Verification and validation procedures with applications to plasma-edge turbulence simulations

The methodology used to assess the reliability of numerical simulation codes constitutes the Verification and Validation (V&V) procedure. V&V is composed by three separate tasks: the code verification, which is a mathematical issue targeted to assess that the physical model is correctly implemented in a simulation code; the solution verification, which evaluates the numerical errors affecting a simulation; and the validation, which determines the consistency of the code results, and therefore of the physical model, with experimental data.
To perform a code verification, we propose to use the method of manufactured solutions, a methodology that we have generalized to PIC codes, overcoming the difficulty of dealing with a numerical method intrinsically affected by statistical noise. The solution verification procedure we put forward is based on the Richardson extrapolation, used as higher order estimate of the exact solution. These verification procedures were applied to GBS, a three-dimensional fluid code for SOL plasma turbulence simulation based on a finite difference scheme, and to a unidimensional, electrostatic, collisionless PIC code.
Finally, in order to increase the reliability of our SOL modelling, several plasma turbulence simulation codes are validated against measurements taken in a number of experimental devices. First, the blob dynamics is investigated in TORPEX through a multi-code validation project, shedding light on the dynamics of these structures. Furthermore, GBS simulations are validated against RFX-mod experimental measurements, providing interesting insights on the SOL plasma dynamics in this device. Finally, the impact of the shape of the magnetic equilibrium on SOL turbulence is investigated through a rigorous validation of GBS simulations against TCV experimental measurements