Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496125
S. Averkin, N. Gatsonis
New unstructured Particle-In-Cell method on tetrahedral grids is presented. In this method the electric potential on cell vertices is evaluated using Gauss’ law applied to the indirect dual cell formed by connecting centroids of tetrahedra with corresponding face centroids and edge centers. The control-volume discretization follows a finite volume Multi Point Flux Approximation method. The implementation of boundary conditions such as Dirichlet, Neumann and external circuit boundary conditions is presented. The resulting matrix equation for the nodal potential is solved with a restarted GMRES algorithm with ILU(0) preconditioner. The GMRES algorithm is OpenMP parallelized using a combination of node coloring and level scheduling approaches for better computational efficiency. The electric field on vertices is evaluated using the gradient theorem applied to the indirect dual cell. The resulting expression for electric field is consistent with the earlier algorithm that was derived using Delaunay-Voronoi grids 1. Boundary conditions and the algorithms for injection, particle loading, particle motion, and particle tracking are implemented for unstructured tetrahedral grids in the code developed at WPI.
{"title":"Particle-In-Cell Algorithm on Unstructured Tetrahedral Meshes*","authors":"S. Averkin, N. Gatsonis","doi":"10.1109/PLASMA.2017.8496125","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496125","url":null,"abstract":"New unstructured Particle-In-Cell method on tetrahedral grids is presented. In this method the electric potential on cell vertices is evaluated using Gauss’ law applied to the indirect dual cell formed by connecting centroids of tetrahedra with corresponding face centroids and edge centers. The control-volume discretization follows a finite volume Multi Point Flux Approximation method. The implementation of boundary conditions such as Dirichlet, Neumann and external circuit boundary conditions is presented. The resulting matrix equation for the nodal potential is solved with a restarted GMRES algorithm with ILU(0) preconditioner. The GMRES algorithm is OpenMP parallelized using a combination of node coloring and level scheduling approaches for better computational efficiency. The electric field on vertices is evaluated using the gradient theorem applied to the indirect dual cell. The resulting expression for electric field is consistent with the earlier algorithm that was derived using Delaunay-Voronoi grids 1. Boundary conditions and the algorithms for injection, particle loading, particle motion, and particle tracking are implemented for unstructured tetrahedral grids in the code developed at WPI.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"32 1 Pt 1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125708029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496042
S. Fairchild, P. Murray, D. Gortat, T. Back, N. Lockwood, D. Ingram
Dept of Physics and Astronomy, Ohio University Athens, OH USA One of the problems associated with long term operation of high pulsed power, vacuum electronic devices is pulse shortening, which is caused by hydrogen outgassing and by secondary electron emission from the anode. We recently showed the feasibility of Laser Surface Melting (LSM) of stainless steel (SS) anodes to reduce hydrogen outgassing from SS samples subjected to 50 keV electron bombardment. The results showed a reduction in outgassing from LSM-treated SS. This was attributed to a reduction in the number of grain boundaries, which serve as trapping sites for hydrogen. We have since measured the hydrogen depth profiles of treated and untreated samples by Elastic Recoil Detection in order to more completely understand the mechanism for reduced outgassing. The results indicate a significant reduction in residual hydrogen within the melt depth $( sim 15 mu mathrm {m})$ of LSM-treated samples due to the small solubility of hydrogen in molten steel. We describe here a more complete model of the mechanism for reduced hydrogen outgassing that includes both a reduction in the number of trapping sites as well a reduction in the residual hydrogen concentration within the melt depth of LSMtreated samples. We conclude by describing the use of vacuum arc re-melted steel as an anode material and describe the effect of laser patterning of such samples to reduce secondary electron yield.
高脉冲功率真空电子设备长期运行的问题之一是脉冲缩短，这是由氢气放气和阳极二次电子发射引起的。我们最近证明了激光表面熔化(LSM)不锈钢(SS)阳极的可行性，以减少不锈钢样品在50 keV电子轰击下的氢气排放。结果表明，经过lsm处理的SS放气量减少，这是由于作为氢捕获点的晶界数量减少。为了更全面地了解减少放气的机制，我们已经用弹性反冲探测法测量了处理过和未处理过的样品的氢深度分布。结果表明，由于氢在钢液中的溶解度小，lsm处理样品在熔体深度$( sim 15 mu mathrm {m})$内的残余氢显著减少。我们在这里描述了一个更完整的氢脱气机制模型，其中包括捕获点数量的减少以及lsm处理样品熔体深度内残余氢浓度的减少。最后，我们描述了使用真空电弧重熔钢作为阳极材料，并描述了这种样品的激光图像化对降低二次电子产率的影响。
{"title":"Hydrogen Outgassing and Secondary Electron Reduction From Laser-Processed Stainless Steel Anodes*","authors":"S. Fairchild, P. Murray, D. Gortat, T. Back, N. Lockwood, D. Ingram","doi":"10.1109/PLASMA.2017.8496042","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496042","url":null,"abstract":"Dept of Physics and Astronomy, Ohio University Athens, OH USA One of the problems associated with long term operation of high pulsed power, vacuum electronic devices is pulse shortening, which is caused by hydrogen outgassing and by secondary electron emission from the anode. We recently showed the feasibility of Laser Surface Melting (LSM) of stainless steel (SS) anodes to reduce hydrogen outgassing from SS samples subjected to 50 keV electron bombardment. The results showed a reduction in outgassing from LSM-treated SS. This was attributed to a reduction in the number of grain boundaries, which serve as trapping sites for hydrogen. We have since measured the hydrogen depth profiles of treated and untreated samples by Elastic Recoil Detection in order to more completely understand the mechanism for reduced outgassing. The results indicate a significant reduction in residual hydrogen within the melt depth $( sim 15 mu mathrm {m})$ of LSM-treated samples due to the small solubility of hydrogen in molten steel. We describe here a more complete model of the mechanism for reduced hydrogen outgassing that includes both a reduction in the number of trapping sites as well a reduction in the residual hydrogen concentration within the melt depth of LSMtreated samples. We conclude by describing the use of vacuum arc re-melted steel as an anode material and describe the effect of laser patterning of such samples to reduce secondary electron yield.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"76 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121847734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496351
J. Narkis, J. Valenzuela, F. Conti, M. Ross, F. Beg, H. Rahman, E. Ruskov, F. Wessel
The Staged Z-pinch is a magneto-inertial fusion concept in which compression of the target plasma, deuterium (D) or deuterium-tritium (DT) is driven by two mechanisms: inertial compression of the liner plasma, typically a high-Z gas like Kr, driven by the externally-applied JxB force, and shock compression, driven by transport of this force to the target/liner interface.
{"title":"Application of a KDVB Equation to Shock Formation in the Staged Z-Pinch*","authors":"J. Narkis, J. Valenzuela, F. Conti, M. Ross, F. Beg, H. Rahman, E. Ruskov, F. Wessel","doi":"10.1109/PLASMA.2017.8496351","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496351","url":null,"abstract":"The Staged Z-pinch is a magneto-inertial fusion concept in which compression of the target plasma, deuterium (D) or deuterium-tritium (DT) is driven by two mechanisms: inertial compression of the liner plasma, typically a high-Z gas like Kr, driven by the externally-applied JxB force, and shock compression, driven by transport of this force to the target/liner interface.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121747174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496083
S. Miller, A. Steiner, R. Mcbride, D. Yager-Elorriaga, N. Jordan, Y. Lau, R. Gilgenbach
Magnetized liner inertial fusion (MagLIF) [1, 2] is a pulsed-power driven approach to inertial confinement fusion. Electrothermal instabilities (ETI) are thought to seed Magneto-Rayleigh Taylor (MRT), sausage mode, and kink mode instabilities in the imploding liner of MagLIF [3]. Understanding ETI may provide a way to improve fusion performance in MagLIF through instability mitigation. A single-capacitor pulsed power device was built with a low peak current of 4 kA and a long risetime of 600 ns to lengthen the transition time from the solid phase to the vapor phase. We have studied ETI growth rates on this facility. These growth rates have good agreement with ETI theory [4]. Preliminary results have shown the value of this facility and a need to investigate ETI further. We report on recent modifications and improvements to the facility and plans for future ETI studies.
{"title":"Electrothermal Instability Studies on a Small Pulsed Power Device","authors":"S. Miller, A. Steiner, R. Mcbride, D. Yager-Elorriaga, N. Jordan, Y. Lau, R. Gilgenbach","doi":"10.1109/PLASMA.2017.8496083","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496083","url":null,"abstract":"Magnetized liner inertial fusion (MagLIF) [1, 2] is a pulsed-power driven approach to inertial confinement fusion. Electrothermal instabilities (ETI) are thought to seed Magneto-Rayleigh Taylor (MRT), sausage mode, and kink mode instabilities in the imploding liner of MagLIF [3]. Understanding ETI may provide a way to improve fusion performance in MagLIF through instability mitigation. A single-capacitor pulsed power device was built with a low peak current of 4 kA and a long risetime of 600 ns to lengthen the transition time from the solid phase to the vapor phase. We have studied ETI growth rates on this facility. These growth rates have good agreement with ETI theory [4]. Preliminary results have shown the value of this facility and a need to investigate ETI further. We report on recent modifications and improvements to the facility and plans for future ETI studies.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"107 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131427237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496347
B. Esser, J. Dickens, J. Mankowski, A. Neuber
An electrically small antenna (ESA) is evaluated for its potential future use in a Transportable Ionospheric Heating (TIH) array. Consisting of a Small Loop Antenna (SLA) which inductively couples to a Capacitively Loaded Loop (CLL) the antenna provides a high-Q natural match to a $50 Omega $ source. The capacitance of the CLL may be adjusted to tune the antenna in the range of ionospheric heating of approximately 3 – 10 MHz. Several methods are evaluated to achieve this tuning including a horizontal sliding plate design, and a hinged petal design.
{"title":"Next Generation Ionospheric Heater Array","authors":"B. Esser, J. Dickens, J. Mankowski, A. Neuber","doi":"10.1109/PLASMA.2017.8496347","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496347","url":null,"abstract":"An electrically small antenna (ESA) is evaluated for its potential future use in a Transportable Ionospheric Heating (TIH) array. Consisting of a Small Loop Antenna (SLA) which inductively couples to a Capacitively Loaded Loop (CLL) the antenna provides a high-Q natural match to a $50 Omega $ source. The capacitance of the CLL may be adjusted to tune the antenna in the range of ionospheric heating of approximately 3 – 10 MHz. Several methods are evaluated to achieve this tuning including a horizontal sliding plate design, and a hinged petal design.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"89 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132475567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496283
S. Sundar, Hanno Kaehlert, Ingmar Schnell, Jan‐Philip Joost, P. Ludwig, M. Bonitz
Dynamical screening and wake effects in complex plasmas have been the subject of many investigations, including theoretical [1,2] as well as experimental work [3]. It was shown using Linear Response (LR) theory that the characteristic features of the wake potential for non-Maxwellian plasma are qualitatively different from Maxwellian streaming ions. Here, the electrostatic potential of a dust grain in streaming ions in the presence of collisions is computed using three-dimensional particle-in-cell (PIC) code ‘COPTIC’ [4]. We compare our numerical results (PIC) with the wake potential obtained from the LR formalism as well as hydrodynamic simulations for Maxwellian case in linear as well as nonlinear regime. Wakes exhibit interesting physical characteristics for magnetized streaming ions [5]. We discuss the physics of distribution function, flux etc. around the grain and present a parametric study of wake peak position, peak potential vs. collision frequency for the non-Maxwellian streaming plasmas in the absence and presence of magnetic field.
{"title":"Collisional Plasma Wakes of Small Particles","authors":"S. Sundar, Hanno Kaehlert, Ingmar Schnell, Jan‐Philip Joost, P. Ludwig, M. Bonitz","doi":"10.1109/PLASMA.2017.8496283","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496283","url":null,"abstract":"Dynamical screening and wake effects in complex plasmas have been the subject of many investigations, including theoretical [1,2] as well as experimental work [3]. It was shown using Linear Response (LR) theory that the characteristic features of the wake potential for non-Maxwellian plasma are qualitatively different from Maxwellian streaming ions. Here, the electrostatic potential of a dust grain in streaming ions in the presence of collisions is computed using three-dimensional particle-in-cell (PIC) code ‘COPTIC’ [4]. We compare our numerical results (PIC) with the wake potential obtained from the LR formalism as well as hydrodynamic simulations for Maxwellian case in linear as well as nonlinear regime. Wakes exhibit interesting physical characteristics for magnetized streaming ions [5]. We discuss the physics of distribution function, flux etc. around the grain and present a parametric study of wake peak position, peak potential vs. collision frequency for the non-Maxwellian streaming plasmas in the absence and presence of magnetic field.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133832451","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496135
B. Hoff, P. Lepell, T. Montoya, D. Simon
Experimental results from a high power (hundreds of kilovolts, multiple kiloamperes) nonlinear transmission line (NLTL) modulated electron beam driver will be presented and discussed. The experimental configuration utilized for these experiments is based on simulation work described previously by the authors [1]. Simulation results predict the ability to utilize the output of a high power NLTL to modulate GW-class electron beams up to 30% of the average beam current at the output frequency of the NLTL.
{"title":"Experimental Study of A High Power NLTL-Modulated Electron Beam Driver","authors":"B. Hoff, P. Lepell, T. Montoya, D. Simon","doi":"10.1109/PLASMA.2017.8496135","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496135","url":null,"abstract":"Experimental results from a high power (hundreds of kilovolts, multiple kiloamperes) nonlinear transmission line (NLTL) modulated electron beam driver will be presented and discussed. The experimental configuration utilized for these experiments is based on simulation work described previously by the authors [1]. Simulation results predict the ability to utilize the output of a high power NLTL to modulate GW-class electron beams up to 30% of the average beam current at the output frequency of the NLTL.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134511776","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496258
Xudong Li, Yujia Wang, Jian Wu, Xingwen Li, A. Qiu
An experiment platform is designed and set up recently to study the influences of the experimental parameters on the dynamics of the electrical explosion of wires(EEW) and the characteristics of nanoparticles 1. The platform consists of two 50 kA, 5 μs pulsed current generators, a gas recycling system and a nanoparticle collection system. Each of the generators can be work at the extremal-triggered single-shot mode or the repetitive shot mode with a shot frequency of 1000 times per hour.
{"title":"Structural Characteristics of Aluminum Nanoparticles Produced By Electrical Explosion in Argon","authors":"Xudong Li, Yujia Wang, Jian Wu, Xingwen Li, A. Qiu","doi":"10.1109/PLASMA.2017.8496258","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496258","url":null,"abstract":"An experiment platform is designed and set up recently to study the influences of the experimental parameters on the dynamics of the electrical explosion of wires(EEW) and the characteristics of nanoparticles 1. The platform consists of two 50 kA, 5 μs pulsed current generators, a gas recycling system and a nanoparticle collection system. Each of the generators can be work at the extremal-triggered single-shot mode or the repetitive shot mode with a shot frequency of 1000 times per hour.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132974115","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496137
I. Chernyavskiy, A. Vlasov, B. Levush, T. Antonsen
As a rule, codes that operate in the time domain, such as Particle in Cell (PIC) codes, are a more natural choice as a tool to explore the stability of beam-driven devices. However, the extensive computer resources required for PIC simulation as compared with those needed for hybrid codes such as TESLA1, motivate the development presented here. We report recent advances in the development of the TESLAfamily of 2D large-signal codes (such as TESLA-FW2 or TESLA-Z3, for example), with a focus on algorithms to model self-oscillations in TWT amplifiers. The TESLA codes operate essentially in the frequency domain, making it a challenge to find unstable modes without prior knowledge of their frequency.
{"title":"Modeling Oscillations in TWTs by Using the Tesla-Family of 2D Large-Signal Codes","authors":"I. Chernyavskiy, A. Vlasov, B. Levush, T. Antonsen","doi":"10.1109/PLASMA.2017.8496137","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496137","url":null,"abstract":"As a rule, codes that operate in the time domain, such as Particle in Cell (PIC) codes, are a more natural choice as a tool to explore the stability of beam-driven devices. However, the extensive computer resources required for PIC simulation as compared with those needed for hybrid codes such as TESLA1, motivate the development presented here. We report recent advances in the development of the TESLAfamily of 2D large-signal codes (such as TESLA-FW2 or TESLA-Z3, for example), with a focus on algorithms to model self-oscillations in TWT amplifiers. The TESLA codes operate essentially in the frequency domain, making it a challenge to find unstable modes without prior knowledge of their frequency.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127574165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-01DOI: 10.1109/PLASMA.2017.8496005
C. Dumitrache, C. Limbach, A. Yalin
This study describes the ignition and flame dynamics generated using a dual-pulse laser pre-ionization technique. The new technique involves the use of two nanosecond pulses for inducing gas heating and initiating combustion. Initially, a UV pulse $(lambda =266$ nm) from the fourth harmonic of a Nd:YAG laser is used to pre-ionize a small volume of gas inside of the combustion chamber forming a weakly ionized plasma channel $(mathrm {n}_{e} sim 3 mathrm {x}10 ^{16}$ cm-3). The cold plasma produced by the UV pulse (T~ 600 -1000K) is subsequently heated by an NIR $(lambda =1064$ nm) pulse that follows ~ 10ns after the preionization pulse. The NIR beam adds energy into the gas through inverse bremsstrahlung absorption of radiation and increases the temperature of the plasma to T~ 2000-3000 K. Ignition of propane-air mixtures at various equivalence ratios was successfully achieved using the technique presented above and the results are contrasted with the more common laser breakdown/spark ignition technique that uses a single NIR pulse. Preliminary results show that the dual-pulse technique allows for ignition of leaner mixtures ($phi =0.6)$ as compared to conventional laser breakdown ignition ($phi =0.7)$. In addition, analysis of the pressure data collected during the combustion events suggests that the combustion efficiency (defined here as the fraction of the chemical energy of the fuel converted into heat) is also higher using the new technique. Measurements of the plasma energy absorption show that both techniques require similar (absorbed) energy for ignition $(mathrm {E}_{abs} sim 15$ mJ); however, the dual-pulse achieves this with less incident pulse energy, i.e., total combined pulse energy of 50 mJ $(mathrm {E}_{UV}=20$ mJ, $mathrm {E}_{NIR}=30$ mJ), as compared to needing incident 75 mJ for single pulse NIR. Moreover, studying the chemiluminescence emitted by the OH* radical $(lambda _{OHast }=308$ nm) that is naturally produced during the combustion event using an ICCD camera revealed that the flame dynamics can be very different for the two techniques. The NIR initiated flames propagate as a toroidal structure owing to the vorticity induced by the shock wave that follows the spark, a situation that generates excessive flame stretching which can lead to quenching for lean mixtures. In contrast, the flames generated using the dual-pulse technique propagate as a roughly spherical front (depending on the offset of the two beam waists) with less pronounced stretching.
{"title":"A Study of Flame Dynamics Induced by A Dual-Pulse Laser Ignition Technique","authors":"C. Dumitrache, C. Limbach, A. Yalin","doi":"10.1109/PLASMA.2017.8496005","DOIUrl":"https://doi.org/10.1109/PLASMA.2017.8496005","url":null,"abstract":"This study describes the ignition and flame dynamics generated using a dual-pulse laser pre-ionization technique. The new technique involves the use of two nanosecond pulses for inducing gas heating and initiating combustion. Initially, a UV pulse $(lambda =266$ nm) from the fourth harmonic of a Nd:YAG laser is used to pre-ionize a small volume of gas inside of the combustion chamber forming a weakly ionized plasma channel $(mathrm {n}_{e} sim 3 mathrm {x}10 ^{16}$ cm-3). The cold plasma produced by the UV pulse (T~ 600 -1000K) is subsequently heated by an NIR $(lambda =1064$ nm) pulse that follows ~ 10ns after the preionization pulse. The NIR beam adds energy into the gas through inverse bremsstrahlung absorption of radiation and increases the temperature of the plasma to T~ 2000-3000 K. Ignition of propane-air mixtures at various equivalence ratios was successfully achieved using the technique presented above and the results are contrasted with the more common laser breakdown/spark ignition technique that uses a single NIR pulse. Preliminary results show that the dual-pulse technique allows for ignition of leaner mixtures ($phi =0.6)$ as compared to conventional laser breakdown ignition ($phi =0.7)$. In addition, analysis of the pressure data collected during the combustion events suggests that the combustion efficiency (defined here as the fraction of the chemical energy of the fuel converted into heat) is also higher using the new technique. Measurements of the plasma energy absorption show that both techniques require similar (absorbed) energy for ignition $(mathrm {E}_{abs} sim 15$ mJ); however, the dual-pulse achieves this with less incident pulse energy, i.e., total combined pulse energy of 50 mJ $(mathrm {E}_{UV}=20$ mJ, $mathrm {E}_{NIR}=30$ mJ), as compared to needing incident 75 mJ for single pulse NIR. Moreover, studying the chemiluminescence emitted by the OH* radical $(lambda _{OHast }=308$ nm) that is naturally produced during the combustion event using an ICCD camera revealed that the flame dynamics can be very different for the two techniques. The NIR initiated flames propagate as a toroidal structure owing to the vorticity induced by the shock wave that follows the spark, a situation that generates excessive flame stretching which can lead to quenching for lean mixtures. In contrast, the flames generated using the dual-pulse technique propagate as a roughly spherical front (depending on the offset of the two beam waists) with less pronounced stretching.","PeriodicalId":145705,"journal":{"name":"2017 IEEE International Conference on Plasma Science (ICOPS)","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2017-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131190142","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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