Robert Leiweke

Temperature measurement in a high pressure dielectric barrier discharge using pressure induced line broadening and frequency shift

We have demonstrated two gas temperature measurement methods which are applicable to high pressure discharges where the pressure induced line broadening and frequency shift dominate over thermal broadening of atomic transitions. We have used diode-laser absorption spectroscopic measurements of argon 1s3→2p2 transition Doppler linewidth, Lorentzian broadening, and frequency shift to measure gas temperature in a dielectric barrier discharge operating from 5 up to 500Torr with temperature rise less than 100K.

Effects of pulsed-excitation applied voltage rise time on argon metastable production efficiency in a high pressure dielectric barrier discharge

The authors have quantified the effect of pressure scaling on Ar metastable production efficiency in a dielectric barrier discharge with and without dielectric component losses. Estimates of the volume averaged deposited energy were performed for both short or long rise time voltage pulses, using the same total applied voltages of ∼10 and ∼150ns, respectively. The metastable production efficiencies of long-pulse discharge exhibit smaller decrease over the 100–500Torr pressure range, compared to those of the short-pulse one to the extent that the efficiency values and scaling for both cases are essentially the same within the experimental uncertainty.

Effect of Gas Mixture on Plasma Jet Discharge Morphology

The morphology of plasma emission from a streamerlike atmospheric pressure plasma jet initiated inside a glass capillary has been measured with a high spatial resolution for a gas flow of pure helium and He with a 5% Ar admixture using 5-ns time-gated intensified charge-coupled device imaging. In the pure helium plasma jet, emission remains annular and converges gradually along the core gas-air interface. With a 5% argon admixture, however, the plasma emission is initially annular inside the glass capillary but converges to the flow axis within 5 mm outside the capillary tip.

On a dielectric-barrier and a microwave-cavity discharge in synchronized operation?the case of a helium/oxygen mixture

We have investigated the performance of a microwave-cavity discharge (MWD) operating in tandem with a fast rise-time pulsed dielectric-barrier discharge (DBD). The tandem discharge operated in a helium/oxygen mixture, where metastable molecular oxygen could be produced efficiently using MWD in proportionally large quantities (order of 20% of total oxygen number density). In this new arrangement, a DBD operating at high E/N provided a metastables-rich mixture, thereby modifying the discharge kinetics of the MWD, which operated in the E/N range centered around 10?Td. Both discharges operated in synchronized pulse-repetitive mode, which was tailored to maximize the oxygen metastable production efficiency. The system operated at pressures up to 350?Torr with an average power between 3 and 20?W.

Diode laser absorption and emission spectroscopy of a streamer discharge in an atmospheric pressure plasma jet

Research into atmospheric pressure plasma jets (APPJs) that are initiated via a self-sustaining streamer discharge has recently been driven by both their potential for applications to nonthermal material processing, and fundamental questions regarding the basic discharge mechanisms that drive this remarkably stable atmospheric pressure discharge. We have characterized a streamer-initiated atmospheric pressure plasma jet in a 5% Ar / 95% He carrier gas flowing into ambient air using tunable diode laser absorption spectroscopy together with photomultiplier-coupled optical emission spectroscopy and current/voltage measurements. Improvements in the stability of this APPJ have allowed us to isolate the streamer discharge component with a higher precision than we have previously reported, as the shot-to-shot jitter is now comparable to the optical detector bandwidths. This APPJ configuration is similar to that used in previous workl, with the difference that only a single ring electrode is used here. Optical transitions from He, Ar, and various air species were used to characterize the spatiotemporal evolution of the discharge. The optical detector was aligned with the output from an 811.53 nm tunable diode laser that was used to measure the line integrated density of the Ar ls5 metastable.

Simultaneous Measurements of the Argon Metastable 1s3 and 1s5 Number Densities and Gas Temperature Using Diode Laser Absorption Spectroscopy

Diode laser absorption spectroscopic measurements of 1s3 and 1s5 metastable densities have been performed in a short pulse excited dielectric barrier argon discharge operating from 50 up to 500 Torr pressure. The metastable production efficiency was found to be about 20% over the entire pressure range with peak efficiency near 200 Torr. Two novel gas temperature measurement techniques have been developed for these high pressure discharges based on nonresonant collision line broadening and collisional frequency shifts of the transition from both 1s3 and 1s5 metastable states.