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- A DC Voltage-Multiplier Circuit Working as a High-Voltage Pulse GeneratorPublication . Luis RedondoThe intensive use of semiconductor devices enabled the development of a repetitive high-voltage pulse-generator topology from the dc voltage-multiplier (VM) concept. The proposed circuit is based on an odd VM-type circuit, where a number of dc capacitors share a common connection with different voltage ratings in each one, and the output voltage comes from a single capacitor. Standard VM rectifier and coupling diodes are used for charging the energy-storing capacitors, from an ac power supply, and two additional on/off semiconductors in each stage, to switch from the typical charging VM mode to a pulse mode with the dc energy-storing capacitors connected in series with the load. Results from a 2-kV experimental prototype with three stages, delivering a 10-mu s pulse with a 5-kHz repetition rate into a resistive load, are discussed. Additionally, the proposed circuit is compared against the solid-state Marx generator topology for the same peak input and output voltages.
- Characterization of a single electrode focusing lens for ion beam decelerationPublication . Lopes, Jose; Rocha, J.; Catarino, Norberto; Redondo, LuisAn ion beam deceleration system was studied for the highcurrent ion implanter at the Laboratório de Aceleradores e Tecnologias de Radiação at the Campus Tecnológico e Nuclear, of Instituto Superior Técnico. The installed system consists of a target plate and one electrostatic focusing lens with one electrode. This article describes the results of the evaluation of the new system. With this upgrade, the ion implanter provides enhanced versatility for decelerating to 5 keV a high current ion beam at the µA level. This implantation provides a wide area and allows for a continuous magnetic beam scanning, extending the energy range to lower values, opening up a wider set of applications.
- Four channel 6.5 kV, 65 A, 100 ns-100 mu s generator with advanced control of pulse and burst protocols for biomedical and biotechnological applicationsPublication . Kandratsyeu, Aleh; Sabaleuski, Uladzimir; Redondo, Luis; Pakhomov, AndreiFeatured Application Pulsed generator for biomedical and biotechnology applications. Pulsed electric fields in the sub-microsecond range are being increasingly used in biomedical and biotechnology applications, where the demand for high-voltage and high-frequency pulse generators with enhanced performance and pulse flexibility is pushing the limits of pulse power solid state technology. In the scope of this article, a new pulsed generator, which includes four independent MOSFET based Marx modulators, operating individually or combined, controlled from a computer user interface, is described. The generator is capable of applying different pulse shapes, from unipolar to bipolar pulses into biological loads, in symmetric and asymmetric modes, with voltages up to 6.5 kV and currents up to 65 A, in pulse widths from 100 ns to 100 mu s, including short-circuit protection, current and voltage monitoring. This new scientific tool can open new research possibility due to the flexibility it provides in pulse generation, particularly in adjusting pulse width, polarity, and amplitude from pulse-to-pulse. It also permits operating in burst mode up to 5 MHz in four independent channels, for example in the application of synchronized asymmetric bipolar pulses, which is shown together with other characteristics of the generator.
- Review on solid-state-based Marx generatorsPublication . Zhong, Zhengyi; Rao, Junfeng; Liu, Haotian; Redondo, LuisMarx generators are widely used to produce transient high-voltage pulses. The evolution of semiconductor devices and power electronics concepts promotes the development of solid-state Marx generators (SSMGs) and enables them with flexible pulse modulation ability. First, this article sorts out the evolution of SSMGs topologies chronologically. We can see that how the energy efficiency of SSMGs is considerably improved by replacing resistors with diodes and switches and how square-wave pulses are generated by SSMGs based on half-bridge structures. Unipolar and bipolar pulses can be easily produced with different SSMGs. Second, we discuss the influence of rated voltage and rated power of present semiconductor switches on the performances of SSMGs since switches are the key components in pulse generators. To reduce the size and weight of SSMGs, metal–oxide–semiconductor field-effect transistors (MOSFETs) and insulated gate bipolar transistors (IGBTs) with small packages are preferable. Third, synchronous isolated driving of switches as the crucial technique in SSMGs is introduced. Different methods of providing synchronous signals and isolated power to various stages in SSMGs are illustrated. Fourth, the performance including load capacity, droop compensation, waveform modulation, and self-triggering of SSMGs is discussed. In the end, the developing trend of SSMGs is given.
- Mass spectrometry improvement on an high current ion implanterPublication . Lopes, J. Gabriel; Alegria, F. C.; Luis Redondo; Rocha, J.; Alves, E.The development of accurate mass spectrometry, enabling the identification of all the ions extracted from the ion source in a high current implanter is described. The spectrometry system uses two signals (x-y graphic), one proportional to the magnetic field (x-axes), taken from the high-voltage potential with an optic fiber system, and the other proportional to the beam current intensity (y-axes), taken from a beam-stop. The ion beam mass register in a mass spectrum of all the elements magnetically analyzed with the same radius and defined by a pair of analyzing slits as a function of their beam intensity is presented. The developed system uses a PC to control the displaying of the extracted beam mass spectrum, and also recording of all data acquired for posterior analysis. The operator uses a LabView code that enables the interfacing between an I/O board and the ion implanter. The experimental results from an ion implantation experiment are shown. (C) 2011 Elsevier B.V. All rights reserved.
- Multilevel high-voltage pulse generation based on a new modular solid-state switchPublication . Rocha, Luis Lamy; Silva, José Fernandes Alves da; Luis RedondoThis paper describes a modular solid-state switching cell derived from the Marx generator concept to be used in topologies for generating multilevel unipolar and bipolar high-voltage (HV) pulses into resistive loads. The switching modular cell comprises two ON/OFF semiconductors, a diode, and a capacitor. This cell can be stacked, being the capacitors charged in series and their voltages balanced in parallel. To balance each capacitor voltage without needing any parameter measurement, a vector decision diode algorithm is used in each cell to drive the two switches. Simulation and experimental results, for generating multilevel unipolar and bipolar HV pulses into resistive loads are presented.
- Seven-Level Unipolar/Bipolar Pulsed Power GeneratorPublication . Rocha, Luis Lamy; Silva, J. Fernando; Luis RedondoThis paper shows how to use modular Marx multilevel converter diode ( (MCD)-C-3) modules to apply unipolar or bipolar high-voltage pulses for pulsed power applications. The (MCD)-C-3 cells allow the assembly of a multilevel converter without needing complex algorithms and parameter measurement to balance the capacitor voltages. This paper also explains how to supply all the modular cells in order to ensure galvanic isolation between control circuits and power circuits. The experimental results for a generator with seven levels, and unipolar and bipolar pulses into resistive, inductive, and capacitive loads are presented.
- Fault tolerance capability and semiconductor's hold-off voltage of solid-state bipolar Marx modulatorsPublication . Canacsinh, Hiren; Silva, Fernando; Luis RedondoTwo solid-state bipolar Marx modulators are analyzed and compared regarding hold-off semiconductor voltages and open-fault tolerance capability. Normal and abnormal operating conditions are considered, such as switch synchronization mismatches, failures, and open faults. Ten-stage laboratory prototypes of two bipolar Marx modulators have been assembled using 1200-V insulated gate bipolar transistors and matching diodes, to operate at 500-V dc input voltage. Outputs are 4-kV bipolar pulses, 1% duty ratio, into resistive loads, and 1-kHz frequency. Lack of synchronization and open-fault tests confirm that only topologies with redundant switches can operate without semiconductors being subjected to double hold-off voltages while presenting current paths to clear faults.
- Solid-state bipolar Marx modulators and generation of complementary pulses recovering the energy of the magnetizing inductancesPublication . Canacsinh, Hiren; Redondo, Luis; Silva, José FernandoA new methodology to reset an inductive load during the operation of solid-state bipolar Marx modulators is analyzed. In fact, after applying a positive (or negative) pulse to an inductive load, the reset of the magnetizing energy is evaluated considering the application of a voltage amplitude ranging from one to all capacitors voltage after each pulse: i) immediately after the pulse; ii) with a delay after the pulse. These reset alternatives make it possible to produce several current waveforms that can be used to produce magnetic fields used today in magnetic therapy. Four-stage laboratory prototypes of two bipolar Marx modulators have been assembled using 1200 V insulated gate bipolar transistors (IGBTs) and matching diodes, to operate at 1 kV dc input voltage. Outputs are 4-kV bipolar pulses, 0.5% duty ratio, into inductive load and 1 kHz frequency.
- Rise-time improvement in bipolar pulse solid-state Marx modulatorsPublication . Canacsinh, Hiren; Silva, Fernando; Luis RedondoThis paper presents the effect of stray capacitances in bipolar (negative and/or positive) pulses generated by the two different topologies of the solid-state Marx modulators. According to the analysis, the stray capacitances influence the energy transfer from the Marx modulator capacitors to the load affecting the bipolar (negative and/or positive) pulse rise time. This paper deals with the structure design to reduce the influence of the stray capacitance and to improve the pulse rise time of these bipolar solid-state Marx modulators. A four-stage laboratory prototype of the two topologies has been assembled using 1200-V insulated gate bipolar transistors and diodes, operating with 1000-V dc input voltage and 1-kHz frequency, producing 4-kV bipolar pulses, with 5-mu s pulse duration and 120-ns rise time, into a resistive load.