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Optical emission spectral tomography diagnostics have been developed to measure the spatial uniformity of meter-sized processing plasmas. The lines of sight and detector location are selected based on tomographic reconstruction tests using synthetic (phantom) images. The developed collection optics system is composed of slits, a plano-convex lens, optical interference filters and photodiode arrays. Using the collection optics, the line-integrated emission intensity is acquired from a meter-sized rectangular argon plasma (inductively coupled plasma at a frequency of 13.56 MHz), which was developed for display panel manufacturing. From the measured intensity, two-dimensional (2D) spatial distributions of argon atomic line intensity (675.3 nm and 852.1 nm) are obtained via the tomographic reconstruction technique based on the Phillips–Tikhonov regularization. In addition, 2D profiles of the electron excitation temperature (Texc) are obtained from those of Ar intensity at the wavelengths 675.3 nm and 852.1 nm via two line method (in essence, a Boltzmann plot). The 2D argon plasma emission and Texc profiles match well with the shape of the electrode and etch rate profile. [ABSTRACT FROM AUTHOR]

High-energy tail formation in an ion energy distribution function (IEDF) is explained in a Hall thruster plasma with the stationary crossed electric and magnetic fields whose discharge current is oscillated at the ion transit-time scale with a frequency of 360 kHz. Among ions in different charge states, singly charged Xe ions (Xe+) have an IEDF that is significantly broadened and shifted toward the high-energy side, which contributes to tail formation in the entire IEDF. Analytical and numerical investigations confirm that the IEDF tail is due to nonlinear ion dynamics in the ion transit-time oscillation. [ABSTRACT FROM AUTHOR]

Electron diagnostics based on electron–neutral atom (e–a) bremsstrahlung in the UV and visible range emitted from atmospheric pressure plasmas is presented. Since the spectral emissivity of the e–a bremsstrahlung is determined by electron density (ne) and mean electron temperature (Te) representing the Maxwellian electron energy distribution, their diagnostics is possible. As an example, emission spectra measured from capacitive discharges are presented, which show good agreement with the theoretically calculated emissivity of the e–a bremsstrahlung. For a single pin electrode nanosecond-pulsed plasma jet (n-PPJ) in argon, we investigate the electron properties and the temporal behavior of the positive streamers. Streamers with many branches are clearly observed inside the dielectric tube, while a few main streamers propagate outside the tube along the jet axis. A two-dimensional (2D) measurement of the time-averaged Te distribution was developed using a commercial digital camera and optical band pass filters based on the emissivity ratio of two wavelengths of the e–a bremsstrahlung. The viable measurement range of Te is 0.5–7 eV for the choice of two wavelengths of 300s and 900s nm and 0.5–4 eV for two wavelengths of 400s and 900s nm, which are uncontaminated by the atomic and/or molecular spectra. The 2D Te distribution obtained using 514.5 and 632.8 nm emissions helps to reveal the role of electrons in streamer characteristics in the argon n-PPJ. Time-averaged Te of 2.0 eV and 1.0 eV inside and outside the tube, respectively, were measured. The streamer dynamics of the n-PPJ is shown to be dependent on Te. [ABSTRACT FROM AUTHOR]

Due to the lack of convincing experimental evidence for electron information, there are still unclearly understood discharge phenomena in atmospheric pressure radio-frequency (rf) capacitive discharge, e.g. the electron heating, discharge structures, and the alpha–gamma mode transition. Thus, to perceive basic and meaningful principles with an unambiguous interpretation, simple and reliable electron diagnostics are required. Since bremsstrahlung emitted through electron-neutral atom interaction depends on electron density (ne) and temperature (Te), their diagnostic is possible. In particular, Te is easily estimated from the ratio of bremsstrahlung emissivities at two different wavelengths or more. In this paper, 2D Te distribution in an argon atmospheric pressure capacitive discharge measured by using a digital camera and optical band pass filters is described. Time-averaged Te in the bulk region obtained by a digital camera is consistent with that measured by an absolutely calibrated spectrometer. In addition, time-resolved emission spectra and the corresponding ne and Te during one rf cycle of the argon capacitive discharge are discussed. The result shows that Te varied from 2.3 to 3.0 eV, while ne did not change significantly. [ABSTRACT FROM AUTHOR]