1. Design Point Studies for next step device National High-heat-flux Advanced Torus Experiment NHTX C Neumeyer 6/8/6

2. Outline Background Method Physics Assumptions and Plasma Shapes Engineering Assumptions and Issues - TF inner leg cooling - Heat removal from machine - Divertor heat removal - Power supply utilization Results Conclusions

3. NSTX Center Stack Upgrade ~ 10s pulse - adiabatic water cooled, sub-cooled, LN2 - Paux= 10-20MW - full, partial inductive - OH coil, iron core NSTX Center Stack Upgrade ~ 20-60s pulse - active water cooled - retain VV, PF coils, TF outer legs NSTX Upgrade ~ 60s pulse - replace center stack, PF, TF outer legs - retain existing VV (kappa*a <=1.3m) NSTX Replacement ~ 60s pulse - all new machine Background: Options Studied Attractive mission: Ip ~ 4MA Bt ~ 1.5T Paux ~ 38MW Attractive mission: Ip ~ 4MA Bt ~ 1.5T Paux ~ 38MW

4. Highlights of New Machine High P/R - plasma should accept P aux = 32MW NBI + 6MW RF = 38MW Non-Inductive Sustainment - solenoid sized for ramp-up flux only Long Pulse - active water cooling, 60 second pulse Full Use of PPPL/TFTR Infrastructure - full MG energy + grid power - full PS capacity - full NBI capacity Some Incremental Infrastructure Required - water flow - 138kV substation

5. Methodology XL-based “systems code” using non-linear optimizer (‘Solver”) Jardin/Kessel physics algorithms used for NSST were starting point Continued evolution with Peng, Rutherford, Kessel for CTF studies - See PPPL Report 4165 “Spherical Torus Design Point Studies” Engineering & physics algorithms tailored to subject situation

6. Physics Assumptions Solutions maximize Ip*Paux

7. Z=1.3m ~ limit of existing VV Z=1.3m ~ limit of existing VV Range of Cross Sections  = 3.674/SQRT(A_100)  =0.6  = 3.674/SQRT(A_100)  =0.6 R0+a=1.473 Simple limiter shape model:

8. Limiter model vs. Divertor separatrix flux surface from J. Menard equilibria @ A=1.8

9. Engineering Assumptions

10. TF Inner Leg Cooling Typical T v. t fPacking depends on J_avg and dZ fPacking depends on J_avg and dZ KCOOL model Possible x-section Cu H20 Adiabatic

11. Machine Heat Removal TFTR ratings (may not be available anymore TBD)… Water tank = 33000 gallons (adequate) Cooling power = 20MW (adequate) Component cooling = 3300 GPM (~ 1/6 of requirement)

12. Divertor Heat Removal 4” dia pipes are adequate for divertor supply/return manifolds (assume full power capacity on top and bottom)

13. Power Supplies Use PS at 15kA per PSS (continuous rating of SCRs) Rep rate limited to ~ 1200s min due to 3.25kA rms rating Xfmrs OK (8 hrs) Xfmrs OK (8 hrs) 5 parallel 750MCM per PSS ~ 50 parallel 1000MCM cables req’d for 200kA-60s/1200s

14. Results (1)

15. Results (2)

16. Results (3)

17. Results (4) NSTX New

18. Conclusions Sweet spot ~ A=1.8 should be pursued Much work remains to - develop and prove out physics and engineering aspects of design - optimize water cooling aspects Highlighted challenges - TF bundle torsion and joint - large water flows - 200MW from grid - restoration of MG capability