TORBEAM 2.0, a paraxial beam tracing code for electron-cyclotron beams in fusion plasmas for extended physics applications

Abstract

The paraxial WKB code TORBEAM [E. Poli et al., Comp. Phys. Comm. 136 (2001), 90] is widely used for the description of electron-cyclotron waves in fusion plasmas, retaining diffraction effects through the solution of a set of ordinary differential equations. With respect to its original form, the code has undergone significant transformations and extensions, in terms of both the physical model and the spectrum of applications. The code has been rewritten in Fortran 90 and transformed into a library, which can be called from within different (not necessarily Fortran-based) workflows. The models for both absorption and current drive have been extended, including e.g. fully-relativistic calculation of the absorption coefficient, momentum conservation in electron-electron collisions and the contribution of more than one harmonic to current drive. The code can be run also for reflectometry applications, with relativistic corrections for the electron mass. Formulas that provide the coupling between the reflected beam and the receiver have been developed. Accelerated versions of the code are available, with the reduced physics goal of inferring the location of maximum absorption (including or not the total driven current) for a given setting of the launcher mirrors. Optionally, plasma volumes within given flux surfaces and corresponding values of minimum and maximum magnetic field can be provided externally to speed up the calculation of full driven-current profiles. These can be employed in real-time control algorithms or for fast data analysis.

Optimal MSE polarisation angle and q-profile estimation using Kalman filters and the plasma simulator RAPTOR

“…The RAPTOR code has no constraint on the plasma scenario and can be used to model (and control) monotonic and advanced (e.g. reversed shear) q-profiles, using real-time estimates of the driven current from codes such as RT-TORBEAM for electron cyclotron heating [33,34] and RABBIT for NBI [35]. In advanced scenarios, it is important to follow and control the q-profile evolution close to the magnetic axis.…”

Quasioptical modeling of wave beams with and without mode conversion. I. Basic theory

“…Hence, reduced methods have been widely used in practice. These methods are rooted in geometrical optics (GO) [1] and include conventional ray tracing [5][6][7][8], complex ray tracing [9,10], beam tracing [11][12][13][14], and variations of thereof [15]. There are also other "quasioptical" models, such as in Refs.…”

Quasioptical modeling of wave beams with and without mode conversion. II. Numerical simulations of single-mode beams

“…The difference is essential for resonant-plasma heating and current drive, where the wave energy deposition must be calculated accurately, as also discussed in Refs. [4][5][6][7][8][9][10][11][12][13][14].…”

“…Geometrical-optics (GO) ray-tracing simulations [2,3] are much faster but cannot adequately describe the structure of the wave beam in the focal region. Many alternatives have been proposed to improve reduced modeling of ECWs, including complex-eikonal methods [4][5][6][7], beam tracing [8][9][10][11], and the quasioptical approach [12][13][14]. However, none of them account for the possible interaction of the two coldplasma modes (linear mode conversion), which can occur in strongly sheared magnetic field at low density, for example, at the plasma edge [15,16].…”