Linear Transformer Driver Module Research Articles

Modeling and tests of nested transmission lines for current adding on a four-stage linear transformer driver.

Linear transformer driver (LTD) technology allows a pulsed-power generator to be transportable due to its salient features in compactness and modular design. To further reduce the footprint of an MA-class pulsed-power generator, nested transmission lines were designed and tested for current adding in a four-stage gas-insulated LTD module. The current adder assembly contained two modules that were charged in opposite polarities. Each module held two LTD cavities that shared a common electrode of the nested transmission line with deionized water insulation. Post-hole convolutes were installed for the aggregation of the output current of different modules. More specifically, numerical simulations were conducted to calculate the nested line inductance, which revealed that the total system inductance was ∼10 nH in the nested geometry. Experimentally, testing on the four-stage LTD prototype showed that the LTD module can deliver a 1.2 MA current peak with a rise time of 140ns to a short circuit load under the charging voltage of ±50kV, which validated the applicability of using nested lines for current adding in an MA-class LTD module.

Characteristics of Switch Prefire Generated Fault Voltages Transmitted in a Four-Stage LTD Module

Future large-scale pulsed-power accelerators are commonly designed based on linear transformer driver (LTD) topology. With the number of gas switches being significant (~ 100000), gas switch prefire might be an inevitable malfunction in an LTD accelerator. The transmission characteristics of switch prefire and its influences on major components in a multicavity LTD module remain to be investigated. In this article, the mechanism of fault voltage generation by switch prefire and inductive coupling effect of the magnetic core were thoroughly understood. It was found that switch prefire drove the cores to magnetize reversely toward negative saturation state ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- B_{s}$ </tex-math></inline-formula> ), raising the voltage on switches in adjacent stages. A circuit model reflecting both initial states and magnetization dynamics of cores was developed for numerical analysis of switch prefire. From previous tests of a four-stage LTD module with deionized water insulated transmission line, unexpected discharges were captured and recognized by D-dots installed in the internal electrode of the transmission line. Test results indicated that an evident manifestation of switch prefire was the polarity reversion of D-dot voltage pulses. Both theoretical and experimental analyses revealed that single brick prefire generated a peak voltage of 70 kV across the transmission line under the charge voltage of ±70 kV. Circuit simulations were in good accordance with experimental data of D-dot signals in the main pulse. However, discrepancies between simulations and experimental results implied that the model was not precise enough in the magnetization dynamics under saturated state.

Self-triggering topology for high-power nanosecond pulse generators based on avalanche transistors Marx bank circuits and linear transformer driver.

In recent years, several novel avalanche transistor-based power synthesis topologies have been proposed to improve the output performance of pulse generators based on avalanche transistors. The most promising is the topology based on avalanche transistors Marx Bank Circuits (MBCs) and linear transformer driver (LTD). However, it suffers from the same problems as other semiconductor switch-based LTD generators. The greater the number of LTD modules, the higher the requirements for synchronization and drive capability of the trigger system. This paper proposes a new self-triggering topology for pulse generators based on avalanche transistors MBCs and LTD, which significantly simplifies the entire generator's requirement for trigger system synchronization and driving capability. First, the circuit topology and its operation principle are introduced. Then, three prototypes with one trigger LTD module and three self-triggering LTD modules are developed. The output characteristics are experimentally investigated. The results verify the feasibility of the proposed topology. Finally, the output amplitude and the rise time are 3.35 kV/3.7ns, 4.12 kV/3.7ns, and 4.88 kV/4.0ns on a 25 Ω resistive load, respectively. All generators can operate at 1kHz. The topology proposed in the article maximally simplifies the requirements for synchronization and drive capability of the trigger system for generators based on avalanche transistor MBCs and LTD.

Solid-State Bipolar Linear Transformer Driver Using Inductive Energy Storage

There have already a lot of circuit topologies for pulsed power generators using semiconductor switches. In this article, a novel circuit topology concept that can generate bipolar pulses based on linear transformer driver (LTD) topology is presented. Different from traditionally capacitive energy storage (CES) method, we utilize magnetic core as inductive energy storage (IES) medium to accumulate inductive energy before releasing pulses. The repetitive bipolar pulsed power generator is capable of operating in high repetition without reset circuit, because positive magnetization and negative magnetization can lead the magnetic core always back to initial state after every period. In this article, a three-stage laboratory prototype of bipolar IES-based LTD is designed and assembled using six existed CES-based LTD modules, which can generate ~2.4 kV bipolar peak pulses, 55 ns pulsewidth on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150~\Omega $ </tex-math></inline-formula> resistive load with charging voltage of 80 V. Finally, this proposed three-stage LTD is evaluated under burst mode to verified the high repetition capability of this bipolar IES-based LTD. As a result, this generator can operate at repetitive frequency of 400 kHz without reset.

Four-Stage Linear Transformer Driver With Sharing Shell: EM Model, Simulation, and Performance

A four-stage fast linear transformer driver (LTD) with sharing shell was constructed as a fundamental component of China’s next-generation Z-pinch driver CZ34. Separate metal rods replaced conventional independent cavity shells for the ease of installation and maintenance. SF6 was utilized for the first time as insulating medium instead of transformer oil. To investigate the electrical performance of the LTD module, a 3-D full-scale electromagnetic model was developed by field-circuit co-simulation method in Computer Simulation Technology Studio Suite. Fundamental discharging brick was modeled as a conductive current path in 3-D model, excitation was employed through exterior circuits coupled to the field model. The applicability of the simulation model was validated by primary experiments. Compared to circuit simulation, the field-circuit co-simulation modeled the impedances of transmission lines and load impedance accurately since specific structures were included. Annular liquid resistor in experiment configurations brought in extra load inductance, which influenced greatly on output voltage fluctuations in each stage due to the mismatch of load impedance. Simulation results were in good agreement with experiments, except that the switch performances were not entirely up to expectations. It was indicated that several switches showed notable delays according to calculations, leading to voltage and current loss in measurements.

Solid-State Linear Transformer Driver Using Inductive Energy Storage

Pulsed power generation using solid-state linear transformer driver (LTD) with inductive energy storage has been experimentally studied. This is a feasibility study in order to explore this new approach by proving its operation principle and demonstrating its typical performance. Magnetic cores in LTD modules are used as intermediate energy storage from which the electrical energy is extracted when the switches are turned off. Voltage adding has been confirmed by using a three-module stack and, with an input charging voltage 41.5 V, a peak output voltage of ~2.6 kV was obtained on a 120- $\Omega $ resistive load, with pulsed length of ~51 ns and rise time of ~24 ns.

Modular solid‐state pulse generator based on multi‐turn LTD

A modular solid-state pulse generator based on a multi-turn linear transformer driver (LTD) is designed for the application of pulse power techniques with a high voltage, large current and wide pulse width. The LTD adopts the method of multi-turn winding on the magnetic core, which can help to output pulses of wide width. The isolation of the power supply with windings in the same direction of the LTD modules is designed, and the isolation voltage of the magnetic cores is the working voltage of the LTD modules. A modular solid-state pulse generator based on the multi-turn LTD is developed, which is composed of 10 LTD modules. Each module consists of 18 energy storage capacitors, metal-oxide-semiconductor field-effect transistors and their driving circuits connected in parallel. The pulse generator can output pulses with parameters including a voltage ranging from 0 to 5000 V, a pulse current up to −500 A, and a pulse width ranging from 200 ns to 5 μs. When all modules work in synchronisation, rectangular pulses can be produced with a rise time of 30 ns and a fall time of 16 ns. If all modules are asynchronised, trapezoidal pulses are produced with adjustable step-like rising and falling edges. Moreover, a higher-voltage pulse can be achieved by increasing the number of LTD modules.

Development of Solid-State LTD Module Using Silicon Carbide MOSFETs

Linear transformer driver (LTD) is a relatively new circuit method for pulsed power generation. Solid-state LTD-based generators are being developed for industrial applications. A key issue on LTD performance is its efficiency. An LTD module using silicon carbide (SiC) MOSFETs has been developed, aiming at reducing the circuit loss and improving the overall efficiency. This article reports the experimental results on comparison between the LTD modules using silicon MOSFETs and SiC MOSFETs. The intent is to quantitatively confirm the advantage of using SiC power devices on LTD, before we decide to build a multimodule LTD system.

Conceptual design of a 15-TW pulsed-power accelerator for high-energy-density–physics experiments

We have developed a conceptual design of a 15-TW pulsed-power accelerator based on the linear-transformer-driver (LTD) architecture described by Stygar [W. A. Stygar et al., Phys. Rev. ST Accel. Beams 18, 110401 (2015)]. The driver will allow multiple, high-energy-density experiments per day in a university environment and, at the same time, will enable both fundamental and integrated experiments that are scalable to larger facilities. In this design, many individual energy storage units (bricks), each composed of two capacitors and one switch, directly drive the target load without additional pulse compression. Ten LTD modules in parallel drive the load. Each module consists of 16 LTD cavities connected in series, where each cavity is powered by 22 bricks connected in parallel. This design stores up to 2.75 MJ and delivers up to 15 TW in 100 ns to the constant-impedance, water-insulated radial transmission lines. The transmission lines in turn deliver a peak current as high as 12.5 MA to the physics load. To maximize its experimental value and flexibility, the accelerator is coupled to a modern, multibeam laser facility (four beams with up to 5 kJ in 10 ns and one beam with up to 2.6 kJ in 100 ps or less) that can provide auxiliary heating of the physics load. The lasers also enable advanced diagnostic techniques such as X-ray Thomson scattering and multiframe and three-dimensional radiography. The coupled accelerator-laser facility will be the first of its kind and be capable of conducting unprecedented high-energy-density–physics experiments.

Model analysis and simulation of a novel self-triggering linear transformer driver

In this paper, a self-triggering linear transformer driver (LTD) technology based on the principle of electromagnetic induction is presented. A detailed circuit model of the self-triggering LTD module is established in PSPICE to explore the feasibility of the self-triggering method. Through simulation and analysis, an original design of a prototype self-triggering LTD is established. Some factors, which influence the performance of the self-triggering LTD are demonstrated and analyzed thoroughly in this paper, such as peaks of induced trigger voltages and pre-magnetizing. Simulation results indicate that all induction cavities in the self-triggering LTD module can be triggered with an easier external trigger method and the cavity triggering sequence is acceptable. The peak current at the output of self-trigger LTD module is in the range of 0.96 MA to 1.01 MA and the 10-90% rise time is about 31ns in the simulation.

Effect of Cavity-Triggering Sequences on Output Parameters of LTD-Based Drivers

This paper explores the feasibility of improving the load current parameters by optimizing the cavity-triggering sequences for a linear transformer driver (LTD) module with 60 cavities connected in series. The mechanism behind this was analyzed. The results demonstrate that it is necessary for the improvement in the output parameters of the LTD to postpone the closure of the switches in the cavities later than the arrival of the electromagnetic pulse propagating downstream. However, this requires the switches to withstand pulsed voltages higher than their charge voltage before closing. When the LTD switches withstood a pulsed voltage peak of about 400 kV for several tens of nanoseconds before closing, the LTD module could generate a current pulse with a rise time of 12.5 ns and a peak of 1340 kA on the matched load.

Numerical Analysis of the Output-Pulse Shaping Capability of Linear Transformer Drivers

Output-pulse shaping capability of a linear transformer driver (LTD) module under different conditions is studied, by conducting the whole circuit model simulation by using the PSPICE code. Results indicate that a higher impedance profile of the internal transmission line would lead to a wider adjustment range for the output current rise time and a narrower adjustment range for the current peak. The number of cavities in series has a positive effect on the output-pulse shaping capability of LTD. Such an improvement in the output-pulse shaping capability can primarily be ascribed to the increment in the axial electric length of LTD. For a triggering time interval longer than the time taken by a pulse to propagate through the length of one cavity, the output parameters of LTD could be improved significantly. The present insulating capability of gas switches and other elements in the LTD cavities may only tolerate a slightly longer deviation in the triggering time interval. It is feasible for the LTD module to reduce the output current rise time, though it is not useful to improve the peak power effectively.

Solid-State LTD Module Using Power MOSFETs

It is proposed that linear transformer driver (LTD) concept can be applied to compact repetitive pulsed-power generation. For experimental demonstration, a table-top LTD module has been constructed by using power metal-oxide-semiconductor field-effect transistors (MOSFETs) and film capacitors. It consists of 24 basic circuits and a magnetic core, contained in a cavity case having a diameter of 32 cm and a height of 1.1 cm. All MOSFETs can be turned on and off synchronously, controlled by a single optic fiber. This LTD module has been tested with operation voltage of 900 V for single shot and 700 V for repetitive operation at 500 Hz. Near-rectangle waveforms were obtained on a resistive load of 3.2 , with pulsewidth of 200 ns, rise time of 20 ns, and fall time of 40 ns. The overall system efficiency was obtained to be 76%.

“强光一号”加速器电路模拟与分析

The Qiangguang-Ⅰ accelerator is made up of linear transformer driver(LTD), water transmission line, water switch and diode. In this paper, parameters of the LTD, transmission line and water switch were estimated, and circuit models of nonlinear magnetic cores and pulse power drivers were established. In addition, properties of silicon steel magnetic cores were investigated by experiments, the results of which are perfectly in accord with the simulation ones of the LTD module and accelerator. The simulation shows that the magnetic cores was not saturated under current running status. And the output parameters would not alter for the LTD store capacitance changing from 2.8 μF to 4.0 μF with 35 kV charge voltage. These all would establish the basis for the enhancement of energy store and