A spectroscopic investigation of corona discharges in SF6/N2 gas
mixtures has been undertaken using an optical multichannel analyser (OMA). A
point-to-plane geometry has been used with point radii varying from 3 to 10 μm. Spectra are measured for high pressures ranging from 0.2 MPa up to
1.4 MPa and for different concentrations of SF6 in the gas mixture. The
spectra in the 200–850 nm spectral range are mainly made of molecular bands,
which is indicative of a low temperature discharge. It has been noted that
SF6 emits in the region of 420 nm to 510 nm in positive and negative
polarities, although in negative polarity the emission is weaker. For
SF6/N2 mixtures, the main source of light emission is from
N2. The resultant spectra are used to evaluate the rotational Tr
and vibrational Tv temperatures of excited N2, Tr being
considered, due to the high pressure, to be equal to the kinetic temperature
Tkin in the corona discharge. Tr and Tv are determined by
comparing the experimental spectrum of the second positive system
($C^{3}\Pi_{u}\to B^{3}\Pi_{g})$ of N2
and the simulated one, which is obtained using a convolution method. As
expected, the results show that the measured rotational temperature Tr
increases steadily with the mean discharge current, while its increase with
gas pressure is less pronounced. The values of Tr are higher for the
positive corona discharge than the negative and also for mixtures having
higher amounts of SF6. In all conditions, we found $T_{v}>T_{r}$
and Tv is less sensitive to the variation of the current.