Showing papers on "Rise time published in 2018"

Precise rise and decay time measurements of inorganic scintillators by means of X-ray and 511 keV excitation

Abstract: The emergence of new solid-state avalanche photodetectors, e.g. SiPMs, with unprecedented timing capabilities opens new ways to profit from ultrafast and prompt photon emission in scintillators. In time of flight positron emission tomography (TOF-PET) and high energy timing detectors based on scintillators the ultimate coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation rise time, decay time and the reciprocal light yield, C T R ∝ τ r τ d ∕ L Y . Hence, the precise study of light emission in the very first tens of picoseconds is indispensable to understand time resolution limitations imposed by the scintillator. We developed a time correlated single photon counting setup having a Gaussian impulse response function (IRF) of 63ps sigma, allowing to precisely measure the scintillation rise time of various materials with 511keV excitation. In L(Y)SO:Ce we found two rise time components, the first below the resolution of our setup 10 ps and a second component being ∼ 380 ps. Co-doping with Ca 2 + completely suppresses the slow rise component leading to a very fast initial scintillation emission with a rise time of 10ps. A very similar behavior is observed in LGSO:Ce crystals. The results are further confirmed by complementary measurements using a streak-camera system with pulsed X-ray excitation and additional 511 keV excited measurements of Mg 2 + co-doped LuAG:Ce, YAG:Ce and GAGG:Ce samples.

Modeling and control for a magnetic levitation system based on SIMLAB platform in real time

Abstract: Magnetic Levitation system becomes a hot topic of study due to the minimum friction and low energy consumption which regards as very important issues. This paper proposed a new magnetic levitation system using real-time control simulink feature of (SIMLAB) microcontroller. The control system of the maglev transportation system is verified by simulations with experimental results, and its superiority is indicated in comparison with previous literature and conventional control strategies. In addition, the proposed system was implemented under effect of three controller types which are Linear–quadratic regulator (LQR), proportional–integral–derivative controller (PID) and Lead compensation. As well, the controller system performance was compared in term of three parameters Peak overshoot, Settling time and Rise time. The findings prove the agreement of simulation with experimental results obtained. Moreover, the LQR controller produced a great stability and homogeneous response than other controllers used. For experimental results, the LQR brought a 14.6%, 0.199 and 0.064 for peak overshoot, Setting time and Rise time respectively.

Formation of Wide Streamers during a Subnanosecond Discharge in Atmospheric-Pressure Air

Abstract: Results are presented from experimental and computational studies of a subnanosecond breakdown of atmospheric-pressure air in a nonuniform electric field. It is shown that the ionization waves (streamers) formed in the prebreakdown stage have a nearly spherical or conical shape. The diameter of the streamer in its widest part is found to increase with increasing voltage and discharge gap length. For a rise time of the voltage pulse of ≈0.5 ns and its amplitude of ≈250 kV, streamers about 8 cm in diameter were observed in a 7-cm-long gap.

A sealed-off double-gap pseudospark switch and its performance analysis

Abstract: This paper reports the development of a sealed-off double-gap pseudospark switch and its performance analysis. The modular pseudospark geometry has two gaps that are separated by a cavity drift space region. It utilizes a single ferroelectric trigger unit in a hollow cathode region of the first gap to initiate the discharge for rapid breakdown of both the gaps. The switch has been pinched for deuterium gas and a gas reservoir has been used for maintaining optimum gas pressure in the sealed-off device. The switch design has been analyzed for higher hold-off voltage with high charge transfer capability at higher repetition rates. The developed switch holds a 50 kV voltage in vacuum, and 40 kV during gas discharge at optimum gas pressure with a peak anode current of 8 kA and pulse duration of 1.3 μs while it is operated with a resistive load of 2.9 Ω. The switch has been tested using a constant current charging power supply for pulse repetition frequency up to 50 Hz at different voltages and peak currents corresponding to 200 nF energy storage capacitors. Its performance has been analyzed in terms of pulse parameters including hold-off voltage, jitter, fall time, rise time, peak current and delay time to qualify the design.

Formation of 1.4 MeV runaway electron flows in air using a solid-state generator with 10 MV/ns voltage rise rate

Abstract: Fulfillment of the condition that the voltage rise time across an air gap is comparable with the time of electron acceleration from a cathode to an anode allows a flow of runaway electrons (REs) to be formed with relativistic energies approaching that determined by the amplitude of the voltage pulse. In the experiment described here, an RE energy of 1.4 MeV was observed by applying a negative travelling voltage pulse of 860-kV with a maximum rise rate of 10 MV/ns and a rise time of 100-ps. The voltage pulse amplitude was doubled at the cathode of the 2-cm-long air gap due to the delay of conventional pulsed breakdown. The above-mentioned record-breaking voltage pulse of ∼120 ps duration with a peak power of 15 GW was produced by an all-solid-state pulsed power source utilising pulse compression/sharpening in a multistage gyromagnetic nonlinear transmission line.

High speed efficient ultraviolet photodetector based on 500 nm width multiple WO3 nanowires

Abstract: This work presents the fabrication of a photodetector based on multiple WO3 nanowires for ultra-violet detection. This photodetector exhibits a photo-to-dark current ratio of the order of 4 with a high relative change in conductance around 8100 upon 340 nm illumination at 0.87 mW/cm2. The photodetector exhibits a high responsivity of 47.3 A/W and a high 340 nm–450 nm rejection ratio of ∼8800 with excellent stability. A low noise equivalent power of 0.37 fW/√Hz and a high detectivity of ∼1012 Jones are observed. We obtained a fast response with a rise time (tr) of 112 μs and a fall time (tf) of 84 μs. These promising results demonstrate the applicability of the photodetector for high speed ultra-violet detection.

Partial discharge characteristics at ultra-short voltage risetimes

Abstract: This paper describes continuation of author's works on the impact of PWM waveforms characterized by ultra-short rise times on PD characteristics in high voltage insulation systems. The implications of this kind of voltage exposure is becoming increasingly important as with rapid development of silicon carbide (SiC) and gallium nitride (GaN) based power electronic components the rise times used in machine control circuits keep getting shorter and the carrier frequencies higher. There is an imminent need to further develop diagnostic methods for PD detection at such extreme conditions. A PD measurement circuit based on capacitive decoupling and suitable for ultra-short rise times is presented here. Functionality of the circuit is demonstrated for a twisted pair test object insulated by enamel containing chromium oxide (Cr2O3) filler for rise times between 15 and 800 ns. The impact of voltage steepness on the PD extinction voltages (PDEV) and on other measurable parameters is reported. Specifically, the total number of PDs and their amplitude per modulated cycle are shown. The PD magnitude keeps increasing with the gradually decreased rise time, while the PDEV decreases. However, when compensating for voltage overshoot, less difference is noted. It is also demonstrated that the used PD detector allow for measurements at carrier frequencies well exceeding 1 kHz and rise times well below 100 ns as well as how the PD characteristics changes due to voltage overshoots inflicted by reflections.

Partial discharge characteristics within motor insulatioi exposed to multi-level PWM waveforms

Abstract: The frequent use of variable speed drives fed by pulse width modulated (PWM) inverters allow for a more efficient utilization of electric energy. The drawback is however that the stress imposed on motor winding insulation increases and partial discharges (PDs) may appear under such conditions, being considered the major contributor to the reduction of the insulation life time. This paper presents what influence the choice of PWM level and rise time has on the PD characteristics for two different motor insulations as well as introducing suitable high voltage generation test-set ups for these kinds of measurements. The two different test objects were twisted pair and a pig tail motor insulation test objects, the latter aimed for higher voltage levels. These test objects were fed from either two-, three-, four- or five level inverters of similar type, as often used in actual applications. Additionally a six level inverter was used for verification purposes. The twisted pair test objects were insulated by a polyamide-imide enamel, whereas the motor pig tail insulation objects were mica-epoxy based. To compare the performances, measurements of the PD characteristics are reported and observations concentrate on the importance of the voltage rise time, on the size of the voltage step in relation to the extinction voltages (PDEV). Specifically, the total number of PDs and their amplitude per cycle is obtained. The experimental results show that the total summed PD magnitude (exposure) drops considerably when applying the three- or higher level inverters. However the maximum PD magnitude is less dependent, which indicates that a change to a high level inverter alone may still not be sufficient condition for increasing motor insulation system life. In conclusion a combination of the PDEV level, rise time and PWM level must all together be considered in this complex design process.

All Solid-State Rectangular Sub-Microsecond Pulse Generator for Water Treatment Application

Abstract: Low-temperature plasma with reactive species including the hydroxyl radical is found very effective for the degradation of many pharmaceuticals and macromolecular organic matter in wastewater. The most efficient way is to excite plasma directly in the wastewater using high-voltage sub-microsecond pulses which prevents the corona discharges developing into arc discharges. Recently, plasma generated with high-voltage pulses of only several hundred nanosecond durations has been found to be especially efficient. Therefore, an all solid-state sub-microsecond pulse generator prototype based on the Marx concept is constructed, with MOSFET power semiconductor devices. This pulse generator is able to generate rectangular pulses with adjustable durations in impedance-varying wastewater. The sub-microsecond signals are generated by field-programmable gate array, and simulations of the driving circuits are carried out to optimize the driving signals so as to trigger the switches synchronously in a few nanoseconds. First, experiments show that sub-microsecond pulses with amplitudes over 7 kV and a minimum pulse duration of about 100 ns can be generated. Both rise time and fall time are about 22 ns. Pulse frequency up to 30 kHz is achieved. Besides, most of these parameters can be adjusted. The pulse generator itself is compact and portable.

Development and Test of a 400-kV PFN Marx With Compactness and Rise Time Optimization

Abstract: Repetitive high-voltage square pulses are of great importance for producing long-pulse electron beams and high-power microwaves. One of possible technologies for the generation of such pulses is a Marx generator using pulse forming network (PFN) stages, often combined with a pulse sharpening technique to reduce the rise time to a few nanoseconds (peaking stage). This paper presents an innovative design, named the “zigzag design,” for the optimization of the compactness and of the rise time of 400-kV–85-ns PFN-Marx. Thanks to this design, the 16 stages of this generator, which delivers an open circuit output voltage of 720 kV, fit in a 650-mm length. For a slightly overmatched load ( $Z_{\mathrm {load}} = 100 ~\Omega$ ), the output voltage reaches 400 kV with a rise time as less as 5 ns. The inductance reduction associated with the innovative zigzag design, which allows this sharp rise time with no need for a peaking stage, is described. The 85-ns plateau duration of the pulse is given by the PFN construction of each stage, which is based on six ceramic capacitors (2.1 nF–45 kV) connected within a strip line. The 16 PFN stages are housed in a 360-mm diameter gas pressurized vessel. Burst mode operation for a duration of 10 s at a pulse repetition frequency of 100 Hz is reported, for a resistive load and for the electron beam diode of a X-band relativistic backward-wave oscillator (BWO). To reach further compactness, the BWO system is integrated on side of the generator vessel and a U-shaped gas pressurized line connects both systems through a compact conical vacuum insulator.

Fixed Frequency Sliding Mode Control of Power Converters for Improved Dynamic Response in DC Micro-Grids

Abstract: The rapid decrease in conventional energy resources and their harmful impact on the environment has brought the attention of the researchers towards the use of renewable energy technologies. The renewable energy systems are connected to Direct Current (DC) micro-grids via power electronic converters where the load conditions are unknown and network parameters are uncertain. These conditions call for the use of robust control techniques such as Sliding Mode Control (SMC) in order to regulate the grid voltage. However, SMC has a drawback of operating the power converter at variable switching frequency which results in degrading the power quality. This paper introduces a fixed frequency sliding mode controller that does not suffer from this predicament. A novel double integral type switching manifold is proposed to achieve voltage regulation of a DC micro-grid, in the presence of unknown load demands and un-modeled dynamics of the network. Rigorous mathematical analysis is carried out for the stability of the closed loop system and the technique is experimentally validated on position of a DC micro-grid using a specially designed test rig. For benchmarking purposes, a conventional Proportional Integral (PI) controller is also implemented. An improvement of 2.5% in rise time, 6.7% in settling time and reduction of voltage dip by 31.7% during load transaction is achieved as compared to the PI controller. The experiment confirms the hypothesis that fixed frequency SMC shows better performance than its counterpart in the phase of introduced disturbances.

Polymer thermal optical switch for a flexible photonic circuit.

Abstract: Flexible and wearable optoelectronic devices are the new trend for an active lifestyle. These devices are polymer-based for flexibility. We demonstrated flexible polymer waveguide optical switches for a flexible photonic integrated circuit. The optical switches are composed of a single-mode inverted waveguide with dimensions of 5 μm waveguide width, 3 μm ridge height, and 3 μm slab height. A Mach–Zehnder structure was used in the device, with the Y-branch horizontal length of 0.1 cm, the distance between two heating branches of 30 μm, and the heating branch length of 1 cm. The optical field of the device was simulated by beam propagation to optimize the electrode position. The switching properties of the flexible optical switch with different working conditions, such as contact to the polymer, silicon, and skin, were simulated. The device was prepared based on the photo curved polymer and lithography method. The end faces of the flexible film device were processed using an excimer laser with optimized parameters of 28 mJ/cm2 and 15 Hz. The response rise time and fall time on the PMMA substrate were measured as 1.98 ms and 2.71 ms, respectively. The power consumption was 16 mW and the extinction ratio was 11 dB. The response rise and fall times on the Si substrate were measured as 1.08 ms and 1.62 ms, respectively. The power consumption was 17 mW and the extinction ratio was 11 dB. The demonstrated properties indicate that this flexible optical waveguide structure can be used in the light control area of a wearable device.

Design and Development of a Compact All-Solid-State High-Frequency Picosecond-Pulse Generator

Abstract: The Marx circuit structure based on fast high-power semiconductor devices is the classical way of generating picosecond pulses. However, most reported studies suggest that as the number of stages in the Marx circuit increases, the output pulse amplitude tends to saturate. This has of late made high-voltage picosecond-pulse generation a challenge. In this paper, as the number of stages increases, the internal resistance of the avalanche transistor tends to decrease with increasing current flowing through the avalanche transistor. A step-by-step wiring and debugging of the avalanche transistor-based Marx circuit demonstrates this experimentally. That is, for a certain range in the number of stages, saturation of the output pulse amplitude for the Marx circuit of avalanche transistors is not apparent. Introducing a parallel structure for the transistors not only increases the current level of the entire circuit but also further reduces the equivalent resistance of the avalanche transistors, thereby improving the output efficiency. Drawing on microstrip transmission theory, and combining the Marx circuit and avalanche transistor parallel structure, component parameters and circuit topology of the picosecond-pulse generator were redesigned, and a 30-level Marx circuit with a parallel structure of two avalanche transistors was developed. The picosecond-pulse generator outputs a pulse with adjustable voltage amplitude of 0.9–3.1 kV, a 350-ps full-width at half-maximum, a 150-ps rise time, and an adjustable high-stability repetition rate of up to 10 kHz. The number of pulses is precisely controlled. The generator is an all-solid-state compact device with high frequency suitable for research needs.

A compact nanosecond pulse generator for DBD tube characterization.

Abstract: High voltage pulses of very short duration and fast rise time are required for generating uniform and diffuse plasma under various operating conditions. Dielectric Barrier Discharge (DBD) has been generated by high voltage pulses of short duration and fast rise time to produce diffuse plasma in the discharge gap. The high voltage pulse power generators have been chosen according to the requirement for the DBD applications. In this paper, a compact solid-state unipolar pulse generator has been constructed for characterization of DBD plasma. This pulsar is designed to provide repetitive pulses of 315 ns pulse width, pulse amplitude up to 5 kV, and frequency variation up to 10 kHz. The amplitude of the output pulse depends on the dc input voltage. The output frequency has been varied by changing the trigger pulse frequency. The pulsar is capable of generating pulses of positive or negative polarity by changing the polarity of pulse transformer's secondary. Uniform and stable homogeneous dielectric barrier discharge plasma has been produced successfully in a xenon DBD tube at 400-mbar pressure using the developed high voltage pulse generator.

Characteristics of a Pulse-Periodic Corona Discharge in Atmospheric Air

Abstract: Pulse-periodic corona discharge in atmospheric air excited by applying a voltage pulse with a subnanosecond or microsecond rise time to a point electrode is studied experimentally. It is shown that, at a voltage rise rate of dU/dt ~1014 V/s, positive and negative ball-shaped streamers with a front velocity of ≥2 mm/ns form near the point electrode. As dU/dt is reduced to 1010−1011 V/s, the streamer shape changes and becomes close to cylindrical. The propagation velocity of cylindrical streamers is found to be ~0.1 mm/ns at dU/dt ~ 2 × 1010 V/s. It is shown that the propagation direction of a cylindrical streamer can be changed by tilting the point electrode, on the axis of which the electric field strength reaches its maximum value. It is established that, for the negative polarity of the point electrode and a microsecond rise time of the voltage pulse, a higher voltage is required to form a cylindrical streamer than for the positive polarity of the point electrode.

A High-Repetition-Rate Bipolar Nanosecond Pulse Generator for Dielectric Barrier Discharge Based on a Magnetic Pulse Compression System

Abstract: Magnetic pulse compression (MPC) systems are suitable for generating dielectric barrier discharges (DBDs) owing to their capability of producing high-amplitude, short pulse voltage waves. This paper proposes a high-frequency, bipolar magnetic compression system to study DBD plasma characteristics. First, the principle of bipolar MPC is explained [a bipolar MPC system comprises a full bridge inverter circuit, pulse transformer (PT), and magnetic switch (MS)]. Additionally, the design of the PT and MS is described. Then, the waveform of the resistive load is tested and compared with PSpice simulation results. It was found that the nanosecond pulse generator produces a pulse on a resistor with an amplitude of 0–13 kV, a rise time of approximately 100 ns, and a repetition frequency of 0 to several kHz. Finally, this paper studies the plasma characteristics under the application of a high-frequency bipolar pulse, and the charge–voltage Lissajous figure of the discharge waveform is analyzed. Combining discharge photographs and theoretical calculation results yields the relationship between the discharge characteristics and the frequency, which enriches the theoretical study of high-frequency bipolar discharges.

Robust non-overshooting tracking using continuous control for linear multivariable systems

Abstract: A robust continuous control for tracking a step reference signal without any overshoot and arbitrarily small rise time is proposed for a linear multivariable system. Integral sliding mode technique with the super-twisting sliding mode is used to make the control robust against the matched disturbances with bounded derivatives. Moore's eigenstructure assignment is used to compute nominal control part of the integral sliding mode technique which makes the system output to track the step reference with arbitrarily small rise time and without any overshoot under some mild assumptions. The efficacy of the proposed control is validated using simulation results on benchmark quadruple tank model.

Solution Processable 1D Fullerene C60 Crystals for Visible Spectrum Photodetectors.

Abstract: Visible spectrum photodetector devices fabricated using molecular crystals of carbon C60 are reported. The devices operate efficiently, extending over and beyond the full visible light spectrum (300-710 nm) with a bias voltage tunable responsivity of 4 mA-0.5 mA W-1 . Across this range of wavelengths, the noise equivalent power of these devices remains below 102 nW Hz-1/2 , providing a detectivity of 107 Jones. The noise current in these devices is found to have a strong dependence on both bias voltage and frequency, varying by 4 orders of magnitude from 1 nA Hz-1/2 to 0.1 pA Hz-1/2 . The devices also display a near-linear dependence of photocurrent on light intensity over 4 orders of magnitude, providing a dynamic range approaching 80 dB. The 3 dB bandwidth of the devices is found to be above 102 Hz, while the 18 dB bandwidth exceeds 1 kHz. The transient photocurrents of the devices have a rise time of ≈50 µs and a long fall time of ≈4 ms. The spectral photocurrent of the devices is found to quench gradually with a reduction in temperature from ≈300 K and is fully quenched at temperatures below T ≈ 100 K. Upon reheating, the device performance is fully recovered.

Device Failure from the Initial Current Step of a CDM Discharge

Abstract: CDM discharges exhibit a fast initial current step when the stray capacitance of the pogo pin is charged. It is demonstrated that the high slew rate can damage sensitive gate oxides. The miscorrelation of CDM and CC-TLP methodologies is addressed by applying pulses with 20 ps rise time.

Dynamically varying laser output in a vehicle in view of weather conditions

Abstract: To detect an atmospheric condition at the current location of a lidar system, a receiver in the lidar system detects a return light pulse scattered by a target and analyzes the characteristics of the return light pulse. The characteristics of the return light pulse include a rise time, a fall time, a duration, a peak power, an amount of energy, etc. When the rise time, fall time, and/or duration exceed respective thresholds, the lidar system detects the atmospheric condition such as fog, sleet, snow, rain, dust, smog, exhaust, or insects. In response to detecting the atmospheric condition, the lidar system adjusts the characteristics of subsequent pulses to compensate for attenuation or distortion of return light pulses due to the atmospheric condition. For example, the lidar system adjusts the peak power, pulse energy, pulse duration, inter-pulse-train spacing, number of pulses, or any other suitable characteristic.

Nonlinear transmission line high voltage pulse sharpening

Abstract: Some embodiments include a high voltage nonlinear transmission line that includes a high voltage input configured to receive electrical pulses having a first peak voltage that is greater than 5 kV having a first rise time; a plurality of circuit elements electrically coupled with ground, each of the plurality of circuit elements includes a resistor and a nonlinear semiconductor junction capacitance device; a plurality of inductors, at least one of the plurality of inductors is electrically coupled between two circuit elements of the plurality of circuit elements; and a high voltage output providing a second peak voltage with a second rise time that is faster than the first rise time.

An Analytical Design Strategy and Implementation of a Dv/Dt Filter for WBG Devices Based High Speed Machine Drives

Abstract: This paper presents a design strategy of a $dv/dt$ filter for high speed machine drives based on analytical analysis. Both a LCR filter and a LC with a diode bridge are studied and, a choice between two options can be made depending on a length of cable. The way of choosing the value of L, C, and R of the filter is proposed by analyzing the transfer function of the filter output voltage and the filter resonant current. In the same manner, filter characteristics such as $dv/dt$ , rise time, peak voltage, and peak resonant current can be adjusted accurately. The power loss in damping resistors are discussed. The proposed design scheme is evaluated through simulations and experiments with a SiC inverter and high speed IPMSM.

Comparison of CDM and CC-TLP robustness for an ultra-high speed interface IC

Abstract: Challenging the limits of today’s metrology and test setups for CDM and Capacitively Coupled Transmission Line Pulsing (CC-TLP), the study identifies critical stress parameters for A25 Gbps communication device in the CDM-domain. Only CC-TLP stress in combination with a 33/ 63 GHz single shot oscilloscope was able to relate significant differences of failure current distributions to the rise time spread in the order of few tens of picoseconds and to obtain a conclusive sharp pass/fail transition at a certain peak current level.

X-ray radiation and runaway electron beams generated during discharges in atmospheric-pressure air at rise times of voltage pulse of 500 and 50 ns

Abstract: The parameters of X-ray radiation and runaway electron beams (RAEBs) generated at long-pulse discharges in atmospheric-pressure air were investigated. In the experiments, high-voltage pulses with the rise times of 500 and 50 ns were applied to an interelectrode gap. The gap geometry provided non-uniform distribution of the electric field strength. It was founded that at the voltage pulse rise time of 500 ns and the maximum breakdown voltage Um for 1 cm-length gap, a duration [full width at half maximum (FWHM)] of a RAEB current pulse shrinks to 0.1 ns. A decrease in the breakdown voltage under conditions of a diffuse discharge leads to an increase in the FWHM duration of the electron beam current pulse up to several nanoseconds. It was shown that when the rise time of the voltage pulse is of 500 ns and the diffuse discharge occurs in the gap, the FWHM duration of the X-ray radiation pulse can reach ≈100 ns. It was established that at a pulse-periodic diffuse discharge fed by high-voltage pulses with the rise time of 50 ns, an energy of X-ray quanta and their number increase with increasing breakdown voltage. Wherein the parameter Um/pd is saved.

Influence of sinusoidal and square voltages on partial discharge inception in geometries with point-like termination

Abstract: High-voltage equipment involves both electrical and electronic components. In electrical power network, which consists of rotating machine, power transformers and transmission lines, field enhancement at critical regions can lead to local breakdown [partial discharges (PD)]. The continuous occurrence of PDs can lead to complete breakdown. While in large power equipment sharp edges can be avoided, this is not the case in power converter due to the miniature nature of the semiconductor device. Sharp edges can also be present in any power equipment in the shape of conducting particles, either stuck at a barrier or freely moving in the bulk oil. This creates high-field regions, prone to PD activities. Different power equipment operates at different voltages such as AC, DC, square voltage, pulse voltage, fast-rise transient voltage etc. This study presents the influence of sinusoidal voltage, slow- and fast-rise square voltage on PDs in two different geometries using optical PD measurement technique. Fast-rise square voltage has the lowest PD inception voltage while the sinusoidal voltage has the highest. This is may be due to the influence of homo- and hetero-charges. Fast-rise square voltage displayed higher PD magnitude at inception which may be connected to the rise time of the voltage.

Influence of Runaway Electrons on the Formation Time of Nanosecond Discharge

Abstract: In this paper, we present the theoretical results of a self-consistent kinetic simulation, clarifying the influence of runaway electron flows on a delay time of the switching stage of a nanosecond discharge. The simulation is based on an accurate numerical solution of the Boltzmann kinetic equation, with model collision integrals that take into account elastic and ionization collisions of the electrons with neutral atoms. As an example, the breakdown of a cylindrical gap is investigated with respect to the variations of the voltage rise time value. The current and voltage time profiles, power spectrum, and current of high-energy electrons, as well as the electron distribution function, are calculated accordingly. Our numerical solution agrees with the existent experimental data.

A 7.8 kV nanosecond pulse generator with a 500 Hz repetition rate

Abstract: Pseudospark switches are widely used in pulsed power applications. In this paper, we present the design and performance of a 500 Hz repetition rate high-voltage pulse generator to drive TDI-series pseudospark switches. A high-voltage pulse is produced by discharging an 8 μF capacitor through a primary windings of a setup isolation transformer using a single metal-oxide-semiconductor field-effect transistor (MOSFET) as a control switch. In addition, a self-break spark gap is used to steepen the pulse front. The pulse generator can deliver a high-voltage pulse with a peak trigger voltage of 7.8 kV, a peak trigger current of 63 A, a full width at half maximum (FWHM) of ~30 ns, and a rise time of 5 ns to the trigger pin of the pseudospark switch. During burst mode operation, the generator achieved up to a 500 Hz repetition rate. Meanwhile, we also provide an AC heater power circuit for heating a H2 reservoir. This pulse generator can be used in circuits with TDI-series pseudospark switches with either a grounded cathode or with a cathode electrically floating operation. The details of the circuits and their implementation are described in the paper.

Switched-Capacitor-Based Current Compensator for Mitigating the Effect of Long Cable Between PWM Driver and LED Light Source

Abstract: It is sometimes unavoidable to have light-emitting-diode (LED) light sources and their pulsewidth modulation (PWM) drivers connected by long cables in large-scale illuminations. However, long-cable inductance delays the rate of rise of the driving current pulses and thus leads to the reduction of luminous flux output. It also causes the off-state voltage across the light sources negative, which would deteriorate the life expectancy of the LEDs. A switched-capacitor-based current compensator for correcting the wave shape of the driving current pulses is presented. The methodology is based on transferring the energy stored in the cable to a capacitor at the end of the current pulse and then momentarily boosting the voltage with the capacitor applying to the cable at the beginning of the next current pulse. Thus, the rise time of the current pulses can be shortened. The topological states and operations of the compensator will be described. A simplified design procedure will be given. A prototype for a 12-V, 3-A PWM driver has been built and evaluated. Performance comparisons between the proposed current compensator and prior art and between the systems with and without the compensators will be conducted.

A travelling wave Zeeman decelerator for atoms and molecules

Abstract: The design of a modular moving trap Zeeman decelerator capable of decelerating gas pulses produced from a supersonic source is presented here. Unlike the conventional form of Zeeman decelerator, paramagnetic particles are confined in a 3D potential throughout the deceleration process. The decelerator field is produced by flattened helical coils and currents of up to 1000 A peak. As the coils are periodic in nature, each coil produces a number of deep, quadrupole traps along the molecular beam axis. The resultant periodic field is described as a travelling wave. The application of the appropriate time dependent current allows the traps to move through the four coil modules. In order to compensate for the weaker transverse confinement, a quadrupole guide, operating at 700 A DC, is required to prevent further losses during the deceleration process. The operation of the decelerator relies on the power electronics developed specifically for the quadrupole and the decelerator coils. Due to the electromagnetic interference generated through the switching of the large currents, much of the electronics used to control the power electronics had to be developed specifically. The quadrupole power electronics have been designed to produce fast switching edges. This is necessary to minimise the interaction of the particles within the fringe field regions while maximising the interaction time within the pure quadrupole field. Even at a modest voltage applied to the circuitry, the rise time in current to 700 A has been reduced by a half. The decelerator power electronics must be capable of producing an alternating waveform with an amplitude of at least 500 A for each of the coil phases. Furthermore, the frequency of the waveforms must be tunable within a range of 10 kHz to 0 Hz. Through a combination of pulse width modulation and knowledge of the electrical properties of the coil it is possible to synthesise an alternating current waveform from a 800 V DC supply using a suitable switching circuit. %The challenge of switching such high powers is the transient voltage spikes that can be produced, however, these can be avoided through careful consideration of the layout of the circuit. Decelerators such as this do not cool the sample but instead reduces the mean velocity of a subset of particles which remained trapped. This maintains the phase space density of trapped particles. Modelling the magnetic fields generated by the decelerator coils has been necessary in order to understand the phase space acceptance of the decelerator. The helical nature of the coils required the development of a specific algorithm in order to calculate the field generated by each wire element. The resultant potential can then be interpolated using a tricubic interpolator to extract the field gradients necessary for numerical simulations of the particle trajectories. Including the effects of the pulse width modulated on the trap facilitates the characterisation of the acceptance of the decelerator and the limitations of the current iteration of the design. The numerical simulations can also be compared to experimental results gathered for metastable argon. The 3D guiding, or velocity bunching, of the gas packet over a range of velocities has been demonstrated. The ability to 3D guide and decelerate were severely hampered by the failure of key electronic components, limiting three coils to 100 A peak, moreover, these traps were sub-optimally loaded. Deceleration from 350 to 347 m/s and 342 to 310 m/s has been observed. The design of a trap capable of simultaneously loading samples of decelerated CaH and Li while allowing the cooling of Li would potentially allow for the sympathetic cooling of a molecular species with an atomic refrigerant. This particular atom-molecule system would also facilitate the examination of controlled chemistry and collisions over a range of temperatures through state selection of the reactants. The loading of the trap has been optimised in 1D for CaH with a loading efficiency of 52.2 % while only 7.3 % of Li is loaded when each of the gas packets has a mean velocity of 11 m/s. This implies that the source of the Li must be at least 130 times brighter than that of the CaH.