An interferometric and spectroscopic argon arc plasma diagnostic

In the spectral diagnostics of an arc plasma, when the halfwidth of the Balmer
Hbetha line is measured, there is a certain amount of free choice in the selection of equations
giving Ne = F(Ah,,,(Hp)) and AE, = G(N,, T), the lowering of the ionisation energy. In
order to clear up this problem, the argon arc plasma refraction, calculated on the grounds
of end-on spectroscopic diagnostics, is compared with results of interferometric measurements.
The influence of atoms in excited states on plasma refraction is taken into account.
Results show that, for plasma temperature T> 11 000 K, interferometrically measured
refraction is smaller than calculated values. The experiment was performed at four laser
wavelengths: 457.5, 580.3, 581.9 and 632.8 nm. The arc current was varied over a range
from 10 to 100 A.