Speaker
Description
The plasma parameters in the divertor region of fusion devices are highly relevant for characterizing particle and power exhaust in attached and detached regimes or during the injection of impurities. Due to reduced temperatures compared to the core plasma, both atomic and molecular hydrogen can be present in the divertor plasma and, depending on the operational scenario, also isotopes like deuterium, tritium or mixed molecular species.
Reaction probabilities for atomic and molecular hydrogen are essential input for understanding the physics of the divertor plasma and for determining its properties, typically based on transport codes like EIRENE or on collisional radiative models. One input of such codes are probabilities of collisional processes. These can be defined by cross sections or rate coefficients where cross sections are preferable as they enable calculations for non-Maxwell energy distribution functions. Input cross sections are needed for an energy range from the excitation threshold up to at least around 100 eV for accurately describing the different divertor regimes. Particularly critical is the energy range close to the threshold as cross sections for these energies can be determined only by comprehensive quantum-mechanical methods.
Several data bases are used since many years for the needed reaction probabilities, for example [1,2]. These data bases are far from being perfect, in particular for low temperatures; often used are rate coefficients resulting from semi-empirical methods or scaling laws and consequently attributed with a high uncertainty. The collisional radiative models Yacora H and Yacora H$_2$ are used for testing and benchmarking a revisited set of input data, based on recently available atomic cross sections calculated using the CCC method [3] and molecular data from the MCCC method [4]. The presentation introduces the set of input data and the benchmark results. Additionally discussed is the current status of developing molecular models for the isotopes of hydrogen. Widely used for determining cross sections for the isotopes are simple scaling rules; replacing these by specific isotope-dependent cross sections is highly desirable in order to reduce the uncertainty of the model results.
[1]: D. Reiter, “The data file AMJUEL: Additional Atomic and Molecular Data for EIRENE”, FZ Jülich, 2000
[2]: R. Janev et al, “Collision Processes in Low-Temperature Hydrogen Plasmas”, FZ Jülich 2003
[3]: I. Bray et al, Comput. Phys. Commun. 85 (1995) 1
[4]: M. Zammit et al, Phys. Rev. A 95 (2017) 022708