Sheng Liang

Diagnosis of multi-gap gas switch with optical fiber detectors

A set of fiber detector which consists of an optical fiber array detector and a solar-blind plug-in optical sensor was developed for multi-gap gas switch optical diagnosis. The detailed discharging process was monitored using the detector and the influence of trigger voltage, gas pressure and UV pre-ionizing on the performance of the switch was also analyzed. The timing precision of the fiber array detector is better than 0.6 ns, and its time response is 3.2 ns. The solar-blind sensor responds to light whose wavelength lies between 260 nm and 320 nm. The following results were obtained by the diagnostic system: the order of the gaps breakdown is 3rd-2nd-1st-4th-5th-6th, and statistic delay and over-voltage breakdown delay take the majority of the whole time delay. The jitter of the switch can be reduced by raising the trigger voltage, lowering the gas voltage and stabilizing the intensity of the ultraviolet light.

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

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.

R-L Method and BLS-GSM Denoising for Penumbra Image Reconstruction ⁄

When neutron yield is very low, reconstruction of coding penumbra image is rather difficult. In this paper, low-yield (109) 14 MeV neutron penumbra imaging was simulated by Monte Carlo method. The Richardson Lucy (R-L) iteration method was proposed to incorporated with Bayesian least square-Gaussian scale mixture model (BLS-GSM) wavelet denoising for the simulated image. Optimal number of R-L iterations was gotten by a large number of tests. The results show that compared with Wiener method and median filter denoising, this method is better in restraining background noise, the correlation coefficient Rsr between the reconstructed and the real images is larger, and the reconstruction result is better.