Optical Diagnostics of Multi-Gap Gas Switches for Linear Transformer Drivers

Abstract

The trigger characteristics of a multi-gap gas switch with double insulating layers, a square-groove electrode supporter and a UV pre-ionizing structure are investigated aided by a high sensitivity fiber-bundle array detector, a UV fiber detector, and a framing camera, in addition to standard electrical diagnostics. The fiber-bundle-array detector is used to track the turn-on sequence of each electrode gap at a timing precision of 0.6 ns. Each fiber bundle, including five fibers with different azimuth angles, aims at the whole emitting area of each electrode gap and is fed to a photomultiplier tube. The UV fiber detector with a spectrum response of 260-320 nm, including a fused-quartz fiber of 200 µm in diameter and a solar-blinded photomultiplier tube, is adopted to study the effect of UV pre-ionizing on trigger characteristics. The framing camera, with a capacity of 4 frames per shot and an exposure time of 5 ns, is employed to capture the evolution of channel arcs. Based on the turn-on light signal of each electrode gap, the breakdown delay is divided into statistical delay and formative delay. A decrease in both of them, a smaller switch jitter and more channel arcs are observed with lower gas pressure. An increase in trigger voltage can reduce the statistical delay and its jitter, while higher trigger voltage has a relatively small influence on the formative delay and the number of channel arcs. With the UV pre-ionizing structure at 0.24 MPa gas pressure and 60 kV trigger voltage, the statistical delay and its jitter can be reduced by 1.8 ns and 0.67 ns, while the formative delay and its jitter can only be reduced by 0.5 ns and 0.25 ns.

Comparative study on breakdown characteristics of trigger gap and overvoltage gap in a gas pressurized closing switch

“…The experimental results presented above indicate that the radiation from the first-breakdown gap can effectively improve the breakdown characteristics of the next-breakdown gap. As a result, the pre-ionization technology has been invented and used in many kinds of gas switches [8,16]. The technology of pre-ionization, which adds a first-breakdown pre-ionizing gap in the switch, can reduce the breakdown delay and jitter of the switch.…”

“…The multi-gap gas switches, which have the advantages of low trigger threshold and high breakdown stability, are widely used in FLTD-based drivers at present. As a result, many investigations have been already conducted on some typical multi-gap gas switches, and the influences of trigger voltage, working coefficient, air pressure, electrode structure and UV pre-ionization on the trigger characteristics have also been obtained [8][9][10][11][12][13][14][15][16]. However, most of the researches are focused on the performance of the whole switch, the studies on the breakdown characteristics of each gap and their influence on the whole switch are relatively few.…”

Multichannel switching in a multigap gas switch at atmospheric pressure

“…However, insulation requirements are increasing and the technical implementation of the triggering system is becoming more complicated, especially for multisection installations. It is necessary to optimize the parameters of the triggering system that provide the multichannel switching mode, and optical diagnostic methods can be used to study multichannel switching and optimize these parameters [10,20,21].…”

Experimental investigation on the development characteristics of initial electrons in a gas pressurized closing switch under DC voltage

“…These air-insulated switches are usually firstly DC-charged to a voltage lower than the breakdown voltage and then triggered by an external trigger pulse. Therefore, the performance of an LTD strongly depends on the characteristics of these gas pressurized closing switches [5][6][7][8][9][10]. Improving the performance of gas switches is the most important and difficult issue when LTD-based systems are developed.…”