Simple, Solid Dielectric Start Switch
A field-distortion, solid dielectric switch of the type introduced by Martin1 at A. W. R. E. and later extensively investigated by Dokopoulos2 at Jülich is used as a start switch for a fast theta pinch system. Previous solid dielectric switches of this type required extensive electrode and switch package preparation as well as a fast trigger system to provide repeatable, multiple-arc channels during switching. In contrast, this switch was designed to facilitate ease of operation, switch package preparation and replacement. Repeatable performance is obtained with pitted and scarred electrodes and a relatively slow trigger system. The switch, 20 cm wide, produces an average of four arc channels, holds off approximately 110 kV and switches 70 kV with a maximum current of 500 kA. The inductance of the switch, including the connecting stripline inductance of 11 nH, is approximately 12 nH. The theta pinch circuit resistance is 13 mΩ, most of which is due to the four, parallel, Tobe Deutschmann ESC 249 capacitors. A very low switch resistance of 1-2 mΩ is indicated. The trigger system, a compact, photoelectrically triggered Marx circuit, produces a 80 kV, 50 joule pulse with a rise time of 50 ns. The average delay from Marx trigger initiation is. 1 μs with an average jitter of .05 μs. The switching action is performed under oil to decrease switching noise. The oil also prevents high voltage tracking problems and thus reduces the switch package size. All of the current carrying joints in the switch are reinforced by a hydraulic jack that holds the switch plates together during switching.
KeywordsRise Time Capacitor Bank Switching Action Knife Edge Trigger System
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