Repetitive pulsed-power generator "ETIGO-IV"

Power semiconductor devices (MOSFET, IGBT, SIThy, and SOS) have been studied for applications in repetitive pulsed power generation. These switching devices are expected to be used in pulsed high-voltage modulators for accelerators and power supplies for pulsed atmospheric discharges. MOSFET and static-induction thyristor (SIThy) are investigated for their performance in high-voltage modulation at repetition rate on the order of MHz, which is demanded by applications in high-energy particle accelerators. Although the peak voltage and current are not very high (usually a few kV and a few 10s of A respectively), the repetition rate poses fatal problems to the devices due to the thermal effect. The system cooling and waveform control had been the main efforts in this study. IGBT and semiconductor opening switch (SOS) are studied for applications to atmospheric gas discharge, which has become very attractive recently due to its applications in gas-treatment, laser pumping, and sterilization. The electrical circuit scheme is based on inductive energy storage with opening switch, which gives pulsed output high-voltage up to 100 kV for high-impedance load. The study has concentrated on repetition rate and energy efficiency. These developments are joint studies between universities, national laboratories, and industrial companies.

A new configuration of virtual cathode oscillator is proposed and tested experimentally. A resonant cavity is used to enhance the field feedback to the virtual cathode oscillation. The experiments were carried out on repetitive pulsed power generator “ETIGO-IV” (400 kV, 13 kA, 120 ns, 1 Hz). The diagnostic results have shown the peak microwave output power of ∼ 450 MW, giving peak-to-peak microwave power efficiency of ∼ 9 %.

This paper introduces recent activities on Marx-based compact repetitive pulsed power generators at the Institute of Applied Electronics (IAE), China Academy of Engineering Physics (CAEP), over the period 2010–2018. A characteristic feature of the generators described is the use of a simplified bipolar charged Marx circuit, in which the normal isolation resistors or inductors to ground are removed to make the circuit simpler. Several pulse-forming modules developed to generate a 100 ns square wave output are introduced, including thin-film dielectric lines of different structures, a pulse-forming line based on a Printed Circuit Board, and non-uniform pulse-forming networks. A compact repetitive three-electrode spark gap switch with low-jitter, high-voltage, and high-current was developed and is used in the generators. A positive and negative series resonant constant current power supply with high precision and high power is introduced. As an important part of the repetitive pulse power generator, a lower jitter pulse trigger source is introduced. Several typical high-power repetitive pulsed power generators developed at IAE are introduced including a 30 GW low-impedance Marx generator, a compact square-wave pulse generator based on Kapton-film dielectric Blumlein line, a 20 GW high pulse-energy repetitive PFN-Marx generator, and a coaxial Marx generator based on ceramic capacitors. The research of key technologies and their development status are discussed, which can provide a reference for the future development and application of miniaturization of compact and repetitive Marx generators.

Summary form only given. Recent experiments reported an improved efficiency in high power microwave generation by applying a non-uniform slow wave structure (SWS) or using a plasma filling in a backward wave oscillator (BWO). A combined scheme of plasma filling in a non-uniform SWS is investigated to further increase microwave output power. An annular cathode of radius 1 cm produces a 500 keV electron beam of density 10/sup 12/ cm/sup -3/. A plasma of density 10/sub 12/ cm/sup -3/ with temperatures T/sub c//spl ap/T/sub i//spl ap/10 eV is launched into the SWS from a cylindrical plasma gun placed inside the annular cathode. In a 2 1/2 D simulation, the annular electron beam is injected, with the use of a guiding magnetic field, into a cutoff neck with a radius of 11 mm. This electron beam moves into an 18 cm long non-uniform SWS section with an average radius of 1.5 cm, and then is guided into the waveguide wall. The voltage pulse in the simulation rises to 500 kV in 1 ns and remains flat for the remainder of the 20 ns. These simulations have shown that the microwave output power of a few hundred megawatts is nearly doubled when compared with the case without plasma, while the microwave frequency is upshifted on the order of 100 MHz. Most of the plasma electrons are quickly (<13 ns) driven out of the core plasma, leaving only the beam electrons flowing in an ionic background. Such a now might lead to an instability that could help to further bunch the electron beam and increase microwave power production.

Investigation of material migration and characterization of the film layer on the surfaces of HPM generator structures

An autonomous, compact and repetitive pulsed power generator has recently been developed at Loughborough University for use in low-energy, general-purpose experimentation, in either indoor or inclement outdoor environments. Flexibility, reliability and safety were the most important design requirements, which were achieved through the use of interchangeable components, off the shelf units and the development of a fibre-optic controlled charging and triggering system that allows the complete system to run from a single battery source. The present arrangement is based on a General Atomics 1 µF capacitor although many GAEP S/SS and SE/SSE series capacitors are compatible. A Trigatron discharges the capacitor into a transmission line with series connected mounting bays designed to accommodate a range of resistors or inductors if required. A high-voltage coaxial cable connects the generator to an external load or a further pulsed power system. Current and voltage are internally monitored using a Pearson current transformer and a Tektronix high-voltage probe. The completed system is housed in a weatherproof metallic container and mounted on rubber wheels. To date it has been operated successfully on more than 100 occasions, both in the laboratory and in various outdoor conditions.

The need for repetitive high-power microwave systems, for instance within the scope of convoy protection, requires the availability of compact, repetitive pulsed-power generators. The development and the first experimental results of an upgraded balanced ISL Marx generator for future repetitive operations at pulse repetition frequencies in the order of 100 Hz are introduced. A key objective is to keep the fundamental modular coaxial concept by reason of its scalability and compactness. Simulation models were developed under the PSpice software package in order to investigate the charging and discharging phases of the Marx generator and also to determine the design criteria for repetitive operations. The charging resistors were replaced by ultracompact inductors for rapid charging, being able to withstand pulsed voltages up to 60 kV and pulsed currents up to 1.4 kA during the discharge phase. An improved type of strontium–titanate high-voltage ceramic capacitor was successfully tested experimentally up to 70 kV. Each new elementary stage of the Marx generator consists of eight 1.1 nF sectors of a cylinder capacitors mounted in parallel, two charging inductors of about 17.8 μH and two halves of spherical spark gaps. The pressurized self-triggered gas switches are arranged along the axis for fast consecutive breakdown thanks to the UV radiation emitted during the breakdown in each gap. The stages are installed in individual fibreglass housings. First experimental results of a 4-stage Marx generator in repetitive operation, driven by a 4 kW capacitor charging power supply up to a maximum voltage of 40 kV, are presented.

A new scheme of pulsed voltage adding using inductively charged Blumlein lines has been proposed and experimentally demonstrated. The circuit principle is explained based on the analogy with capacitively charged Blumlein lines. In the experiments, striplines have been used for inductive energy storage, and SiC power devices have been used as the opening switches. The experimental results have proved both the circuit behavior and the voltage adding by using multimodule stack. This circuit method is expected to become a new approach to compact and repetitive pulsed-power generation.

This paper briefly reviews the applications of materials science and engineering in the pharmaceutical industry. The materials characterization techniques highlighted in the paper as being utilized in the pharmaceutical industry are dynamic light scattering and photon correlation spectroscopy, mercury intrusion, gas density pycnometry and energy density analysis, thermogravimetric analysis and differential scanning calorimetry, x-ray diffraction, nuclear magnetic resonance and Raman microscopy. The other areas of applications of materials science and engineering in the pharmaceutical industry briefly discussed are materials processing, materials research and development, and materials selection. This paper further highlighted that the program as it is currently offered by various institutions in Nigeria is yet to incorporate the courses in pharmaceutical materials. It concluded by pointing out that some institutions outside Nigeria have incorporated pharmaceutical materials in the programs of materials science and engineering. Suggestions were made for the materials science and engineering programs in Nigeria to build further capacity for effective applications in the pharmaceutical industry. Keywords— Applications, materials engineering, pharmaceutical industry

The RF photoinjector, when coupled with a magnetic pulse compression system, is now a ubiquitous tool for production of sub-picosecond electron beam pulses which are to be used in advanced accelerator and light source experiments. As the time-scale for both pulse lengths and synchronization to external systems approaches the femtosecond level, a clear understanding of the longitudinal dynamics of the electron injector is required. This paper presents an analysis of the longitudinal beam dynamics of electron bunches in the photoinjector/compressor system from birth at the photocathode, through their initial violent acceleration in the RF gun, and subsequent phase space manipulation in the post-acceleration linac and magnetic chicane. The phenomena of phase focusing due to RF forces, and defocusing due to longitudinal space-charge, are discussed, as is the process of magnetic pulse compression. The issues relevant to synchronization of electron pulses with external lasers are examined, using the examples of beat-wave acceleration and Compton light sources, and solutions involving appropriate compressor configurations are proposed. Diagnosis of the relevant physical effects in such schemes is discussed.

We propose a novel scheme for efficient generation of high power microwaves exploiting a four-mode interaction principle 1, 2 occurring in slow-wave-structures (SWSs) with degenerate band edge (DBE). The DBE condition entails the coalescence of four slow-wave eigenmodes (both wavenumbers and eigenvectors) at the band edge in special types of periodic SWSs. Such principle of interaction offers a significantly lower starting oscillation electron beam current 1, compared to conventional backward wave oscillators (BWOs), and also high power efficiency. We demonstrate the existence of the DBE in metallic SWS through cold structure measurements. The DBE enables unique dispersion characteristics as well as giant scaling of the quality factor that are fundamental for enhancing the performance of microwave sources. We demonstrate here for the first time high efficiency and high power generation using electron beam driven degenerate band edge oscillators (DBEO) in Sband.

Experimental operation of a high power microwave source with a metamaterial (MTM) structure is reported at power levels to 2.9 MW at 2.4 GHz in full 1 μs pulses. The MTM structure is formed by a waveguide that is below cutoff for TM modes. The waveguide is loaded by two axial copper plates machined with complementary split ring resonators, allowing two backward wave modes to propagate in the S-Band. A pulsed electron beam of up to 490 kV, 84 A travels down the center of the waveguide, midway between the plates. The electron beam is generated by a Pierce gun and is focused by a lens into a solenoidal magnetic field. The MTM plates are mechanically identical but are placed in the waveguide with reverse symmetry. Theory indicates that both Cherenkov and Cherenkov-cyclotron beam-wave interactions can occur. High power microwave generation was studied by varying the operating parameters over a wide range, including the electron beam voltage, the lens magnetic field, and the solenoidal field. Frequency tuning with a magnetic field and beam voltage was studied to discriminate between operation in the Cherenkov mode and the Cherenkov-cyclotron mode. Both modes were observed, but pulses above 1 MW of output power were only seen in the Cherenkov-cyclotron mode. A pair of steering coils was installed prior to the interaction space to initiate the cyclotron motion of the electron beam and thus encourage the Cherenkov-cyclotron high power mode. This successfully increased the output power from 2.5 MW to 2.9 MW (450 kV, 74 A, 9% efficiency).

A compact high power microwave (HPM) generation system is described in this paper. The main parts of the HPM system are a Marx generator with a pulse forming line and a magnetron with diffraction output. The total weight and length of the system are 250 kg and 120 cm, respectively. The output microwave power of the HPM system at 550 kV of applied voltage and 0.33 T of magnetic field reaches 1 GW at 2.32 GHz of central frequency with 38 ns of pulse duration, 23% of power conversion efficiency, and Gaussian radiation pattern. In the bursts operation, both time and amplitude jitters are less than 4 ns and lower than 1.5 dB, respectively.

Excimer laser systems are often combined with pulse stretchers, e.g., in lithography and Raman spectroscopy to reduce pulse peak intensities. We developed a pulse stretcher which is suited especially for pulse length dependent applications, e.g., in material research. This pulse stretcher is based on imaging and provides identical beam profiles and divergences at different pulse lengths in combination with the possibility of switching between four pulse lengths. Therefore, beam splitters are mounted onto motorized translation stages. These features are important for the characterization and development of improved optical materials for deep-ultraviolet applications. Here, two 193 nm single tube excimer lasers (Lambda Physik: LPX 240i, Cymer: ELS 5600) were evaluated concerning their combinability with an attached pulse stretcher. The wave-front radii of the ELS 5600 are dependent on repetition rate or pulse energy and are changing during warming-up. Without adapted pulse shaping, this can cause destruction of stretcher optics due to moving foci. We found that the LPX 240i could be combined easily with a pulse stretcher using beam shaping with only one cylindrical lens. We could demonstrate that stretched 193 nm laser pulses retard aging of CaF(2) crystals.

The effects of the imposed uniform magnetic field, ranging from 1 MG up to 50 MG, on the production and transport of relativistic electron beams (REBs) in overdense plasmas irradiated by ultraintense laser pulse are investigated with two-dimensional particle-in-cell numerical simulations. This study gives clear evidence that the imposed magnetic field is capable of effectively confining the relativistic electrons in space even when the source is highly divergent since it forces the electrons moving helically. In comparison, the spontaneous magnetic fields, generated by the helically moving electrons interplaying with the current filamentation instability, are dominant in scattering the relativistic electrons. As the imposed magnetic field was increased from 1 MG to 50 MG, overall coupling from laser to the relativistic electrons which have the potential to heat the compressed core in fast ignition was found to increase from 6.9% to 21.3% while the divergence of the REB increases significantly from 64° to 90°. The simulations show that imposed magnetic field of the value of 3–30 MG could be more suitable to fast-ignition inertial fusion.