Hideaki Toya

Anode discharge mode and cathodic plasma state in high‐current vacuum arcs

Anode surface states and traces of the cathode spots after arcing of various anode discharge modes in vacuum have been studied in the current range of 5–20 kA. Spectroscopic measurements of the radial electron temperature profile in the cathode region, which is related to the distribution of the current density, have also been performed to investigate the cathodic plasma state of the arcs in the various anode modes. The arc of a half‐wave sinusoidal current of 60 Hz was burned between a 60‐mm‐diam anode and a 30‐mm‐diam cathode spaced 4 mm apart. The electrodes were made of oxygen‐free, high‐conductivity copper. The cathode spots spread uniformly over the entire cathode and a uniform current density profile was obtained in the diffuse‐arc mode. It was found, however, that the cathode spots bunch together and the current density profiles peak at the center of the discharge in the anode‐spot mode. The cathode‐spot bunching and the nonuniformity in the current density profile become significant with a suffic...

Spectroscopic Measurement and Analysis of High-Current Vacuum Arc near Copper Cathode

A spectroscopic measurement is performed of a 10-kA peak (kAp) vacuum arc in the vicinity of the 30-mm diameter cathode spaced 4 mm apart from the 60-mm anode. The electron temperature is determined from the Boltzmann distribution temperature of Cu II system by assuming the partial local thermodynamic equilibrium (PLTE). The electron temperature varies with the instantaneous arc current, and the radial electron temperature profile is peaked at the center of the arc discharge. It is shown that the arc is the diffuse discharge by comparing the calculated result of the effective arc resistance with the value previously measured in the diffuse arcs. In conclusion, the radial current density profile proves to be concentrated toward the center of the diffuse arc discharge near the cathode.

Voltage/current characteristics at the metal shield surrounding high‐current vacuum arcs

Electron and ion currents collected at the metal shield and floating shield potential are measured to study the behavior of high‐current (up to 40 kA) vacuum arcs. An arc with a half cycle of 60 Hz is burned between 20‐mm‐diam electrodes spaced 4 mm apart bounded by a 200‐mm‐i.d. metal shield in a demountable vacuum chamber. The electron current is measured by connecting the metal shield to the anode and the ion current is collected by connecting the metal shield to the cathode. The floating shield potential is differentially measured relative to the cathode by two resistive potential dividers. It was found that the electron current increases, while the ion current peaks and the shield potential decreases with an increasing arc current. The direction of the ion‐current flow is reversed during the discharge of an arc current at a level of more than 20 kA. Correspondingly, the shield potential becomes negative relative to the cathode. This newly found phenomena is attributed to the radial electric field gen...