.5, P NBI = 2.7 MW W tot : 220 180 kJ A B C n e (m -2 ) d B /dt (T/s) f (kHz) rf (0.2 GHz) Observation has been Time (s) consistent over 3 years High-n suppression or High-n low-n suppression Suppressed time consist of Smaller bursts (bunching and single), brief moment without ELM, and persistent ELM with higher n without crash rf signal (<200 MHz) is a good measure of ELM crash Broad-band dB/dt signal is not from high-n mode crash (Note: e: EX/1-5 Y. Jun )
Illustration of no burst and burst cases (2012) rf signal is much better indicator of the ELM crash Steady Bursting Little change in magnetic signals !! ELM period ELM period
Summary Findings from the HFS ELMs Mode number discrepancies – in/out asymmetry in pressure profile or Ballooning representation incorrect?? Large mode amplitude – high flow shear damping at the HFS?? Rotation direction – asymmetries in toroidal/poloidal velocities + others (e.g., Pfirsch Schluter flow)?? Crash proceeds first at LFS – Ballooning characteristics?? ELM dynamics during the “suppression” period Change of the edge confinement less free energy higher n, higher frequency, smaller crashes (bunching and singles), persistent ELMs without crash and brief moment without ELMs :marginal free energy or intricate physics?? Broad spectra of dB/dt signals during ELM suppression period is not from the high-n mode burst
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