  A switching-off process very similar to those in real high-voltage self-blast
circuit-breakers is emulated in a model chamber to study the arc properties by
optical emission spectroscopy. The arc is operated in a chamber filled with
SF$_6$ between a pin-tulip contact system enclosed by a PTFE nozzle.
Transparent windows in the chamber wall and a slit in the nozzle enable an
optical investigation of the arc cross section less than one millisecond before
current zero. The side-on radiance of a fluorine atom lines has been measured
with an imaging spectroscopic system. Considering rotational symmetry of the
arc the corresponding radial emission coefficients have been determined by Abel
inversion. The radial temperature profiles are calculated from the emission
coefficients including pressure measurements and the corresponding plasma
composition. In contrast to previous studies, a specific iterative approach is
proposed to consider the optical thickness of the plasma. A maximum optical
thickness between 0.2 and 0.4 has been observed. Temperature profiles corrected
for absorption effects show increasing maximum temperature in the arc axis with
decreasing current towards current zero. The effect of the plasma composition
on absolute arc temperatures is discussed. The temperature profiles can be used
to validate CFD simulations of the switching-off process in the model chamber.
