Fast Pulser Research Articles

Integrated Circuit for Subnanosecond Gating of InGaAs/InP SPAD

We present a novel integrated circuit for subnanosecond gating of InGaAs/InP single-photon avalanche diodes (SPADs). It enables the detector in well-defined time intervals (down to 500 ps) and strongly reduces the afterpulsing effect. It includes a fast pulser with rising/falling edge shorter than 300 ps (20%-80%), a wideband comparator and hold-off logic circuitry. The fast avalanche quenching reduces the charge flow in the SPAD, thus decreasing the afterpulsing, a detrimental effect that limits the maximum count rate of InGaAs/InP SPADs. The wideband SiGe comparator guarantees very low timing jitter of the acquired waveforms: <;100 ps (FWHM) at 5 V excess bias voltage, when operated with InGaAs/InP SPAD, whereas we estimate that the time jitter of the circuit is <;30 ps.

Multimodule System for Fast-Rising High-Voltage Pulse Formation Based on Explosive Current Opening Switches

Matching devices in the form of electro-exploded current opening switches (EEOSs) or explosive current opening switches (EOSs) are used for transforming current pulses of magnetocumulative generators (MCGs) into voltage pulses of hundreds of kilovolts at high-impedance loads. Current pulse sharpening is accompanied by significant losses of the stored energy. Using EOSs are more preferable to EEOSs from the point of view of the energy losses since it does not lead to efficiency decrease in the MCG operation. This paper considers magnetocumulative multimodule systems consisting of several synchronously operating and serially connected small helical MCGs. Each generator is equipped with an explosive current opening switch. The voltages generated at each opening switch are summarized into the load. Fast operation of MCGs allows using very thin foils in the opening switches and obtaining the short voltage pulse front. Results of the works on creating high-voltage devices based on helical MCGs of a 60-mm diameter and disk EOSs of a 200-mm diameter are presented in this paper. In the experiment, the device consisting of two modules provides a voltage pulse of 370 kV with a rise time of ~170 ns into a load of 29 Ω and an inductance of 0.5 μH. Maximum power in the load is ~ 4.3 GW, and the emitted energy is ~1.1 kJ. The four-module device forms the pulse with the characteristic current rise time of ~100 ns in the similar load at twice smaller current.

Vacuum surface flashover: experiments and simulations

It is conjectured that vacuum dielectric surface flashover can be avoided by preventing its initiation. Assuming that the flashover process is initiated by the impact of charged particles on the insulator surface, by deflecting these away from the surface, the development of a flashover avalanche can be repressed. As evidence of this, we present the results of experiments where high-voltage fast-rising microsecond timescale voltage pulses are applied on vacuum insulator samples where we methodically manipulate the magnitude and the orientation of the electric fields at the cathode and anode triple junctions and along the insulator surface.

Gasified singlewire almunum Z-pinch load formed by fast rising current

In order to suppress the core-corona structures commonly observed in the single-wire exploding stage of wire array Z-pinch, the laser probe diagnostic is analyzed, and the exploding characteristics of aluminum wire under negative-polarity and fast-rising current pulses (90-170 A/ns) are investigated using a picosecond laser probe. The aluminum wire with a diameter of 15 μ m and a length of 2 cm, has a peak resistive voltage of 35-50 kV and a resistivity of 30-40 μΩ·cm before the voltage collapsed. The ohmic energy deposited in the load is 1.5-2.5 eV/atom at the voltage peak time, and 2.5-4.0 eV/atom at the time when the Joule heating power drops off to half of its maximum value. A faster rising current would lead to an increase of the energy deposition rate, and enhance the breakdown voltage. In most shots, nearly all the aluminum atoms near the electrodes are in the gaseous state, and liquid drops or clusters existing at the central part of the wire. While in some shots, the load is exploded into a gaseous state homogeneously along the axis. At about 127 ns after the laser peak, 70% of the initial mass is located within a diameter of 1 mm, and all the mass is within a diameter of 2 mm.

탄소블록과 동봉의 접지임피던스 비교 분석

This paper carried out the comparative analysis on ground impedance of a carbon block and a copper rod. Two types of grounding electrode were compared ; a carbon block (L : 1 m, <TEX>${\Phi}$</TEX> : 245 mm) buried at a depth of 0.8 m and a three-linked copper rod (L : 1 m, <TEX>${\Phi}$</TEX> : 10 mm) of equilateral triangles with 1 m spacing. Ground impedance depending on applied current source was evaluated by the application of a sine wave current with 60 Hz ~ 3.5 MHz, a fast-rise pulse with rising time of 200 ns, a standard lightning impulse of <TEX>$8/20{\mu}s$</TEX> and a 600 Hz square wave. Ground impedance for both electrodes were almost the same value below 100 kHz, and increased rapidly afterwards. The maximum ground impedance appeared <TEX>$400{\Omega}$</TEX> at around 1.5 MHz. Ground impedance of the carbon block was lower at the square wave and was higher at fast-rise pulse than that of the copper rod. Also, ground impedance as ages showed no difference for the last 8 months. From the results, it is likely that ground performance for both electrodes shows no difference against commercial frequency and lightning impulse current, while the copper rod shows better performance against a fast-rise pulse with rise-time of a few hundred ns.

HPM Formation in Air and ${\rm SF}_{6}$/Argon Mixture

Using fast-rising voltage pulses, corona discharges are created on the helix. Investigations are carried out in atmospheric air and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> /argon mixture. The corona discharges produce electron beams on the helix. High-power microwaves are obtained in the structure that has two microwave sources. The helix as the slow-wave structure with in situ generated electron beams is one source of microwave generation. The experimental data are presented. The analysis of the data related to the helix is based on the backward-wave oscillator.

High power pulse compression using magnetic flux compression

A design of high power pulse compression by (axial) magnetic flux compression is presented. Optimal model parameters are presented for liner plasma using the thin-shell model code and finite element analyses for stator coils design. Typical model simulation results indicated that a 1.5 μs rise-time pulse with 7.5 MA peak value could be compressed to 20 MA peak value fast rise pulse (∼40 ns rise-time) in the secondary circuit with a 0.5 Ω external load. The limitations resulting from Joule heating and extra high magnetic field diffusion on stator coils are discussed.

Influence of Pulse Rising Time on Plasma Irradiation Effect

Plasma irradiation experiments were performed under atmospheric pressure in N2 using two pulse power supplies with different pulse rising times, and the irradiation effect on a polycarbonate surface was examined. When investigating the effect of the pulse rising time on the contact angle, it was found that a short irradiation time of 5 s had a significant influence on the contact angle and that a larger decrease in the contact angle was observed with a fast-rising pulse. On the Basis of optical emission spectrometry of the plasma and a surface free energy analysis, the decrease in the contact angle was considered to be the result of the introduction of a large amount of hydrophilic groups on the surface. On the other hand, the effect of the plasma irradiation on the contact angle was not very different with a longer irradiation time of 5 min.

Influence of Pulse Rising Time on Plasma Irradiation Effect

Plasma irradiation experiments were performed under atmospheric pressure in N2 using two pulse power supplies with different pulse rising times, and the irradiation effect on a polycarbonate surface was examined. When investigating the effect of the pulse rising time on the contact angle, it was found that a short irradiation time of 5 s had a significant influence on the contact angle and that a larger decrease in the contact angle was observed with a fast-rising pulse. On the Basis of optical emission spectrometry of the plasma and a surface free energy analysis, the decrease in the contact angle was considered to be the result of the introduction of a large amount of hydrophilic groups on the surface. On the other hand, the effect of the plasma irradiation on the contact angle was not very different with a longer irradiation time of 5 min.

High reliability low jitter 80 kV pulse generator

Switching can be considered to be the essence of pulsed power. Time accurate switch/trigger systems with low inductance are useful in many applications. This article describes a unique switch geometry coupled with a low-inductance capacitive energy store. The system provides a fast-rising high voltage pulse into a low impedance load. It can be challenging to generate high voltage (more than 50 kilovolts) into impedances less than $10\text{ }\text{ }\ensuremath{\Omega}$, from a low voltage control signal with a fast rise time and high temporal accuracy. The required power amplification is large, and is usually accomplished with multiple stages. The multiple stages can adversely affect the temporal accuracy and the reliability of the system. In the present application, a highly reliable and low jitter trigger generator was required for the $Z$ pulsed-power facility [M. E. Savage, L. F. Bennett, D. E. Bliss, W. T. Clark, R. S. Coats,J. M. Elizondo, K. R. LeChien, H. C. Harjes, J. M. Lehr, J. E. Maenchen, D. H. McDaniel, M. F. Pasik, T. D. Pointon, A. C. Owen, D. B. Seidel, D. L. Smith, B. S. Stoltzfus, K. W. Struve, W. A. Stygar, L. K. Warne, and J. R. Woodworth, 2007 IEEE Pulsed Power Conference, Albuquerque, NM (IEEE, Piscataway, NJ, 2007), p. 979]. The large investment in each $Z$ experiment demands low prefire probability and low jitter simultaneously. The system described here is based on a 100 kV DC-charged high-pressure spark gap, triggered with an ultraviolet laser. The system uses a single optical path for simultaneously triggering two parallel switches, allowing lower inductance and electrode erosion with a simple optical system. Performance of the system includes 6 ns output rise time into $5.6\text{ }\text{ }\ensuremath{\Omega}$, 550 ps one-sigma jitter measured from the 5 V trigger to the high voltage output, and misfire probability less than ${10}^{\ensuremath{-}4}$. The design of the system and some key measurements will be shown in the paper. We will discuss the design goals related to high reliability and low jitter. While reliability is usually important, and is coupled with jitter, reliability is seldom given more than a qualitative analysis (if any at all). We will show how reliability of the system was calculated, and results of a jitter-reliability tradeoff study. We will describe the behavior of sulfur hexafluoride as the insulating gas in the mildly nonuniform field geometry at pressures of 300 to 500 kPa. We will show the resistance of the arc channels, and show the performance comparisons with normal two-channel operation, and single channel operation.

Stress grading materials for cable terminations under fast-rise time pulses

The paper discusses the material properties and designs of stress grading coatings for cable terminations that can help to reduce the adverse effects of stepped voltages present in voltage source converters. Simulations using transient and quasistatic finite element method, as well as experimental measurements of stress grading materials are presented in this study. The use of two stress grading layers in cable terminations is suggested as an alternative design to reduce the hot spot temperature in conductive stress grading coatings.

Variable gain detection strategy for time-of-flight multiphoton ionization spectroscopy experiments

This note presents a new, simple approach to measure time-of-flight mass spectra containing ions in a wide concentration range as generated by laser photoionization studies of van der Waals complexes. Real-time control of the gain of the microchannel plate detector, applying to it fast-rising high-voltage pulses like in slice imaging experiments, is suggested. Results are presented for a model system study.

SWITCHING INDUCED ELECTROLUMINESCENCE IN PZT CERAMICS IN HIGH-VOLTAGE PULSE FIELD†

ABSTRACT The luminescence features and internal electronic screening in the ferroelectrics ceramics of PZT system at superfast switching in fast-rising pulse fields are investigated. †Originally presented at 10th European Meeting on Ferroelectricity, Cambridge, UK, August 3–8, 2003.

Influence of Peaking Capacitors in Reducing Rise Times of High-Voltage Nanosecond Pulses

High-voltage (a few hundred kilovolt), short pulses (microseconds to to nanoseconds) have been found to be effective for various biological decontamination applications, such as cleaning of water with bacteria/algae. Marx generators are most commonly used for this purpose. A serious disadvantage of Marx generators is the increase in rise times due to series inductance. To alleviate this effect, peaking capacitors have been used to produce early time, fast-rising pulses that the Marx generators otherwise cannot supply due to their relatively high series inductance. This paper presents the results of the design and development of a 600-kV, 50-ns-rise-time, and /spl sim/250-ns-duration pulse generator using a peaking capacitor. A 132-kV condenser-type bushing of 650-kV BIL and 230-pF capacitance was used as a peaking capacitor to reduce rise time. The effect of the peaking capacitor was also studied employing circuit modeling of the generator and the influence of various parameters was investigated. There is a good correlation between the experimental and the numerical results.

Application of pulsed power for the removal of nitrogen oxides from polluted air

Nonthermal plasma discharges using fast-rise (<10 ns) and short-duration pulses (<100 ns) are likely to offer promising prospects for the removal of nitrogen oxides from flue gases and diesel engine exhausts. This is because the energy supplied into the discharge is primarily used to produce energetic electrons, which then create radicals such as N, O, and OH, which lead to the removal of nitrogen oxide pollutants.

A submillimeter-wave gyroklystron: theory and design

New elements of the theory and a preliminary design for a pulse/continuous-wave 360-GHz gyroklystron are presented. Issues germane to very high-frequency operation of gyroklystron amplifiers, including drive power and limits on cavity Q, are discussed. A specific two cavity design is described. That device had a gain of 33 dB and a beam extraction power of 1 kW with an electronic efficiency of 8% and a power output of 700 W after taking into account Ohmic losses. To produce fast-rising pulses, the beam velocity ratio was varied via the modulating anode of a magnetron injection gun. A design for an electron gun through which reduction of the output signal by -50 dB was achieved by a 400-V modulation is given. The input coupler, cavities, electron gun, collector, output coupling optics and collector are described. In addition, issues concerning the fabrication of the high precision, /spl sim/2-mm diameter cavities are discussed.

Ion source electrode biasing technique for microsecond beam pulse rise times

Heavy ion fusion (HIF) induction accelerators require ion sources that can deliver intense heavy ion beams with low emittance. The typical pulse length is 20 μs with a rise time less than 1 μs and a repetition rate of 10 Hz. So far, the surface ionization sources have been used in most HIF induction linac designs. However, there are other ions of interest to HIF (e.g., Hg, Xe, Rb, Ar, and Ne) which cannot be produced by the surface ionization sources, but rather by volume ion sources. In this paper, we describe an experiment that uses a multicusp source with a magnetic filter to produce beam pulses that have a rise time in the order of 1 μs. By applying a positive biasing pulse on the plasma electrode with respect to the source body, the positive plasma ions can be temporarily repelled from the neighborhood of the extraction aperture, leading to a suppression of the ion beam. As the bias is removed, positive ions flow to the extraction region, enabling a fast-rising beam pulse. The beam current pulses show that there are two distinct groups of ions. An initial fast current rise time (&amp;lt;2 μs) corresponding to ions originating from within the magnetic filter region followed by a second group of ions with a longer rise time (10–20 μs) originating from the plasma bulk region. Proper positioning of the filament cathode and the magnetic filter field relative to the extraction aperture was found to be critical.

High-convergence uniform implosion of fusion pellets with the new GEKKO laser

The irradiation uniformity of the GEKKO XII laser has been improved by implementing the state-of-the-art beam smoothing and laser control techniques in the system. Non-uniformity modes higher than 20 are improved to less than 1% RMS by introducing partially coherent light, while the lower modes are improved to 3 - 4% RMS. Implosion experiments were carried out with the new GEKKO XII: a fast-rise square pulse preceded by a pre-pulse was used to suppress the Rayleigh - Taylor instability at the acceptable expense of implosion efficiency. The experimental results are compared with a pusher-fuel mixing model combined with a one-dimensional hydrodynamic simulation. The degradation of experimentally obtained neutrons is mainly attributed to the lower-mode asymmetry. Recent results of planar target experiments on hydrodynamic instabilities are also presented. Particular emphasis is given to the noticeable reduction of fluid instability by the flushing of an external x-ray over the target surface prior to the main drive pulse, leading to suppression of the initial imprint amplitude by the pre-formed plasma

The construction and calibration of an inexpensive PVDF stress gauge for fast pressure measurements

Commercial polyvinylidene difluoride (PVDF) piezoelectric film was used to produce an inexpensive stress sensor with good spatial accuracy to measure the stress state behind a shock wave. The PVDF gauge was found to respond within approximately 100 ns to fast-rising pulses. Since the gauge is piezoelectric no power supply or amplifier was required for the gauge. In order to measure fast signals the gauge was found to perform best in the current mode in which the derivative of the stress was measured; the signal was then numerically integrated. Signals were recorded on a fast (100 MS s-1) storage oscilloscope. The gauges were calibrated against thin-foil manganin stress gauges to approximately 2%. An application in which the gauges were used to measure the response of an alumina to shock loading is described.

Propagation of a de-excitation wavefront in the positive column of a pulsed Xe discharge

When a fast rise pulse voltage is applied to a low pressure, 2-10 mm diameter Xe discharge tube, emission covers the entire positive column region with the breakdown. Within a microsecond, however, the emission intensity starts to decrease from the cathode end of the column and the dark region spreads towards the anode. The speed of this 'de-excitation wavefront' varies from 0.5*103 to 2.5*103 m s-1, depending on the applied voltage, and also on the capacitance which is in parallel with the cathode resistor. The propagation of the de-excitation wave is considered to be due to the migration of excess electrons from the cathode towards the anode, followed by the reduction of impedance, and hence the electric field, of the positive column. In a 1 mm diameter tube, however, the de-excitation wave is not observed, and the emission extinguishes simultaneously over the entire positive column 0.4 mu s after the breakdown. The difference between the two extinction modes is attributed to the discharge current density. It is also shown that, in the positive column, excited species which emit vacuum ultraviolet photons are generated mainly during the initiation stage of the breakdown period. The VUV radiation efficiency can therefore be increased by narrowing the width of the pulse voltage.