Pulsed Mode Operation Research Articles

Two Design Options for Compact Linear Accelerators for High Flux Neutron Source

We describe and compare two optimized design options of RF linear accelerators with different resonant frequencies at 162.5 MHz (f0) and 325 MHz (2∙f0). The RFQ + DTL linacs have been designed to provide 13 MeV acceleration to a proton beam for achieving a fast neutron yield of not lower than 1013 n/s via 9Be(p, n)9B reaction in pulsed-mode operation. Our design studies show that none of the two options is better than the other, but that the choice of operating frequency will mainly be determined by the accelerator length and RF cost consideration. This study can serve as a basis for the design of an initial stage of a new high brilliance Compact Accelerator-driven Neutron Source (CANS), aiming to use neutron scattering techniques for studying material properties in fundamental physics, materials science, nuclear energy, as well as for industries and societal challenges.

Silicon MEMS Thermocatalytic Gas Sensor in Miniature Surface Mounted Device Form

A reduced size thermocatalytic gas sensor was developed for the detection of methane over the 20% of the explosive concentration. The sensor chip is formed from two membranes with a 150 µm diameter heated area in their centers and covered with highly dispersed nano-sized catalyst and inert reference, respectively. The power dissipation of the chip is well below 70 mW at the 530 °C maximum operation temperature. The chip is mounted in a novel surface mounted metal-ceramic sensor package in the form-factor of SOT-89. The sensitivity of the device is 10 mV/v%, whereas the response and recovery times without the additional carbon filter over the chip are <500 ms and <2 s, respectively. The tests have shown the reliability of the new design concerning the hotplate stability and massive encapsulation, but the high degradation rate of the catalyst coupled with its modest chemical power limits the use of the sensor only in pulsed mode of operation. The optimized pulsed mode reduces the average power consumption below 2 mW.

Тонкопленочные поглощающие элементы адаптоаттенюаторов для ГИС

One of the urgent tasks in the design of hybrid integrated circuits (HIC) is the construction of adapter-attenuators – film absorbing elements providing a wide range of attenuations with specified values of input and output resistances. Known variants of adapter-attenuators based on a homogeneous and piecewise homogeneous resistive film provide (by introducing asymmetry in the dimensions of the input and output contacts, changing the location of a piecewise homogeneous resistive film, introducing dielectric or conductive regions) a resistance transformation coefficient of no more than 3 and 10–12, respectively. In this work, promising topologies of adapter-attenuators for HIC with a close to optimal profile of input and output contacts are proposed, which allow not only to obtain a wide range of transformation coefficients (more than 100), but also to reduce the maximum values of the potential gradient and power density by 10‒30 times. The rectangular topology calculations were made using the apparatus of the theory of functions of a complex variable. Modeling of the optimized topology of adapter-attenuators for HIC was carried out by the finite element method implemented in the Elcut software package. The calculated ratios and graphs showing the relationship of attenuation, the transformation coefficient, the gain in the value of the potential gradient and the power density, depending on the ratio of the size of the film element and the resistivity of the resistive films used, have been provided. The features of adapter-attenuators fitting have been considered. The results obtained are especially important for the pulse mode of operation of adapter-attenuators’ film element for HIC.

Radiation Protection Evaluations Following the Installations of Two Cardiovascular Digital X-ray Fluoroscopy Systems

Acceptance testing and commission are essential elements of the quality assurance program for imaging equipment. We present the results of a performance evaluation of Flat Panel-Based Cardiovascular Fluoroscopy X-ray Systems as a part of acceptance testing and commissioning. Measurements were obtained using a calibrated dose rate meter, patient equivalent phantoms, and Leeds image quality test tools. The results were compared with the manufacturer and European acceptability criteria. The entrance surface air kerma (ESAK) rate ranged from 8.0 to 12.0 mGy min−1 in the continuous mode and from 0.01 to 0.04 mGy fr−1 in the pulsed mode of operation. Detector-input air kerma rates ranged from 0.29 to 0.39 mGy min−1 in continuous mode and from 0.02 to 0.07 µGy fr−1 in pulsed mode. Fluoroscopy device half-value layer (HVL) ranged from 2.5 to 3.0 mm Al, and the low resolution ranged from 0.9 to 1.3%. The spatial resolution limit was double that of the image intensifier (2.4 to 3.6) lp/mm. Flat-panel fluoroscopy demonstrated superior image quality and dose performance as compared to conventional image intensifier-based fluoroscopy. The quality assurance measurements presented are essential in the rapid evaluation of the imaging system for acceptance testing and commissioning.

Complementary resistive switching in core–shell nanowires

Highly dense, energy-efficient, and fast neuromorphic architectures emulating the computational abilities of the brain use memristors to emulate synapses in the analog or digital systems. Core–shell nanowires provide us with new opportunities for neuromorphic hardware integration. In this work, we have fabricated core–shell nanowires using a combination of bottom-up and top-down techniques. Additionally, we have demonstrated eightwise and counter-eightwise bipolar resistive switching (BRS). Remarkably, for the first time along with BRS, we have also demonstrated complementary resistive switching (CRS) in core–shell nanowires. Here, Pt was used as the conductive core and HfO2 as the memristive shell with Ti as the top electrode. The resistive switching properties were characterized by I–V curves and pulse operation modes. The cycling endurance in the BRS mode was 1000 cycles with an off–on ratio of ∼13 and resistance was retained for 104 s. Additionally, the compliance current used to form the nanowire in the BRS mode influenced the CRS operation by lowering the peak operating current. Additionally, current density–electric field analysis performed to determine charge conduction mechanisms revealed that the wires exhibit a thermionic emission mechanism in the high resistance state and Ohmic conduction mechanism in the low resistance state during the BRS mode of operation and hopping conduction mechanism in state 0 and space-charge-limited conduction mechanism in state 1 during the CRS mode of operation. This observed versatility in the mode of operation makes core–shell nanowires of significant interest for use as synaptic elements in neuromorphic network architectures.

Tunable quantum-cascade VECSEL operating at 1.9 THz.

We report a terahertz quantum-cascade vertical-external-cavity surface-emitting laser (QC-VECSEL) emitting around 1.9 THz with up to 10% continuous fractional frequency tuning of a single laser mode. The device shows lasing operation in pulsed mode up to 102 K in a high-quality beam, with the maximum output power of 37 mW and slope efficiency of 295 mW/A at 77 K. Challenges for up-scaling the operating wavelength in QC metasurface VECSELs are identified.

Flexible multijunction solar cells embedded inside smart dust modules for outdoor applications to Smart Grids

The functioning of self-sustaining smart dust modules plays a vital role in the development of the smart electric grid. In this work, we first devise a flexible triple-junction III-V solar cell embedded inside a smart dust module suitable for outdoor applications. These flexible solar cells are demonstrated to have a bending radius of over 5 cm and exhibit a conversion efficiency of around 25% under air mass 1.5G (1 sun) conditions. Under normal incidence of sunlight at the same conditions, our cell with its small active area of 0.4 cm2 can generate around 10.1 mW of electrical power. This is sufficient to meet the direct current power consumption (∼5.4 mW) requirements of our dust module, which includes a temperature/moisture sensor, a 3-axis linear accelerometer, and a Bluetooth chip. In comparison to a silicon-based flexible solar cell, our demonstrated III-V solar cell is smaller, requiring approximately 40% of the area to produce the same electrical power output. Our dust module is controlled using a self-developed Android application installed on a smartphone and can sustain continuous-wave operation for data collection and wireless transmission even when the incident angle of the sunlight reaches 75°. Pulse-mode operation is still possible even in the case of nearly 90° illuminations (for example, at sunset). Overall, the measurement results for this flexible solar cell are promising, allowing for further reduction in the size of a self-sustaining smart dust module with improved reliability. These advantages could facilitate development of the next generation of energy saving smart electric grids.

EUV-induced hydrogen plasma: pulsed mode operation and confinement in scanner

In recent years, EUV lithography scanner systems have entered high-volume manufacturing for state-of-the-art integrated circuits, with critical dimensions down to 10 nm. This technology uses 13.5-nm EUV radiation, which is shaped and transmitted through a near-vacuum H2 background gas. This gas is excited into a low-density H2 plasma by the EUV radiation, as generated in pulsed mode operation by the laser-produced plasma in the EUV source. Thus, in the confinement created by the walls and mirrors within the scanner system, a reductive plasma environment is created that must be understood in detail to maximize mirror transmission over the lifetime and to minimize molecular and particle contamination in the scanner. In addition to the irradiated mirrors, reticle, and wafer, the plasma and radical load to the surrounding construction materials also must be considered. We provide an overview of the EUV-induced plasma in the scanner context. Special attention is given to the plasma parameters in a confined geometry, such as that found in the scanner area near the reticle. It is shown that plasma confinement and resulting contributions from secondary electron emission delay the formation of the plasma sheath and thereby reduce the peak ion energies to below the sputtering threshold for mirrors and construction materials. Furthermore, for a confined pulsed plasma with a pulse period shorter than the decay time of the plasma, the plasma consists of a quasi-steady-state cold background plasma and periodic transient peaks in ion energy and ion flux. In terms of modeling, this means that no assumptions can be made on the electron distribution functions and a (Monte-Carlo) particle-in-cell (PIC) model is needed. We present an extension of the PIC model approach to complex three-dimensional geometries and to multiple pulses using a hybrid PIC-diffusion approach. Also, the translation of these specific plasma parameters to off-line setups and the aspects that must be included to make a meaningful translation from off-line laboratory EUV setups to the scanner plasma are discussed.

EXPERIMENTAL STUDIES OF THE THERMOCATALYTIC METHOD FOR MEASURING THE HEAT OF COMBUSTION OF NATURAL GAS

The paper describes the design of a laboratory bench for experimental studies of thermocatalytic methods for determining the heat of combustion of a gas using natural gas samples. The technique of measurements performed on the developed experimental stand is described in detail. The design of the described model was developed with the possibility of conducting research in a pulsed mode of operation, it significantly reduces the time for conducting experimental research and allows for each experiment to control the initial signal level of the measuring bridge circuit. The developed measuring stand allows one to measure one sensor in a bridge circuit, and also provides the ability to quickly replace the investigated transducer, which is important when conducting routine experimental research. The regularities of the change in the output signal of the measuring circuit were experimentally established when using a gas sample of a known composition and heat of combustion at a gas flow rate of 0.5 to 1.5 ml and a carrier gas (air) of 1-5 l / h. The results of testing thermocatalytic converters are presented. in a natural gas environment. Experimental studies have confirmed the possibility of using a thermochemical analyzer to measure low volumetric specific heats of combustion of natural gases. An important advantage of the described analyzer is that it provides the ability to measure the heat of combustion of a gas in a pulsed mode of operation with a small (0.5 - 2 ml) sample of the analyzed gas, which eliminates the need to use special means for stabilizing the volumetric flow rate of a variable gas composition, significantly reduces the time required for research, and also significantly reduces the costs associated with the purchase of pure gases.

Electrical and optical characteristics of highly transparent MOVPE-grown AlGaN-based tunnel heterojunction LEDs emitting at 232 nm

We present the growth and electro-optical characteristics of highly transparent AlGaN-based tunnel heterojunction light-emitting diodes (LEDs) emitting at 232 nm entirely grown by metalorganic vapor phase epitaxy (MOVPE). A GaN:Si interlayer was embedded into a highly Mg- and Si-doped Al 0.87 Ga 0.13 N tunnel junction to enable polarization field enhanced tunneling. The LEDs exhibit an on-wafer integrated emission power of 77 μW at 5 mA, which correlates to an external quantum efficiency (EQE) of 0.29% with 45 μW emitted through the bottom sapphire substrate and 32 μW emitted through the transparent top surface. After depositing a highly reflective aluminum reflector, a maximum emission power of 1.73 mW was achieved at 100 mA under pulsed mode operation with a maximum EQE of 0.35% as collected through the bottom substrate.

ТУРБИДИМЕТРИЧЕСКИЙ ФОТОМЕТР ДЛЯ ИССЛЕДОВАНИЯ СЕДИМЕНТАЦИИ НАНОРАЗМЕРНЫХ ОБЪЕКТОВ

A turbidimetric photometer with a pulsed mode of operation of a light source is analyzed. The device makes it possible to conduct sedimentation studies of nanoscale object in terms of laboratory background illumination with a study duration of more than 500 hours. The functional diagram of the laboratory device sample is described and experimental surveys of some characteristics are presented.

An investigation on physical phenomena of water-jet assisted underwater wet laser welding technique under continuous and pulsed mode operation

This work presents the development and demonstration of a novel underwater wet laser welding technique, where unlike the conventional underwater wet laser welding, a water-jet parallel to the weld pool surface was introduced inside the water environment. The water flow was found to enhance the removal of water vapour formed at the laser-water-workpiece interface without creating hindrance to the molten weld bead, resulting in lower energy loss due to absorption and scattering, thus enhancing the laser energy coupling efficiency to the material. The process was studied for bead-on-plate welding on 4 mm stainless steel (SS) sheets using a 2 kW Yb-Fiber laser (wavelength 1.07 µm), with water column height of 5–15 mm, and a parallel water jet of speed 2–3 m/s, under continuous (CW) and pulsed mode (modulated power) laser operation. The major objective of the work was to study the effect of water flow and mode of laser operation on the formation and growth of vapour layer at the processing zone and investigate its effect on laser energy coupling efficiency. Further, their effect on weld bead geometry and microstructure was investigated. Welding operation with modulated laser power was found to produce higher weld depth compared to CW mode with same average laser power due to lower scattering loss and better energy coupling under pulsed mode operation. The micro-structural investigation has showed the formation of finer grains and oxide or carbide precipitation in case of underwater welding, indicating the enhanced cooling phenomena in this technique.

The effect of ultrasound duty cycle in biodiesel production from Ceiba pentandra

This study investigated the effect of the duty cycle for the transesterification of Ceiba pentandra oil. The important parameters of a duty cycle (pulse-mode operation) and energy usage in the transesterification reaction process were presented and showed that a maximum biodiesel yield of 99.24 % was achieved for 75% duty cycle with a pulse combination of 6 sec ON and 2 sec OFF. That was under the optimum conditions of 60% methanol to oil ratio, 1.00 wt% of KOH, reacted for 50 minutes. The obtained biodiesel was then analyzed using FTIR spectroscopy, and physiochemical properties of the Ceiba pentandra biodiesel then determined. It found that all the properties comply with the fuel specifications set by both ASTM D6751 and EN 14214 standards.

Design of a Low Cost Solar Simulator by using Light Emitting Diode (LED)

Solar simulators based on light emitting diodes (LEDs) have shown great promise as alternative light sources for indoor testing of PV cells with certain characteristics that make them superior to the traditional solar simulators. However, large-area uniform illumination, more suitable for larger cells and module measurements still remain a challenge today. In this paper, we discuss the development and fabrication of a scalable large-area LED-based solar simulator that consists of multiple tapered light guides. We demonstrate fine intermixing of many LED light rays and power delivery in the form of a synthesized air mass (AM) 1.5 spectrum over an area of 25 cm by 50 cm with better than 10 % spatial no uniformity. We present the spectral output, the spatial uniformity and the temporal stability of the simulator in both the constant current mode and the pulsed-mode LED operation, and compare our data with the International Electro technical Commission (IEC) standards on solar simulators for class rating. Although the light intensity with our current design and settings falls short of the standard solar AM 1.5intensity, this design and further improvements open up the possibility of achieving large-area, high power indoor solar simulation with various desired spectra.

About generation of short probing signals by echoscope piezotransducer

The paper deals with the problem of studying the pulsed operating mode of an electroacoustic piezoelectric transducer and determining the parameters of the correcting electrical circuit necessary to obtain probing signals of the shortest duration during medical diagnostic procedures. A piezoelectric transducer in the form of a plate emitting short acoustic signals in the tissues of the human body is considered. To reduce the duration of the probing signal as much as possible, an electrical inductive- resistive circuit is connected to the electrical side of the transducer. An algorithm for calculating the probe pulse at the output of the transducer is presented. On the basis of a theoretical and computational study, the values of the parameters of the emitting system have been determined, which make it possible to obtain the minimum duration of the probing signals. The form of the amplitude-frequency characteristic (AFC) of the transducer, corresponding to the minimum pulse duration, has been determined. It is noted that it differs (as in the case of a piezoelectric plate with a matching quarter-wave layer) from the shape of the frequency response for the case of the maximum bandwidth.

Process parameter dependencies of continuous and pulsed laser modes on surface polishing of additive manufactured aluminium AlSi10Mg parts

AbstractLaser powder bed fusion is a well‐established 3D printing technique for metal alloys, but exhibits a poor surface quality. Laser polishing provides the possibility of a fast contact‐free and fully‐automatable surface treatment. This paper deals with the experimental investigation of laser polishing of laser powder bed fusion parts made of aluminium AlSi10Mg. Laser polishing is done with a 4 kW solid state disc laser in combination with a multi‐axis system and a one dimensional scanner optic. The laser is operated at continuous and pulsed operation mode. The parameter study reveals a high dependency of the achievable roughness on the laser beam intensity, the track and pulse overlap, the energy density and the number of polishing passes and polishing directions. Pulsed laser polishing mode with up to four passes from different directions revealed the lowest surface roughness of 0.14 μm Ra. With respect to the initial average surface roughness of Ra = 8.03 μm a reduction of the surface roughness of greater than 98 % could be achieved. Polishing with continuous laser radiation at one polishing pass resulted in Ra = 0.23 μm at an area rate of 20 cm2/min. Laser polishing using four passes achieved a further improvement up to Ra = 0.14 μm.

Online Detuning Computation and Quench Detection for Superconducting Resonators

Superconducting cavities are responsible for beam acceleration in superconducting linear accelerators. Challenging cavity control specifications are necessary to reduce radio frequency (RF) costs and to maximize the availability of the accelerator. Cavity detuning and bandwidth are two critical parameters to monitor when operating particle accelerators. Cavity detuning is strongly related to the power required to generate the desired accelerating gradient. Cavity bandwidth is related to the cavity RF losses. A sudden increase in bandwidth can indicate the presence of a quench or multipacting event. Therefore, calculating these parameters in real time in the low-level RF (LLRF) system is highly desirable. A real-time estimation of the bandwidth allows for a faster response of the machine protection system in the case of quench events, whereas the estimation of cavity detuning can be used to drive piezoelectric tuner-based resonance control algorithms. In this article, a new field programmable gate array (FPGA)-based estimation component is presented. Such a component is designed to be used either in continuous wave (CW) or pulsed operation mode with loaded quality factors between $10^{6}$ and $10^{8}$ . Results of this component with free-electron LASer in Hamburg (FLASH), European X-ray free electron laser (EuXFEL), cryo module test bench (CMTB), and electron linac for beams with high brilliance and low emittance (ELBE) are presented.

Pulsed Ion Microscope to Probe Quantum Gases

The advent of the quantum gas microscope allowed for the in situ probing of ultracold gaseous matter on an unprecedented level of spatial resolution. The study of phenomena on ever smaller length scales as well as the probing of three-dimensional systems is, however, fundamentally limited by the wavelength of the imaging light, for all techniques based on linear optics. Here we report on a high-resolution ion microscope as a versatile and powerful experimental tool to investigate quantum gases. The instrument clearly resolves atoms in an optical lattice with a spacing of $532\,\text{nm}$ over a field of view of 50 sites and offers an extremely large depth of field on the order of at least $70\,\mu\text{m}$. With a simple model, we extract an upper limit for the achievable resolution of approximately $200\,\text{nm}$ from our data. We demonstrate a pulsed operation mode which in the future will enable 3D imaging and allow for the study of ionic impurities and Rydberg physics.

Feasibility Study of Microsecond Pulsed Microwave Ablation Using a Minimally Invasive Antenna

In this study we established the feasibility of producing localized ablation zones using microsecond pulsed microwave ablation (MWA) as an alternative to conventional continuous wave (CW) MWA. We verified that a thin floating-sleeve dipole ablation probe can withstand pulsed power delivery with peak powers as high as 25 kW, with pulse widths on the order of 1 us. We conducted MWA experiments in egg white using CW and pulsed modes of operation and found that ablation zones achieved via pulsed MWA are comparable in dimension to those created via CW MWA when the average power and procedure duration are equivalent. Finally, we performed pulsed MWA experiments in bovine liver and confirmed that pulsed MWA consistently produces large, localized ablation zones and temperatures that exceed 100{\deg}C. Establishing the feasibility of pulsed MWA opens the opportunity for developing a coupled MWA treatment and imaging system using pulsed MWA and microwave-induced thermoacoustic signals for real-time monitoring of MWA.

The role of radio frequency scattering in high-energy electron losses from minimum-B ECR ion source

The measurement of the axially lost electron energy distribution escaping from a minimum-B electron cyclotron resonance ion source in the range of 4–800 keV is reported. The experiments have revealed the existence of a hump at 150–300 keV energy, containing up to 15% of the lost electrons and carrying up to 30% of the measured energy losses. The mean energy of the hump is independent of the microwave power, frequency and neutral gas pressure but increases with the magnetic field strength, most importantly with the value of the minimum-B field. Experiments in pulsed operation mode have indicated the presence of the hump only when microwave power is applied, confirming that the origin of the hump is radio-frequency-induced momentum space diffusion. A possible mechanism of the hump formation is considered based on the quasi-linear model of plasma–wave interaction.