The value of W_{и} for each atom cannot be precisely calculated. However, if we assume that the quantity W_{и} and depends linearly on T, then its value can be calculated by the formula

W_{и} =(U_{i}/T_{i})*T,

where T_{i} — the temperature at which almost all the atoms in the plasma are ionized, for example, when the degree of ionization reaches 0.95.

The U_{i}/T_{i} ratio for each class of atoms constantly and can be denoted by с, then the formula can be written as

W_{i} = U_{i} – cТ,

where с — the coefficient constant for each substance.

For argon, the value of c is с ≈ 8,2*10^{–4} eV/deg (Fig. 1 shows the graph of the degree of ionization (α), constructed from experimental data).

It is known that the plasma temperature in the argon arc is ~1,3 ・ 10^{4}К at the center of the arc, therefore, according to the formula W_{и} = 10,7 eV, and W_{i} at U_{i}_{Ar} = 15,76 eV is W_{i} = 5,06 eV. From the data obtained, it follows that W_{и} and W_{i} in the welding arc vary appreciably from its cross section (see Fig. 2).

The same should be observed at the frontal surface of the drop located in the arc, in which the plasma flow going from the electrode to the product is slowed, which leads to the increase in its temperature. The similar phenomenon should, according to the above, be observed at the surface of the weld pool.

This phenomenon is especially important for the study of processes in the cathode region of welding arcs, since the external source of ionization-a beam of electrons emitted from the surface of the cathode-acts on the plasma in this region and consists of atoms of the material of the melting electrode. It follows from this that the energy of electrons in this beam during ionization of atoms is not spent on ionization of atoms with W_{i} = U_{i}, but on the ionization of atoms with a much smaller value of W_{i}, which requires the lower electron energy, and therefore a lower cathode voltage drop (U_{к}). Perhaps, this can explain the small value of the cathode voltage drop (U_{к}) for the argon arc burning between tungsten electrodes. The anode voltage drop (U_{a}) is independent of U_{i }(anode material) and is ~ 4.5 V. At the same time, for the argon arc burning between tungsten electrodes, U_{к} + U_{а} ≈ 10V, hence in this case U_{к} ≈ 5,5V, which corresponds to the W_{i} value defined above. The same can be said for the value of U_{k} for welding aluminum with the tungsten electrode in argon and in helium, for which U_{к} + U_{а} are ~ 10 V and ~ 11 V, respectively, and the ionization potential of the helium atom is Ui = 24.58 eV, which also allows It is also possible to explain the appreciably smaller value of U_{к} when welding in helium in comparison with its U_{i} (for helium U_{к} ≈ 0,25U_{i}).