Racetrack FFAGs for medical, PRISM and energy applications

固定场交替梯度加速器(FFAG)是粒子加速器历史早期使用的传统回旋加速器和主导粒子物理学的同步加速器的混合体：欧洲核子研究中心的大型强子对撞机是质子存储环的最大例子，质子存储环是同步加速器的一种。尽管它们最初是在50多年前的小实验中进行研究的，但最初被认为计算过于复杂，而且早期旨在发射高能粒子的设计比其他设计更大。然而，最近在加速质子等重粒子所需的射频腔技术以及环本身的计算工具和磁性设计方面都取得了进展。这种复兴最近在2012年曼彻斯特领导的一个合作项目中达到了顶峰，在一个名为Emma的实验中展示了第一个无比例的FFAG例子。无比例FFAG通过拥有更小的磁体而改进了它们的前身，这使得它们适用于高能加速器。然而，这些环中加速过程的性质可能会产生复杂的共振效应，必须通过仔细的计算设计以及聚焦和弯曲磁铁的现代设计来管理。EMMA证明了无标度原理是有效的，但它具有高度对称的布局，使加速器比可能的尺寸更大。所谓的跑道设计消除了这种对称性，允许更紧凑的设计，同时增加了必要的注射和取出系统的灵活性和空间：空间放在跑道部分，但节省在其他地方。赛道设计还可以解决一些突出的问题，如在许多应用中所需的那样，在高能下提供大电流的粒子。但目前还没有合适的赛道设计来详细检查所有部件如何装配在一起，以及磁铁需要多大的公差才能工作。我们的计划正是要做到这一点。在这个项目中，我们将研究赛道FFAG的一个有用的应用，即提供足够的能量质子(330 MeV)，以便将患者的放射治疗和成像结合起来。这种治疗和成像的结合目前在商业加速器中是不可能的，我们认为赛道FFAG可以变得足够简单，与其他解决方案竞争，同时提供所需的质子能量。从设计这台样机中学到的经验教训将被用来决定如何在另外两个重要的应用中最好地使用赛道FFAG原理。其中第一个是棱镜实验，该实验试图测量µ子是否能自发转化为电子，这是一种探索当前粒子物理标准模型局限性的方法。在进行衰变实验之前，棱镜需要一个FFAG来帮助清理介子束，而赛道FFAG可以极大地简化设计。第二个应用是帮助可持续的核能。高功率粒子加速器可以用来帮助快速核反应堆处理当前和未来的核废料，包括英国的钚储备，但目前的技术还不能以低成本提供足够可靠的加速器。无标度的FFAG可以做到这两点，但在紧凑型加速器中输送高电流的好方法还没有被证明。同样，可以使用赛马场计划来实现这一点。在这两个应用中，我们将使用在医学研究中获得的解决方案来概述可能可行的方案。因此，这个项目将试图展示最近在英国开展的世界领先的FFAG工作如何应用于一系列有用的科学和技术。

Fixed-field alternating gradient accelerators (FFAGs) are a hybrid between the traditional cyclotrons used early on in the history of particle accelerators, and the synchrotrons that have come to dominate the world of particle physics: CERN's Large Hadron Collider is the largest example of a proton storage ring, which is a type of synchrotron. Although they were first studied over 50 years ago in small experiments, they were initially considered too computationally complex, and early designs intended to deliver high energy particles were larger than alternative designs. However, recent advances have been made both in the radio frequency cavity technology needed to accelerate heavy particles such as protons, and in the computational tools and magnetic designs of the rings themselves. This renaissance has recently culminated in the demonstration by a Manchester-led collaboration in 2012 of the first non-scaling example of an FFAG, in an experiment called EMMA. Non-scaling FFAGs improve on their forebears by having much smaller magnets, which makes them feasible for high energy accelerators. However, the nature of the acceleration process in these rings can give rise to complex resonant effects that must be managed through careful computational design, and modern designs of the focusing and bending magnets.EMMA demonstrated that the non-scaling principle works, but it has a highly-symmetric layout that makes the accelerator larger than it might be. A so-called Racetrack design dispenses with this symmetry and allows a more compact design whilst increasing flexibility and space for the essential injection and extraction systems: the space is put into the racetrack sections, but is saved elsewhere. Racetrack designs can also solve some of the outstanding problems in delivering a high current of particles at high energies, as required in a number of applications. But no proper racetrack design has yet been produced that examines in detail how all the parts would fit together, and what tolerances would be needed in the magnets to allow it to work. Our proposal intends to do just that.In this project we will look at one useful application of a racetrack FFAG, to providing sufficient energy protons (330 MeV) to allow combined patient radiotherapy treatment and imaging. This combination of treatment and imaging is not currently possible with commercial accelerators, and we think that a racetrack FFAG can made simple enough to compete with other solutions whilst delivering the proton energies required. The lessons learned from designing this example machine will then be used to decide how best to use the racetrack FFAG principle in two other important applications. The first of these is the PRISM experiment, which seeks to measure whether muons can spontaneously transform into electrons, a method which probes the limits of the current Standard Model of Particle Physics. PRISM needs an FFAG to help clean up the muon beam before the decay experiment is performed, and a racetrack FFAG could simplify the design greatly. The second application is to help sustainable nuclear energy. A high-power particle accelerator can be used to help fast nuclear reactors dispose of current and future nuclear waste, including the UK plutonium stockpile, but current technology does not yet provide reliable enough accelerators at low cost. A non-scaling FFAG could do both, but a good method of delivering high currents in a compact accelerator has not yet been demonstrated. Again, a racetrack scheme could be used to enable this. In both these applications we will use the solution obtained in the medical study to outline schemes that could be workable. Thus, this project will try to show how the world-leading work in FFAGs recently carried out in the UK can be applied across a range of useful science and technology.