llnl / tango

Transport solver for coupling with turbulence

Tango

Tango is a transport solver intended for coupling with codes that return turbulent fluxes. In many physics problems, including magnetically confined fusion plasmas such as a tokamak, a separation of timescales exists between the timescale of turbulence and the timescale for evolution of mean, macroscopic quantities such as density and temperature in response to turbulent fluxes. In the numerical simulation of such scenarios, it is desirable to efficiently exploit the separation of timescales. Furthermore, because in general the turbulent fluxes depend nonlinearly on the macroscopic quantities and their derivatives, certain numerical instabilities arise and special methods are required to handle them.

For the kind of situation just described, Tango solves a one-dimensional transport equation. That is, the macroscopic quantities are assumed to depend on a single spatial variable. Tango is designed to accept fluxes from a separate turbulence simulation code in order to evolve the transport equation on a longer timescale. Tango will communicate the updated macroscopic quantities back to the turbulence simulation code and proceed with solution. The fundamental ideas are laid out in Shestakov et al., J. Comp. Phys. (2003).

Note: Tango is under active development. New features and capabilities will be coming at some point in the future and these will most likely be incompatible with the current code.

Coupling with gyrokinetic turbulence

Tango is designed to couple with the gyrokinetic turbulence simulation code GENE through a Python-Fortran interface. In principle, Tango could couple to other simulation codes if suitable interfaces are available.

More details will be presented in a forthcoming journal article.

Contact

For questions and inquiries, including regarding possible collaborations, please contact the author, Jeff Parker, at [email protected].

tango's Issues

Allow selection of which channels to evolve

Often, one wants to evolve only a subset of the possible "channels" (e.g., keep temperature fixed and evolve only plasma density). This should be enabled in a systematic, user-friendly way, rather than needing to be done in an ad-hoc way.

Add citation file to the repository

Might I suggest adding a citation file to the repository?

I was looking for the Tango paper, and I first found the repository, from which I didn't see the reference in the README or in a citation file.
GIthub should now support citation.cff files, adding the reference directly to the repo.

Allow x0 to be an input to the python interface of libgene_tango

The current version of libgene_tano.F90 has x0 = 0.5 (on two separate lines). This overrides what is in the GENE parameters file. If a value other than x0=0.5 is desired, currently one would have to manually change this value and recompile libgene_tango.

Modify calculation of effective transport coefficients for geometrical factors

Currently we calculate D = Gamma / (dn/dx), etc.

For noncircular geometry, geometrical factors of <|grad x|^2> and <|grad x|> appear in the formula for projected flux. These geometrical factors should be accounted for in the calculation of D and c.