Advanced Tokamak Research in JT-60U and JT-60SA

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1 I-07 Advanced Tokamak Research in and JT-60SA A. Isayama for the JT-60 team 18th International Toki Conference (ITC18) December 9-12, 2008 Ceratopia Toki, Toki Gifu JAPAN

2 Contents Advanced tokamak development in Physics understanding in AT regime Physics assessment for JT-60SA Summary JT-60SA DEMO ITER

3 Advanced tokamak development in

4 This talk Sakamoto (Thu, AM) Advanced Tokamak research in In ITER & DEMO, simultaneous achievement of - High beta (β N ) - High confinement (H H98(y,2) ) - High non-inductive CD fraction f NI (=f BS +f CD ) with sufficient duration is required In AT research, - High β p H-mode (~ITER Hybrid) - Reversed shear (~ITER SS) have been developed β N N T M ITER SS ITER Hybrid Positive shear JT-60SA R W M DEMO No-wall β limit: 3-4 l i Reversed shear f BS AT target Standard Advanced Progress in ITER Physics Basis, Chap.1

5 β N H H98(y,2) >2.6 was sustained for 25s (~14τ R ) in high β p H-mode plasma β N =2.6, H H98(y,2) = , f BS ~0.4: >~ ITER Hybrid performance Avoidance of NTM onset by p & q optimization: q=1.5, 2 surfaces far from steep p 0.9MA/1.55T, q 95 =3.2, H H ~1, n e /n GW ~

6 Central heating is effective in keeping ITB E45436(2006) E48158(2008) 2008 w/o FST w/ FST ITER Hybrid FST 2006 Fast ion loss has been reduced by installing ferritic steel tile (FST) (2005) Power supply of 3 PERP-NBs for central heating was modified for 30s injection (2007) Peaked pressure can be kept with smaller P net

7 Physics understanding in AT regime - NTM suppression - RWM suppression Last shot of (2008/8/29)

8 NTM stabilization with ECCD in Neoclassical Tearing Modes (NTMs) - appear in a high β plasma with positive shear ITER Standard and Hybrid scenarios - set achievable beta at β N <β N ideal - sometimes cause disruption NTM control is important: m/n=3/2 and 2/1 NTM avoidance long-pulse high-beta exp. NTM stabilization: ECCD Previous results in with ECCD Stabilization with O1 & X2 ECCD Stabilization with real-time mirror steering Preemptive stabilization Simulation with TOPICS-IB code NTM research in Stabilization with modulated ECCD Modulation Frequency [khz] Progress in modulation NTM stabilization Heat wave propagation Year

9 Stabilization effect is significantly affected by the phase difference between db/dt and ECCD Modulated ECCD: phasing is required for O-point ECCD 0º 90º 180º 0º phase difference: stabilization effect 90º phase difference: no clear effect 180º phase difference: destabilization effect Phasing is important

10 Detailed phase scan showed that phase error should be smaller for effective stabilization ECCD efficiency: η EC Hegna, PoP 97 Perkins EPS 97 Giruzzi, NF 99 50% degradation O-point ECCD ~exp[-t/τ decay ] 300ms B ~ time Modified Rutherford equation dw/dt=f(w) η EC (W) g(w) τ decay : minimum at ~ 10º O-point ECCD τ decay ~4s for unmodulated ECCD modulated ECCD : > x2 more effective α c Similar to experiments

11 RWM study in Resistive Wall Modes (RWMs) - appear at β N > β N - terminate the plasma by disruption Rotation can stabilize RWM RMW control by V t control : Variety of NBI pattern Previous RWM study Identification of minimum V t for RWM stability V crit t ~0.3% of V A M. Takechi PRL (2007) C β = β N β N β N ideal-wall β N RWM research in Detailed study on RWM stability (dv t /dr, etc) Sustainment of β N > β N plasma

12 Two new instabilities have been observed just before RWM: EWM and RWM precursor Discharge duration was limited by a variety of MHD instabilities Two new instabilities at β N >β N (1) Energetic particle driven Wall Mode (EWM) directly induce RWM even at V t >V t crit (2) RWM Precursor strongly affects V t profile at q=2, and finally induces RWM Strategy for longer sustainment - Sustain enough V t & dv t /dr to avoid RWM - Reduce perpendicular NB to avoid EWM/RWM precursor G. Matsunaga, IAEA2008

13 High β N (> β N ) was sustained for ~5s (~3τ R ) β N ~3.0 (C β ~0.4) was sustained by keeping V t > V t crit Sustained duration: ~5s (~3τ R ) limited by increase of β N due to gradual j(r) penetration f NI >80% and f BS ~50% (ACCOME code calculation) Successful sustainment by RWM suppression β N ~5s (~3τ R ) High β N regime above β N has been extended

14 Physics assessment for JT-60SA

15 JT-60SA program JT-60SA (JT-60 Super Advanced) Combined program of - ITER Satellite Tokamak Program of JA and EU - Japanese National Program Mission of JT-60SA Early realization of fusion energy by - supporting exploitation of ITER - research toward DEMO Target area of JT-60SA plasma Wide range of operational regime - Break-even class plasmas at I p <~5.5 MA - High β N full-cd plasmas for 100 s Wide range of plasma equilibrium - High shape parameter: S~6 - Low aspect ratio: A~2.5 S=(I p /ab)q 95 A -1 {1+κ 2 (1+2δ 2 )} Better stability with higher A -1, κ, δ a measure of stability improvement β t (=Sβ N /q 95 ) increases with S

16 Main parameters in JT-60SA Active MHD stabilization tools - 110GHz ECRF for NTM - In-vessel coils for RWM Nominal Parameter Major radius R [m] Minor radius a [m] Plasma current I p [MA] Toroidal Field B t [T] Plasma Volume [m 3 ] Greenwald density [10 20 m -3 ] Shape Parameter S Flattop [Wb] TF Ripple at R+a Aspect ratio A 2.5 Elongation κ x Triangularity δ x Safety factor q 95 ~ ~ ~8 0.85%

17 Profiles in full consistent calculations of CD for steady-state scenarios j (MA/m 2 ) T e, T i (kev), n e (10 19 m -3 ) Total q 0.4 BS NB EC ρ n e T i 4 T e ρ q Example of Full-CD I p =2.3MA B t =1.76T q 95 =5.4 f GW =0.85 f BS =0.65 β N =4.1 H H =1.3 I BS =1.49MA I NB =0.821MA I EC =0.015MA P PNB =20MW P NNB =10MW P EC =1.5MW

18 Summary advanced tokamak research Long pulse high β p H-mode - High integrated performance plasma with β N =2.6, H H98(y,2) ~1.0, f BS =0.4 was sustained for 25s (~14τ R ) by NTM avoidance NTM control - Importance of phasing was demonstrated - Modulated ECCD is >x2 superior to unmodulated ECCD RWM control - 2 new instabilities at β N >β N : EWM & RWM precursor - β N >β N was sustained for 5s (~3τ R ) by RWM suppression JT-60SA advanced tokamak research Design activity & physics assessment - Wide range of operational regime and plasma equilibrium - Full CD capability confirmed by simulation