Richard J. Van Brunt

Characterization of point‐plane corona pulses in SF6

The properties of streamer or electron avalanche pulses have been investigated for point‐plane, and positive and negative dc corona discharges in gaseous SF6 over the pressure range of 50–500 kPa. Measurements were made of the voltage and pressure dependence of electrically detected corona pulse‐height distributions, pulse shapes, and repetition rates. Positive corona pulses appear at onset as low‐level electron avalanches which, at higher voltages, develop into large streamers usually followed by a burst of many smaller pulses. The burst characteristics of positive corona show a definite dependence on pressure and voltage which is evident in the pulse‐height distribution data. Negative corona displays characteristics which are sensitive to cathode surface conditions. For a point electrode that is either exposed to UV radiation or has been conditioned by prior discharges, the negative corona appears predominantly in a quasiglow mode consisting of relatively low‐level pulses of high repetition rate.

Electron‐Impact Studies of Aromatic Hydrocarbons. III. Azulene and Naphthalene

The observed ionization energies of naphthalene (8.26 eV) and azulene (7.72 eV) and the heats of formation of these compounds provides an energetic scheme consistent with the measured appearance potentials of secondary ions and the assumption of ionic intermediates common to both compounds. The occurrence of these common intermediate ions which lead to the observed fragmentation in these compounds is also demonstrated by the similarity of the mass spectra of these two compounds. Additional evidence is provided by observations made on the metastable ion transitions found in their mass spectra.

PARTIAL-DISCHARGE PULSE HEIGHT DISTRIBUTIONS AND FREQUENCIES FOR POSITIVE AND NEGATIVE DC CORONA IN SF6 AND SF6-N2 MIXTURES

The voltage and pressure dependence of partial-discharge pulse height distributions and pulse repetition rates have been investigated for compressed SF 6 and SF 6 -N 2 mixtures using a fast multichannel analyzer. Positive and negative dc corona were generated using a point-plane stainless steel electrode geometry with a gap spacing of 1.24 cm and a tip radius of 0.07 mm. For SF 6 the positive corona pulses are typically an order of magnitude larger in amplitude than negative corona pulses although their repetition rate is lower. The tendency for SF 6 positive corona pulses to develop as bursts with a burst length that increases with increasing voltage and decreasing pressure is clearly exhibited by the pulse height spectra. The negative corona in SF 6 tends to begin as large pulses which eventually give way to a near glow condition as voltage is increased, although a steady glow, such as occurs in pure N 2 , was never observed. The observed pulse height spectra appear to be sensitive to gas composition as is evident from measurements made with gases containing varying relative concentrations of SF 6 and N 2 . Attempts are underway to correlate observed changes in pulse height spectra with corona-induced chemical changes in the gas using a gas chromatograph-mass spectrometer system.

Evidence for inelastic processes for N3+ and N4+ from ion energy distributions in He/N2 radio frequency glow discharges

The ion energy distributions (IEDs) striking surfaces in rf glow discharges are important in the context of plasma etching during the fabrication of microelectronics devices. In discharges sustained in molecular gases or multicomponent gas mixtures, the shape of the IED and the relative magnitudes of the ion fluxes are sensitive to ion–molecule collisions which occur in the presheath and sheath. Ions which collisionlessly traverse the sheaths or suffer only elastic collisions arrive at the substrate with a measurably different IED than do ions which undergo inelastic collisions. In this article we present measurements and results from parametric calculations of IEDs incident on the grounded electrode of a rf glow discharge sustained in a He/N2 gas mixture while using a Gaseous Electronics Conference Reference Cell (33.3 Pa, 13.56 MHz). We found that the shape of the IEDs for N+3 and N+4 provide evidence for inelastic ion–molecule reactions which have threshold energies of <10 eV.

Characteristics of Partial Discharges on a Dielectric Surface in SF6-N2 Mixtures

An important tool for improving the reliability of HV-insulation systems relies on partial discharge (PD) measurements. the assessment of the insulation failure of HV equipment using PD measurements requires an interpretation of the PD measurements themselves. the statistical characterization of pulsating PD signals has been shown1-3 to play an important role in understanding PD phenomena. the development of diagnostic systems which utilize statistical data on partial discharges for pattern recognition is important for the identification of types of defects in electrical insulation.

Appearance Potentials of Ions Produced by Electron-Impact Induced Dissociative Ionization of SF6, SF4, SF5Cl, S2F10, SO2, SO2F2, SOF2, and SOF4

The identification of S2F10, a highly toxic compound,1 in SF6 that has been subjected to electrical discharges, including negative corona discharges,2,3 sparks,4 and arcs,5 has raised issues of safety and proper handling of SF6 removed from electrical equipment, and motivates the need for trace detection of S2F10 in SF6. 6 A reliable measurement protocol for trace detection of S2F10 may be applied to: 1) develop safe handling procedures for SF6 gas removed from operating machinery, 2) ensure compliance with regulatory agencies, 3) monitor the purity of SF6 supplied both by manufacture and reprocessing, and 4) replace animal toxicity tests of commercial SF6.