Stability, Transport, and Conrol

1. IEA/LT Workshop (W59) combined with DOE/JAERI Technical Planning of Tokamak Experiments (FP1-2) 'Shape and Aspect Ratio Optimization for High Beta Steady-State Tokamak’ 14-15 Feb. 2005 at San Diego, GA Stability, Transport, and Conrol for the discussion Y. Miura

2. Stability (1) • by Ferron, • fbs pqN • fusion gain ENH89/q952 (increase qmin than q95) • peaked pressure profile reduces achievable N • near ideal N limit tearing mode still have significant effects on confinement • highest N obtained in balanced DN • high shape, but soften by Type I ELM • squareness reduces ELM size (it reduces pedestal pressure?) • by Rimini, • What are the changes when operating at high ? • ITBs are not compatible with large ELMs • Gas (light impurity) -> to reduce ELM size

3. Stability (2) • by Kurita, • critical N values (n=1) for NCT are shown to be increased by increasing S (shape factor through  and A) • Max N using sector coil set is estimated • by Miura and Matsukawa, • The shape and aspect ratio are important to increase the critical  limit for NCT • By Menard, • For no wall limit • < N > ~3.2 nearly invariant ( extend to low A) • < N >/li is not A invariant • High d is required to take full advantage of high k at low A • < N > and q*=(1+2)/0IN are good measure for NSTX data • For ideal limit • N limit increases from 6 to 9 as A->1 • Are high , high  and low A always good for high N? • Where is an optimum condition for these parameters?

4. Transport • by Petty, • Transport dependence on elongation and safety factor are weaker than IPB98(y,2) relation but close to EGB relation • For “optimum tokamak”, fusion gain is optimized between aspect ratio of 2.2 and 3.0 (depending upon which confinement scaling relation is used) • If stability limit and elongation are assumed independent of aspect ratio, then fusion gain optimizes at higher R/a • by Field, • BE0.73[IPBy2] => 0.83[IPBy2-PBXM +MAST] • Pedestal scaling => HFS pedestal width scaling • by Saibene, • High plasma shaping (d, k, QDN)  common element to all small ELM experiments in JET • At low bp, mixed Type I-II ELMs are observed in SN and QDN – increasing q95 closes off access to high nped and no Type II ELMs • High bp: “threshold” similar to JT-60U, but different collisionality Can we reduce ELMs at highly shaped plasma?

5. Control (1) • by Litaudon, • Increasing the H & CD at P~45MW(NB & IC upgrade) • Access to bootstrap-dominated regimes at 2.5MA, N>2.5 • Explore -scaling • ~1/3 of PNB in counter to control V • Upgrade of LHCD launcher • Reliable PLHCD~3MW in H-mode • by Miura, Kurita and Matsukawa, • Control of NTM by ECCD in NCT • Further optimization is necessary to improve response time of feedback field to the plasma • Shaping controllability

6. Control (2) • by Sabbagh, • In NSTX, N ~6.8. The RWM control in NSTX was discussed. • by Hubbard, • Current profile control by LH was discussed. • In C-MOD, 3MW LH (4.6GHz) is ready for the experiment. • by Moreau, • Real time current profile, shape, profile and flux control were discussed. • It is towards controlled advanced scenarios on JET There are some methods to control plasma in this workshop. High fbs plasma is a self-oganized plasma. We have to find the way to control a burning plasma with high fbs.