Demonstration of sawtooth period control with EC waves in KSTAR plasma J. H. Jeong , M. Joung, M. H. Woo, S. H. Hahn, W. S. Han, Y. S. Bae and J. G. Kwak National Fusion Research Institute, Daejeon, Korea D. H. Kim, T. Goodman and O Sauter CRPP CRPP - EPFL, Lausanne, Switzerland EPFL La sanne S it erland K. Sakamoto, K. Kajiwara and Y. Oda Japan Atomic Energy Agency, Naka, Japan W. Namkung and M. H. Cho Department of Physics, POSTECH, Pohang, Korea H. Park School of Electrical and Computer Engineering, UNIST, Ulsan, Korea J. Hosea and R. Ellis Princeton Plasma Physics Laboratory, Princeton, USA KSTAR Conference 2014 February 24~26, 2014, Gangwon-do, Korea Email address: jhjeong@nfri.re.kr
Sawtooth instability � Destructive periodic magnetic instability (divided into three phases): τ sawtooth • Ramp-up phase � precursor phase � Collapse • Ramp-up phase � precursor phase � Collapse n e & T e increase in n e & T e crashes toward MHD instability grows with the core outside of q =1 surface internal kink structure � Sawtooth crash criterion [F. Porcelli et al, PPCF (1996)] : ′ = ⋅ S 1 > S 1 , crit s r q (r ) where, I. 1 1 1 δ δ ω ω τ τ ˆ W W Ideal-MHD unstable when δ W <0 δ W <0 π < − i A A Id l MHD t bl h * * II. S 2 δ = δ + δ + δ ˆ ˆ ˆ ˆ W W W W 1 MHD KO FAST 2
Sawtooth control actuator: localized ECCD � Change the magnetic shear near q =1 surface ( S 1 = r 1 · q ′ ( r 1 )) using localized CD as follows; • Deposition location of ECCD power influences period • Direction of current change the period • Feedback control: measure the period, then, change the deposition F db k t l th i d th h th d iti ( � slow and determined by the performance of antenna mechanics) • Another method: sawtooth locking (or pacing) • Active control using modulated power � locking to the requested period • Possibility of open-loop control S ( q =1) ( q ) ECCD 3
Motivation: Link between sawteeth and TM/NTMs � Sawtooth lengthening by the ICRF resonance q ~ 1 (JET shot number of 51794) � Purpose of sawtooth lengthening � Increase the n & T in the core by long inter crash time � Increase the n e & T e in the core by long inter-crash time � Result � Increased sawtooth period � big crash � triggering of n =2 MHD activity Sauter O et al 2002 Phys. Rev. Lett. 88 105001 4
Motivation: KSTAR & ITER KSTAR #7950 ITER will have large fusion born alpha particle population in the core population in the core Long sawtooth periods are expected NB1 NB2 ECRH ECRH ICRH Trigger NTMs are expected Sawtooth crash ☞ Sawtooth period has to be controlled with ECE @1.855 m small & frequent (to avoid NTM triggering) Triggering of n = 1 tearing modes in H-mode plasma 5
Sawtooth behavior by the EC beam deposition position � Actuator: • 110 GHz, 0.4 MW X2 mode • co-CD 15 deg oblique injection co CD 15 deg oblique injection � β N =0.45, I p = 0.4 MA 110 GHz ECH us nversion radiu #7072: Off-axis ECCD #7072: Off-axis ECCD #7072: Off-axis ECCD In rsion radius Ray tracing using y g g Invers #7070 O #7070: On-axis ECCD i ECCD Toray-GA code #7070: On-axis ECCD 6
Sawtooth behavior according to the direction of CD � Actuator: • Off-axis injection with z=10 cm in R res • 110 GHz, 0.4 MW X2 mode • co-CD 20 deg oblique injection co CD 20 deg oblique injection � β N =0.45, I p = 0.4 MA q =1 surface q 1 surface r 1 =2.07, ρ =0.37 20 deg. cnt-CD injection 20 deg. co-CD injection � Stabilization: cnt-CD injection inside the q =1 surface � Destabilization: co-CD injection inside the q =1 surface 7
• Preliminary results of sawtooth locking by the periodic Preliminary results of sawtooth locking by the periodic forcing of EC beam in KSTAR (year 2013) – System upgrade: feed-forward control of antenna mirror system in poloidal direction Feed-forward control of antenna mirror counts] Requested position q p r position [c Measured position Launcher latency ~ 100 ms 8
Background & Motivation of sawtooth locking � ECH/CD is very efficient to modify the sawtooth period [1] 1 1. By tailoring the profiles of j CD which is associated by the magnetic shear on the q =1 surface (= s 1 ) By tailoring the profiles of j CD which is associated by the magnetic shear on the q =1 surface (= s 1 ) Experimental results are well corresponded with the other tokamaks (year 2012, using 110 GHz ECH) � 2. Possible of injection locking by the modulated EC beam [2,3] (year 2013, using 170 GHz ECH) [1] C. Angioni, T.P. Goodman, M.A. Henderson and O. Sauter, Nucl. Fus. 43 455 (2003) [2] T. P. Goodman et al ., Phys. Rev. Lett. 106 245002 (2011) [3] G. Witvoet et al ., Nucl. Fusion 51 103043 (2011).
Activities on Real-time sawtooth period control in 2013 KSTAR - Implementation of Launcher Control System in PCS Scan of vertical position PCS wave server � To find optimized EC target position R ECR PCS wave server Vertical target position q=1 RFM PCSrt1 cal Optic RFM PCSrt5 Time (HICS) (HICS) RS232, 115200 bps (100Hz/50Hz) Antenna pivot: (launcher status, encoder) TCP/IP (2.8m, 0, -0.3m) ETOS RS232 (19200 bps, 150 msec) � All PCSs have a real time processor and RFM. ECH OPI � Preset time evolution of the vertical target position (EPICS) DC motor � motor Driver � But calculate the angle with position in real time � But calculate the angle with position in real time Micro PLC Micro-PLC Encoder � Transfer the angle to ECH local launcher controller based T/L PLC Upgraded by FPGA Antenna in PLC � Mirror angle is changed by motor. (after campaign) � Returned angle from encoder is also calculated in EC b beam target position at PCS in real time. t t iti t PCS i l ti Block diagram for controlling antenna mirror by PCS 10
EC beam poloidal scan (#9145) � Target position: just outside q =1 surface for stabilization of sawtooth • Poloidal mirror scan: z =10 cm ~ 30 cm (from mid-plane) • τ saw maximized at z ~26 cm (= EC-beam deposit position for the sawtooth locking experiments) KSTAR #9145 (EC sweeping) Te [keV] τ saw [ms] EC [MW] EC [MW] τ τ saw maximized with 100 ms at Z [cm] z=26 cm Poloidal mirror scan Z EC beam Time [sec] EC start EC start 11
Sawtooth locking experiments (#9215) � 170 GHz X2 at B T =2.9 T EC beam � I P = 700 kA Target position fixed at z=26 cm g p � <ne> = 2.7 × 10 19 m -2 ECE � β N = 0.5 � q 95 = 5.43 locking locking τ saw Sawtooth period is fully extended with τ saw =100 Sawteeth are regulated at τ saw =43 msec msec by CW EC beam injection outside q =1 surface C C f by EC modulation freq. of 23 Hz & 70 % duty 12
Injection-locking range in KSTAR 2013 � B T =2.9 T, I P = 700 kA, <ne> ≈ 2.7 × 10 19 m -2 EC � β N ≈ 0.5 modulation period � q 95 ≈ 5.43 95 5 43 � #9147 Non-locking Sawtooth locking range in KSTAR during 2013 campaign #9146 #9146 non- locking partially-locking (#9146) #9147 sawtooth period alternates two values two values locking #9215 #9146 partially locking p y g τ saw EC beam Sawtooth locking range during 2014 campaign? g g g p g Modulation enabled at t=3.5 sec to 6.5 sec 13
Future work: Injection-locking range in KSTAR ? What do we need? Wh t d d? � We can find two X points: min τ saw, min w/o EC and max τ saw max with full EC power τ saw, max with full EC power � We have to choose proper EC period and duty cycle for both locking and non-locking cases � possibility of locking in KSTAR can be proved l ki i KSTAR b d � We can obtain the condition of τ saw NTM triggering � We can control the sawtooth period in real-time to avoid NTM triggering gg g D. H. Kim, sawtooth locking range in TCV g g 14
Future plan : Conceptual design & requirements for the real-time sawtooth control RF modulation for sawtooth Timing & synchronization for Gyrotron locking and pacing RF modulation RF modulation Feedback reference KSTAR τ saw signal PI controller PCS (d t (determination of i ti f +/- antenna angle & EC freq.) rt- Detect crash ECHres equili R INVERSION (real-time τ saw determination) (ray-tracing) brium Corr- Antenna elation T e profile T fil controller Mag. Soft X-ray N e ECE & (detect crash) (detect crash) (T ) (T e ) profile profile Flux Flux (B, Ψ ) Plasma 15
Future plan (system upgrades) � Goal: real-time feedback control using ECCD • Feed-forward control of the ECCD mirror to investigate relation between the sawtooth (2013) (2013) period and triggering NTM i d d t i i NTM TCV #42357 • Conceptual design of real-time sawtooth p g control (2014) • Development of real-time sawtooth control system by PCS • Upgrade of antenna for fast movements and • Upgrade of antenna for fast movements and feed-back control (2015) • Validation & application of the real-time feedback sawtooth control in KSTAR (2016) Goodman T. P. et al 2011 Phys Rev. Lett ., 106 245002 16
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