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[IEEE 2018 International IEEE Conference and workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Budapest, Hungary (2018.11.20-2018.11.21)] 2018 International IEEE Conference and Workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Plasma ignition and current control considerations for magnetron sputtering power supplies
摘要： Physical vapor deposition processes require different types of special power supplies for the ignition and sustaining of the plasma inside the sputtering chamber. The paper identifies some requirements for the design of a pulsed DC converter. Experiments have been carried out to identify the current-voltage characteristics of the vacuum chamber with the supply of different gases, and gas mixtures in the usable pressure domain. The vacuum chamber was supplied with voltage and current impulse trains with various parameters in order to acquire relevant data regarding the gas breakdown in pulsed power mode. A power electronic converter topology and control routine has been proposed, which is suitable for plasma ignition and discharge current control. The proof of concept has been demonstrated with the help of the magnetron sputtering chamber supplied by a test circuit.
关键词： current control,power electronic converter,plasma ignition,magnetron sputtering
更新于2025-09-23 15:23:52
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Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry
摘要： Heavy-duty diesel engines can convert to lean-burn natural-gas spark-ignition operation through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector to initiate and control combustion. However, the combustion phenomena in such converted engines usually consist of two distinct stages: a fast-burning stage inside the piston bowl followed by a slow-burning stage inside the squish area. This study used flame luminosity data and in-cylinder pressure measurements to analyze flame propagation inside a bowl-in-piston geometry. The experimental results showed a low coefficient of variation and standard deviation of peak cylinder pressure, moderate rate of pressure rise, and no knocking for the lean-burn (equivalence ratio 0.66), low-speed (900 r/min), and medium-load (6.6 bar IMEP) operating condition. Flame inception had a strong effect on the flame expansion velocity, which increased fast once the flame kernel established, but it reduced near the bowl edge and the entrance of the narrow squish region. However, the burn inside the bowl was very fast. In addition, the long duration of burn inside the squish indicated a much lower flame propagation speed for the outside-the-bowl combustion, which contributed to a long decreasing tail in the apparent heat release rate. Furthermore, cycles with fast flame inception and fast burn inside the bowl had a similar end of combustion with cycles with delayed flame inception and then a retarded burn inside the bowl, which indicated that the combustion inside the squish region determined the combustion duration. Overall, the results suggested that the spark event, the flame development inside the piston bowl, and the start of the second combustion stage affected the phasing and duration of the two combustion stages, which (subsequently) can affect engine efficiency and emissions of diesel engines converted to a lean-burn natural-gas spark-ignition operation.
关键词： spark ignition,Optical engine,combustion,bowl-in-piston,natural gas
更新于2025-09-23 15:22:29
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Ignition of Different Metamorphic Grade Coals by Free-Running Laser Pulses
摘要： We studied laser ignition (1064 nm, 120 μs) of coals of grades DG, G, Zh, and K. For all grades of coal, three successive ignition stages were found that were characterized by threshold radiation energy densities that have characteristic values for each grade of coal.
关键词： coke residue,ignition,coal,degree of coalification,volatiles,laser
更新于2025-09-23 15:21:01
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Laser Ignition and Flame Temperature for Low-Density Mixtures of Lignite Coal and Pentaerythritol Tetranitrate (Petn)
摘要： We have studied laser ignition (1064 nm, 120 μs) of mixtures of lignite coal (brown coal) particles of size ≤0.1 mm and pentaerythritol tetranitrate (PETN) additives. We established that as the amount of PTEN additives increases in the range 0–50 wt.%, the critical ignition energy density of the mixtures decreases monotonically from 2.9 to 2.0 J/cm2. We used spectral pyrometry to determine that the ?ame temperature for the mixture increases from 1800 K to 2100 K.
关键词： laser ignition,pentaerythritol tetranitrate (PETN),spectral pyrometry,lignite (brown coal),spectroscopy
更新于2025-09-23 15:21:01
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Bremsstrahlung x-ray generation for high optical depth radiography applications on the National Ignition Facility
摘要： We have tested a set of x-ray sources for use as probes of highly attenuating, laser-driven experiments on the National Ignition Facility (NIF). Unlike traditional x-ray sources that optimize for a characteristic atomic transition (often the n = 2 → n = 1 transition in ionized, He-like atoms), the design presented here maximizes the total photon ?ux by optimizing for intense, broadband Bremsstrahlung radiation. Three experiments were performed with identical targets, including a uranium x-ray source foil and a tungsten substrate with a narrow (25 μm wide) collimating slit to produce a quasi-1D x-ray source. Two experiments were performed using 12 beams from the NIF laser, each delivering approximately 46 kJ of laser energy but with different laser spatial pro?les. This pair yielded similar temporal x-ray emission pro?les, spatial resolution, and inferred hot electron temperature. A third experiment with only 6 beams delivering approximately 25 kJ produced a lower hot electron temperature and signi?cantly lower x-ray ?ux, as well as poorer spatial resolution. The data suggest that laser pointing jitter may have affected the location and intensity of the emitting plasma, producing an emission volume that was not well centered behind the collimating slit and lower intensity than designed. However, the 12-beam design permits x-ray radiography through highly attenuating samples, where lower energy line-emission x-ray sources would be nearly completely attenuated.
关键词： high optical depth radiography,laser-driven experiments,Bremsstrahlung radiation,x-ray sources,National Ignition Facility
更新于2025-09-23 15:21:01
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New Method for Studying the Ignition Characteristics of Condensed Systems by Laser Radiation
摘要： A method for determining the characteristics of laser ignition of the condensed systems is presented, which ensures uniform distribution of the heat flux density over the surface during ignition. The method consists in measuring the ignition delay time of a rotating cylindrical sample when the continuous laser heat flux is applied to its end surface. The theoretical estimation of the required angular rotation velocity of the sample is carried out, which ensures averaging with a given error of the radiation flux density on the surface of the sample, as well as the degree of surface cooling due to the convective heat transfer. The experimental results on the pyroxylin sample ignition at the radiant heating by a CO2 laser with and without rotation of the sample are presented.
关键词： pyroxylin,laser ignition,ignition delay time,condensed system,convective heat transfer,angular velocity of rotation
更新于2025-09-23 15:19:57
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Generation of kinetic Alfv??n wave and whistler waves by parametric decay of high power laser in lasera??plasma interaction
摘要： In this paper, we report theoretical modeling for parametric decay instability of the high-intensity elliptically polarized laser beam [pump wave, (x0)]. A wave–wave interaction model is investigated, based on the decay of the high-intensity elliptically polarized laser (x0) into an oblique whistler wave (OWW, ex1T) and a kinetic Alfv(cid:2)en wave (KAW, ex2T). The importance of oblique whistler waves (OWWs, ex1T) and kinetic Alfv(cid:2)en waves (KAWs, ex2T) similar to solar wind spectra [Chatterjee et al., Nat. Commun. 8, 15970 (2017)] has been pointed out, as a means to understand the turbulent magnetic ?eld ampli?cation, implicating electron and ion dynamics [Chatterjee et al., Nat. Commun. 8, 15970 (2017); Tzeferacos et al., Nat. Commun. 9, 591 (2018); Meinecke et al., Proc. Natl. Acad. Sci. 112, 8211 (2015); Mondal et al., Proc. Natl. Acad. Sci. 109, 8011 (2012); Romagnani et al., Phys. Rev. Lett. 122, 025001 (2019); Perri et al., Phys. Rev. Lett. 109, 191101 (2012); and Adak et al., Phys. Rev. Lett. 114, 115001 (2015)]. In the nonlinear stage, the decay instability is expected to attain the turbulent state, via a cascade process or ?lamentation/modulation instability (oscillating two stream instability). Therefore, in the present paper, we have considered the ?rst part of this research, namely, the beating mechanism ex2 ? x0 (cid:2) x1T, induced due to the nonlinear interaction of elliptically polarized laser velocity and oblique whistler wave density perturbation. The nonlinear saturation will be conferred in future investigations. Besides turbulence, the relevance of the present work to terahertz radiation generation [Singh et al., Europhys. Lett. 104, 35002 (2013); Dewan et al., Phys. Plasmas 25, 103105 (2018); Singh et al., Phys. Plasmas 18, 022304 (2011); M. Singh and R. P. Sharma, Contrib. Plasma Phys. 53(7), 540–548 (2013); Adak et al., Phys. Rev. Lett. 114, 115001 (2015); G. Brodin and L. Sten?o, Contrib. Plasma Phys. 54, 623 (2014); L. Sten?o, Phys. Scr. T50, 15–19 (1994); Li et al., Phys. Rev. E 84, 036405 (2011); L. Sten?o, Phys. Scr. T107, 262 (2004); and R. Boyd, Nonlinear Optics, 3rd ed. (Elsevier, 2008), Chap. 2] and fast ignition laser fusion [Kumar et al., arXiv:1804.02200 (2018)] by ion heating has been emphasized. The coef?cients for the nonlinear coupling pertaining to this parametric decay process and the growth rate of the decay instability are investigated.
关键词： high-intensity elliptically polarized laser beam,terahertz radiation,oblique whistler wave,kinetic Alfv(cid:2)en wave,parametric decay instability,fast ignition laser fusion
更新于2025-09-23 15:19:57
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Calculation of Direct Drive Targets for Megajoule Laser Facilities with Radiation in the Second and Third Harmonics of Nd Laser
摘要： The numerical results for cryogenic direct drive targets of megajoule facilities with radiation in the second and third harmonics of a Nd laser are presented. The calculations were performed with the 1D radiation hydrodynamics code ERA with the laser light absorption model that takes into account stimulated Brillouin scattering (SBS), generation of fast electrons in the processes of two-plasmon decay (TPD), and stimulated Raman scattering (SRS). The verification of the developed models was carried out on the basis of the comparison with experiments performed at the OMEGA and NIF facilities. The ignition margin (WQ) of nonuniform fusion targets with an allowance for energy losses due to radiation transfer and heat conduction from the hot spot was the objective of the target optimization. The calculations showed that SBS and target heating by fast electrons generated in TPD and SRS fatally reduce WQ of targets with a CH ablator for the megajoule laser with wavelength λ = 0.53 μm. The possibilities of decreasing these effects by replacing a CH ablator with a glass ablator and reducing the laser intensity upon increasing the target aspect ratio are considered. However, in both cases, WQ remains substantially below unity for the laser with wavelength λ = 0.53 μm. The ignition margin increases by a factor of ~2 upon transition from the second to the third harmonic of a Nd laser. A glass ablator almost eliminates fast electrons in calculation with the laser wavelength λ = 0.35 μm. In this case, if SBS is reduced by a factor of 3–4 via shifting the laser emission lines in the neighboring channels by Δλ ≈ 10–20 ?, the ignition margin WQ ~ 2 and a fusion energy yield of ~50 MJ are obtained in the 1D calculation for a laser energy of ~2 MJ and the third harmonic of a Nd laser.
关键词： megajoule laser facilities,two-plasmon decay,fast electron generation,direct drive targets,stimulated Raman scattering,thermonuclear ignition margin of target,stimulated Brillouin scattering
更新于2025-09-23 15:19:57
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Comparison of 1-Propyl-5H-tetrazole and 1-Azidopropyl-5H-tetrazole as Ligands for Laser Ignitable Energetic Materials
摘要： Laser ignitable explosives are potential candidates in future applications for replacing toxic and very sensitive primary explosives, which are used in current devices. In this study, the literature unknown ligand 1-azidopropyl-5H-tetrazole (APT, 1) was synthesized for the first time and applied in energetic coordination compounds (ECC). The complexes are based on different 3d transition metals (Mn2+, Fe2+, Cu2+, and Zn2+) as well as various oxidizing anions (NO3?, ClO4?, ClO3?) and were tested towards their capability as laser ignitable explosives. Furthermore, analogous complexes based on the literature known ligand 1-propyl-5H-tetrazole (PT, 2) were investigated, for comparing the influence of the additional azide group towards the performance of the ECC. Toxicity measurements using Vibrio fischeri and the decreased sensitivities prove their usability as safer laser ignitable explosive with lower toxicities compared to currently used explosives.
关键词： tetrazole ligands,laser ignition,nitrogen heterocycles,structure elucidation,energetic coordination compounds
更新于2025-09-23 15:19:57
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Debris and shrapnel assessments for National Ignition Facility targets and diagnostics
摘要： High-energy laser experiments at the National Ignition Facility (NIF) can create debris and shrapnel capable of damaging laser optics and diagnostic instruments. The size, composition and location of target components and sacrificial shielding (e.g., disposable debris shields, or diagnostic filters) and the protection they provide is constrained by many factors, including: chamber and diagnostic geometries, experimental goals and material considerations. An assessment of the generation, nature and velocity of shrapnel and debris and their potential threats is necessary prior to fielding targets or diagnostics. These assessments may influence target and shielding design, filter configurations and diagnostic selection. This paper will outline the approach used to manage the debris and shrapnel risk associated with NIF targets and diagnostics and present some aspects of two such cases: the Material Strength Rayleigh-Taylor campaign and the Mono Angle Crystal Spectrometer (MACS).
关键词： diagnostics,shrapnel,debris,National Ignition Facility,targets
更新于2025-09-23 15:19:57