Dongqun Chen

Comparison of three current sources for single-electrode capacitance measurement

The capacitance of a single electrode is usually measured by injecting a current to the electrode and measuring the resultant voltage on the electrode. In this case, a voltage-controlled current source with a high bandwidth is needed because the impedance is inversely proportional to the excitation frequency. In this design note, three different current sources are discussed: (1) the Howland current source, (2) a modified Howland current source, and (3) a dual op-amp current source. The principle and dynamic performances are presented and compared. Simulation and experimental results show that although the Howland current source has the lowest (i.e., worst) output impedance, its output is the most stable among the three current sources when the frequency changes. Therefore, it is suitable for single-electrode capacitance measurement. Initial tests have proven the feasibility of single-electrode capacitance sensor with the Howland current source.

Research of an electromagnetically actuated spark gap switch

As an important part of pulsed power systems, high-voltage and high-current triggered spark gap switch and its trigger system are expected to achieve a compact structure. In this paper, a high-voltage, high-current, and compact electromagnetically actuated spark gap switch is put forward, and it can be applied as a part of an intense electron-beam accelerator (IEBA). A 24 V DC power supply is used to trigger the switch. The characteristics of the switch were measured for N2 when the gas pressure is 0.10-0.30 MPa. The experimental results showed that the voltage/pressure (V/p) curve of the switch was linear relationship. The operating ranges of the switch were 21%-96%, 21%-95%, 21%-95%, 19%-95%, 17%-95%, and 16%-96% of the switchs self-breakdown voltage when the gas pressures were 0.10, 0.14, 0.18, 0.22, 0.26, and 0.30 MPa, respectively. The switch and its trigger system worked steadily and reliably with a peak voltage of 30 kV, a peak current of 60 kA in the IEBA when the pressure of N2 in the switch was 0.30 MPa.

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.

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...

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.

A vacuum-sealed, gigawatt-class, repetitively pulsed high-power microwave source

A compact L-band sealed-tube magnetically insulated transmission line oscillator (MILO) has been developed that does not require bulky external vacuum pump for repetitive operations. This device with a ceramic insulated vacuum interface, a carbon fiber array cathode, and non-evaporable getters has a base vacuum pressure in the low 10−6 Pa range. A dynamic 3-D Monte-Carlo model for the molecular flow movement and collision was setup for the MILO chamber. The pulse desorption, gas evolution, and pressure distribution were exactly simulated. In the 5 Hz repetition rate experiments, using a 600 kV diode voltage and 48 kA beam current, the average radiated microwave power for 25 shots is about 3.4 GW in 45 ns pulse duration. The maximum equilibrium pressure is below 4.0 × 10−2 Pa, and no pulse shortening limitations are observed during the repetitive test in the sealed-tube condition.

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.

The investigation of a compact auto-connected wire-wrapped pulsed transformer

For the power conditioning circuit used to deliver power efficiently from flux compression generator (FCG) to the load with high impedance, an air-cored and wire-wrapped transformer convenient in coaxial connection to the other parts is investigated. To reduce the size and enhance the performance, an auto-connection is adopted. A fast and simple model is used to calculate the electrical parameters of the transformer. To evaluate the high voltage capability, the voltages across turns and the electric field distribution in the transformer are investigated. The calculated and the measured electrical parameters of the transformer show good agreements. And the safe operating voltage is predicted to exceed 500 kV. In the preliminary experiments, the transformer is tested in a power conditioning circuit with a capacitive power supply. It is demonstrated that the output voltage of the transformer reaches -342 kV under the input voltage of -81 kV.