Design Point Studies for Next Step Device National High-power Advanced Torus Experiment NHTX C Neumeyer 7/25/06

Outline Objectives 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

Objectives 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

Method XL-based “Systems Code” using non-linear optimizer (“Solver”) Jardin/Kessel algorithms used for NSST were starting point for Systems Code Continued evolution with Peng, Rutherford, Kessel for CTF studies - See PPPL Report 4165 “Spherical Torus Design Point Studies” Engineering & physics algorithms tailored to suit NHTX situation

Physics Assumptions

Range of Cross Sections  = 3.674/SQRT(A_100)  =0.6  = 3.674/SQRT(A_100)  =0.6 Simple limiter shape model:

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

Engineering Assumptions

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

Machine Heat Removal TFTR ratings… Water tank = gallons (adequate) Cooling power = 20MW (adequate) Component cooling = 3300 GPM (~ 1/6 of requirement) Not limiting Compared to PS (1200s) Not limiting Compared to PS (1200s)

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

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

Procedure Scan over R0 and A with SOLVER set to maximize P_aux running at beta limit - R0 from 0.8 to A from 1.7 to 2.5 Select R0 and A and set SOLVER to maximize Ip With P_aux at 38MW and P_cd ≤ 32MW

Scan Results

Design Point R0=0.95/A=1.8 Yields 4MA/1.8T and P/R ~ 40

Plan View 12 outer legs (3 turns per leg) NBI 90, 100, 110cm

Elevation View TF, OH and PF coil dimensions as represented in systems code Extra +/-50cm in dZ TF would reduce performance by ~ 5% in Ip TF, OH and PF coil dimensions as represented in systems code Extra +/-50cm in dZ TF would reduce performance by ~ 5% in Ip

Conclusions More work is needed on parameter scans More careful study of A=1.8 to A=2.0 range Much work remains to… - develop & prove out physics and engineering aspects of design - optimize water cooling aspects Highlighted challenges… - TF bundle torsion - TF joint - large water flows