High Voltage Pulse Transformer Research Articles

Pulse operation mode of inertial electrostatic plasma confinement devices

The paper discusses the operation features of the inertial electrostatic plasma confinement (IEC) devices in the pulsed high voltage mode. The pulse operation mode offers significant advantages in IEC devices, which are associated with high discharge currents that are inaccessible for continuous operating modes. However, the implementation of such operating modes is associated with a number of physical limitations and technical difficulties.A stand with an IEC chamber powered by a high-voltage pulse transformer and a unit for gas preliminary ionization in the IEC chamber has been developed. In the chamber, ions are accelerated from a background glow discharge. A study of the burning background discharge in the IEC chamber, background discharge current Ipre influence on the duration of current and voltage pulses of the main discharge and the delay between them was carried out. The results of the neutron yield measuring in an IEC chamber operating in pulsed mode are presented at a charging voltage up to 105 kV, a discharge current amplitude of several tens of amperes, a preionization current of 8 mA, and a pulse repetition rate from single to 300 Hz. A stable neutron flux with an energy of 2.5 MeV at a level of 106 neutrons/s was experimentally obtained.

Design of a Pulse Transformer for X-band Klystron

Future linear accelerators require klystrons with higher radio frequency (RF) to drive higher gradient accelerating structure. An x-band accelerator structure was used to accelerate electrons at the Shanghai Soft X-ray Free Electron Laser Facility (SXFEL) in Shanghai Advanced Research Institute, Chinese Academy of Sciences (SARI-CAS). A pulse transformer is a crucial device in an RF system. This study presents a high-voltage pulse transformer used for a 50 MW x-band pulsed klystron in SXFEL. Typical specifications of the pulse transformer are peak pulse voltage 420 kV, peak pulse current 300 A, 50 Hz repetition rate and 1.5 μs flat-top pulse width. Design and optimization of pulse transformer are achieved by using equivalent circuit analytic methods and computational aided simulation. The relevant experiments show that this pulse transformer can meet the requirements of 50MW x-band klystron.

Parasitic Parameters Design Consideration and Its Optimization Technique of High-Voltage Pulse Transformer for Ignition Module

Parasitic Parameters Design Consideration and Its Optimization Technique of High-Voltage Pulse Transformer for Ignition Module

Development of a Self-Coupling High-Voltage Square Waveform Pulse Transformer

Development of a Self-Coupling High-Voltage Square Waveform Pulse Transformer

High-voltage pulse bushing with induced voltage distribution between sections

The article presents test results of a sectioned vacuum bushing with induced voltage distribution. The bushing was tested with voltage pulses with amplitudes of 24 and 90 kV. The setting of the voltage along the gradient rings was carried out using a galvanic coupling with the turns of a high-voltage pulse transformer. The presented method has allowed distributing the applied voltage between the sections with a deviation of less than 3.5% from the uniform distribution throughout the entire pulse duration (0.25 μs FWHM). The tests with 90 kV pulses were carried out at a pressure of 10−4 Тоrr. The conical design of the bushing provided a decrease in the average electric field strength in vacuum insulating gaps and a higher rate of the residual atmosphere pumping out, as compared to the traditional cylindrical design of pulse vacuum bushings. The investigated bushing can be used in designs of vacuum electron diodes of pulsed accelerating systems.

Evaluation of Feasibility of High-Power Long-Pulse Transformers Using Single-Layer and Pancake Winding Techniques

Solid-state klystron modulators are typically based on oil-immersed high-voltage (HV) pulse transformers because of their high performance, robustness, simplicity, and straightforward design. However, pulse transformer size is fundamentally linked to application pulse length, pulse power, and pulse rise time. For high-power applications transformer size quickly becomes very problematic when approaching pulse lengths on the order of one millisecond. This article presents a systematic study of the applicability of HV pulse transformers for such long-pulse high-power applications. Both the single-layer and pancake winding techniques are evaluated, keeping reduction of transformer volume as the main design objective. First, design models and efficient optimization procedures are developed. The proposed models are validated through circuit simulation, 3-D finite element analysis, and comparison with a commercial HV long-pulse transformer. Then, the developed optimization procedure is used in studying the evolution of pulse transformer size when pulse length is varied from 500 μs to 5 ms assuming peak pulse power requirements corresponding to that of the European Spallation Source (ESS) klystron modulators (115 kV, 100 A, 14 Hz). Finally, the developed trends are used to derive general analytical equations expressing maximum attainable pulse length as a function of application parameters and system constraints.

EMC improvement for high voltage pulse transformers by pareto-optimal design of geometry structure based on parasitic analysis and EMI propagation

High voltage pulse transformers have an essential role in pulsed power systems and power conversion applications. Improving the electromagnetic behavior of such devices leads to better efficiency and low-level electromagnetic interference (EMI) noise propagation in systems. In this paper, a high voltage pulsed power system is considered and analyzed to improve the electromagnetic compatibility (EMC). The new generation of pulsed power systems that use SiC and GaN fast switches in capacitor charger power electronic circuit, face far more EMI challenges. Moreover, in this paper, the EMI propagation paths in the pulsed power system are realized and analyzed. The EMI noise level of the system is obtained and compared to the IEC61800-3 standard. To improve the EMC, the parasitic parameters of the transformer, as the main path of EMI circulation, are optimized to block the EMI propagation in the pulsed power system. For this aim, the parasitics are modeled and calculated with a novel and accurate energy distribution model. Then, by defining a cost function the geometry structure of the transformer is optimized to lower the parasitics in the system. Three pareto-optimal techniques are investigated for the cost function optimization. The models and results are verified by 3D-finite element method (FEM) and experimental results for several given scenarios. FEM and experimental verifications of this model, make the model suitable for any desirable design in any pulsed power systems. Finally, the EMI noise level of the system after optimization is shown and compared to the IEC61800-3 standard.

High‐voltage pulse transformer for IOT modulators

Neutron sources like European Spallation Source consist of linear proton accelerator and beam target. The linear accelerator is supplied by inductive output tubes (IOTs) or klystrons that require high-voltage DC supply (40 kV). This study describes the design and experimental evaluation of high-voltage dry-isolation pulse transformer design evaluation prototype for interleaved IOT supply modules. In order to withstand high-voltage stress, a modular secondary winding module with multistage voltage field equalisation are designed. Inter-winding connections are realised in the air as the separate winding outputs are routed together through common high-voltage isolators. The novelties of the current manuscript are new pulse transformer design and the experimental work. Experiments with full-scale prototype verified the advantages and revealed, also, some drawbacks of this construction. Proposed transformer design could be used not only in IOT or klystron power supplies but also in high-voltage DC/DC or AC/AC converters and power electronic transformers, used in the medium-voltage distribution grids.

Submicrosecond electron accelerator based on pulsed transformer

The article describes the test results of a submicrosecond electron accelerator based on a high-voltage pulse transformer. The transformer uses a self-supporting coil design with transformer oil insulation, which ensures high reliability of the device. A transformer-based high-voltage generator produces voltage pulses with an amplitude up to 475 kV, a pulse duration of 0.25 μs (FWHM) with a repetition rate up to 5 pps. A vacuum electron diode with a carbon fiber cathode is installed directly at the generator output and provides electron beam current amplitude up to 1.5 kA in the accelerating gap. An exit window with a titanium membrane 60μm thick is used to output the electron beam into the atmosphere. The exit window can be replaced by a converter to generate pulsed bremsstrahlung X-rays. The accelerator is designed to carry out research in the fields of studying the properties of materials in extreme conditions and the practical application of a pulsed electron beam.

Investigation on a fast rise time high voltage pulse transformer.

A pulse transformer has advantages of compactness and long lifetime achievability, and is considered an important candidate for the development of high voltage pulse generators. In this paper, a fast rise time high voltage pulse transformer with a compact structure is studied numerically and experimentally. Specifically, the structure of the pulse transformer was designed with paralleled winding groups. The response and insulation characteristics of the pulse transformer are investigated numerically. After that, a fast rise time high voltage pulse transformer was built, and scaling experiments were performed to analyze the influence of the feed structure of the pulse transformer. Importantly, the pulse transformer was successfully used in a low impedance generator, and high voltage pulses with a peak voltage of about 260 kV, a pulse duration of 170 ns, and a rise time of 65 ns were achieved on a resistive load of 32 Ω. The ratio of the transformer is approximately 1:3. Experiments show reasonable agreement with the numerical analysis.

Analysis and optimization of high-power pulse transformer for SXFEL

A C-band accelerator structure was used to accelerate electrons at the Shanghai soft X-ray free-electron laser test facility (SXFEL-TF) in Shanghai Institute of Applied Physics (SINAP). The microwave system of this accelerator structure used a 110 MW pulse modulator and a klystron (PV-5050) to provide the power supply. A pulse transformer is a crucial device in a modulator klystron system and plays significant roles in voltage level transformation, matching impedances, and polarity inversion. This study presents the optimization of a high-voltage pulse transformer. The design considerations of reducing flattop ringing and flattop droop, and shortening leading edge are provided. The model simulation, mechanical design, and the relevant experimental results are also presented.

HV Pulse Transformer Generalized Equivalent Circuit Identification Based on Detailed Mechanical Structure

A modeling methodology of high-voltage pulse transformers based on high-order generalized equivalent circuits (HOGECs) identified from 3-D finite-element analysis is applied to a prototype, and experimental validation tests are performed. The identified HOGEC of the prototype is used to investigate the influence of the detailed mechanical structure and the local winding configuration on the pulse transformer operation performance.

Design a high power pulse transformer for c-band klystron modulator

Shanghai soft X-ray Free Electron Lasers (SXFEL) used C-band accelerator structure to accelerate electrons at SINAP (Shanghai Institute of Applied Physics). 50MW C-band klystron and 110MW modulator are used to provide power supply for accelerator structure. In order to meet the modulator-klystron demands, a reliable and stable high power pulse transformer is indispensable. In this paper, the key design points for the high voltage pulse transformer are presented. The methods of shortening rise time and diminishing flattop droop are highlighted.

Design of a 6-MW Solid-State Pulse Modulator Using Marx Generator for the Medical Linac

The linear accelerators (linacs) producing high energy and high power of electron-beam or X-ray beam have been used in medicine, industry, national security, etc. In the linac, the electrons are generated by the electron gun and accelerated in the accelerating column with the high-power RF fields. The high-voltage pulses from the pulse modulator are supplied to the RF power source and the electron gun. The pulse modulator is one of the big and expensive components in the linac. The commercial medical linacs commonly use the pulse modulator based on the thyratron-switched pulse-forming network. In order to improve the power efficiency, achieve the system compactness, and optimize the cost and space, the solid-state pulse modulator based on the Marx generator was proposed. The low-power solid-state pulse modulator was developed for the electron gun operation. The conceptual design and functional results were confirmed. In order to apply it to the RF power source, such as a magnetron or a klystron, the 6-MW pulse modulator with the same Marx scheme is proposed. It consists of 40 storageswitch stages and one high-voltage pulse transformer, producing the pulse of 50 kV and 120 A required by the magnetron in the medical linac. A storage-switch stage was designed for insulated gate bipolar transistors to switch high current of 280 A and 720 V and to use the capacitor of 25 μF which was chosen for the voltage droop of 10% with the pulsewidth of 5 μs. The prototype system with eight storage-switch stages was fabricated and tested with a load system. The performance results show that it can be extended to be the 6-MW solid-state pulse modulator. In this paper, we describe the design features, and discuss the results and also the future plan to optimize the solid-state pulse modulator in the medical linac.

High-intensity pulsed beam source with tunable operation mode

The report presents the design of an electron and an ion pulsed accelerator. The powerful high-voltage pulse generator of the accelerator and the vacuum bushing insulator is able to change the polarity of the output voltage. The low-inductance matching transformer provides an increase in the DFL output impedance by 4 times. The generator based on a high voltage pulse transformer and a pseudo spark switch is applied for DFL charging. The high-impedance magnetically insulated focusing diode with Br magnetic field and the “passive” anode was used to realize the ion beam generation mode. The plasma is formed on the surface of the anode caused by an electrical breakdown at the voltage edge pulse; as a result, the carbon ion and proton beam is generated. This beam has the following parameters: the current density is about 400 A/cm2 (in focus): the applied voltage is up to 450 kV. The accelerator is designed for the research on the interaction of the charged particle pulsed beams with materials and for the development of technological processes of a material modification.

Minimized Field Enhancement Cylindrical Air-Core High-Voltage Pulse Transformer

An air-core strip-type high-voltage pulse transformer (HVPT) features a relatively simple structure in terms of design and fabrication. However, this HVPT requires considerable attention to prevent dielectric breakdown between the conductor windings. Because each spiral winding must be very thin, the field enhancement at the edges of the windings is very high. Therefore, it is important to develop proper methods to reduce the field enhancement factor and to prevent the dielectric breakdown at the winding edges. In this paper, in order to minimize the field enhancement, the proposed HVPT winding edges were folded, and each winding width was designed to decrease gradually to form a reverse trapezoid. These windings were insulated by multilayer insulators arranged in a specific manner. The requirement specifications are a maximum input voltage of 50 kV and an output voltage of 400 kV. This paper describes a design process and an electric field analysis to reduce the field enhancement. The simulation and experimental results confirmed the validity of the fabricated HVPT. The dielectric breakdown strength was tested up to 467 kV.

Hybrid design optimization of high voltage pulse transformers for Klystron modulators

This paper presents a generic hybrid optimization methodology based on space mapping techniques for the design of various high voltage pulse transformer structures used in klystron modulators. It is using two dimensioning models with different levels of complexity: a coarse model based on 2D FEA less accurate but cheaper to evaluate and a fine 3D FEA model more accurate but time consuming. A specific correction mechanism is applied to align the 2D FEA dimensioning model with the more accurate 3D FEA dimensioning model. With a suitable selection of the correction factors, the convergence of this hybrid optimal design methodology is obtained with a limited number of time consuming 3D FEA simulations. The method is applied to the optimal design of a monolithic high voltage pulse transformer for the CLIC klystron modulator. The influence of the klystron operating voltage on the size of the optimal pulse transformer is evaluated with the proposed design methodology.

Design and Optimization Procedure for High-Voltage Pulse Power Transformers

A design and optimization procedure for high-voltage pulse transformers is presented. The procedure is enhanced by the integration of core loss measurements under pulsed excitation, by electrical peak field calculations and by checking of the isolation distances, which are compared to scaled high-voltage breakdown data. The procedure is applied with specifications of the compact linear collider, and the sensitivity of system parameters such as the number of primary turns, core material, transformer oil, and high-voltage cable length is investigated by comparing their Pareto fronts. With amorphous core material, the highest efficiency is achieved. Replacing mineral oil by natural ester results in an efficiency reduction of 0.5%, and an increase in HV cable length from 1.5 to 5 m reduces the efficiency by 0.6%. Finally, the optimized transformer’s pulse shape is investigated over the entire load range.

Finite-Element-Based Optimal Design Approach for High-Voltage Pulse Transformers

This paper presents an optimal design methodology of monolithic high-voltage (HV) pulse transformers based on the direct 2-D finite-element analysis (FEA) identification of the electrical equivalent circuit parameters without any simplified analytical modeling. This method is applied to the preliminary optimal design of the monolithic HV pulse transformer for the future compact linear collider modulators under study at CERN. The feasibility of such a transformer with tight specifications is demonstrated. The predicted performance obtained with the direct 2-D FEA optimization process is validated by 3-D FEA simulation. The dimensioning model based on the direct 2-D FEA identification of the electrical equivalent circuit parameters is validated on a prototype.

Frequency-Domain Maximum-Likelihood Estimation of High-Voltage Pulse Transformer Model Parameters

This paper presents an offline frequency-domain nonlinear and stochastic identification method for equivalent model parameter estimation of high-voltage pulse transformers. Such kinds of transformers are widely used in the pulsed-power domain, and the difficulty in deriving pulsed-power converter optimal control strategies is directly linked to the accuracy of the equivalent circuit parameters. These components require models which take into account electric fields energies represented by stray capacitance in the equivalent circuit. These capacitive elements must be accurately identified, since they greatly influence the general converter performances. A nonlinear frequency-based identification method, based on maximum-likelihood estimation, is presented, and a sensitivity analysis of the best experimental test to be considered is carried out. The procedure takes into account magnetic saturation and skin effects occurring in the windings during the frequency tests. The presented method is validated by experimental identification of a 2-MW-100-kV pulse transformer.