To generate HCD plasma, high-voltage power was supplied to the cathode. To keep the HCD glow stable, the potential was just above the gaseous breakdown voltage threshold. For the ion source pressures of 5 and 28 Torr, the potential and current were kept constant at -1.30 kV (0.3 mA) and -1.62 kV (0.3 mA), respectively. The discharge current was kept relatively low in this study to allow soft ionization of the labile explosives, but claimed that the HCD ion source may be operated over a wide range of currents, ranging from a few mA to several hundreds of mA .In order to investigate the ionization mechanism of the relevant explosives with ion source pressure of 1 Torr, a dc plasma was generated between the transfer tube and the S-lens by applying +0.85 kV (0.12 mA) and -0.85 kV (0.15 mA) to the transfer tube in the positive and negative ion modes, respectively (Fig. ).