A comparative study of transient characteristics of argon and hydrogenated-argon pulse-modulated induction thermal plasma

Hossain, M. Mofazzal; Hashimoto, Y.; Tanaka, Yasunori; Paul, K.C.; Sakuta, Tadahiro

doi:10.1109/tps.2002.1003877

Cited by 10 publications

(5 citation statements)

References 18 publications

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“…A specific discussion on the ignition and extinguishing or decaying mechanisms of plasma is in order to explain the deviations of experimental and simulated critical discharge boundaries. In our previous paper [8,16] it was discussed that the experimental rising time was shorter and falling time was longer compared with simulated ones. This means, in practical pulse modulated discharge, the ignition process (on-pulsation) is faster, and diminishing or decaying process (off-pulsation) is slower.…”

Section: Discussionmentioning

confidence: 96%

Extinguishing phenomenon and critical discharge boundaries of argon and molecular-gas-seeded argon pulse-modulated induction thermal plasmas

Hossain

Tanaka

Sakuta

2002

Plasma Sources Sci. Technol.

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A stable discharge region of pulse modulated induction thermal plasma at atmospheric pressure has been determined in terms of the duty factor (DF) and the shimmer current level (SCL) both experimentally and numerically. The experiment was performed with a MOSFET-employed inverter-feed pulse modulated power supply unit having a maximum power of up to 50 kW. The on-time of the pulsing signal was fixed at 10 ms while the off-time was varied to determine the critical/minimum DF up to which plasma discharge sustained, for a fixed SCL. In this way, for different SCLs, critical/minimum DFs were determined for different gas combinations. The gas flow was composed of 100 lpm argon and 2.5 lpm H 2 , N 2 or CO 2 as secondary gas through the sheath channel only. Steady state coil currents for Ar, Ar-H 2 , Ar-N 2 and Ar-CO 2 were 244 A, 263 A, 296 A and 296 A, respectively. In the numerical part, a two-dimensional local thermodynamic equilibrium (LTE) code was used to predict the discharge boundary for the same operating conditions as those of the experiment. Both experimental and simulated results reveal that injection of dissociative molecular gases greatly shrinks the stable discharge region, which is attributed to the lowering of temperature and particle density. It was found that the stable discharge region predicted numerically was smaller than that of the experimental one. This implies that a non-LTE plasma has a discharge zone wider than that of an LTE plasma.

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Section: Discussionmentioning

confidence: 96%

Extinguishing phenomenon and critical discharge boundaries of argon and molecular-gas-seeded argon pulse-modulated induction thermal plasmas

Hossain

Tanaka

Sakuta

2002

Plasma Sources Sci. Technol.

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“…Specifically, the instantaneous large-jump of electron temperature with the on-transition will help to reduce or eradicate the discrepancy observed when a LTE model is used (for instance, in the results of [25]- [28]). Only a kinetic nonequilibrium model may sufficiently explain the correct plasma field properties in a transient thermal plasma.…”

Section: Discussionmentioning

confidence: 99%

“…A number of articles have been published recently on the transient behavior of an RF-ICP assuming LTE [22]- [29]. The time-dependent LTE model has been found to fail in explaining plasma behavior in some instants of a pulse modulated RF-ICP, as reported by Paul et al [25]- [27] and Hossain et al [28]. The discrepancy seen between the experimental and LTE-based theoretical results for an RF-ICP has been explained as due to the nonequilibrium condition within a transient plasma.…”

Section: Introductionmentioning

confidence: 99%

Transient Behavior of Current Modulated 2-T Inductively Coupled Plasma

Paul

2004

IEEE Trans. Plasma Sci.

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Time-dependent thermal plasmas are not in an equilibrium condition even if they are operated at a very high pressure. Therefore, nonequilibrium modeling is required in order to understand the underlying physics. Unfortunately, substantial modeling complexities have prevented significant advancements in the state-of-the-art. This paper presents new information for the nonequilibrium situation where the electron temperature is generally assumed to be higher than the heavy particle or gas temperature. Calculations are done for a radio-frequency inductively coupled thermal plasma where the coil current is pulse modulated. The discharge medium is argon at one atmosphere of pressure. The high-level current (representing the on-time state) is 170 A and is reduced to 80% of the high-level current or 136 A during the off-time state. The on-time and off-time durations are 10 and 5 ms, respectively. The electron temperature is observed to be higher by a factor of two or three compared to the gas temperature in the cooler region of the discharge. The difference between electron and heavy-particle temperature is negligible in the plasma core. The temporal behavior of the electron and heavy-particle temperatures are similar during the off-time, whereas the electron temperature's response is much faster than that of the heavy particle during the on-time. The response of the electron temperature to a step change in input power is almost instantaneous and enhances the energy exchange mechanism through elastic collisions between electron and heavy particles.Index Terms-Chemical nonequilibrium, duty factor, kinetic nonequilibrium, local thermodynamic equilibrium (LTE), response time, simmer current level (SCL). Khokan C. Paul (M'99) received the B.Sc. degree in electrical and electronic engineering from Bangladesh Institute of Technology, Chittagong, Bangladesh, in 1990, and the M. Eng. and Ph.D. degrees from the

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“…Mostaghimi et al [12], for example, developed a two-dimensional model and used it to investigate the response of an RF plasma to a step-like change in active power. Sakuta et al have recently studied the transient response of an Ar-H 2 plasma to different operating conditions [13], the responses of PM-ICPs in a long-coil torch to power changes [14], and the transient and nonequilibrium behaviours of PM-ICPs in different working gases [15,16]. Tanaka and Sakuta have also successfully developed a current-control-type power source and modulated the coil current into an almost square waveform.…”

Section: Introductionmentioning

confidence: 99%

Controlled generation of pulse-modulated RF plasmas for materials processing

Ishigaki

Sakuta

2005

Plasma Sources Sci. Technol.

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Pulse-modulated radio frequency (RF) inductively coupled plasmas for materials processing applications were generated using a voltage-control-type power source, and the operating ranges for controlled generation were extended to sufficiently low shimmer power levels. When the plasma was generated at atmospheric pressure and a high power level of 17 kW, the low power level typically went down to about 4 kW for an Ar-H 2 plasma and 3 kW for an Ar-N 2 plasma, levels too low to sustain the continuous plasmas. The overshoot and undershoot at the beginnings of power change were reduced considerably by using an exponential voltage control signal. Spectroscopic measurements of the radiation intensity of the Ar atomic spectral line (751.5 nm) showed that the plasma temperatures varied with time and that the characteristic times of the plasmas depended on the operating conditions and the position in the plasma generator. The characteristic times in the discharge zone may be largely determined by the competition among ionization, recombination and convection in the pulsed plasmas. The characteristic times estimated using an electron transportation model are reasonably in line with those determined from measured emission intensities. The difference between the plasma properties at the higher and lower power levels was large enough to give rise to the nonequilibrium states at the instances of pulse-on and pulse-off, and to the increase in the concentration of chemically active radical species. This offers a unique physico-chemical condition for materials processing. The ranges of controlled generation were determined for the Ar-H 2 and Ar-N 2 plasmas at pressures from 27 to 101 kPa.

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A comparative study of transient characteristics of argon and hydrogenated-argon pulse-modulated induction thermal plasma

Cited by 10 publications

References 18 publications

Extinguishing phenomenon and critical discharge boundaries of argon and molecular-gas-seeded argon pulse-modulated induction thermal plasmas

Extinguishing phenomenon and critical discharge boundaries of argon and molecular-gas-seeded argon pulse-modulated induction thermal plasmas

Transient Behavior of Current Modulated 2-T Inductively Coupled Plasma

Controlled generation of pulse-modulated RF plasmas for materials processing

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