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John Power

Publications and source records attributed to John Power.

At least 19 recordsLinked to original sources
arXiv2025

Short-Pulse Driven Radiofrequency X-Band Photoinjector: Electromagnetic Properties and Beam Dynamics in the Transient Regime

This paper presents a study of the radiofrequency (RF) characteristics and beam dynamics of an X-band photogun (Xgun) operating in the transient state. The photoinjector is designed to operate with short RF pulses (9 ns) to achieve high accelerating gradients. Short-pulse operation potentially reduces breakdown risks, as experimentally demonstrated by achieving a gradient exceeding 350 MV/m. However, the short pulse duration causes the cavity to operate in a transient regime where the electromagnetic field deviates from the conventional steady-state condition. To investigate the effects of deviations from steady-state operation, the time-dependent spatial evolution of the cavity fields was examined using both 9-ns and 50-ns RF pulses. The 50-ns pulse served as a reference to characterize the cavity behavior under a fully filled steady-state condition. Beam dynamics simulations were conducted to explore the impact of transient RF effects on beam kinetic energy, transverse emittance, and bunch length; these simulations employed a new dynamic field mapping approach to model transient RF fields.

physics.acc-ph↗
arXiv2024

Experimental demonstration of cascaded round-to-flat and flat-to-round beam transformations

Magnetized beams beam with significant canonical angular momentum are critical to electron cooling of hadron beams such as contemplated in next-generation hadron and electron-ion colliders. The transport of magnetized electron beams over long distances in a locally non-axisymmetric external field is challenging. An alternative is to transform the beam into an uncoupled "flat beam", transport the produced "flat" beam over a long distance, and reintroduce the cross-plane coupling to "re-magnetize" the beam. In this paper, we demonstrate via numerical simulation and laboratory experiments such a cascaded-transformation approach.

physics.acc-ph↗
arXiv2024

Efficient 6-dimensional phase space reconstruction from experimental measurements using generative machine learning

Next-generation accelerator concepts which hinge on the precise shaping of beam distributions, demand equally precise diagnostic methods capable of reconstructing beam distributions within 6-dimensional position-momentum spaces. However, the characterization of intricate features within 6-dimensional beam distributions using conventional diagnostic techniques necessitates hundreds of measurements, using many hours of valuable beam time. Novel phase space reconstruction techniques are needed to substantially reduce the number of measurements required to reconstruct detailed, high-dimensional beam features in order to resolve complex beam phenomena, and as feedback in precision beam shaping applications. In this study, we present a novel approach to reconstructing detailed 6-dimensional phase space distributions from experimental measurements using generative machine learning and differentiable beam dynamics simulations. We demonstrate that for a collection of synthetic beam distribution test cases that this approach can be used to resolve 6-dimensional phase space distributions using basic beam manipulations and as few as 20 2-dimensional measurements of the beam profile, without the need for prior data collection or model training. We also demonstrate an application of the reconstruction method in an experimental setting at the Argonne Wakefield Accelerator, where it is able to reconstruct the beam distribution and accurately predict previously unseen measurements 75x faster than previous methods.

physics.acc-ph↗
arXiv2024

Four-Dimensional Phase-Space Reconstruction of Flat and Magnetized Beams Using Neural Networks and Differentiable Simulations

Beams with cross-plane coupling or extreme asymmetries between the two transverse phase spaces are often encountered in particle accelerators. Flat beams with large transverse-emittance ratios are critical for future linear colliders. Similarly, magnetized beams with significant cross-plane coupling are expected to enhance the performance of electron cooling in hadron beams. Preparing these beams requires precise control and characterization of the four-dimensional transverse phase space. In this study, we employ generative phase space reconstruction (GPSR) techniques to rapidly characterize magnetized and flat-beam phase-space distributions using a conventional quadrupole-scan method. The reconstruction technique is experimentally demonstrated on an electron beam produced at the Argonne Wakefield Accelerator and successfully benchmarked against conventional diagnostics techniques. Specifically, we show that predicted beam parameters from the reconstructed phase-space distributions (e.g. as magnetization and flat beam emittances) are in excellent agreement with those measured from the conventional diagnostic methods.

physics.acc-ph↗
arXiv2023

An Integrated Multi-Physics Optimization Framework for Particle Accelerator Design

The overarching goal of beamline design is to achieve a high brightness electron beam from the beamline. Traditional beamline design studies involved separate optimizations of radio-frequency cavities, magnets, and beam dynamics using different codes and pursuing various intermediate objectives. In this work, we present a novel unified global optimization framework that integrates multiple physics modules for beamline design as simulation functions for a two-stage global optimization solver.

physics.acc-ph↗
arXiv2023

Observation of Skewed Electromagnetic Wakefields in an Asymmetric Structure Driven by Flat Electron Bunches

Relativistic charged-particle beams which generate intense longitudinal fields in accelerating structures also inherently couple to transverse modes. The effects of this coupling may lead to beam break-up instability, and thus must be countered to preserve beam quality in applications such as linear colliders. Beams with highly asymmetric transverse sizes (flat-beams) have been shown to suppress the initial instability in slab-symmetric structures. However, as the coupling to transverse modes remains, this solution serves only to delay instability. In order to understand the hazards of transverse coupling in such a case, we describe here an experiment characterizing the transverse effects on a flat-beam, traversing near a planar dielectric lined structure. The measurements reveal the emergence of a previously unobserved skew-quadrupole-like interaction when the beam is canted transversely, which is not present when the flat-beam travels parallel to the dielectric surface. We deploy a multipole field fitting algorithm to reconstruct the projected transverse wakefields from the data. We generate the effective kick vector map using a simple two-particle theoretical model, with particle-in-cell simulations used to provide further insight for realistic particle distributions.

physics.acc-ph↗
arXiv2023

Demonstration of Autonomous Emittance Characterization at the Argonne Wakefield Accelerator

Transverse beam emittance plays a key role in the performance of high brightness accelerators. Characterizing beam emittance is often done using a quadrupole scan, which fits beam matrix elements to experimental measurements using first order optics. Despite its simplicity at face value, this procedure is difficult to automate due to practical limitations. Key issues that must be addressed include maintaining beam size measurement validity by keeping beams within the radius to diagnostic screens, ensuring that measurement fitting produces physically valid results, and accurately characterizing emittance uncertainty. We describe a demonstration of the Bayesian Exploration technique towards solving this problem at the Argonne Wakefield Accelerator, enabling a turnkey, autonomous quadrupole scan tool that can be used to quickly measure beam emittances at various locations in accelerators with limited operator input.

physics.acc-ph↗
arXiv2023

Beam Delivery and Beamstrahlung Considerations for Ultra-High Energy Linear Colliders

As part of the Snowmass'21 community planning excercise, the Advanced Accelerator Concepts (AAC) community proposed future linear colliders with center-of-mass energies up to 15 TeV and luminosities up to 50$\times10^{34}$ cm$^{-2}$s$^{-1}$ in a compact footprint. In addition to being compact, these machines must also be energy efficient. We identify two challenges that must be addressed in the design of these machines. First, the Beam Delivery System (BDS) must not add significant length to the accelerator complex. Second, beam parameters must be chosen to mitigate beamstrahlung effects and maximize the luminosity-per-power of the machine. In this paper, we review advances in plasma lens technology that will help to reduce the length of the BDS system and we detail new Particle-in-Cell simulation studies that will provide insight into beamstrahlung mitigation techniques. We apply our analysis to both $e^+e^-$ and $\gamma\gamma$ colliders.

physics.acc-ph↗
arXiv2022

Evaluating Effects of Geometry and Material Composition on Production of Transversely Shaped Beams from Diamond Field Emission Array Cathodes

Field emission cathodes (FECs) are attractive for the next generation of injectors due to their ability to provide high current density bright beams with low intrinsic emittance. One application of FECs worthy of special attention is to provide transversely shaped electron beams for emittance exchange that translates a transverse electron beam pattern into a longitudinal pattern. FECs can be fabricated in a desired pattern and produce transversely shaped beams without the need for complex masking or laser schemes. However, reliable and consistent production of transversely shaped beams is affected by material properties of the FEC. This paper reports the results of testing two diamond field emitter array (DFEA) FECs with the same lithography pattern and emitter geometry but different material and tip characteristics. Although both cathodes were able to sustain gradients of 44 MV/m and produce maximum output integral charge of 0.5 nC per radiofrequency (rf) pulse, their emission patterns were quite different. One cathode did not produce a patterned beam while the other one did. Differences in field emission characteristics and patterned beam production were explained by the differences in the tip geometry and the cathode material properties. The main practical takeaway was found to be that the tip sharpness was not a prerequisite for good patterned beam production. Instead, other material characteristics, such as the ballast resistance, determined cathode performance.

physics.acc-ph↗
arXiv2022

Phase Space Reconstruction from Accelerator Beam Measurements Using Neural Networks and Differentiable Simulations

Characterizing the phase space distribution of particle beams in accelerators is a central part of accelerator understanding and performance optimization. However, conventional reconstruction-based techniques either use simplifying assumptions or require specialized diagnostics to infer high-dimensional ($>$ 2D) beam properties. In this Letter, we introduce a general-purpose algorithm that combines neural networks with differentiable particle tracking to efficiently reconstruct high-dimensional phase space distributions without using specialized beam diagnostics or beam manipulations. We demonstrate that our algorithm accurately reconstructs detailed 4D phase space distributions with corresponding confidence intervals in both simulation and experiment using a single focusing quadrupole and diagnostic screen. This technique allows for the measurement of multiple correlated phase spaces simultaneously, which will enable simplified 6D phase space distribution reconstructions in the future.

physics.acc-ph↗
arXiv2022

Report of the Snowmass 2021 e$^+$e$^-$-Collider Forum

A summary of the Snowmass 2021 e$^+$e$^-$-Collider Forum discussions, white papers submitted to the Snowmass 2021 community study, submissions of the Energy Frontier (EF) subgroups and the Accelerator Frontier (AF) Integrated Task Force (ITF) are presented.

hep-ex↗
arXiv2022

Electron Sources for Accelerators

Electron sources are essential to an array of electron accelerator supporting research in high-energy physics and beyond. This report summarizes the "Snowmass 2021 Electron Source Workshop" which reviewed the current state-of-the art research and identified some possible research directions.

physics.acc-ph↗
arXiv2022

Proposal for a Damping-Ring-Free Electron Injector for Future Linear Colliders

The current designs of future electron-positron linear colliders incorporate large and complex damping rings to produce asymmetric beams for beamstrahlung suppression. Here we present the design of an electron injector capable of delivering flat electron beams with phase-space partition comparable to the electron-beam parameters produced downstream of the damping ring in the proposed international linear collider (ILC) design. Our design does not employ a damping ring but is instead based on cross-plane phase-space-manipulation techniques. The performance of the proposed configuration, its sensitivity to jitter along with its impact on spin-polarization is investigated. The proposed paradigm could be adapted to other linear collider concepts under consideration and offers a path toward significant cost and complexity reduction.

physics.acc-ph↗
arXiv2022

Feedback and control systems for future linear colliders: White Paper for Snowmass 2021 Topical Group AF07-RF

Particle accelerators for high energy physics will generate TeV-scale particle beams in large, multi-Km size machines colliding high brightness beams at the interaction point [1-4]. The high luminosity in such machines is achieved by producing very small asymmetric beam size at the interaction point, with short durations to minimize beam-beam effects. Tuning energy, timing and position of the beam for optimal performance will require high-precision controls of amplitude and phase of high-frequency electromagnetic fields and real-time processing of complex algorithms. The stability of the colliding beams has a large impact on the collider's effective luminosity. Therefore, the technology readiness level of diagnostic and control systems will be a major consideration in the collider design. The technical requirements of such systems depend on the specifics of beam parameters, such as transverse and longitudinal dimensions, charge/pulse and beam pulse format, which are driven by the accelerating technology of choice. While feedback systems with single bunch position monitor resolution below 50 nm and latency <300 ns have been demonstrated in beam test facilities, many advanced collider concepts make use of higher repetition rates, brighter beams and higher accelerating frequencies, and will require better performance, up to 1-2 order of magnitude, demanding aggressive R&D to be able to deliver and maintain the targeted luminosity.

physics.acc-ph↗
arXiv2022

C$^3$ Demonstration Research and Development Plan

C$^3$ is an opportunity to realize an e$^+$e$^-$ collider for the study of the Higgs boson at $\sqrt{s} = 250$ GeV, with a well defined upgrade path to 550 GeV while staying on the same short facility footprint. C$^3$ is based on a fundamentally new approach to normal conducting linear accelerators that achieves both high gradient and high efficiency at relatively low cost. Given the advanced state of linear collider designs, the key system that requires technical maturation for C$^3$ is the main linac. This white paper presents the staged approach towards a facility to demonstrate C$^3$ technology with both Direct (source and main linac) and Parallel (beam delivery, damping ring, ancillary component) R&D. The white paper also includes discussion on the approach for technology industrialization, related HEP R&D activities that are enabled by C$^3$ R&D, infrastructure requirements and siting options.

physics.acc-ph↗
arXiv2022

Advanced RF Structures for Wakefield Acceleration and High-Gradient Research

Structure wakefield acceleration (SWFA) is one of the most promising AAC schemes in several recent strategic reports, including DOE's 2016 AAC Roadmap, report on the Advanced and Novel Accelerators for High Energy Physics Roadmap (ANAR), and report on Accelerator and Beam Physics Research Goals and Opportunities. SWFA aims to raise the gradient beyond the limits of conventional radiofrequency (RF) accelerator technology, and thus the RF to beam energy efficiency, by reducing RF breakdowns from confining the microwave energy in a short (on the order of about 10 ns) and intense pulse excited by a drive beam. We envision that the following research topics, within the scope of AF7, are of great interest in the next decade: advanced wakefield structures, terahertz and sub-terahertz (THz) structures, and RF breakdown physics. Research on SWFA in the above directions would directly contribute to long-term large-scale applications, including AAC-based linear colliders and compact light sources. There is also potentially a strong synergy between SWFA and other AAC concepts, when structures are combined with plasmas into hybrid AAC schemes. Research on novel structures is at the core of advancing SWFA, and is critical to future AAC-based linear colliders; at the same, it has a strong synergy with other directions, such as cavity designs, high-power microwave systems and sources, and compact light sources.

physics.acc-ph↗
arXiv2022

Continuous and Coordinated Efforts of Structure Wakefield Acceleration (SWFA) Development for an Energy Frontier Machine

Structure wakefield acceleration (SWFA) is well suited for the linear collider (LC) application due to its natural ability to accelerate positrons and preserve emittance. Under the SWFA roadmap, which was developed in response to Snowmass 2013 recommendations, four principal technologies: drive beam, main beam, wakefield structure, and LC facility design, have been investigated. The two SWFA schemes under development are the collinear wakefield accelerator (CWA), in which the drive and main beam follow the same path through a structure, and the two-beam accelerator (TBA), where the drive and main beam pass through different structures. To further advance the SWFA technology in the next decade, continuous and coordinated efforts must be carried out in a more synchronized way. This whitepaper is written to address the research needs in SWFA for preparation of Snowmass 2022.

physics.acc-ph↗