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25 th Fusion Energy Conference, St. Petersburg Oct 13-18 2014 1 Si-Woo Yoon on behalf of KSTAR Team and collaborators National Fusion Research Institute (NFRI), Daejeon, Korea Contents 2 Introduction Extension of Operation Boundary

  1. 25 th Fusion Energy Conference, St. Petersburg Oct 13-18 2014 1 Si-Woo Yoon on behalf of KSTAR Team and collaborators National Fusion Research Institute (NFRI), Daejeon, Korea

  2. Contents 2  Introduction  Extension of Operation Boundary Upgrade of KSTAR heating system Long-pulse extension of H-mode duration High Beta operation  Advances of Tokamak Physics Research Error field identification Mitigation and Suppression of ELM H-mode & rotation physics  Future Plan

  3. Original Mission and Key Parameters of KSTAR 3 Machine design is optimized for advanced target operation Strong shaping, Passive plates, low TF ripple, …

  4. Recent Major Milestones of KSTAR 4

  5. Contents 5  Extension of Operation Boundary Upgrade of KSTAR heating system Long-pulse extension of H-mode duration High Beta operation  Advances of Tokamak Physics Research Error field identification Mitigation and Suppression of ELM H-mode & rotation physics  Future Plan

  6. Current Machine Status (2014) : long-pulse compatible NBCD and ECCD systems 6 NBI-1 (PNB, co-tangential, CW) (3 beams, 5.0 MW/95keV ) 170 GHz ECH (1 MW/ CW ) Full Graphite PFCs ( with Water cooling pipe) 110 GHz ECH 30 MHz ICRF 5 GHz LHCD (0.7 MW/4 s) (1.0 MW/10 s) (0.5 MW/2 s) Divertors in-situ cryo-panel is ready Baffle IVCP

  7. Long-pulse H-mode discharge (~ 30 s) achieved in 2014 campaign 7 Successful Extension of H-mode pulse-length upto 30 sec β N ~ 2 , I p =0.4 MA, B T =2.0 T , f NBCD ~ 0.55, κ ~ 1.8, δ ~ 0.6 1 [MA] Shot 10123 0.5 p I 0 [MW] 5 P NBI P ext ~3.8 MW (NBI) + 0.2 MW ECCD(3 rd Harmonic) ext P P ECRH 0 ] -3 5 m 19 [10 9 e 8 x 10 n 0 Da [a.u.] 6 midplane 4 divertor 2 ECE [keV] 4 R=1.8 m (core) 2 R=1.35 m (edge) f NI ~ 0.70 0 [MJ] 0.5 f NBCD ~ 0.55 tot W f BS ~ 0.15 0 kappa 2 J || (MA m -2 ) 1 J NB 4 Wb 2 J BS 0 -2 J EC -4 0 5 10 15 20 25 30 35 time[s] ρ φ

  8. Pulse-length is further increased (~40 s) adding more ECCD and using in-vessel cryo-pump 8 Successful extension of H-mode pulse-length upto 40 sec I p =0.5 MA, B T =3.0 T , P ECCD ~ 0.8 MW , P NBI ~ 3.8 MW, f NBCD ~ 0.50, β N ~ 1.4 Experiments for longer pulse is planned using Motor-Generator in this campaign 1 Interlock by T div I p [MA] 0.5 0 5 P ext [MW] P NBI P ECRH 0 n e [10 19 m -3 ] 5 9 x 10 0 Ha [a.u.] midplane 3 2 divertor 1 ECE [keV] R=1.8 m (core) 10 R=1.35 m (edge) 5 0 0.5 W MHD [MJ] 0 3 \Beta_n 2 1 0 elongation 2 1 0 5 10 15 20 25 30 35 40 time[s]

  9. High Beta above no-wall limit is achieved transiently by optimal I p /B T and with P ext ~ 3 MW 9 Sabbagh, EX/1-4 b N /l i = 5 - By Early heating for low l i b N /l i = 4 MP2014-05-02-007 by Sabbagh and Y.S. Park (Better Ip ramp-up scenario) - Optimizing B T & I p Recent operation in 2014 B T in range 0.9-1.5 T n = 1 with-wall limit n = 1 no-wall limit I p in range 0.4-0.7 MA - Prior published maximum was b N =2.9 Operation Present maximum b N ~4 - in 2012 Operation in 2011 First H-mode in 2010

  10. Contents 10  Extension of Operation Boundary Upgrade of KSTAR heating system Long-pulse H-mode operation High Beta & high Ip operation  Advances of Tokamak Physics Research Error field identification Mitigation and Suppression of ELM H-mode & rotation physics  Future Plan

  11. Unique features of KSTAR : 11 Ideal machine for 3D & rotation physics • Intrinsically low toroidal ripple and low error field also Error field : very low value was detected (  B m,1 /B 0 ~10 -5 ) - • Modular 3D field coils (3 polidal rows / 4 toroidal column of coils) - Provide flexible poloidal spectra of low n magnetic perturbations n=1, +90 phase n=1, 0 phase  n=2, odd + + - - + + - - + - + - top top - + + - B P + + - - mid mid + + - - - - + + - + - + bot bot  Full angle scan shows that the error field would be lower than sub Gauss (resonant field at q=2/1 based on IPEC calculations) 11

  12. A complete set of compass scan using mid-RMP coils in 2014 again confirms the record-low intrinsic EF in KSTAR 12 (typically 10 -4 in other devices) 𝒐 𝒇 𝒆𝒎 𝑭𝟐𝟘𝒏 −𝟑 = 𝟐. 𝟔 *The exact definitions slightly differ, as referenced Purest plasma response against externally applied non-axisymmetric fields in KSTAR

  13. The presence of low EF is also supported by accessing low 13 q 95 Ohmic discharges without any external means Pa Pass ssing ing q 95 95 =3 3 (li=1.0 1.0) without out (violent iolent )MHD MHD Min q 95 =2.06 at li=0.55 l i =0.87 at q 95 =3

  14. ELM-suppressions have been demonstrated using 14 both n=1 or n=2 RMP with specific q 95 windows #7821 #806 0 n=1 (+90 phase) RMP at q 95 ~6.0 n=2 RMP (mid-FEC only) at q 95 ~4.1

  15. ELM suppression is transiently achieved also at intermediate q 95 ~ 4.5 combining of n=1 & 2 RMPs 15 n =1 (middle) and n =2 (top/bottom) • The q -window (4.3~4.5) in ELM suppression is observed during I p scan ( q -scan). • • NB : q~6 6 at n n=1, , q~ q~3.7 3.7 at n= n=2, q~4. 4.5 5 at n= n=1+2 2 ( wide e q 95 95 window) dow) I p RMP V t n e , W tot q 95 D alpha Extending q 95 window space at ELM suppression

  16. Depending on the n=2 RMP configuration, either suppression or mitigation of ELMs could be selected 16 Jeon, EX/1-5 #9286: I p =0.65MA, B T =1.8T  q 95 ~4.0  ELM suppression under 6.0kAt n=2 RMP at q 95 ~4.0 Initially ELMs mitigated by n=2 even (top/bot) RMP As mid-FEC currents added (n=2,+90 RMP), ELMs further mitigated and then suppressed #9286 Note that ELM-suppressed phase showed better confinements than that in ELM-mitigated phase - See changes on <n e >, W tot , and b p n=2 (+90 top/mid/bot) n=2 (even top/bot) suppression mitigation 16

  17. Reduced Heat flux at outer divertor is confirmed for RMP (n=1) ELM mitigation with newly installed IRTV 17 IRTV on outer divertor KSTAR #10503 600 500 500 400 W MHD [kJ] I p I p [kA] 400 300 300 200 W MHD B 200 A 100 100 5 0 4 I IVCC [kA] Top Middle 3 Bottom 2 1 0.6 0 RMP off D  [a.u.] 0.4 0.2 100 o C] 80 T div [ Broader heat 60 1 2 3 4 5 6 7 8 9 10 11 flux near SP Time [sec] RMP on

  18. ELM mitigation by Supersonic Molecular Beam injection with small confinement degradation 18  Typical features of ELM mitigation by SMBI H. Lee, EX/P8-9 Δn e ~ 5-15 % H 98(y,2) τ I  Characteristics of ELM mitigation by SMBI - Δ n e ~ 5-15 % after SMBI - τ I ~ 200-400 ms SMBI / f ELM 0 ~ 2.0-3.1 - f ELM  Degradation of global confinement is insignificant - H 98(y,2) : 0.9-1.0  0.8-1.0 (Too small for ELM type transition)

  19. ELM mitigation sustained by multiple SMB injection 19 H. Lee, EX/P8-9 ~8 % ~ 2.0-3.1 ~15 % • f ELM 0 ~ 180 Hz , f ELM SMBI ~ 430 Hz → f ELM SMBI / f ELM 0 ~ 2.4  Δn e ~ 5-15 %  Change of f ELM 0 with 30% of n e increase ~ 15 %  f ELM SMBI ~ 2.0-3.0x f ELM 0  Change in f ELM owing to SMBI is much larger than that due to increase in n e

  20. Strong ELM mitigation (~ x10) observed also by injecting 20 ECH at pedestal Poloidal angle scan ρ pol ~ 0.86 ρ pol ~ 0.94 ρ pol ~ 0.86 ρ pol ~ 0.90 ρ pol ~ 0.94 ρ pol ~ 0.98 P NBI 3 P ECRH P ext [MW] 2 1 0 8 TORAY-GA 6 n e [10 19 m -3 ] 2 nd Harmonics deposition at LFS 4 2 Mitigation stronger at larger ρ pol 0 2.5 divertor f ELM ~30 [Hz] 2 ∆ W ELM ~20 [kJ] Ha [a.u.] No ECH 1.5 ∆ NeL ~0.16 [10 19 /m3] 1 ∆ T e,ped ~0.4 [keV] 0.5 0.2 f ELM ~60 [Hz] 0.18 ρ pol ∆W ELM W tot [MJ] ~ 4 [kJ] 0.16 ~ 0.86 ∆ NeL 0.05 [10 19 /m3] 0.14 ∆ T e,ped 0.3 [keV] 0.12 0.1 2 ρ pol f ELM ~90 [Hz] 1.5 ∆W ELM ~ 0.98 ~2 [kJ ] Te [keV] ∆ NeL 0.16 [10 19 /m3] 1 ∆ T e,ped 0.4 [keV] 0.5 3.5 4.5 5.5 6.5 7.5 time[s] Strong coherent oscillation (~10 kHz) exists during ECH injection

  21. High-field side ECE imaging of ELM filaments 21 Δ𝑈 𝐹𝐷𝐹 O1 Park, EX/8-1 𝑈 𝐹𝐷𝐹 100 𝐹×𝐶 𝑊 𝑞𝑝𝑚 ~ 𝑊 50 ECEI ~5.569s ECEI ~5.569s HFS FS ima mage LFS LFS ima mage z [cm] (O1) (O (X2) (X 0 LFS-0902 X 𝒐 𝑰𝑮𝑻 ~𝟗 𝒐 𝑰𝑮𝑻 ~𝟐𝟓 -50 𝑊 𝑢𝑝𝑠 × tan 𝛽 -100 HFS-0306 X 150 200 250 R [cm]  The HFS mode does not fit into the conventional ballooning mode picture  Investigating the possibility of simultaneous existence of two modes of the same helicity • Opposite poloidal rotations between HFS and LFS • A strong Pfirch-Schlüter flow (~25km/s) at the edge is suggested, which makes a poloidal asymmetry in the toroidal flow

  22. High toroidal rotation at pedestal top is likely 22 due to both low EF & TF ripple in KSTAR KSTAR Ripple amplitude vs Major radius KSTAR #7244 H-mode 1.6 0.08 LCFS Machine δ TF (%) at edge 1.4 0.07 0.08 (32 coils) ~ JET 1.5 (16 coils) 1.2 Ripple amplitude,  TF [%] 0.06 DIII-D 0.5 JT-60U 0.5 ~ 1 1 Mach number 0.05 ITER 0.5 ~ 1 0.8 0.04 N N R + R inner 0.6 δ TF = 0.03 R outer R 0.4 0.02 Mach D 0.2 Mach C 0.01 0 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2 2.25 2.3 0 R [m] 1.8 1.9 2 2.1 2.2 2.3 R [m] Mach number ( ≡ 𝒘 𝝔 /𝒘 𝒖𝒊𝒇𝒔𝒏𝒃𝒎 ) is also found to be high ( Mach D ~ 0.6, when V ϕ,D = V ϕ,C )  The clear observation of the toroidal rotation velocity pedestal seems to come from a low toroidal  field ripple ( ~ 0.05%) and error field of the KSTAR tokamak In JET, Mach number is 0.5 for δ TF ~ 0.08 % whereas 0.2 for δ TF ~ 1 % (Mach number in KSTAR is ~  0.6)

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