Search

The optical diagnostic method can provide much more information about the physical process of surface flashover. In this paper, the vacuum surface flashover spectra of five different insulator materials (including both organic and inorganic insulator materials) under pulsed excitation are presented. According to the spectrum analysis results, many molecular spectral bands emerge in the spectrum of surface flashover as well as the atomic lines. The flashover band spectra of different insulators are nearly the same, most of these band spectra might be generated by ionized gases which are desorbed from insulator surface. Besides, some of the atomic lines are identified to be emitted by material element, which implies that the material was decomposed during the flashover process, and the decomposed material together with desorbed gas contribute to the final stage of flashover.

A time-resolved measurement system of spot size for X-ray sources was constructed by coupling a gated CCD camera with a fast scintillator crystal. The spot size of the high-energy pulsed X-ray source from the Dragon-Ⅰ linear induction accelerator was measured at 10 ns intervals, and a curve of spot size versus time was obtained. An LYSO crystal array with a pixel size of 0.78 mm was also designed and tested in X-ray field, and primary experimental results show the array can be used for time-resolved spot size diagnosis of the high energy X-ray source and significantly improve the spatial resolution of X-ray images.

Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter to yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.

A kind of laser diode with high power and short duration is described in this paper. The laser diode is used for triggering gallium arsenide photoconductive semiconductor switch (GaAs PCSS) in the experiment. The driver of the laser diode is based on RF MOSFET and it provides an ultra-fast pulse current, which has the rise-time, FWHM and peak current are 4ns, 17ns and 130A, respectively. The characteristics of the laser diode have been researched, including laser pulse waveform, optical field distribution, and limiting drive current. Using a combination of two laser diodes, the PCSS has a better performance than being triggered by single laser diode in the experiment.

A high precision laser trigger system is built up in the single test module of Primary Test Stand (PTS) facility. A fourth harmonic, with a wavelength λ of 266 nm, Q-switched Nd:YAG laser was used to trigger the 5 MV multi-gap multi-channel gas switch which was filled with high pressure SF6-N2 mixture gas. The maximum deviation and the standard deviation in the jitter time of the trigger system is ± 0.7 ns and 0.3 ns respectively. The maximum deviation and the standard deviation in the jitter time for the multi-gap multi-channel laser triggering switch is ± 2.4 ns and 1.5 ns respectively. The curve of switch delay-time versus laser energy is obtained, which is helpful for the choice of fitting laser energy. The successful test with two lasers indicated that the design of using twenty-four lasers to trigger twenty-four switches respectively is feasible in ``PTS''.

A compact, low-jitter, and high repetitive rate all-solid-state flash x-ray generator making use of photo conductive semiconductor switches was developed recently for the diagnostic purpose of some hydrokinetical experiments. The generator consisted of twelve stages of Blumlein pulse forming networks, and an industrial cold cathode diode was used to generate intense x-ray radiations with photon energy up to 220 keV. Test experiments showed that the generator could produce >1 kA electron beam currents and x-ray pulses with ∼40 ns duration under 100 Hz repetitive rates at least (limited by the triggering laser on hand), also found was that the delay time of the cathode explosive emission is crucial to the energy transfer efficiency of the whole system. In addition, factors affecting the diode impedance, how the switching synchronization and diode impedance determining the allowable operation voltage were discussed.

A new type of surface flashover switch, suitable for multiplex pulse generation, is studied. The switch is composed of several parallel rail gaps (PRGs). Each multistage PRG is composed of several serial subgroup gaps (SSG) formed by intermediate electrodes. The trigger electrode of the switch is a common electrode isolated from the main discharge circuit and located parallel to the central line of PRGs. The multistage scheme of PRG is helpful to multi-channel discharge. The switch has some advantages, such as a low jitter, low conduct inductance and short switching time. These advantages and the multiplex scheme make the switch suitable for short frontal rising time pulse formation and accurate synchronization for a multi-module parallel operation device. In a primary test, the jitter of the switch is about 3.3 ns. It has been applied in a linear transformer device successfully.

Summary form only given. In this article, we discuss the emitting mechanisms of a velvet cathode (VC) emitting an intense e-beam on basis of conclusions of three sets of experiments, and give some principles for selecting velvet to get higher a brightness e-beam. In the experiment, Marx is used as the energy equipment, a 300 kV, 50 ns pulse-width (FWHM) voltage pulse of negative polarity is put through the parallel board water-media pulse-formative-line. The diode is a parallel board model. The diameter of the cathode is 90 mm. The emitting surface is an inlayed velvet cathode of 50 mm-diameter, the velvet patch is glued onto a copper base with silver glue to make the standard cathode. The A-K gap is 13 mm. The anode is a 100 mm-diameter copper board, and there are 9 symmetrically cross-distributing 1.2 mm-diameter holes in it. So, we could simultaneously measure the beam current and the emittance at the anode plane with using the anode as an electron beam collector and pepper-board.

Basic research for repetition of blowing gas field distortion spark switch is described in this paper. The switch designed by ourselves can work repetitively, the maximum repetition rate is up to 130 Hz during 80 ns, and the maximum working voltage is up to 60 kV; and delay time is less than 100 ns, jitter is less than 10 ns; the variation of the switch's peak voltage is no more than 1%.

The solid-state pulse forming lines (PFL) of CaO-TiO2-Al2O3 composite ceramic are designed and manufactured for the dielectric wall accelerator. The PFLs geometric parameters are 300 mm long, 15 mm wide, 1mm thick of ceramic dielectric and 280 mm long, 2 mm wide of silver electrode. The electrical parameters are 23.5 relative dielectric constant, about 26 characteristic impedance, 4.5 ns characteristic time, 20 kV/mm and 25 kV/mm breakdown field strength for DC and pulsed high voltage. The solid-state PFLs design gives consideration to operating requirement of photoconductive semiconductor switches (PCSS), design parameters of high gradient insulator, charged particle beams transport and accelerators structural design. Combined with the PCSS, the experimental research of solid-state Blumlein PFL is performed. The solid-state Blumlein PFL could output about 23 kV pulsed voltage on the load under about 25 kV pulsed voltage.