Reliability of DC-link capacitor in pulsed power supply for accelerator magnet

Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage,store energy,and decrease power variation.In this study,DC-link capacitors in pulsed power supplies were investigated.By deriving an analytical method for the capacitor current on the H-bridge topology side,the root-mean-square value of the capacitor current was calculated,which helps in selecting the DC-link capacitors.The proposed method solves this problem quickly and with high accuracy.The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement,and the capacitor’s hotspot temperature and temperature rise are calculated using the FFT transform.The test results showed that the error between the calculated and measured temperature increases was within 1.5℃.Finally,the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis.The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.

Synthesis and properties of Cr-Al-Si-N films deposited by hybrid coating system with high power impulse magnetron sputtering (HIPIMS) and DC pulse sputtering

The CrN and Cr-Al-Si-N films were deposited on Si wafer and SUS 304 substrates by a hybrid coating system with high power impulse magnetron sputtering (HIPIMS) and a DC pulse sputtering using Cr and AlSi targets under N2/Ar atmosphere.By varying the sputtering current of the AlSi target in the range of 0-2.5 A,both the Al and Si contents in the films increased gradually from 0 to 19.1% and 11.1% (mole fraction),respectively.The influences of the AlSi cathode DC pulse current on the microstructure,phase constituents,mechanical properties,and oxidation behaviors of the Cr-Al-Si-N films were investigated systematically.The results indicate that the as-deposited Cr-Al-Si-N films possess the typical nanocomposite structure,namely the face centered cubic (Cr,Al)N nano-crystallites are embedded in the amorphous Si3N4 matrix.With increasing the Al and Si contents,the hardness of the film first increases from 20.8 GPa for the CrN film to the peak value of 29.4 GPa for the Cr0.23Al0.14Si0.07 N film,and then decreases gradually.In the meanwhile,the Cr0.23Al0.14Si0.07N film also possesses excellent high-temperature oxidation resistance that is much better than that of the CrN film at 900 or 1000 °C.

Design and Simulation for the Pulse High-Voltage DC Power Supply (HVPS) of 1.2 MW/2.45 GHz HT-7U Lower Hybrid Current Drive System

The superconducting tokamak HT-7U [1] has been designed by the Institute of Plasma Physics since 1998 and will be set up before 2003. The 1.2 MW /2.45 GHz HT-7U LHCD (Lower hybrid current drive) system which being the most efficient non-induction device can heat the plasma and drive the plasma current has been efficiently in operation 'owl and a particular design of the 2.8 MW/-35 kV high-voltage DC power supply has been already completed and will apply to the klystron of LHCD on HT-7 and the future HT-7U, and the project of the power supply has been examined and approved professionally by an authorized group of high-level specialist in the institute of Plasma Physics. The detailed design of the power supply and the simulation results are referred in the paper.

Deposition of Ti-Si-N coatings in deep blind-hole with pulsed dc power

Multiphase nanocomposite Ti-Si-N coatings deposited by pulsed dc plasma enhanced chemical vapor deposition technique on the surface of HSS substrate, which were bolted with deep blind-hole to simulate the complexshaped surface of various tools, were investigated. The micrographs show that the surface morphologies of the coatings become coarser with an increasing depth of the bottom holes. And the silicon content increases in Ti-Si-N coatings, which are composed of nanocrystalline TiN, nano-sized amorphous Si3N4, and occasionally amorphous or nanocrysralline TiSi2. The thickness of the coatings decreases with the increasing depth of holes, which may result from the changes of the composition in the coatings. The microhardness of the coatings increases firstly with the increasing depth of holes, reaches a maximum value of about HV5 700 at 10mm depth, and then decreases at larger depth.

As-cast structure and tensile properties of AZ80 magnesium alloy DC cast with low-voltage pulsed magnetic field

The effects of a low-voltage pulsed magnetic field on the solidified structure and mechanical properties of DC casting AZ80 magnesium alloy were investigated.The results showed that the solidified structure of the DC casting AZ80 magnesium alloy was refined obviously by the low-voltage pulsed magnetic field and significant grain refinement in the DC casting ingot of AZ80 magnesium alloy was achieved.Meanwhile,the morphology of the dentritic in the DC casting ingot was transformed from coarse dentritic to fine rosette with the application of low-voltage pulsed magnetic field.The ability of deformation of the ingot was enhanced and especially the plasticity of the ingot center after upsetting was improved greatly by more than 80%after deformation.

CLOSE-LOOP DESIGN OF PULSE POWER SUPPLY FOR ELECTRICAL DISCHARGE MACHINING

The dynamic performance and the stability are essential for a system. A new circuit topology used for electrical discharge machining (EDM) power and made up of complex-pulse (voltage-pulse and current-pulse) is presented. The large-signal model of it is also derived. Based on the comprehensive analysis of the system model, the compensator is designed to make the system match better and to improve its dynamic performance and the stability under perturbations. Finally, the design methods and the analysis are verified by simulation and experimental results.

Influences of working pressure on properties for TiO_2 films deposited by DC pulse magnetron sputtering

TiO2 films were deposited at room temperature by DC pulse magnetron sputtering system.The crystalline structures,morphological features and photocatalytic activity of TiO2 films were systematically investigated by X-ray diffraction（XRD）,atomic force microscopy（AFM） and ultraviolet spectrophotometer,respectively.The results indicated that working pressure was the key deposition parameter in？uencing the TiO2 film phase composition at room temperature,which directly affected its photocatalytic activity.With increasing working pressure,the target self-bias decreases monotonously.Therefore,low temperature TiO2 phase（anatase） could be deposited with high working pressure.The anatase TiO2 films deposited with 1.4 Pa working pressure displayed the highest photocatalytic activity by the decomposition of Methyl Orange solution,which the degradation rate reached the maximum（35%） after irradiation by ultraviolet light for 1 h.

Design and manufacture of a 100 kA coaxial pulsed power cable for plasma generator and PPS in ETC guns

Based on our previous pulsed current and internal overvoltage test data and the experience of common commercial high power cables,a 100 kA coaxial pulsed power cable is designed and manufactured to adapt the coaxial electric energy breech transmission between the plasma generator and the pulsed power supply(PPS) in electrothermal-chemical(ETC) guns.The index parameters are analyzed and determined.Semi-conductor layers and a shield stiffener are introduced to prevent the deformation and burst of the pulsed power cable structurally.The semi-conductor layer can eliminate the air gap and balance the electric field in the cable.The shield stiffener can multiply the mechanical strength to restrain the strong electrodynamic force produced by the core dislocation of the outer conductor.The multi-coupling of electromagnetic field,stress field and thermal field analysis are established to assist in aided design of electrical strength,mechanical strength and temperature rise characteristics.Both a DC voltage withstand test and pulsed discharge tests are introduced to verify and inspect the performance and dynamic response of the pulsed power cable.The 25 kV/5 min DC voltage withstand test result shows that the sample leakage current is nearly 3 μA and no abnormal phenomena of the pulsed power cable sample occurred.The pulsed discharge tests show that the sample can sustain the 100 kA peak current.Furthermore,this 100 kA coaxial pulsed power cable can satisfy the ETC test requirements.

Conceptual design of a 15-TW pulsed-power accelerator for high-energy-densityephysics experiments

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

Dielectric barrier discharge plasma-assisted catalytic ammonia synthesis:synergistic effect of Ni-MOF-74 catalyst and nanosecond pulsed plasma

Ammonia is one of the most important chemical raw materials in both manufacture and life of human.Traditionally Haber-Bosch method for ammonia synthesis involves high temperature and high pressure conditions,leading to significant energy consumption and environmental pollution.Non-thermal plasma(NTP) is a promising alternative approach to ammonia synthesis at low temperature and atmospheric pressure.In this study,the synergistic effect of nanosecond pulsed dielectric barrier discharge(np-DBD) and Ni-MOF-74 catalyst was investigated in ammonia synthesis by utilizing nitrogen and hydrogen as feedstock.The results demonstrated that the plasma catalytic-synthesis process parameters play a crucial role in the synthesis process of ammonia.The highest ammonia synthesis rate of 5145.16 μmol·g^(-1)·h^(-1)with an energy efficiency of 1.27 g·kWh^(-1)was observed in the presence of the Ni-MOF-74 catalyst,which was3.7 times higher than that without Ni-MOF-74 catalyst.The synergistic effect of Ni-MOF-74catalyst and nanosecond pulsed plasma was explored by in-situ plasma discharge diagnostics.

A Novel Nanosecond Pulsed Power Unit for the Formation of ·OH in Water

A novel nanosecond pulsed power unit was developed for plasma treatment of wastewater, based on the theory of magnetic pulse compression and semiconductor opening switch （SOS）. The peak value, rise time and pulse duration of the output voltage were observed to be -51 kV, 60 ns and 120 ns, respectively. The concentrations of .OH generated by the novel nanosecond pulsed plasma power were determined using the method of high-performance liquid chromatography （HPLC）. The results showed that the concentrations of .OH increased with the increase in peak voltage, and the generation rates of .OH were 4.1 ×10^-10 mol/s, 5.7× 10^-10 mol/s, and 7.7× 10^-10 mol/s at 30 kV, 35 kV, and 40 kV, respectively. The efficiency of OH generation was found to be independent of the input parameters for applied power, with an average value of 3.23×10^-12 mol/J obtained.

High-power terahertz pulse sensor with overmoded structure

Based on the hot electron effect in a semiconductor, an overmoded resistive sensor for 0.3-0.4 THz band is investi-gated. The distribution of electromagnetic field components, voltage standing wave ratio （VSWR）, and the average electric field in the silicon block are obtained by using the three-dimensional finite-difference time-domain （FDTD） method. By adjusting several factors （such as the length, width, height and specific resistance of the silicon block） a novel sensor with optimal structural parameters that can be used as a power measurement device for high power terahertz pulse directly is proposed. The results show that the sensor has a relative sensitivity of about 0.24 kW 1, with a fluctuation of relative sensitivity of no more than ±22%, and the maximum of VSWR is 2.74 for 0.3-0.4 THz band.

A reusable planar triggered spark-gap switch batched-fabricated with PCB technology for medium- and low-voltage pulse power systems

Triggered spark-gap switch is a popular discharge switch for pulse power systems.Previous studies have focused on planarizing this switch using thin film techniques in order to meet the requirements of compact size in the systems.Such switches are one-shot due to electrodes being too thin to sufficiently resist spark-erosion.Additionally,these switches did not employ any structures in securing internal gas composition,resulting in inconsistent performance under harsh atmospheres.In this work,a novel planar triggered spark-gap switch(PTS)with a hermetically sealed cavity was batched-prepared with printed circuit board(PCB)technology,to achieve reusability with low cost.The proposed PTS was inspected by micro-computed tomography to ensure PCB techniques meet the requirements of machining precision.The results from electrical experiments demonstrated that PCB PTS were consistent and reusable with lifespan over 20 times.The calculated switch voltage and circuit current were consistent with those derived from real-world measurements.Finally,PCB PTS was used to introduce hexanitrostilbene(HNS)pellets in a pulse power system to verify its performance.

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.

Development of high frequency pulse power source using two powersfor TIG welding

A high frequency pulse power source for TIG welding is developed. The structure of two powers is adopted. The by pass circuit effectively eliminates the effect of the cable equivalent inductance. The maximum frequency of the output pulse current reaches to 16 kHz . The base current and the peak current can be regulated separately.

DC microgrid stability control with constant power load:a review

The DC microgrid has the advantages of high energy conversion efficiency,high energy transmission density,no reactive power flow,and grid-connected synchronization.It is an essential component of the future intelligent power distribution system.Constant power load(CPL)will degrade the stability of the DC microgrid and cause system voltage oscillation due to its negative resistance characteristics.As a result,the stability of DC microgrids with CPL has become a problem.At present,the research on the stability of DC microgrid is mainly focused on unipolar DC microgrid,while the research on bipolar DC microgrid lacks systematic discussion.The stability of DC microgrid using CPL was studied first,and then the current stability criteria of DC microgrid were summarized,and its research trend was analyzed.On this basis,aiming at the stability problem caused by CPL,the existing control methods were summarized from the perspective of source converter output impedance and load converter input impedance,and the current control methods were outlined as active and passive control methods.Lastly,the research path of bipolar DC microgrid stability with CPL was prospected.

Systematic evaluation of a holmium:yttrium-aluminum-garnet laser lithotripsy device with variable pulse peak power and pulse duration

Objective:The Holmium:yttrium-aluminum-garnet(Ho:YAG)laser is the standard lithotrite for ureteroscopy.This paper is to evaluate a Ho:YAG laser with a novel effect function in vitro,which allows a real-time variation of pulse duration and pulse peak power.Methods:Two types of phantom calculi with four degrees of hardness were made for fragmentation and retropulsion experiments.Fragmentation was analysed at 5(0.5 J/10 Hz),10(1 J/10 Hz),and 20(2 J/10 Hz)W in non-floating phantom calculi,retropulsion in an ureteral model at 10(1 J/10 Hz)and 20(2 J/10 Hz)W using floating phantom calculi.The effect function was set to 25%,50%,75%,and 100%of the maximum possible effect function at each power setting.Primary outcomes:fragmentation(mm^3),the distance of retropulsion(cm);
5 measurements for each trial.Results:An increase of the effect feature(25%vs.100%),i.e.,an increase of pulse peak power and decrease of pulse duration,improved Ho:YAG laser fragmentation.This effect was remarkable in soft stone composition,while there was a trend for improved fragmentation with an increase of the effect feature in hard stone composition.Retropulsion increased with increasing effect function,independently of stone composition.The major limitations of the study are the use of artificial stones and the in vitro setup.Conclusion:Changes in pulse duration and pulse peak power may lead to improved stone fragmentation,most prominently in soft stones,but also lead to increased retropulsion.This new effect function may enhance Ho:YAG laser fragmentation when maximum power output is limited or retropulsion is excluded.

Effects of O_(2) addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges(DBDs)have been widely used in ozone synthesis,materials surface treatment,and plasma medicine for their advantages of uniform discharge and high plasmachemical reactivity.To improve the reactivity of DBDs,in this work,the O_(2) is added into Ar nanosecond(ns)pulsed and AC DBDs.The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O_(2) contents are investigated with optical and electrical diagnosis methods.The DBD uniformity is quantitatively analyzed by gray value standard deviation method.The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_(e).The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_(e) with the ratio of two emission lines.It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time.With the addition of O_(2),the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O_(2)^(-),which promotes the filamentary formation.While,in AC DBD,the added O_(2) can reduce the intensity of filaments,which enhances the discharge uniformity.The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD.The ratio of Ar emission intensities indicates that the T_(e) drops quickly with the addition of O_(2) both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_(e) and n_(e) than AC DBD.The results are helpful for the realization of the reactive and uniform low temperature plasma sources.

Laser shaping and optical power limiting of pulsed Laguerre–Gaussian laser beams of high-order radial modes in fullerene C60

We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.

TiN coating on wall of holes and stitches by pulsed DC plasma enhanced CVD

TiN coating samples with narrow stitch or deep hole of different sizes and real dies with complex shape were processed by a larger scale pulsed plasma enhanced CVD(PECVD) reactor. Scanning electron microscopy, optical microscopy, Vickers hardness and interfacial adhesion tests were conducted to find the relation between the microstructure and properties of TiN coating on a flat and an inner surface. The results indicate that the inner wall of holes ( d >2 mm) and inner surface of narrow stitches ( d >3 mm) can be coated with the aid of pulsed DC plasma in an industrial scale reactor. The quality of coatings on different surfaces is almost the same. The coating was applied to aluminum extrusion mould, and the mould life was increased at least by one time.