K.M. Hock

University of Liverpool, Liverpool, England, United Kingdom

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Publications (35)47.3 Total impact

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    ABSTRACT: The positron source for the International Linear Collider (ILC) is dependent upon a ~200 m long helical undulator to generate a high flux of multi-MeV photons. The undulator system is broken down into a series of 4 m cryomodules, which each contain two superconducting helical undulators. Following a dedicated R&D phase and the construction and measurement of a number of short prototypes a full scale cryomodule has now been manufactured for the first time. This paper reports on the design, manufacture, and test results of this cryomodule.
    Full-text · Article · May 2015
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    ABSTRACT: Contribution to a conf. proceeding (book/online)
    Full-text · Article · May 2015
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    ABSTRACT: In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a ‘scaling’ principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12–18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators.
    Full-text · Article · Apr 2015
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    ABSTRACT: We present PyZgoubi, a framework that has been developed based on the tracking engine Zgoubi to model, optimise and visualise the dynamics in particle accelerators, especially fixed-field alternating-gradient (FFAG) accelerators. We show that PyZgoubi abstracts Zgoubi by wrapping it in an easy-to-use Python framework in order to allow simple construction, parameterisation, visualisation and optimisation of FFAG accelerator lattices, Its object oriented design gives it the flexibility and extensibility required for current novel FFAG design. We apply PyZgoubi to two example FFAGs; this includes determining the dynamic aperture of the PAMELA medical FFAG in the presence of magnet misalignments, and illustrating how PyZgoubi may be used to optimise FFAGs. We also discuss a robust definition of dynamic aperture in an FFAG and show its implementation in PyZgoubi. (C) 2014 The Authors. Published by Elsevier B.V.
    No preview · Article · Mar 2015 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: We present a design for a 30-350 MeV scaling racetrack FFAG accelerator for medical application - NORMA (NOrmal-conducting Racetrack Medical Accelerator)-which utilises normal-conducting magnets. NORMA consists of 12 FDF triplet cells with a maximum drift length of ∼2 m; an additional drift space inserted into two places forms a racetrack lattice with enough space for injection/extraction. Optimisation routines in PyZgoubi are used to find optimum cell parameters and working point.
    No preview · Article · Jul 2014
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    ABSTRACT: Beam tomography research at Daresbury Laboratory has focussed on the development of normalised phase space techniques—starting with the idea of sampling tomographic projections at equal phase advances. This idea has influenced the design and operation of the tomography sections at the Photo Injector Test Facility at Zeuthen (PITZ) and at the Accelerator and Lasers in Combined Experiments (ALICE) at Daresbury. We have studied the feasibility of using normalised phase space to measure the effect of space charge. Quadrupole scan measurements are carried out at two different parts of a beamline. Reconstructions at the same location give results that are clearly rotated with respect to each other in normalised phase space. We are able to show that a significant part of this rotation can be attributed to the effect of space charge. We show how the normalised phase space technique can be used to increase the reliability of the Maximum Entropy Technique (MENT). While MENT is known for its ability to work with just a few projections, the accuracy of its reconstructions has seldom been questioned. We show that for typical phase space distributions, MENT could produce results that look quite different from the original. We demonstrate that a normalised phase space technique could give results that are closer to the actual distribution. We also present simpler ways of deriving the phase space tomography formalism and the Maximum Entropy Technique.
    Full-text · Article · Jul 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: In high chromaticity circular accelerators, rapid decoherence of the betatron motion of a particle beam can make the measurement of lattice and bunch values, such as Courant-Snyder parameters and betatron amplitude, difficult. A method for reconstructing the momentum distribution of a beam from beam position measurements is presented. Further analysis of the same beam position monitor data allows estimates to be made of the Courant-Snyder parameters and the amplitude of coherent betatron oscillation of the beam. The methods are tested through application to data taken on the linear nonscaling fixed field alternating gradient accelerator, EMMA.
    No preview · Article · May 2014 · Physical Review Special Topics - Accelerators and Beams
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    ABSTRACT: This is a review on beam tomography research at Daresbury. The research has focussed on development of normalised phase space techniques. It starts with the idea of sampling tomographic projections at equal phase advances and shows that this would give the optimal reconstruction results. This idea has influenced the design, construction and operation of the tomography sections at the Photo Injector Test Facility at Zeuthen (PITZ) and at the Accelerator and Laser in Combined Experiments (ALICE) at Daresbury. The theoretical justification of this idea is later developed through simulations and analysis of the measurements results at ALICE. The mathematical formalism is constructed around the normalised phase space and the idea of equal phase advances become the basis of this. This formalism is applied to a variety of experimental and simulated situations and shown to be useful in improving resolution, increasing reliability and providing diagnostic information. In this review, we also present the simplifying concepts, formalisms and simulation tools that we have developed.
    Full-text · Article · Nov 2013
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    K. M. Hock · A. Wolski
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    ABSTRACT: We present a method to measure and reconstruct the full 4D transverse phase space of a particle beam. The method assumes that it is possible to freely and independently rotate the separate 2D transverse phase spaces in the horizontal and vertical directions. Using images of the beam that would be captured on a screen, we develop a mathematical procedure that will reconstruct the full 4D particle distribution. We simulate this procedure for a hypothetical distribution and show that the reconstruction agrees with the actual distribution. Finally, we demonstrate for the practical case of a two-quadrupole setup that it is indeed possible to adjust the quadrupole strengths so that the separate 2D transverse phase spaces can be rotated independently. However, in this setup, the rotation angles are restricted to smaller ranges. Even so, the reconstructed results reproduce the actual distribution clearly.
    Preview · Article · Oct 2013 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
  • I. McGregor · K. M. Hock
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    ABSTRACT: In this paper, we present theoretical and simulation-based analyses of a novel, normal-conducting, multiple-cell, traveling wave accelerating structure. Instead of the conventional circular apertures, we utilize asymmetric complementary split-ring resonators to couple pillbox cavities and bring the phase velocity below that of the speed of light in vacuo. We show that this architecture exhibits a low, negative, group velocity and that the 0 through π modes decrease in order of frequency—in contrast to conventional electrically coupled structures in which the 0 mode has the lowest frequency and the π mode the highest. We illustrate the efficacy of the proposed design via electromagnetic and particle simulation results for a four-cell structure operating around 1.9 GHz. Results are given for operation in the π, 2π/3, and π/3 modes. Our design achieves accelerating gradients of around 3.3 MV/m and a cavity voltage of 0.594 MV for an applied rf power of 82 kW (π mode). The accelerating gradients achieved are up to 3.3 times that of a conventional circular aperture-coupled design with the same phase velocity, rf excitation power, operating frequency, mode type, and number of cells.
    No preview · Article · Aug 2013 · Physical Review Special Topics - Accelerators and Beams
  • I McGregor · K M Hock
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    ABSTRACT: We describe a novel particle accelerating structure consisting of Complementary Split-Ring Resonators (C-SRRs) etched into the lower and upper walls of a copper rectangular waveguide. Outer cylindrical cavities enclosing the C-SRR sections allow a vacuum to be maintained. The accelerating gradient of a 1 GHz cavity is simulated to be 8.76 MV/m, when referenced to the actual accelerating gap, for only 10.7 kW of input power. Particle simulation results confirm the efficacy of the proposed structure. A simple analytical model of the structure is given as a design aid to compute the relationship between the key geometrical parameters and the resonance frequency.
    No preview · Article · May 2013 · Journal of Instrumentation
  • K M Hock · M G Ibison
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    ABSTRACT: We study a problem with the Maximum Entropy Technique (MENT) when applied to tomographic measurements of the transverse phase space of electron beams, and suggest some ways to improve its reliability. We show that the outcome of a phase space reconstruction can be highly sensitive to the choice of projection angles. It is quite likely to obtain reconstructed distributions of the phase space that are obviously different from the actual distributions. We propose a method to obtain a ``good'' choice of projections angles using a normalised phase space. We demonstrate that the resulting reconstructions of the phase space can be significantly improved.
    No preview · Article · Feb 2013 · Journal of Instrumentation
  • I. McGregor · K.M. Hock
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    ABSTRACT: We report on the progress of our research into metamaterial-based accelerating, bending and focusing structures at the Cockcroft Institute. The effort during the last year has been directed towards designing and investigating practical RF structures that are suitable for industrial and medical applications. We have shown that, by introducing structures based on metamaterial resonators, RF accelerating structures can be made more compact and higher gradient. This year, we will concentrate on focusing and bending structures.
    No preview · Article · Jan 2013
  • K.M. Hock · A. Wolski · R.B. Appleby
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    ABSTRACT: The "Simple Accelerator Modelling in Matlab" (SAMM) code is a set of Matlab routines for modelling beam dynamics in high energy particle accelerators. It includes a set of CUDA codes that can be run on a graphics processing unit. These can be called from SAMM and can potentially give a significant increase in tracking speed. To make use of this potential for the computationally intensive LHC upgrade simulations, we have developed additional Matlab and CUDA routines to simulate the full set of elements that are present in the Large Hadron Collider. We present the results of applying these codes to dynamic aperture calculations. These results are benchmarked against PTC and MADX. Copyright © 2013 by JACoW- cc Creative Commons Attribution 3.0 (CC-BY-3.0).
    No preview · Article · Jan 2013
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    ABSTRACT: We report on the progress of phase space tomography research at Daresbury. The effort over the past three years has been focussed on measuring the electron beam at the ALICE tomography section. Based on the results, we have developed techniques for improving resolution using normalised phase space and for removing streaking artefacts. We have developed in-house reconstruction codes using both Filtered Back Projection and MaximumEntropy Technique. We use a combination of simulation and measurements to investigate the onset of space charge effects at over short distances. We are currently developing methods for full 4D phase space reconstruction.
    No preview · Article · Jan 2013
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    ABSTRACT: The ALICE tomography section at Daresbury is a diagnostic setup in the injection line of EMMA, the world's first non-scaling FFAG accelerator. We present our measurements and analysis of the transverse emittance, Twiss parameters and phase space distribution of the electron beam that is injected into EMMA. The measurements are carried out at 12 MeV, for bunch charges from 20 to 80 pC. Quadrupole scans and tomography are used. The results show that space charge effect does not change the beam emittance significantly over the length of the tomography section. Starting from projections of the beam images, the quadrupole scan technique can be applied to give the emittance and Twiss parameters. The same projections can be processed using tomography to give the phase space distribution. A careful treatment of the background noise is required to produce consistent emittances between quadrupole scans at different locations. Extending this in a natural way to tomography, we are also able to remove most of the the streaking artefacts from reconstructions obtained using the Filtered Back Projection technique.
    No preview · Article · Apr 2012 · Journal of Instrumentation
  • K. M. Hock · C. S. Edmonds
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    ABSTRACT: We study a ray tracing method that uses tiny arcs to track a proton through a magnetic field. We show how to apply this to an FFAG and a synchrotron that are designed for cancer therapy. Assuming that the field traversed by a proton is uniform over each time step, the required equations and a simple scheme for treating a lattice are developed. We compare the computation time with the code Zgoubi for a FODO lattice. To test its usefulness, it is applied to the spiral FFAG, designed in the RACCAM project, to find the horizontal phase space trajectories. It is also applied to a compact synchrotron, designed in Japan, to determine the phase space trajectories during slow extraction of the proton beam.
    No preview · Article · Feb 2012 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment
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    ABSTRACT: In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a ‘scaling’ principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12–18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators.
    No preview · Article · Jan 2012 · Nature Physics
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    ABSTRACT: ALICE is an experimental electron accelerator designed to operate over a range of energies up to 35 MeV, and with up to 80 pC bunch charge. A dedicated tomography diagnostic section allows measurement of the transverse phase space with different beam parameters. In the lowenergy, high-charge regime, space charge effects must be considered: to quantify these effects, the tracking code GPT has been used to simulate beams in the tomography diagnostic section. The results can be compared with simplified models, and with experimental measurements.
    No preview · Article · Jan 2012
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    ABSTRACT: EMMA (Electron Model for Many Applications) is a prototype non-scaling electron FFAGoperating at Daresbury Laboratory. After demonstrating serpentine channel acceleration andfast resonance crossing in 2011, studies continue of the beam dynamics to explore the largetransverse and longitudinal acceptance, the detailed effects of integer tune crossing atslow acceleration rates, comparison of measurements to detailed field measurements, and theexperimental mapping of the machine by relating the initial and final phase spacecoordinates. These recent results are reported in this paper, together with more practicalimprovements such as injection orbit matching with real-time monitoring of the bunchcoordinates in transverse phase space.
    No preview · Article · Jan 2012