Neural Networks for Modeling and Control of Particle Accelerators

We describe some of the challenges of particle accelerator control, highlight recent advances in neural network techniques, discuss some promising avenues for incorporating neural networks into particle accelerator control systems, and describe a neural network-based control system that is being developed for resonance control of an RF electron gun at the Fermilab Accelerator Science and Technology (FAST) facility, including initial experimental results from a benchmark controller.Comment: 21 p

Beam Longitudinal Dynamics Simulation Suite BLonD

The beam longitudinal dynamics code BLonD has been developed at CERN since 2014 and has become a central tool for longitudinal beam dynamics simulations. In this paper, we present this modular simulation suite and the various physics models that can be included and combined by the user. We detail the reference frame, the equations of motion, the BLonD-specific options for radio-frequency parameters such as phase noise, fixed-field acceleration, and feedback models for the CERN accelerators, as well as the modeling of collective effects and synchrotron radiation. We also present various methods of generating multi-bunch distributions matched to a given impedance model. BLonD is furthermore a well-tested and optimized simulation suite, which is demonstrated through examples, too

Systematic study of instrumental mass discrimination in multi-collector inductively coupled plasma-mass spectrometry

Multi-collector inductively coupled plasma - mass spectrometry (MC-ICP-MS) has gained substantial importance in isotopic analysis over the last two decades. In the beginning, MC-ICP-MS was almost solely deployed in geo- and cosmochemistry and in nuclear sciences and industry. Nowadays, many other scientific fields make use of the technique, which is mostly based on the high versatility of the ICP ion source and the high sample throughput in comparison to methods with equal or even slightly better precision, such as thermal ionization mass spectrometry (TIMS). The major benefit of MC-ICP-MS is clearly the high ionization power of the ICP, compared to, e.g. that of thermal ionization. A major limitation of MC-ICP-MS is the omnipresent instrumental mass discrimination. It is the effect that light isotopes are discriminated against heavier isotopes during the measurement. The goal of this PhD research project was to identify and possibly quantify the major contributors to instrumental mass discrimination in MC-ICP-MS. Commonly, instrumental mass discrimination is attributed to space-charge effects. Even though this is an easy to comprehend effect at first glance, it becomes more complicated once studied more closely. Firstly, space-charge effects are present in charged particle beams only. Secondly, space-charge effects are most severe for low energetic particle beams with high current. Certainly, the space-charge effects are not the only contributors to mass discrimination. Several other contributors have been identified in the past, namely: collisions, sample introduction and ion formation and energy-selective ion transmission. The effect of the above mentioned processes in terms of mass discrimination were investigated by several strategies. The processes occurring during the ion beam formation were addressed by the Direct Simulation Monte Carlo method. Due to the nature of the ion source, the plasma is extracted from ambient pressure into the vacuum of the mass spectrometer; leading to drastically reduced fluid density. Yet, sufficient collisions between particles take place to possibly contribute to mass discrimination. The modeling results show a significant alteration of the fluid composition after the skimmer cone. Also a radial fractionation of the fluid was found. The ion beam is formed shortly after the plasma is extracted through the skimmer cone, the electrons are lost; a process known as charge-separation. During this phase, the space-charge effects are strongest. Thus a radial dependence of the isotopic composition of the ion beam might occur. This particular effect was investigated by two experiments, one comprising of ion implantation for the subsequent determination of the radial composition of the ion beam, the second experiment with a variable aperture addressing the shortcomings of the ion implantation and provide reliable \emph{in situ} information about the beam composition and diameter. These beam diameters are in contradiction to those expected from typically reported ion beam current. In order to measure the gross beam current, a Faraday cup was placed after the first ion lens of the mass spectrometer. The results reveal a much lower ion current than reported in literature, but are in reasonable agreement with estimations by the Child-Langmuir law for space-charge limited beams. Finally, it has to be pointed out that no dominant contributor to the mass discrimination could be identified. However, the energy-selective transmission can be excluded from the list of contributors, given the low ion beam current with the associated quasi complete beam transport. Since sample introduction a priory can be ruled out, only two contributors remain: collisions and space-charge effects. Both contributors can hardly be separated from one another experimentally, i.e., a higher throughput through the interface will lead to more collisions in the interface and consequently, to a higher ion beam current after charge-separation. Yet, the isolated treatment of both effects in computer simulations might provide a tool to solve this problem. Of course, the same simulator would need to have the capability to model both effects simultaneously, as well as separately, which is not yet possible

Monte Carlo simulations of ultra high vacuum and synchrotron radiation for particle accelerators

With preparation of Hi-Lumi LHC fully underway, and the FCC machines under study, accelerators will reach unprecedented energies and along with it very large amount of synchrotron radiation (SR). This will desorb photoelectrons and molecules from accelerator walls, which contribute to electron cloud buildup and increase the residual pressure - both effects reducing the beam lifetime. In current accelerators these two effects are among the principal limiting factors, therefore precise calculation of synchrotron radiation and pressure properties are very important, desirably in the early design phase. This PhD project shows the modernization and a major upgrade of two codes, Molflow and Synrad, originally written by R. Kersevan in the 1990s, which are based on the test-particle Monte Carlo method and allow ultra-high vacuum and synchrotron radiation calculations. The new versions contain new physics, and are built as an all-in-one package - available to the public. Existing vacuum calculation methods are overviewed, then the steady-state and time-dependent algorithms behind the ultra-high vacuum simulator Molflow are presented. Some practices to tackle the most common problems that arise when simulating large systems are also discussed. Results are compared to theory, and validated through two experiments. Next the the main steps of synchrotron radiation simulations are presented. Properties of SR are summarized, along with optimizations that allow simulating the rather complex underlying physics at a higher speed. The resulting software's photon generation algorithm is benchmarked against published data. The phenomenon of photon stimulated desorption and its literature is overviewed, then two dedicated photodesorption experiments carried out in KEK (Tsukuba, Japan) are presented: one with six room-temperature samples and an other at liquid nitrogen temperature. A simple synchrotron radiation calculation is performed for the LHeC interaction region, allowing to compare Synrad+ results with published analytic calculations. Then the calculations are repeated for a more precise geometry description. The pressure profile of a crotch absorber of the recently started Max IV light source is calculated using Molflow+ and Synrad+ together. Finally the pressure analysis of the SuperKEKB interaction region is presented, consisting of modeling the vacuum chamber and the optics, calculating synchrotron radiation, then performing vacuum simulations. It is confirmed that pressure is expected to meet the design requirements during operation of the machine

2022 Review of Data-Driven Plasma Science

Data-driven science and technology offer transformative tools and methods to science. This review article highlights the latest development and progress in the interdisciplinary field of data-driven plasma science (DDPS), i.e., plasma science whose progress is driven strongly by data and data analyses. Plasma is considered to be the most ubiquitous form of observable matter in the universe. Data associated with plasmas can, therefore, cover extremely large spatial and temporal scales, and often provide essential information for other scientific disciplines. Thanks to the latest technological developments, plasma experiments, observations, and computation now produce a large amount of data that can no longer be analyzed or interpreted manually. This trend now necessitates a highly sophisticated use of high-performance computers for data analyses, making artificial intelligence and machine learning vital components of DDPS. This article contains seven primary sections, in addition to the introduction and summary. Following an overview of fundamental data-driven science, five other sections cover widely studied topics of plasma science and technologies, i.e., basic plasma physics and laboratory experiments, magnetic confinement fusion, inertial confinement fusion and high-energy-density physics, space and astronomical plasmas, and plasma technologies for industrial and other applications. The final section before the summary discusses plasma-related databases that could significantly contribute to DDPS. Each primary section starts with a brief introduction to the topic, discusses the state-of-the-art developments in the use of data and/or data-scientific approaches, and presents the summary and outlook. Despite the recent impressive signs of progress, the DDPS is still in its infancy. This article attempts to offer a broad perspective on the development of this field and identify where further innovations are required