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General Atomics System Code (GASC) and Benchmarking with CFETR
by V.S. Chan (GA) A.M. Garofalo (GA), J.A. Leuer (GA retired), B.N. Wan (ASIPP), A.E. Costley (Tokamak Solutions, CIC) Presented at 2nd IAEA DEMO Programme Workshop IAEA Headquarters, Vienna, Austria 17-20 December 2013
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FNSF-AT DEMO
ITER
GASC has Evolved from Cu to SC Tokamak Modeling to Support the Path to Fusion DEMO Development
DIII-D
EAST
CFETR
SC tokamak requires specification of SC material properties and cooling requirements
Cu tokamak requires detailed modeling of dissipative power
GASC
Physics
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GASC is a 0-D System Code with Comprehensive Physics and Technology Required for DEMO Design
Accomplished by • Keeping 1-D physics in models by accounting for
– Transport profiles effects – Penetration of beams and RF waves – Core/edge radiation
• Integrating coupled physics and technology into reduced models – Combining beta-limit and vertical stability limit – Durham model for SC material stress and temperature limits – Correlation of bootstrap current fraction and βT
• Use of past experience and external calculations to constrain inputs – Blanket/shield thickness – Model for TF/OH geometry
Chan, Fus. Sci. & Tech. (2010), Stambaugh, Fus. Sci & Tech. (2011)
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Stability Limit is Directly Related to the Aspect Ratio
• Operating βN taken as fβ (safety margin) times the calculated (Lin-Liu) wall stabilized
limit.
Vertical Stability
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Current Drive Efficiencies are Adjusted Based on Projected Transport Profiles
• External current driven given by Ip (1-fbs), where fbs is the input bootstrap fraction
gLH ≡
n20 IMARmPMW
=0.037BT 0 Tped
5+ Zeff( ) nped0.33 (MA/MWm
2)
!
gEC =0.09 Te5+ Zeff( )
!
gNNBI ≡n20 IMARmPMW
=0.025 Te
1(MA/MW/m2)
Lower Hybrid penetration an issue
Electron Cyclotron efficiency changes with
launch location
Negative NBI may compete with blanket
space
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Impurity Seeding to Enhance Core Radiation May be Needed to Meet Divertor Heat Load Constraint
• Brehmsstrahlung power is ~ 10% of power in the core • Synchrontron radiation is non-negligible at high temperature
– Model from F. Albajar, et al, Nucl. Fus. 2001
• High Z impurity seeding at the plasma boundary assumed – Input fraction of core power radiated by line radiation – Consistency check with Post and Jenson [Atomic Data and Nuclear Data (1977)] – Assumed no impact on core confinement (single Zeff) – 1-D transport simulation for confirmation remains to be done
• Divertor – Radiation in divertor not accounted for.
PBEHM =0.00534VpZeff ne
2 (0)[Te(0)]1/2
1+ 2SN + 0.5ST
Te
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Past Experience Guides Thermal/Hydraulic/Stress Analysis of Magnets in GASC
Two types of designs are investigated - DIII-D constant tension D shape TF - C-MOD sliding joint design Model characteristics - Hydraulics: Moody friction factor for
tube flow - Heat transfer: Nusselt number
correlation - Conductor: Copper/coolant or SC/
Durham - channel/insulator - Stress: Simple analytic center post
formulation for tokamak - Optimization: Stress and temperature
constrainable
Constant Tension TF !
Ntf= 16!Ntf = 20!Ntf = 24!
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Machine Geometry Factors Guided by Experimental Experience and Supporting Calculations
• Gaps
– Inner and outer plasma to wall gaps set to ~10 heat flux decay lengths, (Loarte, DIII-D experience)
• Blanket/Shield (dimensions suggested by neutronics calculations) – Inner blanket/shield (CFETR 80 cm) – Outer blanket/shield (CFETR 100 cm) – Divertor blanket/shield: Needed for TBR>1 – Space may be added for vacuum vessel structural support
• Divertor – Realistic depth for standard inclined plate divertor – Consistency of advanced designs with magnets and blankets
requires further study
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Device Optimization Procedure: Free Parameters and Constraints
• Free Parameters
– Aspect ratio – Radial build of the TF coil – Current density in the TF coil – Radial build of the OH solenoid – Current density in the OH coil – Filling fraction of TF and OH – Ion temperature – Durham model of SC Jc
• Constraints
– Peak mid-plane neutron wall load specified, generally less than 2 MW/m2 – H98y2 constrained, generally less than 1.6. – Ratio of density to Greenwald limit, generally less than 0.8. – TF and OH coil stress set by engineering (ITER 90 ksi) – Fraction of flux OH coil provides for start-up – Divertor heat load – Net electric power (for DEMO)
• Optimization – Minimize the device size, facility electric power consumption, Qplant, etc.
Adjusted by optimizer
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The FNSF/CFETR/DEMO Design Point Resulted from a Systematic Study Versus Aspect Ratio
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CFETR Conceptual Design Overview
B.N. Wan, SOFE25, San Francisco, Jun 10-15, 2013
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CFETR Could be a Near-Term Facility to Bridge the Gaps between ITER and DEMO (B.N. Wan, SOFE 2013)
Mission
• Complementing ITER (CFETR not necessarily high gain)
• Demonstration of fusion energy production
• Demonstration of tritium self-sufficiency with TBR ~1.2
• Exploring options for DEMO blanket and divertor solution
• Solution for easy remote maintenance of in-vessle components
Baseline plasma of CFETR
• Fusion power Pfus= 50 ~ 200 MW
• Long-pulse or SS operation with an annual duty factor of 0.3 ~ 0.5
• Physics based on existing experiments
• Adopting ITER physics and technical basis
Build in capabilities and flexibilities for research of advanced physics and new technologies
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Summary of CFETR Conceptual Design Study To-Date
• The engineering parameters of the device have been
determined by considering engineering constraints
• Possible operating modes based on conservative physical
assumptions - should be readily achievable
• More ambitious operating modes potentially possible if the more
advanced physics is achievable
• Transport analysis using a drift-wave-based model with an edge
boundary condition is under way
• EAST will provide opportunities to address key physics issues and
demonstrate operating regimes of CFETR
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CFETR Operating Modes (B.N. Wan, SOFE 2013)
R(m) = 5.7 a(m) = 1.6 A=3.56 κ = 2.0 δ = 0.4
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Benchmarking GASC Predictions with ITER and CFETR Designs
See A. Garofalo talk at this workshop for GASC study of FNSF-AT
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GASC Reproduces ITER Operating Mode Parameters
Accounting for Paux
Input parameters
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GASC Matches Qualitatively CFETR Engineering Parameters (from Conceptual Design Case B)
CFETR GASC
R(m) 5.7 5.72
a(m) 1.6 1.63
A 3.56 3.5
κ 2.0 2.0
δ 0.4 0.4
Vp(m3) 576 592
Sp(m2) 587 583
B0(T) 5.0 5.14
Ip(MA) 10~8 10.69
P(MW) 50/80 61.3
CFETR GASC
TF radial build+VV (m) 1.29 1.54
OH radial build (m) 0.65 0.53
Inner blanket/shield (m) 0.80 0.80
Outer blanket/shield (m) 1.20 1.00
VonMises Stress(Mpa)
200 207
GASC was used with optimizer for size
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Good Agreement in Physics Parameters for CFETR Operating Mode B
Start-Up CFETR GASC
Ramp-up Flux (V-s) 120 125.8 Heat Losses GASC
Zeff 2.0
Bremsstrahlung Loss(MW)
5.5
Core Line Rad. Fraction
0.10
Core Line Rad. (MW) 10.4
Synchrotron Loss (MW) 7.82
Power into SOL (MW) 80.2
Power SOL radiated (MW/m)
14.0
Peak Divertor Rad. Total (MW/m2)
6.65
CFETR: SN=0.5, ST=1 fi=0.7, fHe=0.1 GASC: SN=0.5, ST=0.75 fi=0.8, fHe=0.05
Operating Mode
CFETR Case B
GASC
IP (MA) 10 10.7
Paux (MW) 65 61
q95 3.9 3.9
W (MJ) 193 195
Pfus (MW) 209 213
Qpl 3.2 3.5
Ti0 (keV) 29 26
Nel (1020/m3) 0.52 0.42
nGR 0.42 0.33
βN 1.8 1.8
βT (%) 2.3 2.1
fbs (%) 35.8 36.0
τ98Y2 (s) 1.55 1.88
PN/A(MW/m2) 0.37 0.37
ICD (MA) 7.0 6.84
H98 1.3 1.34
Tburning (s) SS SS
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Comparison of Predictions for CFETR Case B using GASC and Tokamak Solutions System Code (TSSC)
Differences in red accounted for by dilution fraction of 0.86 in GASC
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CFETR is Designed with Engineering Flexibility for Higher Performance
Operating Mode E A=3.5
GASC A=3.5
GASC A=3.0
Ip (MA) 8 7.77 11.38
Paux (MW) 65 72 85.3
q95 4.9 5.25 5.61
W (MJ) 255 244 495
Pfus (MW) 409 430 1066
Qpl 6.3 6.0 12.5
Ti0 (keV) 21 15.2 20.6
Nel (1020/m3) 0.94 1.01 1.04
nGR 0.95 1.02 1.03
βN 2.97 3.0 3.13
βT (%) 2.97 2.8 3.4
fbs (%) 73.9 74 74
H98 1.5 1.5 1.5
PN/A(MW/m2) 0.73 0.80 1.6
SOL Heat (MW/m) 14.0 21.1 25.9
Div. Plate (MW/m2) 6.65 7.88 7.79
VonMises Stress (Ksi) 30 30 68.45
CFETR: SN=0.5, ST=1 GASC: SN=0.5,ST=0.75
Vacuum space for larger plasma A<3.5
Need better metric
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Summary
• The physics and engineering models in GASC and their complex relations
have been verified by – Reproducing the ITER baseline operation parameters – Independently reproducing the CFETR conceptual design – Benchmarking with an independent system code TSSC
• GASC study of CFETR supports the following conclusions – The fusion performance of the baseline mode (case B) is consistent with
the assumed physics parameters – The machine dimensions and engineering capabilities from the
conceptual design appear reasonable – Higher fusion performance is possible given the built-in machine flexibility
• Future improvements in GASC have been identified – Optimization of launcher location and frequency for RFCD – Consistency of core radiation by impurity seeding and core performance – Need of a better divertor heat load metric to constrain the system code
optimization
