For the last couple of years we have been studying 2.45 GHz-microwave plasma production in the gap of a coaxial pipe under the electron cyclotron resonance. The purpose of this research is to expand the plasma generation conditions into the much lower pressure (0.01-0.1 Torr) and much shorter gap length (several 100 mum). As the first step for this purpose, we have investigated the breakdown and maintenance of plasmas numerically. In the present numerical calculation, we have focused on the influences of applied magnetic field, gas pressure, gap length, applied voltage, and gas species on the breakdown and maintenance of plasmas. (C) 2003 Elsevier Science B.V. All rights reserved.