1. 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

2. 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

3. 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 

4. 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

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

6. 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.

7. 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

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

10. 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: ICRF @ 68 MHz 4 MW - Off-axis: LHW @ 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

11. 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: ICRF/FW @ 68 MHz & 4 MW - Off-axis: NBI @ 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

12. Physics Comparison between ARIES-RS and ARIES-AT RSAT Plasma current, I P (MA)11.313.0 Plasma Shape,  1.9,.762.2,.86 ,  N (%) 5.0, 4.99.2, 5.4 Bootstrap Fraction0.880.94 B T at coil, plasma (T)15.8,8.011.1,5.9 ITER 89P H factor2.32.7 CD power8025 Major Radius R (m)5.55.2 COE7653 Both have: A=4 1GW net electric

13. 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

14. 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) = 0.2 2 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