Collaborative Research: Pre-Ionization Controlled Laser Plasma Formation for Ignition Applications

点火应用的预电离控制激光等离子体形成azer Yalin（科罗拉多州立大学），Anthony Marchese（科罗拉多州立大学），Mikhail schneider（普林斯顿大学），Zhili Zhang（田纳西大学诺克斯维尔分校）该奖项是根据美国国家科学基金会/美国能源部合作伙伴关系基础等离子体科学与工程联合招标NSF 13-596提交并审查的提案作出的。该奖项提供资金支持本科生参与整体研究工作，由美国能源部根据与科罗拉多州立大学的合同（授予号待定）单独资助。”更广泛的意义和重要性：由聚焦激光束形成的等离子体提供反应性加热气体，有点类似于传统点火系统产生的火花。因此，激光等离子体对包括点火在内的许多应用都很感兴趣。我们将发展基础等离子体科学，为点火和激光诱导击穿光谱（LIBS）应用提供量身定制的激光脉冲方案。在燃烧方面，激光点火有许多潜在的好处。对于往复式天然气发动机，人们可以点燃更稀薄的混合物（减少氮氧化物排放和污染物形成）和更高压力的混合物（导致更高的发动机效率和节省燃料）。在航空航天应用中，人们可以在航空涡轮中获得更好的光。多脉冲方法可以降低所需激光源和光纤传输实现的负担。我们将向当地少数民族公立学校（K-12）展示我们的活动，并将研究进展纳入我们大学的课程中。我们将特别针对代表性不足或少数群体，将该项目作为他们的博士论文研究。技术描述：提出的研究重点是采用预电离脉冲（ns-ps-fs）的创新方法来增强和控制气体中的激光等离子体形成。特别是，我们将检查的情况下，其中一个初始脉冲是用来实现预电离，然后是第二个脉冲，提供可控的能量补充。第二脉冲的能量添加是通过由第一脉冲引起的预电离实现的。其结果将是激光等离子体不处于完全击穿条件（即没有火花），但温度升高（~2000 K）。这种激光等离子体通过避免不必要的高温、强冲击波和伴随完全激光击穿（火花）的激光脉冲能量升高，可以提供新颖和改进的点火源。我们将考虑一系列脉冲持续时间（ns-ps-fs）以及预电离的非谐振和谐振方案。我们还将研究非共振预电离脉冲以及共振增强多光子电离（REMPI）方案。REMPI方案将发展为未来在空气中的应用，初步研究合成气体混合物，例如我们将研究空气中丰富的氩气和氧气的REMPI。等离子体将进行实验研究和表征以及数值模拟。我们将确定最佳的激光脉冲参数（波长，持续时间，时间分离等），以提供充分的预电离，并允许随后的能量添加。由于缺乏可见发射，这种等离子体的研究是具有挑战性的，我们的建议的一个关键特点是使用新开发的微波散射技术来测量电子参数。拟议的研究将在激光等离子体形成方面具有变革性；尽管对单脉冲激光击穿进行了大量的研究，但对多脉冲方法和预电离的研究却很少。这个为期三年的项目将由科罗拉多州立大学（CSU）、田纳西大学诺克斯维尔分校（UTK）和普林斯顿大学（PU）共同开展，并结合实验研究、先进诊断、计算等离子体和燃烧模型。

Pre-Ionization Controlled Laser Plasma Formation for Ignition ApplicationsAzer Yalin (Colorado State University), Anthony Marchese (Colorado State University), Mikhail Shneider (Princeton University), Zhili Zhang (University of Tennessee - Knoxville)This award is made in response to a proposal submitted to and reviewed under the NSF/DOE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 13-596. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DOE under contract to Colorado State University contract (Grant Number TBD)." Broader Significance and Importance: Plasmas formed from focused laser beams provide reactive heated volumes of gas, somewhat analogous to the sparks produced by conventional ignition systems. Laser plasmas, therefore, are of interest for a number of applications including ignition. We will develop the basic plasma science to provide tailored laser pulse schemes for ignition and laser induced breakdown spectroscopy (LIBS) applications. In terms of combustion, laser ignition has many potential benefits. For reciprocating natural gas engines one can ignite leaner mixtures (reducing NOx emissions and pollutant formation) and higher pressure mixtures (leading to higher engine efficiencies and fuel-savings). In aerospace applications one can achieve better relight in aero-turbines. The multi-pulse approaches may lower the burden on required laser sources and fiber delivery implementations. We will present our activities to local minority-serving public schools (K-12) and include research advances in courses at our universities. We will specifically target underrepresented or minority groups to work on the project as their Ph.D. thesis research.Technical Description: The proposed research focuses on innovative approaches employing pre-ionizing pulses (ns-ps-fs) to enhance and control laser plasma formation in gases. In particular, we will examine cases in which an initial pulse is used to achieve pre-ionization, and is followed by a second pulse that provides controllable energy addition. The energy addition of the second pulse is enabled by pre-ionization due to the first pulse. The result will be a laser plasma that is not at full breakdown conditions (i.e. no spark), but that has elevated temperature (~2000 K). Such laser plasmas can provide novel and improved ignition sources by avoiding the unnecessarily high temperatures, strong shock waves, and elevated laser pulse energies that accompany full laser breakdown (sparks). We will consider a range of pulse durations (ns-ps-fs) as well as both non-resonant and resonant schemes for pre-ionization. We will also study both non-resonant pre-ionizing pulses as well as Resonant Enhanced Multi-Photon Ionization (REMPI) schemes. The REMPI schemes will be developed for future applications in air with initial studies in synthetic gas mixtures, e.g. we will study REMPI of argon and oxygen which are abundant in air. The plasmas will be experimentally studied and characterized as well as modeled numerically. We will determine optimal laser pulse parameters (wavelength, duration, temporal separation etc.) to provide sufficient pre-ionization and to allow subsequent energy addition. Owing to the lack of visible emission, the study of such plasmas is challenging and a key feature of our proposal is the use of a newly developed microwave scattering technique to measure electron parameters. The proposed research will be transformative in terms of laser plasma formation; despite a large body of research in laser breakdown using single laser pulses there has been minimal research on multi-pulse approaches and pre-ionization. The three-year program will be conducted by Colorado State University (CSU), University of Tennessee at Knoxville (UTK), and Princeton University (PU) and combines experimental studies, advanced diagnostics, and computational plasma and combustion modeling.