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Based on high pulsed power technology, electrical explosion is increasingly utilized to generate shock waves with high pressure. To further magnify the shock wave pressure, we have proposed a novel technique by using energetic materials ignited by the plasma of microsecond wire explosion. Organic derivatives of nitramide, termed nitroamines, are widely used as powerful and relatively insensitive explosives. In this paper, we investigated the shockwave characteristics of nitramine (RDX and HMX) powders ignited by exploding copper wire (diameter 0.3 mm and length 60 mm). With charge voltage of 24 kV and powder mass about 6.0 g, the most evident experimental results suggested that the RDX load possessed higher peak pressure of 11.38 MPa and larger areal impulse of 503.02 MPa $\cdot \mu \text{s}$ , comparing with the shock wave of HMX load (7.22 MPa and 371.28 MPa $\cdot \mu \text{s}$ ). Moreover, the RDX load also had greater ascent rate of pressure, which was nearly twofold of that of the HMX load. Finally, a simple multi-factor ignition mechanism for nitramine powder under microsecond exploding wire plasma was proposed and discussed.

Due to its low-loss and high dielectric strength, polypropylene is widely used as electrical insulation material in pulse capacitors. In order to study its breakdown characteristics for nanosecond voltage pulses, an experimental setup was designed to generate voltage pulses with a 10%–90% rise time of 38 ns and a full width at half maximum of about 90 ns. Tests of the three polypropylene films with thicknesses of 12, 15, and $18~\mu \text{m}$ were performed. In addition, hundreds of nanoseconds pulse and dc voltage were also applied for comparison. The experimental results reveal that most of the breakdown occurs during the front edge of the pulse for tens of nanoseconds pulse, and the breakdown strengths of the three kinds of polypropylene films are almost identical for different applied voltages, which show a weak correlation between the thickness of the dielectric and the breakdown field. The expected breakdown strength of tens of nanoseconds pulse defined in this paper is not significantly higher than the mean value of the hundreds of nanoseconds pulse and the dc condition, suggesting that the breakdown of a thin polypropylene film is mainly determined by the electrical field but not the voltage-time cumulative effect. All these observations strengthen the conclusion that the breakdown of a thin polypropylene film is an intrinsic phenomenon.

Based on high pulsed-power technology, electrical explosion is increasingly utilized to generate shock waves (SWs) with high pressure and short duration. To further magnify the SWs, we have proposed a novel technique by using energetic material (EM) loads. In this paper, we investigated the SW characteristics of ammonium nitrate (AN) powders ignited by the plasma of different kinds of refractory wire explosion. Evident results suggested that compared with $\Phi ~0.5$ -mm wires, $\Phi ~0.2$ -mm molybdenum and tantalum wires were able to finish vaporization, undergo the breakdown and eventually produce stronger SWs. After introducing the AN powders, the peak pressure of SW was scarcely enhanced, while the duration was significantly increased. Moreover, it was implied that various factors would affect the SW characteristics, including the EM charge density, the diameter, and material of metal wire. Finally, a simple plasma ignition mechanism based on multifactors was proposed.

Ultraviolet (UV) illumination can effectively shorten the statistical lag and jitter in gas breakdown processes. The spark gap discharge can produce abundant spectrum including UV waveband. In this paper, a simple but reliable spark gap operating with $N_{2}$ at atmospheric pressure is used to test optical radiation characteristics, such as spectrum intensity, rise time, fall time, and duration of optical pulse, which are adjusted by changing the circuit or configuration parameters. Three UV-illuminated switches with different UV spark gap configurations have been tested. The experimental results approve our assumption. With a uniform electric field UV spark gap, the breakdown voltage standard deviation percentage of the switch is 0.74%.

In a wide variety of high-power pulsed devices, the megavolt switch plays a key role in the system performance. A capacitance-resistance coupling structure was designed to produce UV light which triggered the switch to decrease the breakdown jitter. High-speed electrical measurements with a circuit integrating probe in the nanosecond range were employed to measure the voltage before the switch. From the experimental results, the breakdown characteristic of a 3-MV UV-illumination switch was obtained in the range of 1.6-2.5 MV: The jitter of the breakdown voltage is lower than 25 kV, and the jitter of the breakdown time is shorter than 5 ns.

To get the better choice for achieving higher stability and reproducibility of the output voltage pulse of the generator, two pancake switches commonly used in the low energy, high peak power Marx generator have been compared. The comparison is done in several aspects including the structure, the electric field distribution, and the breakdown characteristics. Some useful conclusions are drawn. And there is a big difference between the structural capacitances of the two gas switches as a result of the different configuration of their electrodes. So a circuit simulation of the switch used in a simple, basic, two-stage Marx circuit has been done on both switches respectively.

The behavior of explosive emission cathode plasma was a fundamental physical problem in the study of high current electron beam diode. A diagnosis system was designed for getting the time-resolved and spectrum-resolved emission spectra of cathode plasma on a 1MV diode with dozens of kilo amperes in this paper. A full spectrum of direct reading spectroscopic diagnostic system which includes a high band pass spectrograph with 200–1000nm detection wavelength and an ultra high-speed intensified imaging with 2ns gate time was used in the experiment. The characteristics of emission spectra in different stages during the process of cathode plasma of several cathode materials were obtained. These results are helpful for improving the uniformity of cathode plasma emission in high current diode by choosing suitable surface treatment method of cathode.

In a wide variety of high-power pulsed devices, vacuum surface flashover plays a key role in the system performance. High-speed electrical measurements with temporal resolution in the nanosecond range were employed to measure the flashover characteristics, and high-speed three-frame photography was used to image the flashover channels at different phases along the insulator surface. From these test results, the flashover under nanosecond pulse would experience a process with three typical phases: initial phase, developing phase, and extinguishing phase. Spectra luminosity of the flashover channel is also discussed for better understanding the mechanism of the flashover process.

Structural design and tests on the characteristics of the SF6 gas switch with a small gap are presented. This kind of switch often works under high pressure and nanosecond pulse for getting pulse with faster risetime. The breakdown voltage and breakdown delay of a number of switches with different geometries, gas pressures and pulse waveforms were investigated. Experimental results suggested that the breakdown voltage increases linearly with the gas pressure, and the breakdown delay decreases with an increase in the gas pressure and a reduction in the gap distance of the switch under the same applied pulse. By using this kind of switch with a gap of 3 mm as a peaking switch, a pulse generator can provide an output voltage with a peak voltage of 300 kV and a risetime of 3 ns on a resistance load of 150 Ω.

In order to restrain the prepulse of a high energy fluence diode, a flash-over switch made of a nylon cylinder was inserted in between the cathode stalk and the cathode. Secondary prepulse technique was developed to lower the flash-over voltage of the switch. It was found that the surface resistivity of the nylon insulator changes considerably after each shot and this resistivity on the order of 107 Ω/m is most suitable for a 20-mm long flash-over switch to operate stably at a lower flash-over voltage.

An extremely compact high voltage peaking capacitor is developed. The capacitor has a pancake structure with a diameter of 315 mm, a thickness of 59 mm, and a mass of 6.1 kg. The novel structural design endows the capacitor with a better mechanical stability and reliability under hundreds of kilovolts pulse voltage and an inner gas pressure of more than 1.5 MPa. The theoretical value of the capacitor self-inductance is near to 17 nH. Proved by series of electrical experiments, the capacitor can endure a high-voltage pulse with a rise time of about 20 ns, a half-width duration of around 25 ns, and an amplitude of up to 800 kV in a single shot model. When the capacitor was used in an electromagnetic pulse simulator as a peaking capacitor, the rise time of the voltage pulse can be reduced from 20 ns to less than 3 ns. The practical value of the capacitor's inductance deduced from the experimental date is no more than 25 nH.

The preliminary experimental results of the generation and diagnostics of high-power ion beams of FLASH II accelerator are reported. The high-power ion beams presently are being produced in a pinched diode. The method for enhancing the ratio of ion to electron current is to increase the electron residing time by pinching the electron flow. Furthermore, electron beam pinching can be combined with electron reflexing to achieve ion beams with even higher efficiency and intensity. The anode plasma is generated by anode foil bombarded with electron and anode foil surface flashover. In recent experiments on FLASH II accelerator, ion beams have been produced with a current of 160 kA and an energy of 500 keV corresponding to an ion beam peak power of about 80 GW. The ion number and current of high power ion beams were determined by monitoring delayed radioactivity from nuclear reactions induced in a 12C target by the proton beams. The prompt γ-rays and diode bremsstrahlung x-rays were measured with a PIN semi-conductor detector and a plastic scintillator detector. The current density distribution of ion beam were measured with a biased ion collector array. The ion beams were also recorded with a CR-39 detector.

The solid dielectrics such as epoxy, high density polyethylene(HDPE), polytetrafluoroethylene (PTFE), nylon and polymethylmethacrylate(PMMA) are often used as vacuum insulator in pulsed power device, in which they were applied under pulse voltage with risetime from several to several tens nanoseconds. Flashover characteristics must be paying more attention because they are the major breakdown models in their applications. A pulse source with output voltage of 50 ns risetime, 320ns pulse width and peak voltage up to 200 kV has been developed in this research. The flashover characteristics including flashover voltage and flashover current of the materials mentioned above under plane electrode were tested under 5E-3Pa vacuum. In order to get the relationship between surface charge deposition and the flashover characteristics, the surface potential distribution before flashover and after once, seventh and thirty-fifth flashovers are presented in this paper.

In a wide variety of high-power pulsed facilities, megavolt switches play a key role in determining the system performance. In particular, ultraviolet (UV)-illuminated switches have been widely used for their high-voltage, low-jitter characteristics. In this paper, two factors that may affect the breakdown jitter of a 3 MV UV-illuminated switch under pulsed voltages were investigated, namely, the electric field enhancement factor of a UV-illuminating gap (UV gap) and the number of UV gaps. The experimental results show that the electric field enhancement factor is important for adjusting the average E/p of the main switch gap when the UV gaps breaks down under certain N2 pressures. When the electric field enhancement factor of the UV gaps is approximately that of the main switch gap, the breakdown jitter percentage goes down to less than 1.9%. Comparatively, the number of UV gaps affects breakdown voltage and jitter in a limited-way. When only one UV gap is functioning and the electric field enhancement factor of UV gap is approximately that of the main switch gap, the breakdown jitter is less than 1.3%.

The preliminary experimental results obtained for the energy spectra of high-power ion beam(HPIB) with a pile of thin films on FLASH Ⅱ accelerator are reported. Code was developed to calculate the theoretical energy-loss of proton and C ion beams transmited through the Mylar films with different thickness. T he apertures of Faraday Cups are covered with Mylar films of different thicknes s, and then the signal attenuations can be recorded with oscilloscope. The energ y spectra of HPIB and the diode voltage are obtained according to the signal al lenuations. The diode voltage measured with a pile of thin films agrees with the voltage measured with a differential ring. And the ion number versus time curv e was given. In addition, the ion energy of HPIB is also measured with Thomson spectrometer and time of flight method and the results agree with those measured with a pile of thin films.