Enhanced Plasma Uniformity in RF Plasma With Side Multihole
Capacitively coupled plasma source with side multihole is studied. Due to the hollow cathode effect at the multihole, edge plasma density is strongly increased and thus, plasma uniformity is significantly enhanced.
Skin effect in a small symmetrically driven capacitive discharge
The so-called ‘electrostatic’ approximation postulates that the electric field can be represented by the gradient of a scalar potential, even under dynamical conditions. This assumption reduces the set of Maxwell's equations to the much simpler Poisson equation and is often employed for modeling and simulation of radio frequency driven capacitive low pressure discharges. While it is now widely acknowledged that the neglect of induction phenomena breaks down for large-area plasma sources driven at high frequencies (such as used for VLSI processing), smaller experimental devices excited at moderate frequencies (e.g. 13.56 MHz) are generally thought to be uncritical. This paper demonstrates the opposite: even small plasma reactors of the size of the Gaseous Electronics Conference reference cell exhibit a considerable skin effect in the low pressure, high density regime and render the electrostatic approximation invalid. The point is made, however, that this phenomenon is not ‘fully electromagnetic’ (in the sense that its analysis requires the full set of Maxwell's equations), but can be understood by means of a simplified model which assumes quasi-neutrality and may therefore be called ‘magnetostatic’.
Discovery of Two New, Carbon-rich Proto-Planetary Nebulae:IRAS Z02229+6208 and IRAS 07430+1115
We report the discovery of two new carbon-rich proto-planetary nebulae (PPNs), IRAS Z02229+6208 and 07430+1115. Optical spectroscopy of these sources and another previously discovered PPN, IRAS 05431+0852, reveals the presence of C2 and C3 in absorption. All three objects have the spectra of G-K supergiants, consistent with the expectations of their being PPNs. New ground-based optical and infrared photometry, combined with the IRAS measurements, show double-peak spectral energy distributions for each; this suggests that the asymptotic giant branch (AGB) mass loss has ended and these objects are in the post-AGB phase of evolution. The remnant of the molecular envelope is detected in CO emission for the first time in all three objects, using the CO (3-2) line. The 3.3 and 11.3 μm emission features commonly attributed to the polycyclic aromatic hydrocarbon molecules have been detected in IRAS 07430+1115. Strikingly absent in IRAS 07430+1115, however, is the 21 μm emission feature, found in the other two and in all but one of the other PPNs known to show C2 in absorption.