Optical Visualization of Beam-driven Plasma Wakefield Accelerators

这项研究项目旨在创造和诊断由电离气体或“等离子体”组成的柔韧微观结构，这种结构适合于加速、整形和聚集电子束及其反物质双胞胎，称为“正电子”，比传统加速器更紧凑、更便宜。世界上几乎所有的3万个常规粒子加速器都在为工业、医院和发现科学服务，它们都在加速电子和质子等普通物质粒子。仅有几个巨型设备加速了平行物质/反物质粒子束--例如电子和正电子，或者质子和反质子。当相互碰撞时，这样的孪生光束产生了一个新粒子宝库，它们的名字很奇特，比如“W”、“Z”和“Higgs”玻色子，这些粒子已经获得了几个诺贝尔奖。不幸的是，支撑过去这些突破的技术已经变得过于庞大和昂贵，无法支持新的突破。在这个项目中，一个高能电子束穿过充满锂气体的管道，产生并为短暂的等离子细丝提供能量，长度只有一码，比人的头发还细，就像一艘船在池塘中疾驰而产生的尾迹一样。这种“尾迹”可以将电子和正电子都加速到与一英里长的传统加速器一样宽的18个轮子的能量。计算机模拟表明，电子船后面1/1000英寸处的等离子体尾迹是一个很好的电子加速器，而后面1英寸处是一个很好的正电子加速器。尾迹的这些部分的闪光全息图测试了模拟。此外，仔细计时的电子和正电子束可以在尾流上冲浪，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，而且还可以带来正电子成像的新的医疗和工业应用，这些应用利用了来自加速器的正电子束的独特强度、窄度和能量一致性。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(FEET-II)进行了经批准的实验E-324“束驱动等离子体尾场加速器的光学可视化”。在密度为10^17个电子/cm~3的一米长的锂等离子体中，小面II的10GeV电子束驱动强非线性等离子体尾迹。与电子束同步的近红外、近同传的100fs光探测脉冲以掠射角的方式撞击在束流路径上，时间延迟从0到50ps不等，并与尾迹绕射。下游探测器记录了探测器的衍射图，根据它可以重建尾迹演变中的电子密度分布，并与计算机模拟的预测进行比较。科学目标是：(1)观测到计算机模拟预计将在~50ps处形成的尖锐的轴上离子密度峰值；(2)激发和诊断出这种带有二次电子束流的离子密度结构中的电子尾流，并测试其对稳定正电子加速的适用性；(3)首次观测到主电子束后延迟低于1ps的泡状电子尾流，这非常适合于加速电子。智能优势在于首次观测到粒子束驱动的等离子体尾迹，并创造和确定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-正电子加速器铺平道路。更广泛的影响包括开发紧凑、负担得起的加速器技术和培训下一代劳动力，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优势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.