Influence of pressure and mixing with air on the equilibrium composition of laser-induced plasma on ODS steel

Laser induced plasma (LIP) is transient, the part of the time evolution of its emission used for the Laser induced breakdown spectroscopy (LIBS) technique corresponds to plasma pressures that are comparable to atmospheric, where a certain degree of mixing of the ablated material and air must be taken into account. The aim of this work was to discuss the influence of pressure change and air mixing of laser ablated material on the equilibrium composition of plasma obtained on an ODS steel target, which is a material of great interest for nuclear technology. Special care is devoted to the influence of pressure and mixing on the equilibrium relationship between the temperature T and the electron number density Ne, which is important for plasma diagnostics. The obtained results show that the concept of local thermodynamic equilibrium (LTE) can be used for the LIBS plasma diagnostics and the optimization of spectrochemical analysis parameters. The conclusion refers to the expected interval of plasma pressure during its evolution (10?0.1 bar) and the expected degree of mixing of the ablated material and air, in the temperature range 5,000?15,000 K, relevant for the LIBS technique.