Accelerator Physics Research Articles

Very high energy sky monitoring with the Southern Wide-field Gamma-ray Observatory

The Southern Wide-field Gamma-ray Observatory (SWGO) is the proposal for a new ground-based γ-ray instrument in the Southern Hemisphere, which will use an array of water-Cherenkov based particle detectors to provide continuous monitoring and regular scanning of a large portion of the sky at the very- and ultra-high-energies (VHE and UHE, respectively). At the low energy side, SWGO aims to push the observational range of wide-field ground-based γ-ray facilities down to a few hundred GeV, thus bridging the gap between space and ground-based facilities in the monitoring of the VHE sky. In the high energy domain, on the contrary, it will benefit from the optimal coverage of the Galactic Plane to map the distribution of UHE sources in the inner parts of the Galactic disk and close to the Galactic Center, leading to an extraordinary improvement in our ability to identify their most likely counterparts. In this contribution, we describe the concept of SWGO and its potential to constrain the physics of VHE emission and particle acceleration in γ-ray sources powered by relativistic jets and energetic shocks. We finally discuss its role within the global network of multi-messenger facilities.

The AMS-02 detector on the ISS - Status and highlights after 11 years on orbit

The Alpha Magnetic Spectrometer, AMS-02, is a magnetic spectrometer detector operating on the International Space Station (ISS) since May the 19th, 2011. More than 200 billion events have been collected by the instrument in the first 11 years of data taking, providing detailed and novel insights on the composition and energy spectra of cosmic rays up to TeV energies. We review the most recent AMS-02 measurements and the advances in the understanding of cosmic ray origin, acceleration and propagation physics.

Cosmic-Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters

Cosmology models predict that external accretion shocks form in the outer region of galaxy clusters owing to supersonic gas infall from filaments and voids in the cosmic web. They are characterized by high sonic and Alfvénic Mach numbers, M s ∼ 10–102 and M A ∼ 102–103, and propagate into weakly magnetized plasmas of β ≡ P g /P B ≳ 102. Although strong accretion shocks are expected to be efficient accelerators of cosmic rays (CRs), nonthermal signatures of shock-accelerated CRs around clusters have not been confirmed, and detailed acceleration physics at such shocks has yet to be understood. In this study, we first establish through two-dimensional particle-in-cell simulations that at strong high-β shocks electrons can be pre-energized via stochastic Fermi acceleration owing to the ion Weibel instability in the shock transition region, possibly followed by injection into diffusive shock acceleration. Hence, we propose that the models derived from conventional thermal leakage injection may be employed for the acceleration of electrons and ions at accretion shocks as well. Applying these analytic models to numerical shock zones identified in structure formation simulations, we estimate nonthermal radiation, such as synchrotron and inverse Compton (IC) emission due to CR electrons and π 0-decay γ-rays due to CR protons, around simulated clusters. Our models with injection parameter Q ≈ 3.5–3.8 predict synthetic synchrotron maps, which seem consistent with recent radio observations of the Coma Cluster. However, the detection of nonthermal IC X-rays and γ-rays from accretion shocks would be quite challenging. We suggest that the proposed analytic models may be adopted as generic recipes for CR production at cosmological shocks.

Relativistic space-charge field calculation by interpolation-based treecode

Space-charge effects are of great importance in particle accelerator physics. In the computational modeling, tree-based methods are increasingly used because of their effectiveness in handling non-uniform particle distributions and/or complex geometries. However, they are often formulated using an electrostatic force which is only a good approximation for low energy particle beams. For high energy, i.e., relativistic particle beams, the relativistic interaction kernel may need to be considered and the conventional treecode fails in this scenario. In this work, we formulate a treecode based on Lagrangian interpolation for computing the relativistic space-charge field. Two approaches are introduced to control the interpolation error. In the first approach, a modified admissibility condition is proposed for which the treecode can be used directly in the lab-frame. The second approach is based on the transformation of the particle beam to the rest-frame where the conventional admissibility condition can be used. Numerical simulation results using both methods will be compared and discussed.

Analytical energy eigenvalues of a Dirac particle in focusing field of a quadrupole magnet

In this study, the motion of a charged spin-1/2 fermion is found out. It is assumed, in the system, that the free fermion is subjected to a linearly space-dependent magnetic field that can be supposed to be a focusing magnetic field of a quadrupole magnet in beam dynamics in the accelerator physics. In such an examination, two-component Dirac equation is solved via perturbation approximation of the asymptotic iteration method (AIM), which has been widely used for the last decades. The results show that the fermion is bounded to the magnetic field for a certain condition of the strength of the field. For such a system, the analytical form of the energy eigenvalues are obtained. Moreover, to see whether this analytical expression works properly, the numerical eigenvalues are compared with the ones obtained by direct use of the AIM. We have an inspiration that the studies on beam dynamics and magnet design in particle accelerator physics may gain from this work.

Science and technologies in targets for laser accelerators

<p indent="0mm">Laser plasma acceleration (also referred to as laser acceleration) employs ultra-strong electric fields generated when an ultra-intense laser pulse interacts with the plasma to accelerate charged particles. As a promising novel acceleration method, its acceleration gradient can be 10³–10⁶ times that of conventional accelerators. Laser accelerators based on the laser acceleration process can not only generate ultra-short pulse particle/photon beams for fundamental research, but also provide high-energy protons/heavy ions for tumor radiotherapy devices, benefiting people’s lives and health. Under the strong national investment around the world, basic and applied research related to laser accelerators has developed rapidly in recent years. Unlike conventional accelerators, which use macroscopic electromagnetic fields to accelerate particles in a vacuum, the laser acceleration process is realized by shooting targets with laser pulses. The scientific and technical problems related to the “target” are the core problems of the laser accelerator. In order to build an accelerator that can stably output high-energy particle beams, on the one hand, developing new target systems and deeply studying laser acceleration physics is highly necessary. On the other hand, overcoming a large number of key technical issues related to the preparation and characterization of targets and shooting is also very crucial. This paper gives an introduction to the key problems in the science and technologies for laser accelerators and highlights the progress in this field made by our team at the Institute of Heavy Ion Physics of Peking University. By exploiting nanotechnology and nanomaterials, we developed novel targets made of carbon nanotubes, which can serve as long-awaited perfect near-critical-density (NCD) targets. With such targets, we observed the laser focusing and pulse steepening in NCD plasmas for relativistic laser pulses for the first time. We also successfully achieved cascaded ion acceleration scheme by designing and building double-layer CNT targets, which solves the long-standing dilemma between the ionization and long-time acceleration of heavy ions acceleration. By collaborating with the Institute for Basic Sciences (IBS, Korea), we generated record-breaking <sc>580 MeV</sc> carbon ions and <sc>1.2 GeV</sc> Au ions in experiments. Recently, we numerically and experimentally studied how an ultra-intense femtosecond laser pulse interacts with a nanowire array target and eventually creates a high-energy-density plasma. The generation of soft-X-rays/EUV radiations and fusion neutrons from such a plasma were measured and studied in detail. Micro-channel targets are very interesting targets for us as well. We revealed how a laser pulse propagates through a micro-channel, peels off and accelerates electrons to GeV level, and produces corpus gamma rays with very small divergence angles. Experiments collaborating with the China Academy of Engineering Physics confirmed our prediction. Besides the above breakthroughs in acceleration sciences, we solved many key technical problems in laser ion accelerators. For example, we developed some mass-preparation methods for high-quality targets, including nanometer-thin diamond-like-carbon foils and metal foils, measured the target damage thresholds of a majority of existing targets in laser plasma experiments, figured out how to precisely locate transparent targets with high-precision. For non-stop running of the laser ion accelerators, we recently developed liquid sheets, which is highly promising to realize continuous beam delivery for weeks.

Multimodal Multi-User Mixed Reality Human–Robot Interface for Remote Operations in Hazardous Environments

In hazardous environments, where conditions present risks for humans, the maintenance and interventions are often done with teleoperated remote systems or mobile robotic manipulators to avoid human exposure to dangers. The increasing need for safe and efficient teleoperation requires advanced environmental awareness and collision avoidance. The up-to-date screen-based 2D or 3D interfaces do not fully allow the operator to immerse in the controlled scenario. This problem can be addressed with the emerging Mixed Reality (MR) technologies with Head-Mounted Devices (HMDs) that offer stereoscopic immersion and interaction with virtual objects. Such human-robot interfaces have not yet been demonstrated in telerobotic interventions in particle physics accelerators. Moreover, robotic operations often require a few experts to collaborate, which increases the system complexity and requires sharing a multi-user Augmented Reality (AR) workspace. The multi-user telerobotics with shared control in the AR has not yet been approached in the industrial state-of-the-art. In this work, the developed MR human-robot interface using the AR HMD is presented. The interface adapts to the constrained wireless networks in particle accelerator facilities and provides reliable high-precision interaction and specialized visualization. The multimodal operation uses hands, eyes and user motion tracking, and voice recognition for control, as well as offers video, 3D point cloud and audio feedback from the robot. Multiple experts can collaborate in the AR workspace locally or remotely, share the robot’s control and monitor robotic teleoperation. Ten (10) operators tested the interface in intervention scenarios in the European Organization for Nuclear Research (CERN) with complete network characterization and measurements to conclude if operational requirements were met and if the network architecture could support single and multi-user communication load. The interface system has proved to be operationally ready at the Technical Readiness Level (TRL) 8 - and was validated through successful tests and demonstration in single and multi-user missions. Some areas of system limitations and further work were identified, such as optimising the network architecture for multi-user scenarios or high-level interface actions applying automatic interaction strategies with the robot depending on network conditions.

Very high energy sky monitoring with the Southern Widefield Gamma-ray Observatory

The Southern Wide-field Gamma-ray Observatory (SWGO) is the proposal for a new ground-based γ-ray instrument in the Southern Hemisphere, which will use an array of water-Cherenkov particle detectors to provide continuous monitoring of a large portion of the sky at the very- and ultra-high-energies (VHE and UHE, respectively). At the low energy side, SWGO aims to push the observational range of wide-field ground-based γ-ray facilities down to a few hundred GeV, thus bridging the gap between space and ground-based facilities in the monitoring of the VHE sky. In the high energy domain, on the contrary, it will benefit from the optimal coverage of the Galactic Plane to map the distribution of UHE sources in the inner parts of the Galactic disk and close to the Galactic Center, leading to an extraordinary improvement in our ability to identify their most likely counterparts. In this contribution, we describe the concept of SWGO and its potential to constrain the physics of VHE emission and particle acceleration in γ-ray sources powered by relativistic jets and energetic shocks. We finally discuss its role within the global network of multi-messenger facilities.

Preface

The 13th International Particle Accelerator Conference, IPAC’22, took place at IMPACT Exhibition and Convention Center, Bangkok, Thailand from Sunday, June 12 to Friday, June 17, 2022. IPAC’22 was organized as the first in-person IPAC since the emergence of COVID-19 as a global pandemic and was attended by 742 delegates from 37 countries on all continents. The total includes 118 industry and exhibitor delegates. Hosted by Synchrotron Light Research Institute (Public Organization) - SLRI. SLRI was established in 1996 (originally as National Synchrotron Research Center - NSRC) and is the national synchrotron research institute which also known as “Thai Synchrotron National Lab”, situated in Nakhon Ratchasima, Thailand. SLRI performs its main duties on development, operation, and management of synchrotron light source “Siam Photon Source (SPS)” in order to achieve one of its main goals in production of synchrotron light and provide it for user application on research. The Local Organizing Committee (LOC) consisted of 66 staff from SLRI.There were 169 young scientists or students from all over the world attending the conference. Student grants were offered to 60 of these students thanks to the sponsorship of societies, institutes and laboratories worldwide. The Americas region grants were sponsored by APS-DB, ODU, CLS, SLAC, FRIB, and Jefferson Lab. The Europe region sponsors are EPS-AG, GSI, CNRS/IN2P3, INFN/LNL, CERN, DESY, PSI, CEA Saclay, ELETTRA, CELLS/ALBA, HZB, ESS, Cockcroft Institute, KIT, SOLEIL, ESRF, STFC/DL/ASTeC, MAX IV, and FZJ. The Asian region was sponsored by IPAC’22, SLRI, IPAC’19, ANSTO, SUT, GIT, LION, NSF, iRCT, Ti, Prime Street Advisory, NXPO, PUDITEC, and SPECS. The organizers of IPAC’22 are grateful to all sponsors for their valued support of students.Welcome remarks were made by Prapong Klysubun (SLRI), Chair of the Organizing Committee (OC). Yoshihiro Funakoshi (KEK), Enrica Chiadroni (INFN/LNF), and David Tarazona (Cornell University) opened the scientific program with presentations, respectively, on “The SuperKEKB Has Broken the World Record of the Luminosity”, “Progress Towards Demonstration of a Plasma Based FEL”, and “The Accelerator and Beam Physics of the g-2 Experiment”. The conference opening ceremony was on Monday afternoon and presided over by H.R.H. Princess Maha Chakri Sirindhorn featuring Special Plenary Talks from Chris Polly (Fermilab) on “Growing Expectations for New Physics” and Prapaiwan Sunwong (SLRI) on “SPS-II: A 4th Generation Synchrotron Light Source in Southeast Asia”.The program was closed with illuminating presentations by Mike Seidel (PSI) on “Towards Efficient Particle Accelerators - a Review”; Manjit Dosanjh (CERN/Oxford University) on “Accelerating the Future: Designing a Robust and Affordable Radiation Therapy Treatment System for Challenging Environments”; and Tomoki Nakamura (Tohoku University) on “Synchrotron Light Illuminates the Origin of the Solar System”.There were 36 invited and 52 contributed oral presentations of very high quality presented during the week. The regional distribution of talks was 16.7 % from Asia, 59.1 % from Europe, and 24.2 % from the Americas. The gender ratio for oral presentations was 71.6 % male and 28.4 % female. The oral presentations were 79.5 % onsite talks and 20.5 % remote talks.

Study of coil configuration and local optics effects for the GaToroid ion gantry design

GaToroid, a novel gantry configuration for hadron therapy, is based on superconducting coils that generate a toroidal magnetic field to deliver the beam to the tumour location. Designing the complex GaToroid coils requires careful consideration of the local beam optical effects. We present a Python-based tool for charged particle transport in complex electromagnetic fields. The code implements fast tracking in arbitrary three-dimensional field maps, and it does not require a definition of specific or regular reference trajectories, as is generally the case for accelerator physics codes. The tool was used to characterise the beam behaviour inside the GaToroid system: to automatically determine the reference trajectories in the symmetry plane and analyse three-dimensional beam dynamics around these trajectories. Beam optical parameters in the field region were compared for various magnetic configurations of GaToroid. This paper introduces the new tracker and shows the benchmarking results. Furthermore, first-order beam optics studies for different arrangements demonstrate the main code features and serve for the design optimisation.

Direct Measurement of Beam-Induced Heating on Accelerator Pipes With Fiber Optic Sensors: Numerical Analysis Validation

In the field of accelerator physics it is crucial to account for heating caused by the passage of high intensity beams into accelerator components. This phenomenon is known as Radio Frequency (RF) Beam Induced Heating (BIH) and requires, other than an accurate design stage, to constantly monitor temperature-related parameters during the accelerator operations. This enables to warn for critical malfunctions and to prevent possible damages. Monitoring needs to meet various requirements, such as multiplexing capabilities, distributed sensing possibilities, and robustness in harsh environments. Fiber Bragg Grating sensors (FBGs) have been proven to be an ideal solution that meets all these requirements. This study aims to validate the use of FBGs for direct measurement of RF BIH. A section of the beam pipe in the CERN Large Hadron Collider was modeled in terms of impedance, and the resulting RF BIH was computed based on the traveling beam. The results of the numerical simulation were compared with experimental data obtained by FBGs installed along the beam pipe. The analysis shows that FBGs can be a valuable beam diagnostic tool for monitoring accelerated high energy particle beams by measuring RF BIH and may provide useful insights for improving the design and operation of future accelerators. The study highlights the significant advancements of FBG technology in direct temperature measurement and assessment of RF BIH and serves as a promising solution for mitigating RF BIH in the demanding environment of particle accelerators.

Cosmogenic 10Be and 26Al sample preparation at the University of Wollongong

The University of Wollongong (UOW) cosmogenic 10Be and 26Al sample preparation laboratory has been in operation since the start of 2017. As primarily a feeder laboratory to ANSTO’s Centre for Accelerator Science, our sample preparation procedures have been optimised with consideration to the setup of ANSTO’s 6MV SIRIUS accelerator, and aim to achieve a balance between sample throughput as well as Be and Al target purity. A comparatively small number of samples (n = 68) have also been prepared for measurement at the Australian National University 14UD accelerator. 10Be/9Be ratios of procedural blanks measured on SIRIUS have fluctuated over time with the median for the year 2017 being 5.16 × 10−16 (IQR = 4.11 × 10−16 to 7.16 × 10−16, n = 18), increasing to 1.62 × 10−15 (IQR = 1.05 × 10−15 to 2.17 × 10−15, n = 31) for 2018 and 2019, a period coinciding with elevated boron levels in our samples, and finally decreasing to 1.15 × 10−15 (IQR = 8.63 × 10−16 to 1.60 × 10−15, n = 34) for 2020 and 2021. In contrast, 26Al/27Al ratios of procedural blanks measured on SIRIUS have shown a slight but continuous improvement over time with the median for 2017 of 1.70 × 10−15 (IQR = 8.19 × 10−16 to 5.25 × 10−15, n = 12) decreasing to 1.07 × 10−15 (IQR = 8.5 × 10−16 to 1.53 × 10−15, n = 13) for 2021. Median 10Be/9Be relative uncertainty of procedural blanks analysed on SIRIUS is 18 % (IQR = 15 % to 22 %; n = 86) whereas the median 26Al/27Al relative uncertainty of procedural blanks is higher at 60 % (IQR = 41 % to 100 %; n = 56), statistic resulting from most blanks yielding low 26Al counts (median = 2; IQR = 1–4.5). Average 9BeO− output relative to standard is between ∼ 70 % – 80 % for samples analysed on SIRIUS (n = 895) and ∼ 130 % for samples analysed at ANU (n = 68). 27Al− output relative to standard is lower for samples pressed into cathodes at UOW (∼60 %, n = 432) and analysed on SIRIUS than for those pressed at ANSTO (∼90 %, n = 119). Average 27Al− output relative to standard for samples analysed at ANU is ∼ 80 % (n = 62). 10Be and 26Al measurements of various laboratory intercomparison materials prepared at UOW between 2017 and 2022 yield results in agreement with consensus values confirming that our chemistry procedures are robust and in line with those elsewhere.

Design and Construction of a Traveling Wave Electron Linear Accelerator at Institute for Research in Fundamental Sciences (IPM)

In this paper, the design and construction process of a traveling wave electron linear accelerator is presented briefly. The machine consists of an electron gun followed by a prebuncher, a traveling wave buncher, an accelerating tube and the diagnostics instruments. Solenoid magnets provide the beam focusing. A klystron has been used as the RF power source. The linac components are controlled and monitored by a comprehensive control system. All the sub systems of this accelerator are designed and developed based on the domestic technology. The output beam has a maximum energy of 4.5 MeV. The beam parameters like energy, intensity, transverse size and emittance are measurable and tunable. The IPM Linac is a unique tool for experimental R&D in accelerator and beam physics in Iran.

Enabling Large Scale Simulations for Particle Accelerators

International high-energy particle physics research centers, like CERN and Fermilab, require excessive studies and simulations to plan for the upcoming upgrades of the world's largest particle accelerators, and the design of future machines given the technological challenges and tight budgetary constraints. The Beam Longitudinal Dynamics (BLonD) simulator suite incorporates the most detailed and complex physics phenomena in the field of longitudinal beam dynamics, required for providing extremely accurate predictions. Modern challenges in beam dynamics dictate for longer, larger and numerous simulation studies to draw meaningful conclusions that will drive the baseline choices for the daily operation of current machines and the design choices of future projects. These studies are extremely time consuming, and would be impractical to perform without a High-Performance Computing oriented simulator framework. In this article, at first, we design and evaluate a highly-optimized distributed version of BLonD. We combine approximate computing techniques, and leverage a dynamic load-balancing scheme to relax synchronization and improve scalability. In addition, we employ GPUs to accelerate the distributed implementation. We evaluate the highly optimized distributed beam longitudinal dynamics simulator in a supercomputing system and demonstrate speedups of more than two orders of magnitude when run on 32 GPU platforms, w.r.t. the previous state-of-art. By driving a wide range of new studies, the proposed high performance beam longitudinal dynamics simulator forms an invaluable tool for accelerator physicists.

A one-time sampling method for the real-time measurement of bunch-by-bunch three-dimensional positions in storage rings

Bunch-by-bunch (BbB) technique, which allows accelerator physicists to monitor beam information on finer timescales, is an efficient tool for studying longitudinal and transverse beam dynamics. However, the real-time measurement in BbB technique can only monitor one beam parameter, thus focusing only on the longitudinal phase or transverse positions of bunches. Therefore, to solve this issue, we put forward a one-time sampling method (OSM) to evaluate the longitudinal phase and transverse positions of bunches simultaneously, taking as one way of the real-time measurement for BbB three-dimensional (3D) positions. And we carried out related experiments in Hefei Light Source II and Shanghai Synchrotron Radiation Facility. As a result, experiments show that OSM obtains 12 μm of x-direction resolution, 10 μm of y-direction resolution, 0.57 ps of z-direction resolution at Hefei Light Source II, and 10 μm of x-direction resolution, 10 μm of y-direction resolution, 0.35 ps of z-direction resolution at Shanghai Synchrotron Radiation Facility. All these experimental results reveal that OSM is feasible to measure the BbB 3D positions.

The measurement of photocathode transverse energy distribution curves (TEDCs) using the transverse energy spread spectrometer (TESS) experimental system.

The minimum achievable particle beam emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. This is measurable as the mean longitudinal and transverse energy spreads in the photoemitted electron beam (MLE and MTE respectively); consequently, MLE and MTE are notable figures of merit for photocathodes used as electron sources in particle accelerators. The overall energy spread is defined by the sum of the MTE and the MLE, and the minimization of MTE is crucial to reduce emittance and thus generate a high-brightness electron beam. Reducing the electron beam emittance in an accelerator that drives a Free-Electron Laser (FEL) delivers a significant reduction in the saturation length for an x-ray FEL, thus reducing the machine's construction footprint and operating costs while increasing the x-ray beam brightness. The ability to measure the transverse energy distribution curve of photoelectrons emitted from a photocathode is a key enabler in photocathode research and development that has prompted the Accelerator Science and Technology Centre (ASTeC) at the STFC Daresbury Laboratory to develop the Transverse Energy Spread Spectrometer to make these crucial measurements. We present details of the design for the upgraded TESS instrument with measured data for copper (100), (110), and (111) single-crystal photocathodes illuminated at UV wavelengths around 266nm.

Mathematical Modeling and Optimization of Low Energy Beam Line in 2MV Pelletron Accelerator

The 2 MV 6SDH-2 tandem pelletron accelerator installed at CASP, GC University Lahore has evolved over the past years from acceptance tests to an extremely reliable and convenient research tool in the field of particle accelerator physics, hav-ing capability of providing variety of ion beams from few keV to several MeV in energy. Many electrostatic and magnetic devices are employed to steer an ion beam in an accelerator system all the way from ion source to experimental setup. Mathematical modeling and optimization of low energy beamline has been done for this accelerator. Several ion optics and steering devices are provided in the pre-acceleration beamline for ion beam manipulation and in order to optimize the overall beam transmission. As the quality of the beam from the accelerator depends upon the design of these electrostatic and magnetic devices, optimum settings are derived by manually adjusting voltages and currents provided to low energy beam-line components. From these calibrations and optimization measurements, calculations has been done for mass analysis magnets, steering and focusing components and the results has been represented. From the results, it has been found that there exists a complex relationship between the effects of different voltages and currents in order to tune the desired output current and beam profile at the end-stations. Details of experiments and data analysis are presented.

A neural network model of a quasiperiodic elliptically polarizing undulator in universal mode.

Machine learning has recently been applied and deployed at several light source facilities in the domain of accelerator physics. Here, an approach based on machine learning to produce a fast-executing model is introduced that predicts the polarization and energy of the radiated light produced at an insertion device. This paper demonstrates how a machine learning model can be trained on simulated data and later calibrated to a smaller, limited measured data set, a technique referred to as transfer learning. This result will enable users to efficiently determine the insertion device settings for achieving arbitrary beam characteristics.

Comparison of multiobjective optimization methods for the LCLS-II photoinjector

Particle accelerators are among some of the largest science experiments in the world and can consist of thousands of components with a wide variety of input ranges. These systems can easily become unwieldy optimization problems during design and operations studies. Starting in the early 2000s, searching for better beam dynamics configurations became synonymous with heuristic optimization methods in the accelerator physics community. Genetic algorithms and particle swarm optimization are currently the most widely used. These algorithms can take thousands of simulation evaluations to find optimal solutions for one machine prototype. For large facilities such as the Linac Coherent Light Source (LCLS) and others, this equates to a limited exploration of many possible design configurations. In this paper, the LCLS-II photoinjector is optimized with three optimization algorithms. All optimizations were started from both a uniform random and Latin hypercube sample. In all cases, the optimizations started from Latin hypercube samples outperformed optimizations started from uniform samples. All three algorithms were able to optimize the photoinjector, with the model-based methods approximating the Pareto front in fewer simulation evaluations. This work, in combination with previous optimization observations, indicates objective penalties have a strong impact on the efficiency of such methods. In general, we recommend heuristic methods for initial optimizations and model-based methods when information about the objective space is available.

Design and operation of transfer lines for plasma wakefield accelerators using numerical optimizers

The Advanced Wakefield (AWAKE) Experiment is a proof-of-principle experiment demonstrating the acceleration of electron beams via proton-driven plasma wakefield acceleration. AWAKE Run 2 aims to build on the results of Run 1 by achieving higher energies with an improved beam quality. As part of the upgrade to Run 2, the existing proton and electron beamlines will be adapted and a second plasma cell and new 150-MeV electron beamline will be added. The specification for this new 150-MeV beamline will be challenging as it will be required to inject electron bunches with micron-level beam size and stability into the second plasma cell while being subject to tight spatial constraints. In this paper, we describe the techniques used (e.g., numerical optimizers and genetic algorithms) to produce the design of this electron line. We present a comparison of the methods used in this paper with other optimization algorithms commonly used within accelerator physics. Operational techniques are also studied including steering and alignment methods utilizing numerical optimizers and beam measurement techniques employing neural networks. We compare the performance of algorithms for online optimization and beam-based alignment in terms of their efficiency and effectiveness.