Non-equilibrium effects in pulse modulated induction thermal plasma for advanced material processing

An induction thermal plasma system has been newly designed for advanced operation with a pulse modulated mode to control the plasma power in time domain and to create non-equilibrium effects such as fast quenching of the plasma to produce new functional materials in a high rate. The system consists of MOSFET power supply with a maximum power of 50 kW with a frequency of 450 kHz, an induction plasma torch with a 10-turns coil of 80 mm diameter and 150 mm length and a vacuum chamber. The pulse modulated plasma was successfully produced at a plasma power of 30 kW and a pressure of 760 torr, with taking the on and off time as 5 ms, respectively. Measurements were carried out on the time variation of the spectral lines emitted from Ar species. The dynamic behavior of the plasma temperature in an on-off cycle was estimated by the Boltzmann plot method and the excitation temperature of Ar atom changed periodically from around 0.5 to 2.5 eV during the cycle. Non-equilibrium effects are found in this Ar exciting temperature as well as species number of Ar, H and N, in the plasma under pulse mode operation.