Numerical Verification and Improvement of the B2.5 Time‐Stepping Scheme for Time‐Dependent Plasma Boundary Simulations With SOLPS ‐ ITER

ABSTRACT Time‐dependent plasma boundary simulations can be an important contributor to power exhaust control design in ITER and future fusion reactors. These simulations are known to be computationally challenging due to the coupled fluid‐kinetic plasma edge models, strong nonlinearities, and different timescales involved. Recently developed Advanced Fluid Neutral (AFN) models allow for an accurate fluid description of hydrogenic neutrals in high collisionality regions. Thus, a first assessment of the detachment timescales in ITER can be done already with a fluid description, only using the B2.5 module of the SOLPS‐ITER code. This study employs the Method of Manufactured Solutions (MMS) for rigorous numerical verification of the time‐stepping schemes of B2.5. Additionally to the original first‐order implicit Euler (IE) scheme, two second‐order schemes have been implemented: the Crank–Nicolson (CN) linear multi‐step method and the second‐order backward differentiation formula (BDF2). The MMS tests are used to conduct a rigorous numerical error analysis, comparing these schemes and assessing the potential improvement in computational time. Using second‐order schemes is found to substantially reduce the time‐discretization error. Therefore, the same level of time accuracy can be achieved with larger time steps, enabling faster transient simulations.