H. Craig Miller

Analysis of the Electrode Products Emitted by dc Arcs in a Vacuum Ambient

We have examined the particles emitted radially by dc arcs drawn in a vacuum ambient on cathodes of several elements, as well as the axial (through‐anode) ion flux from a copper cathode. The axial results for copper agree grossly with the radial copper results. Significant quantities of multiply charged ions were seen for all elements examined. All arc volt‐ampere characteristics were positive in the range of currents observed: 30 to 250 A. We drew the following conclusions (normalizing energy in units of ion energy/ion charge): (1) The energy distributions for the various ions are similar, peaking at potentials well above the arc voltage. (2) The fraction of ions that are singly charged tends to increase with increasing arc current. (3) For a given element, as the degree of ionization increases the location of the ion‐energy distribution peak shifts to lower energies. (4) For a given degree of ionization, the location of the peak tends toward higher energies for elements with greater arc voltages. (5) Th...

A Review of Anode Phenomena in Vacuum Arcs

This paper discusses arc modes at the anode, anode temperature measurments, anode ions, transitions of the arc into various modes (principally the anode-spot mode), and theoretical explanations of anode phenomena. A vacuum arc can exhibit five anode discharge modes: 1) a low-current mode in which the anode is basically passive, acting only as a collector of particles emitted from the cathode; 2) a second low-current mode that can occur if the electrode material is readily sputtered (a flux of sputtered atoms will be emitted by the anode); 3) a footpoint mode, characterized by the appearance of one or more luminous spots on the anode (footpoints are much cooler than the true anode spots present in the last two modes); 4) an anode-spot mode in which one large or several small anode spots are present (such spots are very luminous, have a temperature near the atmospheric boiling point of the anode material, and are a copious source of vapor and ions); and 5) an intense-arc mode where an anode spot is present, but accompanied by severe cathode erosion. The arc voltage is relatively low and quiet in the two low-current modes and the intense-arc mode. It is usually high and noisy in the footpoint mode, and it can be either in the anode-spot mode. Anode erosion is low, indeed negative, in the two low-current modes, and it is low to moderate in the footpoint mode. Severe anode erosion occurs in both the anode-spot and intense-arc modes.

Change in Field Intensification Factor β of an Electrode Projection (Whisker) at Short Gap Lengths

The field intensification factor, β, was found theoretically to be a function of gap length, projection height, and projection tip radius. The electrode projection was approximated by a grounded plane and separate grounded sphere, the opposing electrode by a charged plane. The results may be used to find the height and tip radius of a projection in a small gap by measuring β as a function of gap length.

Constraints imposed upon theories of the vacuum arc cathode region by specific ion energy measurements

The presence of high‐energy ions (with potentials greater than the overall arc voltage) in the flux from the cathode region of vacuum arcs has been well established. While much excellent theoretical work has been done on the cathode region of a vacuum arc, only a modest amount of such work has predicted the energies of the ions leaving the cathode region. Two vacuum arc cathode theories which do predict the ion energies are the potential hump theory—where a positive space charge at the cathode spot accelerates the ions electrostatically, and the gas dynamic theory—where the ions are accelerated by a flow process. Few theorists have taken advantage of the available mass spectrometric data concerning individual ion energies. In this paper I compare such data with theoretical predictions. The best confirmed ion energy data is that for a copper cathode. Additional data are presented concerning the ion flux from a vacuum arc with a ten percent Bi/Cu cathode. Comparison of the copper and bismuth/copper data wit...

Gases released by surface flashover of insulators

The gases released by surface flashovers on alumina ceramics, glass, and quartz, using 20‐μs voltage pulses, were investigated using an ion‐pumped metal vacuum system. Appreciable quantities of gas were measured (approximately 10−6 Torr liter or 1013 molecules). The composition of this gas differed significantly from the background gas. The dominant species in the surface flashover gases were CO2, CO, and H2; a modest amount of CH4 was observed, along with lesser quantities of N2 and H2O. The dominant gas in the system background was nitrogen, accompanied by (in decreasing amounts) H2, H2O, CO/CO2, Ar, CH4, and He. We concluded that the gas released by flashovers on the surface of the insulators was not adsorbed system background gas, but was gas adsorbed during the handling and processing of the insulator.

Improving the Voltage Holdoff Performance of Alumina Insulators in Vacuum Through Quasimetallizing

Treatment of the surface of an alumina insulator with coatings incorporating varying amounts of Cr, Mn, and Ti can increase the vacuum voltage holdoff capability of the insulator significantly (up to 25%). During processing (quasimetallizing) the coating penetrates into the alumina, making it insensitive to mechanical damage. This quasimetallizing treatment is also compatible with subsequent metallizing and brazing of the alumina insulator. A 7/1 Mn/Ti mix performed very well, being found to be as effective on a 94% A12O3 alumina as on the previously investigated 95% A12O3, 1% Cr2O3 alumina. Mixes of 6/1/1 Mn/Ti/Cr and 6/3 Mn/Cr performed about as well as the 7/1 Mn/Ti mix, but no better. Quasimetallizing with pure Mn improved the voltage holdoff capability of alumina by about half as much as when using the 7/1 Mn/Ti mix. Mixes with relatively high titanium content (4/3 Mn/Ti and 3/3/2 Mn/Ti/Cr) significantly increased the voltage holdoff capability of the alumina, but unfortunately were much more prone than the 7/1 Mn/Ti mix (or plain alumina) to suffer severe and permanent damage when a breakdown did occur. Quasimetallizing with appropriate formulations. has been shown to change the surface characteristics of alumina in two ways: (1) it decreases the surface resistivity of the alumina, and (2) it decreases the secondary electron emission yield of the alumina. Each change improves the voltage holdoff characteristics of the alumina.

Measurements on Particle Fluxes from dc Vacuum Arcs Subjected to Artificial Current Zeroes

A mass and energy analyzer capable of time‐resolved analysis of the separate constituents of the flux from vacuum arcs near and through current zero has been constructed. The following results are obtained in looking at the radial flux from 50‐ and 100‐A copper arcs subjected to rapidly forced current zeros: (i) A burst of low‐energy ions is produced at the time of arc extinction (within the resolving power of the apparatus, <5 μsec), this burst being attributed to the collapse of a potential hump near the cathode. (ii) The presence of copper ions depresses the level of background gas signal, especially for hydrogen.

Discharge Modes at the Anode of a Vacuum Arc

Five possible discharge modes can exist at the anode of a vacuum arc. The two most common anode modes are a low current mode, where the anode is basically inert; and a high current mode with a fully developed anode spot. This anode spot is very bright, has a temperature near the boiling point of the anode material, and is a copious source of vapor and energetic ions. Three additional anode modes can occur in appropriate circumstances. A low current vacuum arc with electrodes of readily sputterable material will emit a flux of sputtered atoms from the anode. At intermediate currents, an anode footpoint can form. This footpoint is luminous, but much cooler than a true anode spot. Finally, a high current mode can exist where several small anode spots are present instead of a single large anode spot.

Values of Fowler-Nordheim field emission functions: v(y), t(y), and s(y)

Abstract The functions v(y) and t(y) are useful in evaluating the Fowler-Nordheim field emission equation. The related function s(y) is used in examining the slopes of logarithmic plots of this equation. Six-place tables of v(y), t(y), and s(y) are presented for values of y from 0 to 1.0 inclusive, at intervals of 0.01.

Polarity Effect in Vacuum Breakdown Electrode Conditioning

We wished to determine if an electrode polarity effect existed in vacuum breakdown conditioning. To investigate this conditioning effect, we used a three‐electrode experimental tube constructed in such a manner that one electrode (1) could be made to oppose either of the other two (2 or 3) without destroying the vacuum. High‐current arcs were drawn between both possible electrode pairs to bring them to a reproducible state of apparent deconditioning. These pairs (1 vs 2 and 1 vs 3) were then, in turn, conditioned by a series of high‐voltage pulses at a gap of 2.3 mm. The following conclusions were drawn: (1) within experimental error, all conditioning took place at the pulse cathode, (2) when the arc and pulse polarities were similar, the subsequent pulse breakdown voltage was lower than when the polarities were opposed, and (3) conditioning was not due to the removal of a gas layer from the electrode, but, rather, to removal of cathode deformations. Predictions concerning the polarity effect in vacuum br...