A. Harry Sharbaugh

The Design and Construction of a Stark‐Modulation Microwave Spectrograph

A detailed description of a Stark‐modulation (see reference 1) microwave spectrograph which has been designed and constructed in this laboratory is given. Circuit diagrams and values of the components are given for all the custom‐built equipment. The frequency range is from 17 to 28 kmc/s. Peak Stark‐modulation voltages up to 1500 volts sine wave and 800 volts square wave are used. The sensitivity is better than 1×10−8 cm−1. The absorption lines are about 300 kc wide at half‐power and the practical limit of resolution is between ½ and 1 mc. Frequencies may be measured to better than ±0.08 mc.

The Electric Strength of Nitrogen at Elevated Pressures and Small Gap Spacings

The dc sparking potential of pure nitrogen gas has been measured under uniform electric field conditions in the pressure range 15–3000 psi(1–200 atm) and at electrode separations ranging from 0.25–25 mil (6.3–635 μ). Departures from Paschens law are found to occur at very high fields and to depend upon cathode conditions. A model is proposed in which current is field‐emitted from the cathode under the combined effect of the applied field and a positive‐ion space charge on an insulating layer at the cathode; at sufficiently high fields, the cathode current becomes unstable and breakdown results. The model predicts a relationship between an electron multiplication factor and the applied field, which is found to be consistent with the experimental results.

DC conduction in polymeric insulation

The importance of polymeric insulation in the electrical industry is shown by the many hundreds of published papers concerning the AC electrical conduction (or dielectric loss) of such materials. In contrast, not much attention has been given to the study of DC conduction with which we shall be exclusively concerned in this paper. Difficulty in the interpretation of the DC measurements is primarily responsible for this; however, some progress has been made in this direction and the present state of the art will be summarized in this paper.

On the measurement of the electric strength of gases at elevated pressures. III, hexane

It is generally accepted that electric breakdown in low density gases (e.g. hexane vapor) is completely described by the Townsend mechanism of breakdown1. On the other hand, our recent studies using liquid hexane have shown that breakdown does not occur via a Townsend mechanism but rather by means of a thermal mechanism2. It is therefore, of interest to make a systematic study in the intermediate range of densities where a transition from a Townsend to a thermal mechanism may be expected to occur. Accordingly, the electric strength of hexane vapor has been measured at temperatures near critical under conditions where the vapor density was continuously increased by pressure change up to the critical density. Young3 had previously made such a study in the critical region using carbon dioxide; however, it was desirable to repeat this experiment using hexane because of the large accumulation of breakdown data on liquid and gaseous hydrocarbons. We present in this paper, the results of such a study and a tentative analysis thereof.

Departures from Paschen's law in high pressure nitrogen

It is generally accepted that the mechanism of breakdown in gases at low pressures is completely described by the Townsend mechanism, and that, as the gas pressure is increased, departure from a Townsend process will be indicated by a failure of Paschens Law. The present study was undertaken in order to investigate this transition region, and the high pressure range in general.

The relative importance of some factors influencing the impulse electric strength of 10-C oil

When uniform-field, impulse electric strength measurements were made in different laboratories on liquids having ostensibly the same composition, the resulting values of electric strength often differed by as much as a factor of seven. To resolve this discrepancy, a study of the problem revealed that differences in the following experimental conditions might be responsible for the divergence of results: (1) electrode shape and spacing; (2) electrode composition; (3) physical impurities in the liquid (e.g., dust content); (4) waveshape of the testing voltage; and (5) chemical impurities in the liquid samples. While the findings of Wilson (1) and Weber and Endicott (2) had demonstrated the importance of the electrode spacing and shape in determining the measured strength, it was desirable to make a survey of the relative importance of all these factors. The last named variable, viz., the effect of chemical impurities, was not investigated but merely held constant by using samples from the same batch of oil throughout the experiments. The experimental results are summarized in Figure 1.

On the electric strength of gases at elevated pressures

A systematic investigation of the electric strength of nitrogen gas has been made under conditions where the gas density was continuously increased by pressure change from the ambient value to a density approaching that of the liquid state. Such a study is of interest for several reasons: (1) the increased sparking potential makes the use of pressurized gases very attractive for the insulation of electrical equipment; (2) the study of breakdown in this region of intermediate density yields important information which will elucidate the mechanism of breakdown in condensed phases of matter(1) and (3) virtually no measurements at elevated pressures have been made heretofore in the region of very small electrode spacing used by us (1–25 mils). The use of such spacings makes it possible to generate very high field strengths with relatively low voltage.