Long sustainment of jt-60 u plasmas with high integrated performance long sustainment of jt-60 u plasmas with high integrated performance

LONG SUSTAINMENT OF JT-60U PLASMAS WITH HIGH INTEGRATED PERFORMANCE This paper treats the recent development of quasi-steady ELMy highβp H-mode discharges with enhanced confinement and highβ stability, where i) long sustainment time, ii) increase in absolute fusion performance and iii) expansion of the discharge regime toward low-q 95 (~3) are emphasized. After modification to the new W-shaped pumped divertor, a long heating time (9sec) with a high total heating energy input of 203MJ became possible without harmful increase in impurity and particle recycling. In addition, optimization of the pressure profile characterized by the double transport barriers, electron density and / or high triangularity δ enabled us to extend the performances in long pulses ; the DT equivalent fusion gain QDT eq~0.1 (δ =0.16) was sustained for ~9 sec (~50 τE, ~10τp) and QDT~0.16 (δ = 0.3) for 4.5s at I p=1.5MA. In the latter case, H-factor (= τE/τE) ~2.2, βN~1.9 and βp~1.6 were sustained with 60-70% of noninductive driven current. In the low q 95 (~3 ) region, the β-limit was improved by the high δ (~ 0.46) shape where βN~2.5-2.7 was sustained for ~3.5s with the collisionality close to that of ITER-FDR plasmas. The sustainable βN is limited by onset of the low-n resistive modes. The direct measurement of the island width shows the agreement with the neoclassical tearing mode theory. The edge pedestal width ∆−ped in the ELMy phase evolves gradually with increasing T i at the pedestal shoulder and the saturated width (10-15cm at I p=1MA) is 2-3 times larger than that in the ELM-free phase. The width ∆-ped is proportional to (a/R) ρpi. The limit of the edge α-parameter increases with increasing δ, which is the main reason of the improved high-β stability in a long pulse by highδ. The sustainable value of βNH increases with increasing δ.