Publ. Astron. Obs. Belgrade No. 89 (2010), 281-284 Contributed Paper 281 LOW-PRESSURE DC DISCHARGE IN WATER VAPOUR NIKOLA ŠKORO 1 , DRAGANA MARIĆ 1 , GORDANA MALOVIĆ 1 , WILLIAM G. GRAHAM 2 and ZORAN Lj. PETROVIĆ 1 1 Institute of Physics, University of Belgrade, Pregrevica 118.,11080 Belgrade, Serbia E-mail: nskoro@ipb.ac.rs 2 Centre for Plasma Physics, Queens’ University Belfast, BT7 1NN, UK Abstract. We present investigations of low-pressure breakdown and different regimes of dc discharges in water vapour. Results of measurements include Paschen curves and Volt- Ampere characteristics of the discharge for various pd conditions and with water samples of different purity. 1. INTRODUCTION Over the past several years a wide range of possible applications drew attention to studies of properties of non-equilibrium discharges in water vapour (Bruggeman and Leys 2009). It is expected that development of sources of atmospheric pres- sure non-equilibrium (low temperature) plasmas provide cheaper technologies in treatment of materials (Mohan Sankaran and Giapis 2003, Makabe and Petrović 2006), lighting (Eden and Park 2005) and biomedical applications of plasmas (Stalder et al. 2006). Atmospheric pressure sources operate in ambient air which inevitably contains water vapour so it is of great importance to study basic proc- esses that determine properties of discharges in water vapour. Furthermore, recent development and studies of discharges with liquid electrodes (water or some elec- trolyte) (Bruggeman and Leys 2009) and discharges in heterogeneous water air bubble systems (Bruggeman et al. 2008) are closely connected to water vapour discharges since in both cases the gas would be expected to contain a significant percentage of water vapour that would determine most of its transport properties (Juarez et al. 2008). In spite of increase demand for water vapour data, existing data on breakdown and discharge properties are scarce and often not well docu- mented. We aim to investigate low-pressure dc discharges in water vapour: gas breakdown conditions and the electrical characteristics of the discharge as well as variations of these characteristics in different discharge regimes, from the low- current (Townsend) regime to high current glow discharges.