| 摘要 |
The electrical switch device has an envelope in which is mounted a liquid-metal cathode, an anode, and a condenser. The cathode is capable of very high electron-to-atom emission ratio. A desirable value for the electron-to-atom emission ratio is on the order of 100 or more and is attainable by means of a cathode such as disclosed in U.S. Pat. No. 3,475,636. The condenser has a very much larger area than the exposed liquid metal area on the cathode, and it is kept at a low enough temperature to efficiently condense the liquid-metal vapor emitted by the cathode. With mercury used as the liquid metal, the condenser temperature is kept substantially below 0 DEG C., preferably at about -35 DEG C. which is just above the melting point of mercury. When arcing occurs from the liquid metal, a plasma jet of electrons, ions, and neutral particles is emitted from the arc spot. The anode is mounted between the cathode and the condenser, and it partially intercepts the plasma jet. The combination of the high electron-to-atom emission ratio of the cathode with the large, low-temperature condenser results in an equilibrium background pressure (i.e., pressure outside the plasma jet) of at least as low as 10<->3 Torr during arcing, and lower than 10<->4 Torr during non-arcing periods. These low pressures are obtained by maintaining the condenser in the range of low temperatures defined above. This low background pressure, in turn, permits the essentially unperturbed propagation of the plasma jet between the cathode and the surfaces upon which it impinges, i.e., condenser and anode. Such a discharge mode is commonly referred to as a "vacuum arc." The fact that the plasma jet is emitted only during arcing, and that the pressure within the space surrounding this jet is kept low, results in the ability to hold off electric fields up to 50 kV per centimeter between anode and cathode immediately after cessation of arcing.
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