AbstractA novel system of an inductively coupled thermal plasma with a fundamental frequency of 450 kHz has been developed. This system has a capability of modulating the amplitude of the coil current periodically with a cycle on the order of 10 ms, including an inverter power supply rated with a power of 50 kW, an induction plasma torch with a 10‐turn coil, and vacuum chamber. The controlled modulation of the coil current can lead the plasma to be under various transient states intentionally. A pulse‐modulated inductively coupled plasma of Ar‐H2 plasma was successfully generated at a plasma power of 30 kW under the atmospheric pressure condition. The on‐time and off‐time of the pulsation were set to 10 and 5 ms, respectively, for a stable pulse‐modulated plasma establishment, and the ratio of minimum to maximum of the amplitude of the coil current can be set down to 61.7%. In order to investigate the transient behavior of the plasma dynamics in such a pulsing mode, spectroscopic observations of an argon atomic spectral line at a wavelength of 751 nm were made. It was found that the pulse‐modulated plasma has a characteristic time on the order of 2 to 5 ms to rise or to decrease. The excitation temperature of the Ar atom was estimated from the spectroscopic measurement by the Boltzmann plot method, and it was found to change periodically from 5000 to 10,000 K with the pulse modulation of the amplitude of the coil current. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 26–33, 2002; DOI 10.1002/eej.1135