Japan Atomic Energy Agency Naka Fusion Institute

1. Japan Atomic Energy Agency Naka Fusion Institute EX/5-1 Enhanced H-mode Pedestal and Energy Confinement by Reduction of Toroidal Field Ripple in JT-60U H. Urano, N. Oyama, K. Kamiya, Y. Koide, H. Takenaga, T. Takizuka, M. Yoshida, Y. Kamada and the JT-60 Team 21st IAEA Fusion Energy Conference Chengdu, China, October 16–21, 2006

2. 1.2 1.1 1 0.9 0.8 0.7 0.6 40 50 60 70 80 Introduction Sufficiently high pedestal pressure is required for favorable energy confinement in ELMy H-mode plasmas. Energy confinement in JT-60U tends to be relatively unfavorable particularly at larger volume plasmas. HH98(y,2) The effect of large TF ripple has been pointed out. Losses induced by TF ripple enhances the toroidal rotation (VT) in counter-direction. Vp [m3] Pabs = 7-10MW (co+perp.-NBI) ELMy H-modes To reduce TF ripple and increase VT into co-direction, the ferritic steel tiles (FSTs) have been installed in JT-60U.

3. 2 TF-ripple contour 1 3.0% 2.5% 2.0% 0 1.5% 1.0% 0.8% -1 0.6% 0.4% 0.2% -2 dr [%] 0 p/2 p 3p/2 2p ftor [rad] Objectives Comparing between H-mode plasmas with and without FSTs, the characteristics of pedestal and ELM activities due to the reduction of TF ripple and the variation of VT are investigated in JT-60U. TF ripple Toroidal rotation Core Edge Pedestal separatrix Shoulder Large Vp (~75m3): TF Ripple < 2.0% w/o FSTs Pedestal height p ELM TF Ripple BT = 2.6T Pedestal Width Divertor

4. Outline • Introduction • Objectives • Plasma performance after the installation of FSTs • Effect of toroidal rotation and TF ripple on the pedestal and ELMs • Energy confinement • Summary

5. Energy confinement improved by the installation of FSTs Even at a given Pabs, energy confinement is improved with FSTs. Profile of VT shifts towards co-direction with FSTs at ~fixed Pabs. w/o FST with FST Pabs ~ 8.3 MW Pabs ~ const. co 6 E044292 E046426 with FST 15 P P NBI NBI 0 4 Perp.NB 10 [MW] Te [keV] VT [105m/s] 5 ctr 2 co - NBI co - NBI 0 0 3 w/o FST W ] DIA 2 2 W - -1 0 m DIA 2 [MJ] 0 1 0 1 r/a r/a 20 1 [10 1 T n L 8 4 T n L e e 0 0 2 6 3 D D a a .] Ti [keV] a.u ne [1019m-3] 4 2 1 [ 2 1 0 10 T (r/a=0.2) T (r/a=0.2) i i 0 ] 0 0 1 0 1 keV r/a 5 r/a [ T (r/a=0.8) T (r/a=0.8) i i The Te and Ti profiles are increased in whole range of minor radius by FSTs. 0 3.0 4.0 5.0 4.0 5.0 6.0 7.0 8.0 9.0 time [s] time [s] 1.2MA / 2.6T (q95 = 4.1) Large Vp(~75m3)

6. 0.15 0.1 0.05 0 -0.05 Pedestal and ELM Higher pedestal Ti is obtained in case with FSTs accompanied by wider pedestal width. ELM energy loss becomes larger while ELM frequency decreases. Inter-ELM dW/dt increased at a constant Pabs. Large Vp(~75m3) w/o FST 44292 0.1 2.02 with FST 2 Wdia [MJ] Da [a.u.] Ti [keV] 1 1.92 0 w/o FST 5.3 5.4 5.5 time [s] with FST 0 46426 0.1 2.16 distance from separatrix [m] w/o FST (Pabs = 8.4MW, VTped = -52km/s): fELM = 70Hz, DWELM = 18kJ Wdia [MJ] Da [a.u.] with FST (Pabs = 8.2MW, VTped = -21km/s): fELM = 51Hz, DWELM = 34kJ 0 2.06 7.8 7.9 8 time [s]

7. 1 0 -1 0 2 4 6 0 2 4 6 Edge toroidal rotation enhanced into ctr-direction with increased fast ion loss 1 co-NBI at large Vp When fast ion loss is increased by perp-NBs, VTped is enhanced into counter-direction. with FST VTped [105m/s] 0 PNBperp w/o FST -1 PLfast [MW] Effect of FSTs on VTped is the most remarkable at large Vp with co-NBI. co-NBI at small Vp (No clear difference at small Vp) VTped [105m/s] PLfast [MW]

8. 100 1 100 co-NBI with FST 80 80 co-NBI w/o FST bal-NBI with FST 60 bal-NBI w/o FST 60 ctr-NBI with FST 0 ctr-NBI w/o FST 40 40 20 20 0 -1 0 -1 0 1 0 2 4 6 ELM frequency becomes lower with edge toroidal rotation into co-direction Large Vp (~75m3) with FST (1)Power dependence (fixed VT at the pedestal) fELM Power dependence using perp-NBs of ELM frequency fELM involves the effect of VT in many cases. ne ~ 2x1019m-3 (type-I ELM) [Hz] [105m/s] At a given VTped, ELM frequency fELM increases in proportion to Psep. VTped Psep [MW] (2)Toroidal rotation dependence (fixed Psep) The dynamic range of VTped is expanded towards co-direction by the installation of FSTs. fELM [Hz] At a given Psep, ELM frequency fELM is clearly reduced as the co-toroidal rotation is enhanced. Psep ~ 5MW, ne ~ 2x1019m-3 VTped [105m/s]

9. co-NBI with FST co-NBI w/o FST bal-NBI with FST bal-NBI w/o FST ctr-NBI with FST ctr-NBI w/o FST -1 0 1 50 40 30 20 10 0 -1 0 1 ELM energy loss becomes larger when pedestal toroidal rotation increases into co-direction Large Vp (~75m3) 10 Inter-ELM 8 6 DWELM /Wped [%] PELM /Psep [%] 4 ELM loss power Psep ~ 5MW, Large Vp (~75m3) 2 PELM = fELM DWELM ne ~ 2x1019m-3 0 VTPED [105m/s] VTPED [105m/s] With increasing toroidal rotation towards co-direction, ELM energy loss DWELM clearly becomes larger with the decrease of fELM. When VTped shifts towards co-direction, the ELM loss power tends to increase slightly. In other words, the inter-ELM transport loss is reduced with VTped into co-direction. (Change of PELM/PSEP was small before the installation of FSTs.)

10. 10 co-NBI with FST co-NBI w/o FST 8 bal-NBI with FST bal-NBI w/o FST ctr-NBI with FST 6 ctr-NBI w/o FST 4 2 0 -1 -0.5 0 0.5 1 10 8 6 4 2 0 -1 -0.5 0 0.5 1 Pedestal pressure tends to increase with toroidal rotation into co-direction at the plasma edge Large Vp (~75m3) Pedestal pressure increases with the increase of VTped into co-direction. However, at large Vp config., higher pedestal pressure is obtained in case with FSTs at a given VTped. pped [kPa] At small Vp config., pedestal pressure is not changed by FSTs. VTped [105m/s] Small Vp (~52m3) Since the effect of FST is less significant at smaller Vp config., reduction of TF ripple may affect the increase of the pedestal pressure. pped [kPa] The changes of ELM activities with VTped are more sensitive than the change of pped. VTped [105m/s]

11. 10 co-NBI with FST co-NBI w/o FST 8 bal-NBI with FST bal-NBI w/o FST ctr-NBI with FST 6 ctr-NBI w/o FST 4 2 0 -1 -0.5 0 0.5 1 H-mode pedestal becomes wider with enhanced VT into co-direction and reduced TF ripple Effect of toroidal rotation Effect of TF ripple (A) (C) (B) 1 (C) with FST 0 pped [kPa] VT [105m/s] -1 (D) w/o FST (D) Large Vp (~75m3) -2 0 1 r/a VTped [105m/s] (C) with FST Compare the pedestal profiles with VTped into co- and ctr-direction at fixed TF ripple. 2 2 pedestal shoulder ] keV [ i T 1 1 Compare the pedestal profiles with large (w/o FST) and small TF ripple (with FST) at almost fixed VTped. (D) w/o FST 0 0 0.1 0.05 0 - 0.05 distance from separatrix [m] For both cases, pedestal width of Ti becomes wider while the change in the pedestal Ti gradient is unclear.

12. 1.2 1.1 1 co-NBI with FST 0.9 co-NBI w/o FST bal-NBI with FST 0.8 bal-NBI w/o FST ctr-NBI with FST 0.7 ctr-NBI w/o FST 0.6 Energy confinement improved with enhanced toroidal rotation into co-direction HH98(y,2) Large Vp (~75m3) -1 -0.5 0 0.5 1 VTped [105m/s] As VT is enhanced into co-direction, HH-factor becomes larger for the case of the large Vp plasmas. With the reduction of TF ripple by the installation of FSTs, higher HH-factor is obtained in case with large Vp plasmas. (The effect of TF ripple is small at the small Vp plasmas.)

13. Summary The characteristics of pedestal and ELM activities due to the reduction of TF ripple and the variation of toroidal rotation were investigated in JT-60U. • By the installation of FSTs, enhanced pedestal pressure and energy confinement are obtained at large volume plasmas. • (e.g. HH98(y,2) = 0.84 -> 0.92 at dr ~ 2% -> 1% for the case of co-NBIs) • With increasing VT into co-direction, pedestal pressure tends to be raised accompanied by wider pedestal width. • By the reduction of TF ripple, pedestal pressure is increased and the width of the H-mode pedestal becomes wider. • When VT increases into co-direction in type-I ELMs, ELM frequency decreases and ELM energy loss becomes larger. (The change of ELMs with VT is more sensitive than that of pedestal pressure.) The poster of this talk will be presented on Friday afternoon (EX/5-1).