JT-60U contribution to ITPA/IEA inter-machine experiments 2006 - 2007

1. JT-60U contribution to ITPA/IEA inter-machine experiments 2006 - 2007 Large Tokamak Meeting 21-22 May 2007 Presented by Y. Kamada

2. 1. Confinement Database and Modeling CDB-2 : Confinement scaling in ELMy H-modes: b-degradation Data supplied. No additional experiment. CDB-9 : Density profiles at low collisionality Experiments were performed over wide ranges of eff, Te/Ti and particle source. Density peaking with low central fuelling and electron heating (ECRF+N-NB) is comparable to or even stronger than that with central fuelling and ion dominant heating (P-NB).

3. 2. Transport Physics(1) TP-3 : Determine transport dependence on Ti/Te ratio with high confinement operation ECRF has been found to be affecting Ti ITB in a weak shear (WS) plasmas. Various scans have been carried out, such as PEC, target Ip, target Vt and so on. However, Ti/Te ratio does not seem to be a key parameter. TP-4.2 : Low momentum input operation effects on ExB shear and reduced transport Effects of low momentum input and low central fuelling on density and iontemperature ITBs were investigated using ECRF and N-NB in reversed shear plasmas. Density and ion temperature ITBs were formed with low momentum input and low central fuelling. TP-5 : QH/QDB plasma studies QH-mode plasmas were produced with the new ferritic inserts in the case of balanced and counter-NB. Detailed measurements of the toroidal rotation indicated that the boundary between the QH-mode and ELMing phases is related to the edge toroidal rotation.

4. 2. Transport Physics(2) TP-6.1 : Obtain empirical scaling of spontaneous plasma rotation The intrinsic rotation velocity in ECRF/LHRF wave heated plasmas was found to increase with plasma stored energy as observed in other machines. The rotation velocity was higher than that in other machines at a given beta. TP-6.2 : JT-60U/DIII-D Mach number scan similarity experiment TP-6.3 : NBI-driven momentum transport study There were a number of rotation experiments which, while not directly implementing this proposal, nevertheless were strongly relevant. TP-8.3 : JT-60U/JET ITB similarity experiment Postponed to 2007

5. 3. Pedestal and Edge Physics (1) PEP-1+3 JET/JT-60U similarity exp. ~ripple effect~ • To study effect of TF ripple on pedestal performance and ELM characteristics, dedicated experiments using JET similarity shape with reduced TF ripple (~1.3% to ~0.6% at the separatrix) at 2.2T, q95~3.6 (instead of 3.1T). • CTR rotation became small due to reduced fast ion losses • Achievable pedestal pressure was similar to that w/o FSTs • No clear difference in high Xp configuration was observed, where remaining local ripple near Xp was small • Larger DWELM with similar fELM gives larger PELM(=fELMxDWELM) with FST

6. 3. Pedestal and Edge Physics (2) type I grassy PEP-14 QH/QDB Comparison in JT-60U and DIII-D PEP-17 Small ELM regimes at low pedestal collisionality • Important parameter for grassy ELM: • d,bp, q95, VT (low VT in ITER: 0.23kHz) • To understand accessibility to grassy ELM regime with respect to VT • VT threshold~0.9kHz at q>6 and d>0.5 • DWELM/Wped<1% at 200Hz grassy ELM • waiting for experiments in DIII-D • Comparison of Er profile to understand mechanism of QH-mode transition • DIII-D: Larger Er well in QH phase (~100kV/m) • JT-60U: Similar Er well (~40kV/m)between QH and ELMy phase • next step: How Er profile important? what trigger EHO? Just before ELM QH phase

7. 3. Pedestal and Edge Physics (3) PEP-18: Comparison of Rotation Effects on Type I ELMing H-mode in JT-60U and DIII-D Relevant data were taken in both JT-60U and DIII-D independently. Collaborative comparison study from this Summer. PEP-20: Documentation of the edge pedestal in advanced scenarios JT-60 Pedestal data dbase for the advanced operation modes were constructed and sent to the ITPA database. C. Maggi et al., presented at the last IAEA conference.

8. 4. Seady State Operation (1) SSO-1.1Document performance boundaries for steady state target q-profile Real time q(r) control experiment was conducted. As qmin raised by off-axis LHCD above 2, which is a targeted steady-state profile, the m/n =2/1 NTM disappeared and N retrieved. SSO-2.1: Qualifying hybrid scenario at ITER-relevant parameters Steady-state pulses obtained over wide range of parameters. Under analyses. SSO-2.2: MHD in hybrid scenarios and effects on q-profile Sawteeth were induced by central ECCD and effect of the sawteeth on NTM was investigated in high p discharges and it was found that central ECCD enhanced sawteeth but suppressed the m/n =3/2 NTM. SSO-2.3: ρ* dependence on confinement and stability in hybrid Data were sent to the international DB.

9. 4. Seady State Operation (2) SSO-3: Modulation of actuators to qualify real-time profile control methods for hybrid and steady state scenarios Rreal-time q profile control by means of off-axis LHCD had been investigated. It was confirmed that qmin could be controlled well by this scheme. Effectiveness of the q profile control for optimization of steady-state operation was shown. Real time control of spatial gradient of the Ti profile (Ti) by combining on- and off- axis NB and real time measurement of Ti profile by filter CXRS. And real time control of Ti was demonstrated. SSO-4: Documentation of the edge pedestal inadvanced scenarios See PEP-20 SSO-6: Ability to obtain and predict off-axis NBCD off-axis NB driven current profile, this indicates effectiveness of off-axis NBCD.

10. 5. MHD, Disruption and Control MDC-2: Joint experiments on resistive wall mode physics No dedicated joint experiment. However, critical rotation required for RWM stability was investigated => ~0.3% of Alfvén velocity both in JT-60U and DIII-D MDC-3: Joint experiments on neoclassical tearing modes Database of onset condition for NTMs in Hybrid Scenario experiments is being established by using data from JT-60U, JET, DIII-D, AUG. MDC-5: Comparison of sawtooth control methods for neoclassical tearing mode suppression No joint experiment. However, results suggesting that active destabilization of sawteeth by central co-ECCD is effective in suppressing 3/2 NTM were obtained. MDC-8: Current drive prevention/stabilization of NTMs • Marginal island width at which NTM spontaneous decays during ECCD was investigated in JT-60U, DIII-D, AUG => ~twice ion banana width for m/n=3/2 NTM • Stabilization of m/n=2/1 NTM was performed. MDC-11: Fast ion losses and Redistribution from Localized AEs • Redistribution of fast ions by RSAE and its energy spectrum were measured

11. 6. OL/divertor physics DSOL-2 Hydrocarbon injection to quantify chemical erosion Local puff experiments of CD4, CH4, C2H6 gases in detached divertor were done in 2006. Nakano sent database to ITPA. DSOL-14 Multi-code, multi-machine edge modelling and code benchmarking SOLDOR results of JT-60U L-mode discharge (without drift, and assuming constant ration of C impurity) are prepared using MDSplus database by Kawashima. DSOL-15 Inter-machine comparison of blob characteristics (Parameters of database were not discussed in detail.) DSOL-16: Determination of the poloidal fueling profile Existing JT-60U profile database (3 L-mode and 3 H-mode in 2001) are prepared using MDSplus database by Kawashima. DSOL-19: Impurity generation mechanism & transport during ELMs for comparable ELMs across devices Fast response of the outer divertor plasma during ELMs were investigated using spectroscopy by Nakano, which was presented in ITPA 2007/May. Database will be prepared for ITPA.