Developing the Physics Basis for the ITER Baseline 15 MA Scenario in Alcator C-Mod

Transcription

1 Developing the Physics Basis for the ITER Baseline 15 MA Scenario in Alcator C-Mod C. E. Kessel 1, S. M. Wolfe 2, I. H. Hutchinson 2, J. W. Hughes 2, Y. Lin 2, Y. Ma 2, D. R. Mikkelsen 1, F. M. Poli 1, M. L. Reinke 2, S. J. Wukitch 2, and the C-Mod Team 1 Princeton Plasma Physics Laboratory, Princeton, NJ, USA 2 Plasma Science and Fusion Center, MIT, Cambridge, MA, USA 54 th American Physical Society Division of Plasma Physics October 29-November 2, 2012 Work supported by the US Department of Energy under DE-AC02-CH & DE-FC0299ER54512

2 H-mode Onset Late in the Rampup Can Save More V-s Compared to Heated L-mode Relative V-s savings compared to ohmic rampup Δψ e OH Δψ e ICRF Δψ e OH = 9.6% for 1 & 1-2 MW ICRF in L-mode 11 V-s for ITER = 14.4% for 1-2 MW ICRF with late H-mode 17 V-s = 20.0 % for 1-3 MW ICRF with late H-mode 23 V-s (projected) e, ITER OH = 115 V-s Since ITER targets an H-mode rampdown, it can take advantage of H-mode V-s savings

3 Extended Flattop Experiments to Demonstrate Simultaneous ITER Parameters B T = 2.7 T, 2 nd harmonic H- minority heating E = 20 ms CR = ms ITER Parameters: q 95 = 3.0, = 1.8, 0.45 N = 1.75 n/n Gr = 0.85 H 98 = 1.0 C-Mod: , E 8-13 CR ITER Features: P rad /P input = 20-40% P net /P thr,lh = P e-heat /P i-heat > 2 (P aux +P alpha )/P OH > 30 Regulated H-mode Low and high Z impurities 2 CR duration 16-36% EDA B, Mo 8-13 CR

4 H 98 Drops with Increasing n/n Gr in Spite of Higher P net P net = 0.9P ICRF + P OH P rad dw/dt 2012 discharges pushed to higher P net by increasing P ICRF to access higher H 98 H 98 overlaps with 2011 data In the experiments when P net was increased, primarily by increasing P ICRF, the maximum flattop density decreased Operational constraint coupling heating and fueling? Is 2 nd Harmonic damping weaker at higher density?

5 When P ICRF and P net are Equal, the Higher n/n Gr Shows T ped Dropping Strongly n/n Gr = 0.68, 0.84 P ICRF = 2.8, 2.8 P net = 2.1, 2.0 H 98(y,2) = The n e,bar and n e,ped increases by only 25% Aligning P ICRF and P net shows that the T ped is reduced by > 2x T core shows similar gradient with slightly different values

6 The Impact of MHD on Energy Confinement or Other Discharge Features is Not Clear Mode onset: 1) triggered by H-L-H transients when βn ~ ) sufficiently high βn ~ , without transients 10 khz modes have n = 2 20 khz modes have n = 3, 4 All modes rotate in the co-ip direction Intrinsic bulk rotation is co-ip at ~ 50 km/s (H-modes) For n = 2, soft X-ray data indicates structure near q=1, q=1.5 and pedestal region βnonset(ρiφ*) ~ 3.85, βnonset(5.2υe*0.3) ~ 3.75 for NTMs 10 khz onset when βn ~ 1.5 (no trigger) 10 khz off when βn < khz onset at βn ~ 1.75

7 In H-mode Rampdown Discharges the n ped and T ped Drop, But Not at the Same Rate The electron pedestal temperature and density both show a progressive decrease during the H-mode rampdown Edge Thomson Scattering The n-ped follows Ip, but T-ped drops quickly early and then very slowly up to the H-L transition L-mode L-mode

8 Rampdowns in High Density Flattop Experiments Confirm Earlier Conclusions H-mode rampdowns were routinely obtained in high density flattop expts Rampdown expts at 5.4 T: 2.7 T, H-modes sustained into rampdown with ICRF 2. Faster rampdowns are better to cause I OH to drop 3. nl, n ped drop with Ip 4. H 98 ~ early, late while in H-mode 5. P net /P thr,lh = , with n/n Gr = Rampdowns expts at 2.7 T: 1. Same results as 5.4 T 2. P net /P thr,lh = **, with n/n Gr = H-mode L-mode ** reduction in B T leads to lower P thr,lh Y. Ma

9 New Work on the ITER Baseline Scenario in Alcator C-Mod Rampup phase: H-mode transition in rampup can save 50% more V-s compared to ICRF heating alone in L-mode 11 V-s 17 V-s in ITER Although the benefits of ICRF heating in L-mode rampup appears to saturate, transition to an H-mode with additional ICRF power could double the V-s savings 11 V-s 23 V-s in ITER Flattop Phase: Expanded operating space of quasi-stationary ITER demonstration plasmas to higher P net, but observe strong reduction in H 98(y,2) ~ for n/n Gr ~ Pedestal is severely cooling as n/n Gr 0.85 Rampdown Phase: High density (n/n Gr = ) flattop discharges showed routine H-mode sustainment in rampdown at 2.7 T with ICRF power, and confirmed higher B T conclusions

10 Strong Trade-Off Between H 98 and n/n Gr n/n Gr > 0.82, H 98 ~ > n/n Gr > 0.72 H 98 ~ > n/n Gr > 0.64 H 98 ~ N ~ 1.4 N ~ 1.75 N ~ 1.95 Quasi-stationary phases time, s