This paper presents the design and development of a repetitive Marx generator rated at 1 kJ, 300 kV, 12 kA, and 10 Hz and which is suitable to drive the load directly. Bipolar charging of a Marx generator scheme has been adopted to get the following: 1) faster rise time and 2) relatively low charging voltage. The faster rise time is due to the reduced number of spark gaps down to six for 12 in-series capacitors (0.15 μF and 50 kV) of a six-stage bipolar-charging Marx generator. Interstage inductive charging further enhances the efficiency of the overall system as compared to resistive charging. The generator is characterized by an aqueous resistive load for both polarities at the output voltage. Output voltages of the same magnitude have been achieved for both polarities. The matched impedance is found to be 25 Ω for which a suitable reflex triode is designed. Intense electron beams and high-power microwaves have been generated using this Marx generator and reflex triode system. Experimental results demonstrating the Marx generator and the reflex triode operation are presented and discussed.

Development and Characterization of Repetitive 1-kJ Marx-Generator-Driven Reflex Triode System for High-Power Microwave Generation

A high voltage quasi-square wave pulse with an amplitude of above 500 kV is successfully transmitted using a coaxial-type matched transmission line in vacuum. To enhance the surface flashover voltage and reduce the distortion of pulse shape, the matched symmetric coaxial solid dielectric configuration with the positive angle of 45° and the socket-type field shaper are proposed and applied to the coaxial transmission line. This type of transmission line provides not only the high capability of hold off voltage but also good pulse shape corresponding to the input pulse. The transmission of quasi-square wave short pulse with an amplitude of above 500 kV, a pulse duration of above 20 ns, and a rise time of 20-30 ns without the surface flashover and the pulse distortion phenomena is experimentally and numerically presented.

Design of low distortion high voltage coaxial-type transmission line for quasi-square wave nano-pulse with several hundred kilovolts in vacuum

Many approaches exist for energy storage and delivery to the load, including high-power relativistic applications. One of the best solutions for the driver of high-power relativistic applications is the Marx generator. This paper describes the design, fabrication, and experimental validation of a Marx generator consisting of capacitors, spark-gap switches, and resistors. It is designed as an eight-stage Marx circuit to reach an output voltage level as low as −500 kV, and it is directly connected to the Blumlein pulse-forming line (PFL) to achieve more than 100 ns of the full-width at half-maximum. Experiments are performed with a solution load in a manner similar to having a coaxial structure in a high vacuum with a pressure of below $0.5\, \times \, 10^{-5}$ torr, to prevent breakdown and measure the amplitude of the negative high-voltage pulse waveform. The solution load is designed to capture the short-pulse output of the PFL with a rise time of less than 25 ns and a voltage level of approximately −500 kV. The experimental results show that the output pulse can be used as a source to generate an intense relativistic electron beam at the gun for high-power relativistic applications.

Performance Analysis of a Short-Pulse Marx Generator for High-Power Relativistic Applications With a Solution Load

Complete Measurement System for Measuring High Voltage and Electrical Field Using Slab-Coupled Optical Fiber Sensors Nikola Stan Department of Electrical and Computer Engineering, BYU Doctor of Philosophy A slab-coupled optical fiber sensor (SCOS) falls into a narrow class of all-dielectric optical fiber electric field sensors, which makes it a perfect candidate for measurements of high electric fields in environments where presence of conductors is highly perturbing to the system under test. Its nonlinear response to high fields requires a new nonlinear calibration technique. A nonlinear calibration method is explained and demonstrated to successfully measure high electric fields, as well as high voltages with dynamic range up to 50 dB. Furthermore, a SCOS can be fitted into narrow spaces and make highly localized measurements due to its small size. This allows a SCOS to be integrated inside a standard high voltage coaxial cable, such as RG-218. Effects of partial discharge and arcing is minimized by development of a fabrication method to avoid introduction of impurities, especially air-bubbles, into the cable during SCOS insertion. Low perturbation of the measured voltage is shown by simulating the introduced voltage reflections to be on the order of −50 dB. It is also shown that a SCOS can be inserted into other cables without significant perturbation to the voltage. A complete high voltage and high electric field measurement system is built based on the high-voltage modifications of the SCOS technology. The coaxial SCOS is enhanced for robustness. Enhancements include packaging a SCOS into stronger ceramic trough, strengthening the fiber with kevlar reinforced furcation tubing and protecting the sensor with metal braces and protective shells. The interrogator is protected from electromagnetic interference with an RF-shielded box. Reduction in power losses introduced by the new PANDA-SCOS technology allows interrogator bandwidths to be increased up to 1.2 GHz. The whole measurement process is streamlined with dedicated software, developed specifically for high voltage and electric field measurements with support for the nonlinear calibration.

Complete Measurement System for Measuring High Voltage and Electrical Field Using Slab-Coupled Optical Fiber Sensors

An efficient radio frequency dummy-load structure is designed with ${\rm Al}_{2}{\rm O}_{3}$ ceramic as quarter-wave separation window. The coolant fluid is tap water that rotates in a well designed path between input and output cooling system channels. This dummy load is designed and tested for five kilo watt average input RF power with very low input reflection coefficient $(S_{11}\leqslant-32.1\ {\rm dB})$ and 8% bandwidth at center frequency of 500 MHz. With a higher rate of water flow $(Q)$ this dummy-load with total length of 1115 mm will be able to dissipate higher input RF power.

An Efficient High Power RF Dummy-Load

A coaxial-type water load was used to measure the voltage output from a Marx generator for a high power microwave source. This output had a rise time of 20 ns, a pulse duration of a few hundred ns, and an amplitude up to 500 kV. The design of the coaxial water load showed that it is an ideal resistive divider and can also accurately measure a short pulse. Experiments were performed to test the performance of the Marx generator with the calibrated coaxial water load.

Soo Yong Park

Papers

Coaxial-type water load for measuring high voltage, high current and short pulse of a compact Marx system for a high power microwave source