Chebo Liu

Compact Rep-Rate GW Pulsed Generator Based on Forming Line With Built-In High-Coupling Transformer

In this paper, a compact rep-rate GW pulsed power generator is developed. First, its three key subsystems are theoretically analyzed, engineering designed, and experimentally investigated, respectively. The emphases are put on these four problems: the theoretical analysis of the voltage distribution across the conical secondary windings of the high-coupling transformer, the investigation of the high energy storage density dielectric used in the pulse forming line, the choice of the gas flow velocity of the gas blowing system, and theoretical analysis of the passive stability of the pulsed power generator operated in rep-rate mode. Second, the developed pulsed power generator is described in detail. It has a 0.2-m diameter, a 1.0-m length, and a 20- Ω wave impedance. Across a 100- Ω resistive dummy load, it can steadily operate at a 300-kV output voltage in 50-Hz rep-rate and 250 kV in 150 Hz without gas blowing system. The average power is ~ 1 kW. Finally, the pulsed power generator is applied to drive a relativistic backward-wave oscillator, generating a high-power microwave with peak output power of 200 MW and duration (full-width at half-maximum) of 5 ns in 150-Hz rep-rate. These efforts set a good foundation for the development of a compact rep-rate pulsed power generator and show a promising application for the future.

Relativistic electron-beam generation in a gas-loaded foil-less diode

Relativistic electron beams were generated in a gas-loaded foil-less magnetized diode. The helium gas was employed to fill the diode, and the experimental results have shown that the diode operated normally without the closure problem when the gas pressure was below a certain value (typically, 100 mTorr in the presence of an externally applied guide magnetic field). It has been observed that the current of the electron beam could increase with increasing the gas pressure, and that the presence of helium gas could reduce the operating voltage of the diode producing an electron beam with lower kinetic energy, which implies a decrease in the diode impedance. The externally applied magnetic field along the axial direction also exerted an influence on the electron-beam generation in the gas-loaded diode.

Fast modeling of flux trapping cascaded explosively driven magnetic flux compression generators

To predict the performance of flux trapping cascaded flux compression generators, a calculation model based on an equivalent circuit is investigated. The system circuit is analyzed according to its operation characteristics in different steps. Flux conservation coefficients are added to the driving terms of circuit differential equations to account for intrinsic flux losses. To calculate the currents in the circuit by solving the circuit equations, a simple zero-dimensional model is used to calculate the time-varying inductance and dc resistance of the generator. Then a fast computer code is programmed based on this calculation model. As an example, a two-staged flux trapping generator is simulated by using this computer code. Good agreements are achieved by comparing the simulation results with the measurements. Furthermore, it is obvious that this fast calculation model can be easily applied to predict performances of other flux trapping cascaded flux compression generators with complex structures such as conical stator or conical armature sections and so on for design purpose.

Investigation of a high power electromagnetic pulse source

A high power electromagnetic pulse source with a resonant antenna driven by a compact power supply was investigated in this paper. To match the impedance of the resonant antenna and initial power source, a compact power conditioning circuit based on electro exploding opening switch (EEOS) and pulsed transformer was adopted. In the preliminary experiments, an impulse capacitor was used to drive the system. With the opening of the EEOS at the current of 15 kA flowing trough the primary of the transformer, the resonant antenna was rapidly charged to about -370 kV within a time of about 100 ns. When the switch in the resonant antenna closed at the charging voltage of about -202 kV, the peak intensity of the detected electric field at a distance of about 10 m from the center of the source was 7.2 kV∕m. The corresponding peak power of the radiated electromagnetic field reached 76 MW, while the total radiated electromagnetic energy was about 0.65 J. The total energy efficiency of the resonant antenna was about 22% which can be improved by increasing the closing rapidity of the switch in the antenna.

Ultrathin CuSiN/p-SiC:H bilayer capping barrier for Cu/ultralow-k dielectric integration

Different amount of porosity, which leads to the change in the dielectric constant of films from 4.1 to 2.9, can be created in amorphous SiC:H (a-SiC:H) films. The resultant CuSiN/a-SiC:H bilayered structure, as a copper capping barrier, shows improved thermal stability properties, lower leakage current density, and a low effective dielectric constant (keff) for the integrated ultralow-k a-SiOC:H film. This integrated film structure has the potential to meet the need of the 45 nm and lower technology node. Detailed characterizations of the integrated films were conducted to illustrate the possible mechanisms in the improvement of the film properties.

Experiment on the plasma-loaded backward-wave oscillator using a gas-loaded foil-less diode

High-power microwave radiation of 9.5–13.4 GHz was generated in a plasma-loaded backward-wave oscillator employing a relativistic electron beam of 400–500 keV and 1–3 kA. This experiment was to re-examine and confirm the previous works that had been done in other various institutions. The relativistic electron beam, which was produced from a helium gas-loaded foil-less diode, was injected into the helium gas-loaded rippled-wall waveguide of the backward-wave oscillator, generating a plasma in the waveguide and then the high-power microwave radiation. A sharp increase in the output microwave power has been observed in a narrow range of the helium gas pressure, and two dips in the microwave emission have also been found in a certain range of the axial magnetic field. Additionally, at certain values of the helium gas pressure and guide magnetic field, the total microwave emission of the plasma-loaded backward-wave oscillator was found to be seven times as large as that of the vacuum case. The highest interac...

Two-dimensional analysis of the relativistic parapotential electron flow in a magnetically insulated transmission line oscillator (MILO)

This paper presents a two-dimensional model for studying the relativistic parapotential electron flow in a magnetically insulated transmission line oscillator (MILO). The distribution expressions of the velocity, energy, density, and self-electric and self-magnetic fields of electron flow are derived and then analyzed numerically. Results of the model show that the self-electric and self-magnetic fields and density of the electron flow are quite high near the surface of the slow-wave structure of a MILO where they may reach their peak values. In addition, the formation of the insulated electron flow requires a large current flowing through the inner conductor (cathode) of the MILO, which is identical with the previous works. It is also found that considerable increases in the absolute values of axial and radial velocities of the electron flow occur when electrons approach the surface of the slow-wave structure. The electron flow is mainly along the axial direction in between the surfaces of cathode and slow-wave structure except the regions near the two surfaces. More interestingly, the radial velocity of electron flow ran still be increased but the axial velocity decreased when the electrons go into the region in between the inner and outer radii of the slow-wave structure, where the electron flow is not always dominated by axial flow. The results of the present paper are more realistic than those of the one-dimensional model in describing the parapotential electron flow in a MILO.

Investigation of a compact coaxially fed switched oscillator.

To generate a relative high frequency mesoband microwave, a compact coaxially fed transmission line switched oscillator with high voltage capability is investigated. The characteristic impedance and voltage capability of the low impedance transmission line (LITL) have been analyzed. It is shown that the working voltage of the oscillator can reach up to 200 kV when it is filled by pressurized nitrogen and charged by a nanosecond driving source. By utilizing a commercial electromagnetic simulation code, the transient performance of the switched oscillator with a lumped resistance load is simulated. It is illustrated that the center frequency of the output signal reaches up to ~0.6 GHz when the spark gap practically closes with a single channel. Besides, the influence of the closing mode and rapidity of the spark gap, the permittivity of the insulator at the output end of the LITL, and the load impedance on the transient performance of the designed oscillator has been analyzed in quantification. Finally, the good transient performance of the switched oscillator has been preliminarily proved by the experiment.

Ultra compact high power primary energy source

Ultra compact high power primary energy sources especially for single use can be built in many ways, the high energy density capacitors and the FCGs (Flux compression generators) are the core components. The pulsed power capacitors have made great progress now, for example, the energy storage density of the self-healing type metal film capacitors has more than 2kJ/L [1]. We can use these capacitors to build primary energy sources, but the size and weight of these capacitors under rated conditions still can not meet the requirements in some application cases. An ultra compact primary source by excess using of the self-healing metallized film capacitor will be introduced, which can output more than 100kA current in 4μH inductive load, and the weight is no more than 60 kg. The FCGs are also frequently applied to build ultra compact primary sources. Two typical FCGs weighing about 10 kg will be introduced, one can output 100 kA current in 10μs while the load inductance is 4 μH; The other can output 1 MA current in 100 nH load. The FCGs need initial magnetic flux, In order to guarantee the system compactness, the self-healing type metallized film capacitors will be selected by excess using. In many compact primary energy sources, the discharge switches must be compact and reliable. Several practical switches will be discussed including the mechanical, the membrane, the detonator and the deflated switches.

A compact, high-voltage pulsed charging system based on an air-core pulse transformer

Charging systems of pulsed power generators on mobile platforms are expected to be compact and provide high pulsed power, high voltage output, and high repetition rate. In this paper, a high-voltage pulsed charging system with the aforementioned characteristics is introduced, which can be applied to charge a high-voltage load capacitor. The operating principle of the system and the technical details of the components in the system are described in this paper. The experimental results show that a 600 nF load capacitor can be charged to 60 kV at 10 Hz by the high-voltage pulsed charging system for a burst of 0.5 s. The weight and volume of the system are 60 kg and 600 × 500 × 380 mm(3), respectively.