Simulation Barriers

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Post by GIThruster »

Wow, what a cool post. You just never know what's going to pop up here at T-P.

Hope you get a good answer, Jeff. Have you thought about contacting Rick?

I can tell you that if you ever get an interest in simulating an M-E thruster, the guy to talk with is Andrew Palfreyman. Can't remember what program he kept crashing years ago but his suuped PC was totally not able to the task.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis

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Joined: Tue Jun 09, 2009 4:54 am

Post by BenTC »

Funnily enough, I bumped into the GS2: Gyrokinetic Microturbulence Project only yesterday, though I can't judge how suitable it is.
Fast microstability assessment
Linear microstability growth rates are calculated on a wavenumber-by-wavenumber basis with an implicit initial-value algorithm in the ballooning (or "flux-tube") limit. Linear and quasilinear properties of the fastest growing (or least damped) eigenmode at a given wavenumber may be calculated independently (and therefore reasonably quickly).

Fully gyrokinetic, nonlinear simulations
Nonlinear simulations of fully developed turbulence can be performed by users with access to a parallel computer. All plasma species are treated on an equal, gyrokinetic footing. Nonlinear simulations provide fluctuation spectra, anomalous (turbulent) heating rates, and species-by-species anomalous transport coefficients for particles, momentum and energy.

Good performance
GS2 is a parallel code which scales well to large numbers of processors. There are separate optimizations to work with for small (Beowulf-style) clusters and large supercomputers.

Flexible Simulation Geometry
Linear and nonlinear calculations may be carried out using a wide range of assumptions, including:
Local slab
Local cylinder
Local torus
Vacuum magnetic dipole
High aspect ratio torus (analytic axisymmetric equilibrium)
Numerically generated, local equilibrium (Miller-style)
Axisymmetric, numerically generated equilibria with arbitrary poloidal shaping from
Non-axisymmetric (stellarator) equilibria from VMEC

Community diagnostics
GS2 is fully supported by the GKV suite of IDL-based diagnostics developed for gyrokinetic turbulence simulation codes. Contact William Nevins for more information. Output files are written with NetCDF.

Portable implementation
Because it was designed according to object-oriented principles, GS2 has been kept portable without sacrificing performance. For example, all parallelism is expressed in a single communications module, which can easily be adapted to a new platform. (Presently MPI and SHMEM are supported; serial execution is also available.)

Efficient computational grid
Turbulent structures in gyrokinetics are highly elongated along the magnetic field. GS2 uses field-line following (Clebsch) coordinates to resolve such structures with maximal efficiency, in a flux tube of modest extent. Pseudo-spectral algorithms are used in the spatial directions perpendicular to the field, and for the two velocity space coordinate grids (energy and pitch angle) for high accuracy on computable 5-D grids.
In theory there is no difference between theory and practice, but in practice there is.

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