Cathode Spot Region Research Articles

Erosion products from the cathode spot region of a copper vacuum arc

Combined electrical, optical, and spectroscopic measurements have been used to determine the total flux, ion flux, particle flux, and neutral atom flux emitted from the cathode spot region of a copper vacuum arc of 80 A total current and 2-sec duration. It is found that the cathode erosion products consist predominantly of ions and particles, the emission of neutral atomic flux from the cathode being less than 1% of the total flux. The total and particle flux distributions are peaked in the direction of the cathode plane, whereas the ion-flux distribution is forward peaked. However, both ions and particles are detected in the cathode shadow, a result which is contrary to the hypothesis of purely collisionless transport of cathode erosion products. The neutral atom density measurements are consistent with a model assuming the source of the vapor to be evaporation in flight from the hot particles emitted from the cathode spot region. The size distribution of the particles has a maximum for particles of diameter in the range 0–1 μ.

Deionisation of an interrupted vacuum arc

Measurements have been made of time-dependent saturation ion currents flowing to a probe and to the discharge electrodes following the forced extinction of high-current (1–5 kA) vacuum arcs of short duration (≃1 ms) on copper electrodes.The results have been utilised to derive ion-flux distributions irrespective of ion-charge number, assuming collisionless plasma expansion from the cathode spots, and significant differences have been found compared with previous measurements on steady-state discharges.The results on interrupted and steady-state discharges are reconcilable if a source of low-energy ions exists, which is constrained in the cathode-spot region in the steady state and which is released at the zero current condition when the constraining forces vanish.

The effects of nanosecond atmospheric arcs on various metallic surfaces†

The damage on silver, gold, tungsten and palladium contacts, due to the action of short duration, low current area at atmospheric pressure was examined using a scanning electron microscope. Current densities, obtained from measurements of the are current and the cathode damage dimensions, were of the order of 107 amps cm−2. Electron densities in the are columns have been estimated to reach 1018 electrons cm−3. Pressures of approximately 103 atmospheres and temperatures well above the metal boiling point were calculated for the cathode spot region. The velocity of the cathode spot along the palladium cathode surface was found to be approximately 105 cm sec−1. The electron drift velocity in the cathode spot region in palladium has been calculated to be 2.5 × 103 cm sec−1.

MEASUREMENTS OF CATHODE SPOT TEMPERATURE IN VACUUM ARCS

The cathode spot temperatures of various metals in vacuum arcs have been measured for the first time on the basis of the Maxwellian portion of velocity distribution of the vapor atoms emanating from the cathode spot region by employing the combined technique of time-of-flight and quadrupole mass analysis.

The motion of cold-cathode arcs in magnetic fields

The paper first discusses the way in which theories concerning the motion of cold-cathode arcs when acted upon by a magnetic field have ranged from proposing cathode-fall mechanisms for retrograde motion to column processes for forward motion. A very recent mechanism proposed by Ecker for retrograde motion is then examined and found to be capable of extension to higher pressures where forward motion occurs.Previously published experimental results for forward motion are viewed in the light of this mechanism, which is found to be consistent with them, and some features which had hitherto been anomalous may now be explained. Thus there emerges a unified model for the cathode spot and fall region which appears to be valid for both forward and retrograde movements of the arc. It is suggested that this provides a vital step in the approach to the development of certain devices in which arc discharges take place.

The Negative Glow and Cathode Spots in Low Pressure Arcs†

ABSTRACT Diffusion conditions in the negative glow (or cathode spot) of low pressure thermionic and pool arcs are investigated. It is shown that both plasma density and potential maxima occur and the cases of planar, cylindrical and spherical symmetry are considered in detail. The ion current at the cathode can be an appreciable fraction of the electron current with an upper limit of half the ratio of the cathode foil to the ionization potential in the most favourable case. The cathode fall can exceed the anode potential by several volts in addition to the anode fall. Two modes are possible for arcs with no positive column : one in which the negative glow fills the whole inter electrode space and another in which the glow is confined to the cathode spot region and the rest of the space is filled with a dark plasma corresponding to the Faraday dark space. Investigation of the dark plasma shows that cathode spots or ‘ lines ’ must form for this mode to occur. In this case the current-carrying electrons pass...

Motion and Spectrum of Arc Cathode Spot in a Magnetic Field

The velocity of the cathode spot of a mercury arc at the junction between liquid and metal in a transverse magnetic field has been measured for magnetic field strengths between 0 and 20 700 oersteds. The approximate doubling of retrograde velocity at about 11 000 to 15 000 oersteds was followed by an additional rapid rise of velocity at about 15 000 oersteds. Spectra of the arc showed Hg ii and Hg iii lines at the stronger magnetic fields. Radiation from the cathode spot showed mercury lines and a continuous spectrum which is especially intense at the lines. Some Hg lines are broadened symmetrically and others asymmetrically. If the broadening is due to a Stark effect, the electric field strength in the cathode spot region is greater than 6\ifmmode\times\else\texttimes\fi{}${10}^{6}$ volts/cm.The arc mechanism previously proposed is extended to explain the rapid velocity rises with increasing magnetic field strength by associating them with the effect of ${\mathrm{Hg}}^{++}$ and ${\mathrm{Hg}}^{+++}$ ions.