Articles you may be interested inActively cooled plasma electrode for long pulse operations in a cesium-seeded negative ion source Rev. Sci. Instrum. 76, 013501 (2005); A frame-cooled plasma grid for long pulse operations in a cesium-seeded volume negative ion source Rev. Sci. Instrum. 73, 298 (2002);The wire ion plasma source ͑WIPS͒ is a device that can be utilized as a pulsed ion source for ion-induced secondary-emission electron guns. The pulsed discharges of the WIPS are usually ignited by applying over-voltages onto the wire anode using a thyratron. The shortness of lifetime peculiar to such gas filled switching devices is known to be a major problem when utilizing the WIPS as a high-repetition-rate pulsed ion source. In this article a completely new method for the ignition of the pulsed discharges on the WIPS is proposed. This method, named the built-in electrostatic trigger method, does not need an external gas switching device. The new method also gives rise to another advantage in the pulsed-discharge characteristics since it minimizes the series impedance in the discharge circuit. The feasibility of the method is confirmed experimentally. A few improvements are introduced so as to realize high-repetition-rate pulsed operations of the WIPS.
For a high voltage SF6 circuit breaker equipped with a boron nitride (BN)-filled polytetrafluoroethylene ((C2F4) n ) nozzle, the predominant reaction products in a high-temperature SF6 mixture with vapor decomposition of C2F4 and BN at temperatures of 300–3000 K are determined based on calculations of equilibrium composition. The calculation is performed by considering the molecular products obtained by chemical reactions with boron atoms (e.g. BN, BS, BC, BF, BF2 and BF3), nitrogen atoms (e.g. N2, N3, CN, NS, NF, NF2 and NF3) and carbon atoms (e.g. CS, CS2, C2F4, CF2, CF3 and CF4). The results obtained for the C2F4–BN molar fraction X C F B N of 20%–80% reveal that BF3, N2 and CF4, the molecules originating from the nozzle material, are produced at high molar fractions over a range of 300–3000 K. Such an evaluation of the gas composition allows the derivation of a reduced collision ionization coefficient α/N and a reduced electron attachment coefficient η/N of the gas, considering various electron impact processes such as BF3 + e → BF2 + F− and CF4 + e → CF3 + F−. The evaluation subsequently enables us to determine a critical reduced electric field strength E c r / N causing ( α − η ) / N = 0 . The results suggest that the decomposed C2F4–BN mixture at X C F B N of 80% causes the reduction of E c r / N to 110 Td in the range of 1000–2000 K at a gas pressure of 1.0 MPa. This strength E c r / N is 20 Td lower than that determined separately for the SF6 gas mixture with only 80% C2F4 vapor decomposition, because of the CF4 molar fraction reduction in the SF6/C2F4–BN mixture.
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