1. Recent Progress in Stellarator Optimization
D. A. Gates1, A. H. Boozer2, T. Brown1, J. Breslau1, D. Curreli3, M. Landreman4, S. A. Lazerson1,
J. Lore5, H. Mynick1, G.H. Neilson1, N. Pomphrey1, P. Xanthopoulos6, A. Zolfaghari1
1Princeton Plasma Physics Laboratory, Princeton, NJ , U.S.A.
2Columbia University, New York, NY 10027
3U. Illinois Champaign-Urbana, Champaign, IL 61820
4University of Maryland, College Park, 20742
5Oak Ridge National Laboratory, Oak Ridge, TN
6Max Planck Insitut-fur-Plasmaphysik, Greifswald, Germany
EX/P3-39
EX/P3-39
Coil Simplification
A four part program for improved stellarators
A design activity based on the four new optimization capabilities would lead to an improved stellarator reactor concept
Coil optimization with spatial constraints
Fast Particle Confinement Optimization
Limited access leads to low availability
Basic code changes include:
Modular coil winding topology used on NCSX and ARIES-CS designs leads to small component, port based maintenance approach
Details develop that allow straightened MC back legs and the code revised to receive input of engineering supplied MC surface geometry to locate the MC winding centers,
The MC winding geometry now is developed with spline representations enabling spatial constraints to be placed on the coil locations,
Coding effort was also made to smooth the shaping of the modular coil winding, add torsion constraints, freeze coil geometries and much more.
Fast particle confinement in modern optimized designs such as W7-X and NCSX is much improved compared to conventional stellarators, but remains one of the main challenges for the concept
G. Grieger, et al., Phys. Fluids B 4, 2081 (1992)
STELLOPT has recently been coupled to the gyro-center following parts of the BEAMS3D code allowing massively parallel computations.
M. McMillan and S. A. Lazerson, Plasma Phys. Control. Fusion 56, (2014)
NCSX 4.4 AR
1.4-M Raxis
ARIES-CS 4.5 AR
7.75-M Raxis
ARIES-CS port based maintenance approach
A European tokamak study looking at an equivalent ITER configured DEMO design found that an operating availability barely above 50% could be achieved.
COILOPT++ was run with constraints applied using aspect ratio 6 case from Ku and Boozer
The results of this work is a newly developed stellarator configuration with much improved maintenance features
Primary minimization cost function was combination of rms and max dB/B over the boundary
COILOPT++ with splines was substantially easier to run with the splines than COILOPT with Fourier representation
The use of saddle coils was deemed unnecessary
Magnetic field error after one pass was rms2.27e-2 and Max = 5.28e-2
Spline coil centers from COILOPT++ with applied constraints
Achieved
equilibrium
Target equilibrium
A fast particle loss prediction verification exercise will be undertaken on W7-X using the nearly radially injected neutral beams
Fast lost ion detectors will be installed to verify predicted losses
Future optimization strategies
Plasma boundary well matched after single iteration
Turbulent Transport Optimization
Divertor Heat Flux Optimization
Mynick et al., recently demonstrated the reduction of turbulent heat flux by employing a novel “proxy function” within the STELLOPT code. H. Mynick, et al., Phys. Rev. Letters 105, (2010)
The proxy function is developed to rapidly estimate the transport level of a given configuration
Nonlinear GENE run to corroborate that the evolved configuration in fact has reduced transport.
Most work to date has focused on optimizing for ion temperature gradient (ITG) turbulence.
Without scraper
Overloaded elements (>10MW/m2, rated for 5)
With scraper
MW/m2
Load on low-rated tiles reduced below 1MW/m2
A method has been developed to rapidly determine the heat flux footprint on a stellarator facing surface using field line tracing with diffusion J. Lore, et al., IEEE Transactions on Plasma Science (2014)
This method can be included in STELLOPT with the parallelized FIELDLINES code
The result can then be compared to a more accurate model, such as EMC3- EIRENE
Automated divertor plate design can make machine design much more rapid
Can also verify robustness of the design to equilibrium variations
Poloidal cross-sections and (b)surface-averaged heat flux Q versus time from GENE simulations for NCSX and 2 turbulence-optimized configurations QA_40n (red) and QA_35q (green), showing the reduction in Q from NCSX by factors of 2 to 2.5.
Xanthopoulos has since generated a W7-X-like configuration with turbulent flux minimized across the entire cross-section. P. Xanthopoulos, et al., Phys. Rev. Letters 113, (2014).
The MPX configuration
Comparison between field line tracing and EMC3-EIRENE
Parallelized field line tracing using the FIELDLINES code
Peak flux: ~16MW/m2
Peak flux: ~12MW/m2
DIV3D
EMC3
Comparison of the normalized heat flux between MPX and W7-X