Electron heating in rf capacitive discharges at atmospheric-to-subatmospheric pressures

Abstract

Electron heating is a fundamental and multidisciplinary phenomenon in partially ionized gases, from the planet’s ionosphere to laboratory-scale plasmas. Plasmas produced at ambient or reduced pressures have recently shown potential for scientific and industrial applications. However, electron heating, which is strongly coupled to the physicochemical properties of these plasmas, has been poorly understood. We experimentally found the rapid structural transition from non-local to local electron heating in collisional radio-frequency discharges at atmospheric-to-subatmospheric pressures. As the gas pressure decreased from 760 to 200 Torr, the time-averaged electron density increased from 1.3 × 1012 to 1.3 × 1013 cm−3, and the electron temperature decreased from 2.5 to 1.1 eV at the maximum allowable discharge current in the abnormal α-mode in the plasma bulk. The spatiotemporal evolution of the electron temperature clearly shows that the electron temperature increases uniformly throughout the bulk plasma region during sheath expansion and collapse at 760 Torr, but the electron heating weakens with sheath collapse as the gas pressure decreases.

Time and space-resolved experimental investigation of the electron energy distribution function of a helium capacitive discharge at atmospheric pressure

“…T e shown in figure 2(b) displays a similar evolution as that of the line intensity in figure 2(a) (brief maxima near the cathode). This behaviour is similar to the one reported in [21]. The time lag of about 10 ns between the emission (a) and the electron temper ature (b) is coherent with the time lag between electron heating and ionization in typical capacitive discharges [13].…”

Electron characterization in weakly ionized collisional plasmas: from principles to techniques

“…First, most interference Figure 5. Optical emission spectroscopy results of rf capacitive discharges at atmospheric pressure [177]. Raw optical emission spectra of (a) helium and (b) argon rf capacitive discharges in the spectral range of 250-850 nm.…”

“…ICCD cameras, which have high sensitivity and high gating speed, enable nanosecond-and rf phase-resolved electron characterization in conjunction with optical filters or spectrometers. In this review, we leave practical issues and considerations related to ICCD cameras, which can be easily found in earlier articles [177,178]. Park et al [177] first proposed and reported a 2-D rf phase-resolved electron characterization using a combination of an ICCD camera and optical filters in argon rf capacitive discharges at atmospheric Figure 6.…”

“…In this review, we leave practical issues and considerations related to ICCD cameras, which can be easily found in earlier articles [177,178]. Park et al [177] first proposed and reported a 2-D rf phase-resolved electron characterization using a combination of an ICCD camera and optical filters in argon rf capacitive discharges at atmospheric Figure 6. Illustration of (a) electron-ion and (b) electron-neutral bremsstrahlung mechanisms.…”

“…Nanosecond-resolved visualization of the electron heating structure[177]. Spatiotemporal evolution of 514.5-nm continuum radiation (left side) and T e (right side) at (a) 760 Torr, (b) 400 Torr, (c) 300 Torr, and (d) 200 Torr.…”