Optical Visualization of Beam-driven Plasma Wakefield Accelerators

该研究项目旨在创建和诊断由电离气体或“等离子体”制成的柔韧微观结构，该结构适合加速、成形和聚束电子束及其反物质孪生（称为“正电子”），比传统加速器更紧凑、更便宜。全球有 30,000 台传统粒子加速器，服务于工业、医院和发现科学，几乎所有加速器都对电子和质子等普通物质粒子进行加速。仅有少数大型设施可以加速平行物质/反物质粒子束——例如电子和正电子，或质子和反质子。当相互碰撞时，这样的双光束会产生新粒子的宝库，其中有“W”、“Z”和“希格斯”玻色子等奇特的名字，这些粒子已经获得了多项诺贝尔奖。不幸的是，过去此类突破背后的技术已经变得太大且昂贵，无法支持新的突破。在这个项目中，高能电子束穿过充满锂气的管道，产生并激发短寿命的等离子丝，这些丝只有一码长，比人的头发还细，就像划过池塘的船产生尾流一样。这种“尾流”可以将电子和正电子加速到与 18 轮车宽的一英里长传统加速器相同的能量。计算机模拟表明，电子“船”后面1/1000英寸的等离子体尾流部分是一个很好的电子加速器，而后面1英寸的部分是一个很好的正电子加速器。尾流这些部分的闪光全息图测试了模拟。此外，精心定时的电子和正电子束可以在尾流中冲浪，以直接测试其作为加速器的可行性。成功不仅可以为未来的粒子物理发现带来紧凑、负担得起的技术，而且可以带来正电子成像的新的医疗和工业应用，这些应用可以利用加速器正电子束的独特强度、窄度和能量均匀性。这个为期3年的项目在第二代SLAC高级加速器科学和实验测试设施(FACET-II)上进行了批准的实验E-324“束驱动等离子体尾场加速器的光学可视化”。 FACET-II 的 10 GeV 电子束在一米长的锂等离子体中驱动强非线性等离子体尾流，密度为每 cm^3 10^17 个电子。与电子束同步的 100 fs、近红外、近同向传播光学探测脉冲，以掠射角、0 至 50 ps 的时间延迟撞击电子束的路径，并从尾流中衍射。下游探测器记录探测器的衍射图案，从中可以重建尾流不断变化的电子密度分布，并与计算机模拟的预测进行比较。科学目标是：(1) 观察计算机模拟预测在约 50 ps 时形成的尖锐轴上离子密度峰； (2) 用二次电子束激发和诊断该离子密度结构中的电子尾迹，并测试其预测的稳定正电子加速的适用性； (3) 首次观察到初级电子束后面延迟低于 1 ps 的气泡状电子尾迹，这非常适合加速电子。其智力优势在于首次观察粒子束驱动的等离子体尾迹，以及创建和识别适合电子和正电子加速的互补等离子体结构，从而为基于双等离子体的电子-正电子加速器铺平了道路。更广泛的影响包括开发紧凑、负担得起的加速器技术以及培训下一代劳动力，包括具有不同背景的研究生和本科生。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research project aims to create and diagnose pliable, microscopic structures made of ionized gas, or "plasma", that are suitable for accelerating, shaping and bunching beams of electrons and their antimatter twins called "positrons" far more compactly and cheaply than conventional accelerators. Nearly all of the world's 30,000 conventional particle accelerators, which serve industry, hospitals and discovery science, accelerate ordinary matter particles, such as electrons and protons. A mere handful of mega-facilities accelerate parallel matter/antimatter particle beams - such as electrons and positrons, or protons and anti-protons. When collided with each other, such twin beams yield a treasure trove of new particles, with exotic names like "W", "Z" and "Higgs" bosons, which have reaped several Nobel prizes. Unfortunately, the technology underlying such past breakthroughs has become too large and expensive to support new breakthroughs. In this project, an energetic electron bunch racing through a pipe filled with lithium gas creates and energizes short-lived plasma filaments only a yard long, and thinner than a human hair, just as a boat racing across a pond creates a wake. This "wake" can accelerate both electrons and positrons to the same energy as a mile-long conventional accelerator as wide as an 18-wheeler. Computer simulations show that the part of the plasma wake 1/1000 inch behind the electron “boat” is a good electron accelerator, whereas the part one inch behind is a good positron accelerator. Flash holograms of these parts of the wake test the simulations. Moreover, carefully timed electron and positron bunches can be surfed on the wake, to test its viability as an accelerator directly. Success could lead not only to compact, affordable technology for future particle physics discoveries, but to new medical and industrial applications of positron imaging that take advantage of the unique intensity, narrowness and energy uniformity of positron beams from accelerators.The 3-year project carries out approved experiment E-324 "Optical visualization of beam-driven plasma wakefield accelerators" at the 2nd generation SLAC Facility for Advanced Accelerator Science and Experimental Tests (FACET-II). FACET-II's 10 GeV electron bunches drive strongly nonlinear plasma wakes in a meter-long lithium plasma of density 10^17 electrons per cm^3. A 100 fs, near-infrared, near-co-propagating optical probe pulse, synchronized with the electron bunch, impinges on the bunch's path at grazing angle at time delays ranging from 0 to 50 ps, and diffract from the wake. Downstream detectors record the probe's diffraction pattern, from which the wake's evolving electron density profile can be reconstructed and compared to predictions of computer simulations. Scientific goals are: (1) to observe a sharp on-axis ion density peak that computer simulations predict to form at ~50 ps; (2) to excite and diagnose an electron wake in this ion density structure with a secondary electron bunch, and to test its predicted suitability for stable positron acceleration; (3) to observe the bubble-shaped electron wake at delays below 1 ps behind the primary electron bunch, which is well suited for accelerating electrons, for the first time. The intellectual merit consists in observing particle-beam-driven plasma wakes for the first time, and in creating and identifying complementary plasma structures suitable for electron and positron acceleration, thereby paving the way for a dual plasma-based electron-positron accelerator. The broader impacts include development of compact, affordable accelerator technology and training of the next generation workforce, including graduate and undergraduate students with diverse backgrounds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.