Laser-rf creation and diagnostics of seeded atmospheric pressure air and nitrogen plasmas

Abstract

A laser initiation and radio frequency ͑rf͒ sustainment technique has been developed and improved from our previous work to create and sustain large-volume, high-pressure air and nitrogen plasmas. This technique utilizes a laser-initiated, 15 mTorr partial pressure tetrakis ͑dimethylamino͒ ethylene seed plasma with a 75 Torr background gas pressure to achieve high-pressure air/nitrogen plasma breakdown and reduce the rf power requirement needed to sustain the plasma. Upon the laser plasma initiation, the chamber pressure is raised to 760 Torr in 0.5 s through a pulsed gas valve, and the end of the chamber is subsequently opened to the ambient air. The atmospheric-pressure plasma is then maintained with the 13.56 MHz rf power. Using this technique, large-volume ͑1000 cm 3 ͒, high electron density ͑on the order of 10 11-12 cm −3 ͒, 760 Torr air and nitrogen plasmas have been created while rf power reflection is minimized during the entire plasma pulse utilizing a dynamic matching method. This plasma can project far away from the antenna region ͑30 cm͒, and the rf power budget is 5 W / cm 3. Temporal evolution of the plasma electron density and total electron-neutral collision frequency during the pulsed plasma is diagnosed using millimeter wave interferometry. Optical emission spectroscopy ͑OES͒ aided by SPECAIR, a special OES simulation program for air-constituent plasmas, is used to analyze the radiating species and thermodynamic characteristics of the plasma. Rotational and vibrational temperatures of 4400-4600Ϯ 100 K are obtained from the emission spectra from the N 2 ͑2+͒ and N 2 + ͑1−͒ transitions by matching the experimental spectrum results with the SPECAIR simulation results. Based on the relation between the electron collision frequency and the neutral density, utilizing millimeter wave interferometry, the electron temperature of the 760 Torr nitrogen plasma is found to be 8700Ϯ 100 K ͑0.75Ϯ 0.1 eV͒. Therefore, the plasma deviates significantly from local thermal equilibrium.

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…Vibrational and rotational temperatures of excited molecular nitrogen in two grounding configurations are determined via the spectrum of N 2 (C 3 Π u → B 3 Π g , Δ ʋ = −2). In the discharge at atmospheric pressure, the gas temperature also equals the gas temperature in the atmospheric pressure discharge . The software Specair was used to simulate the spectrum with the determined value of T rot and T vib .…”

Characterization of surface dielectric barrier discharge (SDBD) based on PI/Al2O3 nanocomposite

“…The emission spectra of the second positive bands of N 2 (C 3 П u →B 3 П g ) can be used to determine the N 2 (C 3 П u ) rotational temperature ( T rot ) of the SDBD plasma by fitting the experimental spectra with the simulated ones using Specair software. Gas temperature ( T gas ) can be regarded as being almost equal to the T rot of N 2 (C 3 П u →B 3 П g ) because the equilibrium between rotational and translational motion is easily obtained due to the frequent and fierce collisions among the heavy particles . Figure (a) shows the effect of plasma discharge aging on T gas .…”

Atmospheric Pressure Gas–Liquid Diffuse Nanosecond Pulse Discharge Used for Sterilization in Sewage

“…To determine the plasma gas temperatures, the OES of N 2 (C 3 Π u → B 3 Π g , Δ v = −2) was used to calculate the rotational temperature by comparing the experimental spectra and the best fitted spectra using the Specair code, the results of which are shown in Figure . Because of the small energy gap between rotational levels, the equilibria between the translational and rotational motions are readily achieved by frequent collisions between the heavy particles at AP . Therefore, the gas temperature of the plasma is approximately equal to the rotational temperature of N 2 .…”