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We have carried out cross-correlated high-resolved electrodynamical and spectro-optical measurements of different characterizations in a high-stable regime of the dc positive streamer corona in short gap in atmospheric density laboratory air. Special attention was paid to the measurement of absolute intensities of the second positive (SPS) and first negative (FNS) systems of molecular nitrogen as well as for further improvement in the spatiotemporal resolution along with high synchronization and stability. In the cathode region, the FNS and SPS emission temporal waveforms during primary streamer development have been recorded with the cross-correlated synchronization not worse than 0.1 ns and spatiotemporal resolution around 0.01–0.1 mm along the axis and 0.2–0.4 ns in the multiphoton mode of the PMT-based detector and in the single pulse acquisition mode of the measuring system. The shortest rise-times of the corresponding voltage waveforms were found to be around 0.3–0.4 ns for the SPS (0,0)-band and 0.2–0.3 ns for the FNS (0,0)-band, the full widths at the half-altitude ranging around 1.4–1.5 ns and 0.5–0.6 ns, respectively. Again, the absolute values and the ratio of the synchronized temporal waveforms of the SPS to the FNS (0,0)-bands have been recorded across the entire gap in the accumulation and averaging acquisition mode of the measuring system with somewhat worse temporal resolution but with adequate stability and stochasticity. Various supporting characteristics such as the synchronous anode and cathode electric current waveforms, the streamer velocity and the gas temperature within the streamer channel region have been measured and presented as well. All the data in the aggregate allow reconstruction of the 2D structure of the streamer head generally and of the electric field and the electron number density partially.

In this second of two papers, we have developed a fully self-consistent method of diagnostics of streamer discharge plasmas based on the analysis of absolute intensities of the second positive (SPS) and first negative (FNS) systems of molecular nitrogen. The theory of the method combines a spectroscopic technique for the calculation of temporal waveforms of the nitrogen absolute SPS and FNS (0, 0)-band emission and a self-consistent semi-analytical parametric axially symmetric 1.5D model of the filamentary streamer head. The spectroscopic technique takes into account characterizations of all units of the measuring spectro-optical channel, including spatiotemporal resolution and resolution in wavelength. Also, chromatic aberrations of the focusing lighting lens, errors in the adjustment of the object image onto the input slit as well as the correction of the slit function at the non-uniformly illuminated input slit of the monochromator on width are taken into account. The model of the streamer head is characterized by some trial-consistent allowable parametric on-axis profile of the electric field combined with the electron and total space charge number density profiles fully self-consistent with each other and with the trial electric field. Additionally, the corresponding 2D configuration for the field and the electron number density is constructed via special ellipse-like geodesic lines. The absolute values and the synchronous ratio of the 1L spatially and time-resolved cross-correlated temporal waveforms of the SPS to the FNS (0, 0)-bands, the ratio of their altitudes and the total emission power for both the waveforms measured in paper I have been taken into account to reconstruct the 2D structure of the streamer head. With a procedure fitting the directly computed output voltage waveforms to the experimental ones, the peak values of the electric field and the electron number density within the streamer head at mid-gap distances have been found to be 430?500?Td and (2?3) ? 1014?cm?3, respectively. And the corresponding absolute electric field is thus 70?80?kV?cm?1 at the initial gas temperature within the repetitive streamer region of 450?K.

We have measured the E.coli bactericidal efficiency of DC and AC point-to-plane coronas in air and in argon in the corona modes positive glow, positive streamer, negative Trichel pulse and negative glow. Negative Trichel pulse and positive streamer coronas are the most efficient for production of bactericidal agents in air. Less than 5 minute exposure to the products from 30 μA of these coronas will sterilize the E.coli covered agar surfaces in a 3l volume to a survival ratio of 10−5. Positive glow coronas are two orders of magnitude less efficient. 50 Hz AC coronas seem to mainly work during the negative half cycles. The bactericidal agent(s) produced by the coronas have not all been identified, but ozone O3 with concentration 35–40 ppm is probably the most important one. We show that charged particles and photons can play only a minor role, so the agent(s) must be neutral particles. The main part of them must have a lifetime in the vessel of more than 3 minutes. The much smaller, and volume/distance dependent, efficiency of coronas in humid argon indicates that metastable neutrals or radicals from H2O can play only a minor role. A preliminary test showed negligible effects of the corona treatment on the spores of Bacillus subtilis.

Unipolar space‐charge distribution ρ(t) drifting with constant ion mobility μ in gas under time and space dependent electric fields will evolve according to the unipolar charge drift formula [1/ρ(t)]−[1/ρ(t0)] = (μ/e0)(t−t0), neglecting diffusion effects. This general formula is especially useful as a starting point for approximate treatment of space‐charge effects, both in ion drift and diffusion experiments, and in electrical coronas. A first simple derivation of an equivalent of the Warburg cos5ϑ current‐density distribution for point‐to‐plane coronas is given, together with a formula for the maximum possible unipolar ion current (the unipolar saturation current) Is ≊2μe0 V2/d, for a given corona voltage V and point‐to‐plane distance d. It is demonstrated that corona currents in excess of this limit always involve free electron or bipolar conduction phenomena, like streamers.

The streamer and return stroke concepts in positive corona breakdown are reviewed, and examined critically for the case of short (

Aluminum suffers severe pitting corrosion when used as an anode in negative corona discharges in ambient air. This paper gives a comprehensive account of the electrochemical interaction between a low electric field metal surface, especially aluminum, and the unipolar gaseous electrolyte created by an air corona. Introductory sections on coronas and corona corrosion give the necessary background. Physical and chemical analysis of the gaseous, liquid, and solid corrosion products of aluminum in air coronas demonstrate their close resemblance to the products formed in aqueous nitrate electrolytes.

The ultra-violet pulse response and the associated time constant have been determined for sprayed sodium salicylate coatings of thickness 01-20 mg cm-2, for three solvents (water, methanol and ethanol) and for primary radiations in the range 2200-3400 A. The ultra-violet light source was a pulsed nitrogen arc of 30 A current, 10 nsec duration and 400 pulses/sec repetition frequency. The primary and fluorescence light pulses were detected by a photomultiplier-sampling oscilloscope system. The ultra-violet pulse response of the coatings was found to be independent of coating thickness, solvent and primary wavelength, and could be described by a single exponential decay time of 7 ± 1 nsec. The discrepancies between this value and those previously published are discussed.

The electronic system of this coincidence counter consists of two 13-stage Venetian blind photomultipliers coupled to a simple DeBenedetti-Richings coincidence circuit, followed by a medium-gain amplifier, pulse selector and scaler. The main feature of the system is its simplicity, chiefly realized by utilizing the quasi-linear transfer properties of the take-the-lesser type coincidence circuit. “Balance-point operation” permits the use of multiplier high voltage supplies and pulse amplifiers not possessing the high stability usually required for scintillation counting. The counter has been operated at 26°C with a tritium counting efficiency of 16% at a background of 100 c/min. The minimum detectable tritium concentration in water is 1.7 × 10−8 curie/liter. However, the time needed for the counter to “quiet down” after a change of sample is prohibitively long, 2–3 days. Of the background, nearly 50% seems to be caused by light interaction between the photomultipliers. Some suggestions for future improvements are given.

A complete, simple electronic adaptor unit is described which allows the use of an X-Y recorder with the Tektronix type N sampling oscilloscope system. The unit contains a pulse height averager circuit that is essentially a cathode follower pulse stretcher, and that gives a vertical (Y) channel mean output voltage proportional to the mean height of the short output pulses from the sampling oscilloscope, irrespective of their repetition rate. The unit has proved to be of value when recording electrical pulses of shapes fluctuating about a mean, as photomultiplier pulses due to very weak but identical photon pulses.

The aim of this paper is to review our present knowledge of the physics of electrical coronas and their interaction with surfaces, with some emphasis on phenomena which seem of importance for high voltage insulation. We will concentrate on fundamental and general subjects, in order to limit the scope of the paper and to make it serve as an introduction to the more specialized papers that follow.

The thermally actuated valve described is intended for use as an exhaust control valve in conventional liquid nitrogen automatic refill systems. The valve is of a very simple and purely mechanical construction, and is operated directly by the difference in thermal expansion between an inner rod of copper-stainless steel and an outer tube of Pyrex. The valve will keep the liquid nitrogen level in a cold trap sufficiently constant for all but the most critical applications.