Partially ionized two-fluid shocks with collisional and radiative ionization and recombination – multilevel hydrogen model

Abstract

Explosive phenomena are known to trigger a wealth of shocks in warm plasma environments, including the solar chromosphere and molecular clouds where the medium consists of both ionised and neutral species. Partial ionisation is critical in determining the behaviour of shocks, since the ions and neutrals locally decouple, allowing for substructure to exist within the shock. Accurately modelling partially ionised shocks requires careful treatment of the ionised and neutral species, and their interactions. Here we study a partially-ionised switch-off slow-mode shock using a multi-level hydrogen model with both collisional and radiative ionisation and recombination rates that are implemented into the two-fluid (PIP) code, and study physical parameters that are typical of the solar chromosphere. The multi-level hydrogen model differs significantly from MHD solutions due to the macroscopic thermal energy loss during collisional ionisation. In particular, the plasma temperature both post-shock and within the finite-width is significantly cooler that the post-shock MHD temperature. Furthermore, in the mid to lower chromosphere, shocks feature far greater compression then their single-fluid MHD analogues. The decreased temperature and increased compression reveal the importance of non-equilibrium ionised in the thermal evolution of shocks in partially ionised media. Since partially ionised shocks are not accurately described by the Rankine-Hugoniot shock jump conditions, it may be incorrect to use these to infer properties of lower atmospheric shocks.

Alfvén pulse driven spicule-like jets in the presence of thermal conduction and ion-neutral collision in two-fluid regime

“…Additional physical processes, such as radiative transfer, radiative cooling, radiative transport, ionization, recombination and heating terms, should be incorporated into future models. These additions will enhance the comprehensiveness and accuracy of the simulations [86,87]. MHD may also be an appropriate formalism but it rules out neutrals that are present in the lower solar atmosphere and might be at work there in the formation of spicular jets.…”

Kelvin–Helmholtz-induced mixing in multi-fluid partially ionized plasmas

“…The radiative field is assumed to contribute the exact energy required for the transition and thus does not directly contribute to the macroscopic fluid energy. Full details of the ionization/recombination model are available in [13], which is based on the models presented in [15][16][17].…”

“…It should be emphasized that this is an approximation for optical thickness. Further details of the model are available in [13].…”

The influence of thermal pressure gradients and ionization (im)balance on the ambipolar diffusion and charge-neutral drifts

“…The approach based on the distinguishable particles has been widely used in the solar 2F literature [e.g. 12,17,18,39]. It has the advantage that both hard spheres and CX processes can be simply added by separate.…”

“…Many authors include non-ideal effects derived from the presence of neutrals into their analysis to account for heating or multi-scale physics in the MF approximation (see e.g. [4,5,12,[16][17][18][19][20][21][22]). Several of those works additionally consider other non-ideal effects such as neutral viscosity, heat flux, or thin radiative losses.…”