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E4J PROJECT Beam tracing studies and MHD control by ECCD

E4J PROJECT Beam tracing studies and MHD control by ECCD. D. Farina IFP-CNR, Milano, Italy CONTRIBUTORS L. Figini, S. Nowak, D. Kislov G. Giruzzi, M. Lennholm, and the E4J Project Team JET Science Meeting, 25 January 2010. Outline.

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E4J PROJECT Beam tracing studies and MHD control by ECCD

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  1. E4J PROJECTBeam tracing studies and MHD control by ECCD D. Farina IFP-CNR, Milano, Italy CONTRIBUTORS L. Figini, S. Nowak, D. Kislov G. Giruzzi, M. Lennholm, and the E4J Project Team JET Science Meeting, 25 January 2010

  2. Outline • Beam tracing calculations (D.Farina, L. Figini, IFP-CNR, Italy) • Frequency choice • ECRH&CD performances • MHD control by ECCD • NTM stabilization (S. Nowak, IFP-CNR, Italy) • Sawtooth control (D. Kislov, et al. Kurchatov Institute, Russia) D. Farina, JET Science Meeting

  3. Basis for an EC system design • Main physics ingredients: • EC resonance: w = nwc(R) +k||v|| • Doppler effect (resonance shift – broadening) • refraction effects (cut-offs) • absorption rate / wave polarisation • harmonic overlap: Dw/w ~ 1/n • CD efficiency (trapping effects) • launching geometry EC resonance • Recipe: • Good absorption up-shifted CD: OM1,XM2 ~neTe • Large ECCD efficiency: ICD ~Te/ ne F(Te, N//,…) • Large ICD / JCDfor large/small toroidal angles • HFS EC interaction to minimize trapping effects • use poloidal angle to change r • check refraction effects (cut-offs) • check harmonic overlap: Dw/w ~ 1/n EC resonance radius REC = R0 B0 / (28 fEC) D. Farina, JET Science Meeting

  4. EC frequency & magnetic field • Choice of the optimal EC frequency based on: • E4J physics goals => rEC • B range of operation: 2.5 T ≤ B ≤ 3.4 T EC resonance radius vs B0 REC = R0 B0 / (28 fEC) • 113 GHz: • same frequency of the previous EC Project for JET • OM1 - HFS interaction at high B>3 T • 170 GHz: • ITER EC frequency • XM2 - HFS for B < 3 T, LFS B>3 T • 150 GHz: • option double freq. gyr. 113/150 GHz • XM2 - HFS for B < 2.8 T • Cut-off density: • 113 GHz OM1 nco= 1.6 1020 m-3 • 150 GHz XM2 nco= 1.4 1020cos2f m-3 • 170 GHz XM2 nco= 1.8 1020cos2f m-3 D. Farina, JET Science Meeting

  5. Reference Scenarios #73344, standard H-mode scenario: high ne& low Te, small ratio Te/ ne #77895, advanced scenario: low ne& high Te, large ratio Te/ ne Equilibrium rescaled keeping q95, plasma b and ne/nGW constant:plasma current, density and temperature rescaled with B D. Farina, JET Science Meeting

  6. ECRH&CD calculations B=2.65 T - 170 GHz Two mirror locations: R = 4.3 m z = 34.5 cm UM R = 4.3 m z =-34.5 cm LM Divergent beam(not optimized): waist=3 cm at the mirror a and b poloidal&toroidal angles NR= -cosa cos b Nf= sin b Nz= -cosb sina Wide scan of injection angles: 0º ≤ b ≤ 26º, step Db = 2º -50º ≤ a ≤ 40º, step Da = 2º GRAY code: beam tracing code, relativistic absorption CD via adjoint method D. Farina, JET Science Meeting

  7. 170 GHZ – H-mode&AT scenarios H-mode scenario AT scenario • 170 GHz: XM2 (XM3) • 2.7 T≤ B ≤ 3.2 T: • up to plasma centre • B ≤ 2.7 T: parasitic XM3 • B=2.5 T, large XM3 absorption in AT scen. • B>3.2 T: EC resonance in the LFS • ECCD up to 3 times larger in AT w.r.t. H-mode scenario D. Farina, JET Science Meeting

  8. optimal launching set-up EC driven current EC driven current density poloidal angle toroidal angle toroidal angle Most favorable launching conditions(at any frequency): Upper mirror: upward Lower mirror: downward max J achieved at lower toroidal angle b than max Icd Effective steering range: toroidal angle -25º/+25º, poloidal steering range 30º D. Farina, JET Science Meeting

  9. ECCD summary at 170 GHz • B0 varied in steps DB=0.1T • a, b scan for each B0 value • Data filtering: Pa>95%, dr<0.1 • Data grouping: step Dr=0.1 H-mode scenario • ECCDAT ≈ 2.5 x ECCDH-mode(more favorable Te/ne ratio) • Max ECCD efficiency at: • B0=2.8 T (H-m) and 3.0 T (AT) • region r<0.2 accessible up to: • B0=3.2 T (H-m) and 3.4T (AT) • ECCD affected by • - trapping effects at high B0 (hfs) • - 3rd harm. absorption at low B0 and high T Advanced scenario D. Farina, JET Science Meeting

  10. Frequency choice 113 GHz 150 GHz 170 GHz • Main criteria: • good accessibility • large absorption • Pa > 95%, P3 < 20% • large ECCD • 113+150 GHz : • Broad magnetic field range • Poor performance at B0~3T • Low ITER relevance • 170 GHz : • Best performances at B0~2.8-3T • 3rd harm. absorpt. at B0<2.6T • Low efficiency at B0≥3.4T • Fully ITER relevant D. Farina, JET Science Meeting

  11. NTM Stabilization JET NTM Stabilization by 10 MW EC power at 170 GHz Theoretical model for the island dynamics : Generalized Rutherford Equation (GRE) for the mode amplitude Frequency evolution equation for the mode rotation Stabilization criterion by ECCD : Reduction of the mode amplitude to its marginal stable width by driving the EC current inside the magnetic island to replace the bootstrap current Evaluation of EC power needed to stabilize the NTM : The EC power, PEC,stab , stabilizing the NTM is obtained through the balance of the current drive and heating terms with all the other terms in GRE D. Farina, JET Science Meeting

  12. NTM stabilizationH-mode scenario, 2.5 T-3.2 T  minimum PEC,stab required for stabilization of (2,1) and (3,2) modes  Three values of J profile width dcd : 0.05 m, 0.1 m, and the value from beam tracing beam-tracing • PEC,stab< 6 MW sufficient to control the (3,2) mode for all B and (2,1) for dcd<0.05 m • PEC,stab>10 MW needed to stabilize the (2,1) mode for dcd≥0.1m and B>2.9T • small benefit from EC power modulationfor wm/dcd>0.5 D. Farina, JET Science Meeting

  13. Sawtooth control byco- or cnt-ECCD close to q = 1 INF • Computation method: • Predictive T and j transport simulations  ASTRA (checks with JETTO) • ECCD: beam-tracing / Fokker-Planck code OGRAY (Zvonkov, PPR 1998) • Effect on sawtooth  Porcelli’s model Investigation of 4 ECCD locations at the q = 1 surfac D. Farina, JET Science Meeting

  14. Dynamical sawtooth period computation INF Porcelli’ sawtoooth crash model incorporated in ASTRA code, with fast particle effect included. ft = 7°, fp = 0, B = 2.7 T, PEC = 2.5 MW Results: Cnt-CD Sawtooth period reduced by 2.5 Co-CD Sawtooth period reduced by 1.7 Best results obtained for counter current drive and small J profile width sawtooth period vs rECCD r t t t t r D. Farina, JET Science Meeting

  15. Conclusions • Frequency 170 GHz(same as in ITER) has been chosen since it allows very good performances in the interval 2.7-3.1 T • extensive analysis of ECCD efficiency performed varying the launching angles in a wide magnetic field range. • NTM stabilization • EC power < 5-10 MW sufficient for full island suppression in most cases of interest, without power modulation, provided the driven current is localised in a radial range < 10 cm. • Sawtooth stabilization • Even less power (~ 2.5 - 5 MW) would be sufficent for sawtooth control. D. Farina, JET Science Meeting

  16. ECCD performances at 170 GHz H-mode scenario - Summary NTM q profile Sawtooth 25 January 2010 D. Farina, JET Science Meeting 16

  17. 170 GHz - ECCD for NTM stab. Icd increases with b Icd and J much larger at q=3/2 wrt to q=2 peak J maximum at moderate b J profile width increases with b 25 January 2010 D. Farina, JET Science Meeting 17

  18. EC power modulation Benefit from EC power modulation (50% on - 50% off) centered at the O-point for w/dcd < 0.5 • modulation required only for • wm/dcd<0.5 w/dcd=0.78 : PEC,mod=0.86 PEC,cw • small benefits from modulation for • wm/dcd>0.5 w/dcd=0.38 : PEC,mod=0.52 PEC,cw 25 January 2010 D. Farina, JET Science Meeting 18

  19. ECCD Sensitivity to ne, Te Scenario #73344 at B0 = 2.65 T, independent variations of ne and Te • Dne/ne = ±20%: Icd~ 1/neas expected • Note: Icd maximized for different a, b when ne is varied • DTe/Te = ±25%: Icd ~ Te • DTe/Te > 50%: Icd “saturates” in inner regionsHere no Icd at r<0.3 due to parasitic absorption on 3rd harm. 19

  20. 113 GHz & 150 GHz • 113 Ghz: OM1 • B≤3.0 T: EC resonance in the outer region • B>3.0 T: EC resonance for < 0.8 (HFS) • 150 Ghz: XM2 • B≤3.0 T: EC resonance in a wide region • B>3.0 T: EC resonance in the outer region Driven current versus r injection angles scan #73344 PEC=1 MW 25 January 2010 D. Farina, JET Science Meeting 20

  21. f=113 GHz ORDINARY mode injection - first harmonic Driven current versus r obtained from injection angles scan • B≤3.0 T: EC resonance for >0.8 • B>3.0 T: EC resonance for < 0.8 (HFS) PEC=1 MW #73344 PEC=1 MW #73344 25 January 2010 D. Farina, JET Science Meeting 21

  22. f=150 GHz EXTRAORDINARY mode – 2nd harmonic Driven current versus r obtained from injection angles scan • B<3.0 T: EC resonance in a wide region • B≥3.0 T: EC resonance in the outer region PEC=1 MW PEC=1 MW 25 January 2010 D. Farina, JET Science Meeting 22

  23. f =170 GHz EXTRAORDINARY mode 2nd harmonic (+3rd) • B ≤ 2.7 T: • parasitic 3rd harmonic absorption • B > 3.2T: • EC resonance in the LFS • 2.8 T ≤ B ≤ 3.2 T: • ECCD in a wide region 25 January 2010 D. Farina, JET Science Meeting 23

  24. 170 GHZ - 3rd harm. absorption • Main drawback at 170 GHz: • Third harmonic interaction can take place at low B and/or at high Te. • B=2.5 T: large fraction of power may be absorbed as 3rd harmonic, reducing the power available at the 2nd harmonic. • B= 2.65 T: 3rd harmonic absorption is less than 5%, but it may become relevant at large Te . • P3/P0 is larger in case of the upper mirror, since the beam crosses inner plasma regions (at larger Te). B=2.5 T #73344 25 January 2010 D. Farina, JET Science Meeting 24

  25. Beams superposition (estimate) • Launcher option L1 (steering mirror close to the plasma), UM • Option L2 (steering on back of the port w/ vertical plates), UM (R0,z0)=(447,31) cm (R0,z0)=(560,36) cm 2x3 beams 3x2 beams Dr=Dz=10 cm Dr=Dz=10 cm w0=2.4 cm w0=3.2 cm b0=12.5º b0=6º @R=4.47m • Convergence computed for q=3/2 surface at B0=3.0T, shot 73344 • Current profiles overlap evaluated at B0=2.7, 3.0, 3.3T

  26. Beams Superposition – Option L1 B0=3.0T B0=3.3T Drtot=0.072 Dr=0.067 Drtot=0.074 Dr=0.074 • Convergence needed at B0=3.0T: • Db = 1.5º (in a given row) • Da = 2.7º (in a given column) • Max spread at 3.3T: Drtot = 1.07 Dr • Spread mainly due to vertical offset among beams B0=2.7T Drtot=0.080 Dr=0.079

  27. Beams Superposition – Option L2 B0=3.0T B0=3.3T Drtot=0.062 Dr=0.062 Drtot=0.059 Dr=0.054 • Convergence needed at B0=3.0T: • Db = 0.7º (in a given row) • Da = 1.9º (in a given column) • Max spread at 3.3T: Drtot = 1.09 Dr • In L2 example single profiles are narrower (smaller b0, larger w0) B0=2.7T Drtot=0.057 Dr=0.057

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