K.M. Hock

University of Liverpool, Liverpool, England, United Kingdom

Are you K.M. Hock?

Claim your profile

Publications (26)41.02 Total impact

  • Source
    [Show abstract] [Hide abstract]
    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.
    01/2014; 753:38–55.
  • Source
    [Show abstract] [Hide abstract]
    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.
    11/2013;
  • K.M. Hock, A. Wolski
    [Show abstract] [Hide abstract]
    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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 10/2013; 726:8–16. · 1.14 Impact Factor
  • I. McGregor, K. M. Hock
    [Show abstract] [Hide abstract]
    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.
    Physical Review Special Topics - Accelerators and Beams 08/2013; 16(8). · 1.57 Impact Factor
  • I McGregor, K M Hock
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe full wave simulation results for a compact, novel deflecting structure operating around 2 GHz. The structure consists of a pair of elliptical complementary split-ring resonators (CSRRs) etched into a copper rectangular waveguide along with outer rectangular cavities to maintain the vacuum. Our design utilizes the strong electric fields created by the resonators to impart a transverse deflection to particle bunches traveling through the structure. Simulations suggest a total deflecting voltage of 0.132 MV and a transverse accelerating gradient of 1.55 MV/m for only 4.42 kW of applied rf power. We also present, as a design aid, a simplified, approximate analysis of the operating frequency.
    Journal of Instrumentation 05/2013; 8(05):P05009. · 1.66 Impact Factor
  • K M Hock, M G Ibison
    [Show abstract] [Hide abstract]
    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.
    Journal of Instrumentation 02/2013; 8(02):P02003. · 1.66 Impact Factor
  • K. M. Hock, C. S. Edmonds
    [Show abstract] [Hide abstract]
    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.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2012; · 1.14 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Nature Physics 01/2012; 8(3):243-247. · 19.35 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Journal of Instrumentation 01/2012; 7(04). · 1.66 Impact Factor
  • K.M. Hock, A. Wolski
    [Show abstract] [Hide abstract]
    ABSTRACT: The procedure for calculating the resistive wall impedance is simplified using Gaussian elimination with a sufficiently large floating point precision. This procedure generalises readily to the multilayer beam pipe wall. We apply this to investigate the effect of NEG coating on the transverse wake field coupling between electron bunches in the ILC damping ring. For a 5 GeV electron beam and 3 cm radius aluminium beam pipe, a 1 μm thick NEG coating is found to increase the impedance around 10 GHz. The wake field over a distance of 300 km around the ring is required for the study of the multi-bunch instabilities. This has to be obtained by Fourier transforming over a very wide range of frequencies. To overcome the computation problem, we developed a way of splitting up the frequencies into three overlapping ranges, and then joining the transforms together to obtain the overall wake field. The results for a few NEG coating thicknesses are presented.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 11/2011; 657(1):94–98. · 1.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate that the normalised phase space can be used to improve the quality of the reconstructed image in phase space tomography. This study uses the Filtered Back Projection (FBP) for reconstruction. We simulate the tomographic projections of a Gaussian phase space distribution in real phase space and in normalised phase space. The reconstruction can be carried out in real phase space directly. It can also be done first in normalised phase space, and then the co-ordinates can be transformed to real phase space. Using FBP, we show that the latter procedure produces images that agree well with the original distribution even when there are only three angles. It also gives better resolution for a more complex distribution, which we simulate with a random collection of Gaussian spots.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 642(1):36-44. · 1.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a simulation study on the reconstruction of the phase space distribution of a beam in the EMMA injection line. The initial step has been to use a Gaussian beam to calculate the phase space distribution and the horizontal and vertical beam projections which would be expected at a screen. The projections obtained from a range of optical configurations are provided as input for reconstructing the phase space distribution using a standard tomography method. The result from the reconstruction can be compared with the known phase space distribution. By taking into account the limited range of quadrupole strengths available, we can determine how practical limitations may affect the reconstruction.
    01/2010;
  • Source
    Kai Meng Hock, Andrzej Wolski
    [Show abstract] [Hide abstract]
    ABSTRACT: Injection of fresh bunches into a storage ring can induce jitter in the stored bunches. For machines demanding beams of very low emittance and high stability, such as the damping rings of a future linear collider or the storage rings of a super flavor factory, this could be a potential performance limitation. We present an analysis, for the International Linear Collider (ILC) damping rings, of the transverse jitter induced on the extracted bunches from the jitter on the injected bunches, with the coupling between bunches mediated by the resistive-wall wakefield of the vacuum chamber. We find that it is important to include details of the local transverse focusing around the ring. We consider the impact of the finite thickness of the beam pipe wall, and of nonevaporable getter coating on the inside surface: in the parameter regime of the ILC damping rings, we find that the results are only slightly modified compared to an approximation to the resistive-wall wakefield based on a single-layer wall of infinite thickness. The results from our simulations indicate a tight specification on the jitter of the injected bunches.
    Physical Review Special Topics-accelerators and Beams - PHYS REV SPEC TOP-AC. 01/2009; 12(9).
  • Kai Meng Hock
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigate the band structure of a class of photonic crystals made from only thin wires. Using a different method, we demonstrate that a complete photonic band gap is possible for such materials. Band gap materials normally consist of space filling dielectric or metal, whereas thin wires occupy a very small fraction of the volume. We show that this is related to the large increase in scattering at the Brillouin zone boundary. The method we developed brings together the calculation techniques in three different fields. The first is the calculation of scattering from periodic, tilted antennas, which we improve upon. The second is the standard technique for frequency selective surface design. The third is obtained directly from low energy electron diffraction theory. Good agreements with experiments for left handed materials, negative materials, and frequency selective surfaces are demonstrated.
    Physical Review E 03/2008; 77(3 Pt 2):036701. · 2.31 Impact Factor
  • Source
    KM Hock, A Wolski
    [Show abstract] [Hide abstract]
    ABSTRACT: Injection of fresh bunches into a storage ring can induce jitter on stored bunches, as a result of wake field coupling. This transient effect can lead to an undesirable increase in the emittance of stored bunches; in the case of linear collider damping rings, there can also be jitter in the extracted bunches, which can adversely affect performance. We consider how the wake field coupling in a storage ring depends on the fill pattern, and, for the damping rings of the international linear collider (ILC), present the results of simulations of the transverse dynamics with a resistive wall wake field for two different fill patterns. For constant current in the damping rings, it appears that the extraction jitter is only very weakly dependent on the fill pattern.
    01/2008;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A number of photon collimators are placed inside the helical undulator to protect the cold surfaces of the vacuum vessel from being hit by the photons and thus achieving the baseline pressure requirement. Computer simulations were run in order to determine the energy deposition and instan- taneous temperature rise in these collimators and various material candidates were studied. This paper presents the status of the simulation.
    01/2008;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The clean environment of a lepton linear collider allows high-precision measurements for physics analyses. In or-der to exploit this potential, precise knowledge about the polarization state of the beams is also required. In this pa-per we concentrate on depolarization effects caused by the intense beam-beam interaction, which is expected to be the dominant source of depolarization. Higher-order effects, as well as critical analyses of the theoretical assumptions used in the past and theoretical improvements in the derivation of suitable equations, are given. Updates on existing sim-ulation programs are reported. Numerical results for the design of the International Linear Collider (ILC) are dis-cussed.
    01/2008;
  • Source
    Kai Meng Hock
    [Show abstract] [Hide abstract]
    ABSTRACT: We present an analytical and numerical study of the equations of motion for bunches coupled by transverse wakefields. We base our study on a recent lattice design for the damping rings in the baseline configuration of the International Linear Collider. Using the macroparticle model, and assuming resistive wall wakefield coupling, we present numerical results on the time evolution of the multibunch modes. Decay modes display growth after initial decay, and mode amplitudes exhibit high-frequency oscillations. These phenomena are not expected if the beta function is assumed to have a constant, averaged value. We show analytically that they can come from coupling between modes caused by variation of the beta function in a real lattice. The effect is shown to be comparable to the effect of a nonuniform fill pattern and significantly larger than that of the higher-order mode wakefield localized in the rf cavities. Turning to the case of constant beta function, we develop a more complete treatment of the equations of motion. We derive general formulas for the bunch trajectories, and show that such formulas can only be valid in the limit of small wakefield coupling.
    Physical Review Special Topics - Accelerators and Beams 08/2007; 10(8). · 1.57 Impact Factor
  • Source
    K.M. Hock, A. Wolski
    [Show abstract] [Hide abstract]
    ABSTRACT: We reconsider the equations of motion of wake field coupled bunches in the light of recent developments in Delay Differential Equations. In the case of uniform resistive wall in a storage ring, we demonstrate an alternative way to characterize the growth modes. For each multibunch Fourier mode, an infinite number of time domain modes can arise from an exact solution of the equation of motion. The growth rate as it is commonly defined corresponds to only one of them. The amplitude of each Fourier mode can therefore evolve with time in a way that is not a simple exponential. This is a result that has been observed in simulations of wake field coupled bunches.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
  • K.M. Hock
    [Show abstract] [Hide abstract]
    ABSTRACT: Not Available
    IEEE Transactions on Microwave Theory and Techniques 07/2006; · 2.23 Impact Factor