ASTRA
The code ASTRA (Automated System for TRansport Analysis)[1] solves a user-defined set of transport equations in toroidal geometry. It considers diagonal metric coefficients as it corresponds to axi-symmetric, tokamak-like geometries.
Presently, the code is used for transport simulations of both tokamak and stellarator plasmas. If used for tokamak plasmas, the Grad-Shafranov equation can be solved to update the geometry as the plasma current density and pressure evolve. In the case of stellarators, the geometry can be taken from experimental files where the most relevant metric coefficients and magnitudes are defined. In this case, dedicated subroutines can be added to update at will the metric coefficients depending on the plasma currents. Moreover, despite the one-dimensional nature of the transport equations, appropriate handling of the integration space permits also making calculations that include magnetic islands or ergodic plasma regions[2].
ASTRA includes an extended library of physical modules, a graphic interface, plotting and post-run viewing facilities, etc. Along with the common libraries, every user can have his local libraries of different formulae and functions, experimental data and simulation results. The physics models are defined by the user through a high level programming language –ASTRA specific, but easy to learn– where the different formulae and functions can be directly included from the libraries. In addition, there is a set of subroutines that can be plugged into the models, thus allowing for complex evaluations of e.g. source terms. Subroutines can also be created by the user: every time ASTRA is run, it checks for modifications of the ASTRA environment (functions, formulae, subroutines... ) so the corresponding objects are compiled and included in the ASTRA framework for immediate use. Examples of how the ASTRA suit can be extended for particular needs can be found below for the case of the TJ-II Heliac at CIEMAT.
Extensions of ASTRA for the TJ-II stellarator
ASTRA has been used in many transport analysis works related with the TJ-II device. The citations that follow contain the coding of ASTRA models, so they can serve as a reference for the extension of ASTRA to particular needs, as well as a source of examples of ASTRA programming.
The ASTRA suite was adopted to perform interpretative and predictive transport for TJ-II plasmas considering an approximate geometry[3]. The geometry was improved in collaboration with G. Pereverzev, one of the authors of the ASTRA suite, in order to adapt the non axi-symmetric stellarator geometry[4], which allowed for first estimates of the evolution of the rotational transform according to the net plasma current in the device. A more detailed evolution of the rotational transform, including possible changes of the main metric coefficients depending on the evolution of the plasma pressure has been also programmed in ASTRA[5]. In this case, internal and driven currents (e. g. bootstrap currents or heating-driven currents) can be included in the calculations.
As an extension of the geometrical possibilities in ASTRA, plasma regions occupied by magnetic islands or ergodic regions (limited by flux surfaces) can be treated as well in the transport models[6].
Demanding calculations are conveniently done through system calls from the ASTRA subroutines. One such possible extensions of the ASTRA is the coupling of the calculations to the Montecarlo codes Eirene and FAFNER to obtain respectively recycling and neutral beam injection sources; or the coupling to ray-tracing calculations, including the access to distributed resources[7].
See also
References
- ↑ G.V. Pereverzev, P.N. Yushmanov, ASTRA - Automated System for TRansport Analysis, Max-Planck-Institut Für Plasmaphysik, IPP-Report, IPP 5/98, February, 2002
- ↑ D. López-Bruna, B. Momo, I. Predebon, A. López-Fraguas, F. Auriemma, Y. Suzuki, and R. Lorenzini, “Flux-surface averaged radial transport in toroidal plasmas with magnetic islands,” Nuclear Fusion, vol. 58, no. 10, p. 106031, 2018. [1]
- ↑ D. López-Bruna, F. Castejón, and J. M. Fontdecaba, Transporte con Astra en TJ-II, Informe Técnico Ciemat 1035, Ciemat, Madrid, Spain, Enero 2004, [2]
- ↑ D. López-Bruna, J. A. Romero, and F. Castejón, “Geometría del TJ-II en astra 6.0,” Informe Técnico Ciemat 1086, CIEMAT, Madrid, August 2006., [3]
- ↑ D. López-Bruna, J. M. Reynolds-Barredo, and B. Momo, “Evolution of the rotational transform in TJ-II discharges using the ASTRA code,” Informe Técnico Ciemat 1470, Ciemat, July 2020, [4]
- ↑ D. López-Bruna, B. Momo, and Y. Zhang, “One-dimensional treatment of the effect of small magnetic islands on transport in the TJ-II stellarator,” Informe Técnico Ciemat 1402, CIEMAT, Madrid, May 2017
- ↑ D. López-Bruna, J. M. Reynolds, A. Cappa, J. Martinell, J. García, and C. Gutiérrez-Tapia, “Programas periféricos de ASTRA para el TJ-II,” Informe Técnico Ciemat 1201, CIEMAT, March 2010, [5]