Access to High b p (advanced inductive) and Reversed Shear (steady state) plasmas in JT-60U

1. Access to High bp (advanced inductive) and Reversed Shear (steady state) plasmas in JT-60U S. Ide for the JT-60 Team Japan Atomic Energy Agency the 7th Integrated Operation Scenarios Topical Group Meeting Kyoto University, Kyoto, Japan, 18th – 21st October 2011

2. ITB In JT-60U, the AT development has been pursued base on two types of internal transport barrier (ITB) plasmas mainly with pedestal. strong pressure weak H-mode pedestal 0 1 r q q • High bp plasma (since 1994) • Reversed shear (RS) plasma (since1996) 4 3 3 2 2 1 0 1 0 1 r r • RS w or w/o current hole, bN2.5, fBS80%, full CD • Strong ITB • Candidate for steady state • Monotonic/weak shear, bN5, fBS70%, full CD • ITB are sometimes very weak • Candidate for advanced inductive high bp and RS plasmas in JT-60U • How to access these plasmas?

3. high bp plasmas • monotonic-weak shear (qmin ~1-1.5) • weak-moderate ITB + pedestal • bN ≤ ~3 (for longer sustainment), <~5 (very short) • q95 ~2.5 – 4.5 (roughly) • Can be fully non-inductive with fBS~50% • Not sensitive care is required at ramp-up phase. • NB injection start, just before reaching flattop or even after. So injected energy during ramp-up is not important. • A simple empirical recipes exists • start (strong) NB heating just before sawtooth starts. • central NB deposition is important. • for above two, keeping low density before NB heating is preferred.

4. ITBs in a high bp mode

5. ITER Advanced Op. sustained bN Inductive Op. bN=2.5x16.5s bN= 2.3x22.3s sustained duration (s) T. Suzuki (EX/1-3, Tue.) Long Sustainment of High bN bN=2.3 sustained for 22.3s(~13.1tR) E44092, Bt = 1.56 T In ITER, bNH89p/q952 = 0.4: standard (Q=10) and =0.3: steady state (Q=5) => ITER Hybrid operation Ip (MA) PNB (MW) q95~3.1-3.2 H89p~1.9 P-NB N-NB bN=2.3 Te,i (keV) Ti bN Te ne/1019 (m-3) Da (a.u.) tR : Dr. D. R. Mikkelsen Phys. Fluids B 1 (1989) 333. time (s) bNH89p/q952 > 0.4 bN=2.5 and 2.3 fBS~35-40%

6. Wdia (MJ) time [sec] Pabs (MW) Pth can be also found by power step-upagain no Bt dependence ITB

7. High fusion performance with full CD • High d~0.34 at high Ip=1.8 MA and high power N-NB (5.7 MW) • bN=2.3-2.5, HHy2 = 1.2, nD(0)tETi(0) = 3.1x1020 m-3skeV, full non-inductive CD (BS:50%) •  was suppressed by tailoring p(r)&q(r) in low collsionality regime (ne*~0.02~ITER).

8. q 8.3s jtot jNB jtot,jBS, jNB (MA/m-2) jBS r Integrated performance <=> the ITER steady state domain fBS~45% sustained for 5.8s (~2.8tR) under nearly full CD in weak shear (qmin~1.5) plasma nearly full-CD 1MA, 2.4T, q95~4.5 E44104 • Weak shear with qmin>~1.5 => no NTM. • bN~2.4 (bp~1.75), fCD>90%(fBS~50-43%, fBD>52-47%) , HH98(y,2)~1.0 PNB, NNB (MW) P-NB N-NB bN bp, bN bp Vloop (V) Dadiv (a.u.) time (sec) Y. Sakamoto (EX/4-3, Wed.)

9. reversed shear plasmas • weakly-strongly reversed shear (qmin mostly >2, q0 ~2 - >10) • moderate-strong(box type) ITB + weak pedestal • bN ≤ ~2.7 • q95 ~> 4.5 (typically) • Can be fully non-inductive with fBS<~85% • Empirical recipes • start NB heating as early as possible. For this divertor configuration stars at very early of a discharge (<0.5s from breakdown). • central NB deposition is important. • NB heating at early time, when q is reversed, triggers ITB. The ITB raises the BS current at ITB. The BS current enhances or keep the q profile reversed.

10. reversed shear plasmas • ITB formation • Reversed shear is believed to be an enough condition for ITB formation, but sometimes not sufficient. • Pth to form Ti ITB seems to be lower for lower Ip. Once ITB is formed it is easier to maintain the reversed shear. Therefore, typical recipe to establish a good RS discharge is early NB injection. • For Te ITB formation, Pth seems to be very low or even almost zero if the q profile is reversed. • W/O ITB formed very early in a discharge, target reversed q profile can hardly be maintained until Ip flattop. Therefore early NB injection is required. • However with LHCD, reversed q can be maintained and late ITB formation is possible.

11. PNB (MW) Ip (MA) bp, bN Vloop (V) Dadiv (a.u.) time (sec) fBS~75% sustained for 7.4s (2.7tR) under nearly full CD in reversed shear plasma 0.8MA, 3.4T,q95~8.6 • Very high confinement characteristics: HH98(y,2)~1.7 (H89p~3.0), fBS~75%, fBD~20%, bp=2.2-2.3, bN~1.7, ne/nGW~0.55 • Although q95 is yet high, demonstrates steady state with high fBS q Ti (keV) r Y. Sakamoto (EX/4-3, Wed.)

12. Ti ITB formation - NB power scan - Experimental condition: BT~3.7T, Ip~1.3MA, q95~5, d~0.2, ne~1.0x1019m-3, Balanced momentum injection. NB power (PNB) was varied from 2 to ~17MW in PS and RS plasmas. Change in Ti profiles are significantly different in both PS and RS plasmas. PS RS

13. Ti ITB formation depends on Ip

14. Magnetic shear is a key factor for Te ITB formation Inverse scale length of Te (LTe-1) for PS plasmas stays constant with increasing PEC. Te ITB was not formed without Ti ITB in PS region. The threshold power for PS is large compared with that for RS. Inverse scale length of Te (LTe-1) for RS plasmas increased gradually with PEC. Te ITB was formed without Ti ITB in RS region. Gradual increase suggests that absence of threshold power for Te ITB formation. PS RS LTe-1=-gradTe/Te

15. ECH to raise Te • Before ECH faulted, q profile is reversed. But, qmin is lower and RS region is smaller. <= due to peaked Te, in outer region where Te is not high current penetration is not retarded.

16. off axis LHCD • with LHCD (~ 1.5 MW), well reversed q profile with large RS region was obtained.

17. comparison of three cases • in LHCD case, • qmin is well maintained high. • wide reversed shear region. • low density => matter of CD efficiency and power.

18. Summary • High bp • Simple recipe: apply central heating (just) before ST. • Pth exists, but parameter dependences are not clear yet. • Reversed shear • For Te ITB, low or no Pth., while for TiPth exists and lower for lower Ip. • JT-60U recipe is to apply NB heating as soon as possible at ramp-up. But may suffer, too strong ITB or current hole.