Plasma Ionisation Temperature
The thermal level in the core of the arc plasma at which dissociation and ionisation of shielding gases and metal vapours reach equilibrium. This temperature controls the chemical reactions in the welding zone.
The ionization temperature is the temperature at which the shielding gas in the arc is heated so strongly that it becomes electrically conductive and forms the plasma. This is the basis for a stable arc and heat transfer during welding. If conditions are not right, the arc ignites poorly or burns erratically. You'll notice that by spatter and an unclean weld. The correct setting depends on the shielding gas and the base material. Set the arc so that it burns calmly and stably, then the ionization is right too. If in doubt, rely on empirical values for your gas mixture and fine-tune by feel.