In Situ Thermometry in Noble Gas Dielectric Barrier Discharges at Atmospheric Pressure

Atmospheric pressure (AP) dielectric barrier discharges (DBDs) are increasingly used to treat thermally‐sensitive materials. Reliable measurements of the kinetic gas temperature, T, are therefore of capital importance. Spectroscopically determined rotational temperatures, Trot, are often tacitly assumed to be equal to T. Here, we measured T with fibre‐optic instrumentation that is a priori immune towards high voltages and high‐frequency electromagnetic fields generally encountered in plasmas. Finding Trot > T in AP glow discharge (APGD) DBDs in He and Ne, we believe that Trot ≈ T only during the short (≈ µs) current peaks that characterize APGD. Therefore, T represents the time‐averaged gas temperature; calorimetric measurements using a thermocouple buried in an electrode support this view. Atmospheric pressure (AP) dielectric barrier discharges (DBD) are frequently of interest for treating delicate substrates such as polymers or biological materials. In spite of its capital importance, thermometry in AP plasmas is subject to much uncertainty. We report temperature measurements in He, Ne, and Ar using sensitive, accurate fiber‐optic (FBG) instrumentation that is a priori immune toward high voltages and high‐frequency electromagnetic fields generally encountered in plasma environments.