ARIES-AT Physics Overview presented by S.C. Jardin with input from C. Kessel, T. K. Mau, R. Miller, and the ARIES team US/Japan Workshop on Fusion Power Plant Studies and Advanced Technologies with participation of EU March 16-17, 2000 Copley International Conference Center, UCSD

Physics Goals for ARIES-AT ARIES-RS (1996) has received a lot of attention –provides the U.S. vision of a tokamak power plant –being compared against ARIES-ST, Stellarators, fission, etc –stimulated the tokamak community to explore reversed shear –motivated new prototype experiments ( TPX, KSTAR) It was felt that the ARIES-RS physics analysis lacked the depth it should have received for such an important study –~ 1 year design during time of program change We were asked to revisit ARIES-RS to perform a more aggressive and more complete design – ARIES-AT –More aggressive: use experience gained in ARIES-ST to optimize further –More complete: bring in transport analysis, better edge analysis

ARIES-AT has been optimized to a higher degree than previous studies Uses 99% flux surface rather than 95% –Higher  values are stable More flexible pressure profile –Better bootstrap alignment and higher  –Allows elimination of HHFW, and use only LHCD for off-axis CD Higher triangularity –Allowed by elimination of inboard slot divertor –Higher  N and higher I P to give higher  Higher elongation –Allowed by moving stabilizing shell closer to plasma –Higher  N and higher I P to give higher 

Higher elongation allows higher  Made possible by a closer vertical stabilizer shell b/a =0.5 -> 0.2 Increased elongation has weak impact on  N, but strong impact on      P  a       q    Ballooning stable  and  N  = 0.7 q edge = 3.5 A = 4

Kink Stability requires analysis up to n > 6 NOTE: critical wall location moves in for  > 2.2

Vertical Stability Analysis indicates which plasma elongations are viable based on allowable distance between plasma and shell Feedback control calculations still need to be done to set power requirements.

Including a non-zero edge density allows increased edge radiation ARIES-RS had n(a) = 0.4 n(0) Strong bootstrap reduction Increased CD requirement excessive Z EFF in core we use n(a) = 0.2 n(0) with 0.8% neon, making Z EFF = 2 we have examined  N =5.6,6.0,6.5 cases with n(a)/n(0) = 0.2 to find stable equilibrium and CD requirements off-axis CD is about 1.2 MA

These studies use a accurate formula for the bootstrap current taking into account all collisionality regimes Can lead to significant differences in the optimization

Seed Current Drive on ARIES-AT Current drive is required in two regions: - On-axis: provides bootstrap seed and controls q(0) - Off-axis: controls q min location and enhances  limit. Radio frequency systems are used for integrability to fusion power core. RF power launch location spectra are selected for maximum CD efficiency and profile alignment. For a 1-GW ARIES-AT, CD requirements are: - On-axis: 68 MHz 4 MW - Off-axis: 3.6 GHz 22 MW ARIES-AT:  N = 6.0, I BS /I = 0.94 = 16 keV, Z eff = 1.8  B = 6.3 On-axis CD: ICRF/FW Off-axis CD: LHW

Current and Rotation Drive on ARIES-AT When rotation generation for kink stabilization is considered, we propose using tangential NBI that also drives off-axis current. For efficient rotation drive, we use moderate energy beams based on positive-ion sources. The beam orientation is also set to maximize CD efficiency and profile alignment. A 1-GW ARIES-AT reactor with  N = 6.0, =16 keV will require: - On-axis: 68 MHz & 4 MW - Off-axis: 120 keV & 34 MW - Generated rigid-body rotation speed is 264 km/s ~ 0.05 V ao ARIES-AT:  N = 6.0, I bs /I = 0.94 = 16 keV, Z eff = 1.8  B = 4.0 ICRF/FW NBI

Physics Comparison between ARIES-RS and ARIES-AT RSAT Plasma current, I P (MA) Plasma Shape,  1.9,.762.2,.86 ,  N (%) 5.0, , 5.4 Bootstrap Fraction B T at coil, plasma (T)15.8, ,5.9 ITER 89P H factor CD power8025 Major Radius R (m) COE7653 Both have: A=4 1GW net electric

Plasma Transport Constraints In ARIES-RS the only constraint imposed on kinetic profiles (n,T) was that the dominant gradient lie inside or around the q min location In ARIES-AT, we are attempting to find density and temperature profiles that: provide good bootstrap alignment ideal MHD stability non inconsistent with experimental observations predicted by a transport model (if possible) for some rotation profile to be determined (GLF23) connection to the divertor solution neoclassical tearing mode stable

Summary optimization studies show that  can be increased significantly over ARIES-RS likely configuration has  =2.2,  > 9% finite edge densities allow reasonable divertor solutions, but affect bootstraps current and CD likely configuration has n(a) / n(0) = Current drive systems probably sufficient CD power ~ 25 – 35 MW density and temperature profiles only approximately constrained so far future work by GA will attempt to apply GLF23 transport model