Publications by Suzie Sheehy

Developing innovative, robust and affordable medical linear accelerators for challenging environments

Clinical Oncology Elsevier 31 (2019) 352-355

M Dosanjh, A Aggarwal, D Pistenmaa, E Amankwaa-Frempong, D Angal-Kalinin, S Boogert, D Brown, M Carlone, P Collier, L Court, A Di Meglio, J Van Dyk, S Grover, DA Jaffray, C Jamieson, I Konoplev, H Makwani, P McIntosh, B Militsyn, J Palta, S Sheehy, SC Aruah, I Syratchev, E Zubizarreta, CN Coleman

The annual global incidence of cancer is projected to rise in 2035 to 25 million cases (13 million deaths), with 70% occurring in low- and middle-income countries (LMICs), where there is a severe shortfall in the availability of radiotherapy [1] – an essential component of overall curative and palliative cancer care. A 2015 report by the Global Task Force on Radiotherapy for Cancer Control estimated that by 2035 at least 5000 additional megavolt treatment machines would be needed to meet LMIC demands, together with about 30 000 radiation oncologists, 22 000 medical physicists and 80 000 radiation therapy technologists [2]. Among the main reasons for the shortfall identified in the workshop and thoroughly discussed in the Clinical Oncology special issue on radiotherapy in LMICs [3] are: (i) the initial cost of linear accelerators, (ii) the cost of service on the machines and (iii) a shortage of trained personnel needed to deliver safe, effective and high-quality treatment. A number of authors who contributed to the Clinical Oncology special issue are participating in the CERN, International Cancer Expert Corps (ICEC), Science and Technology Facilities Council (STFC) collaborative effort described in this editorial (Aggarwal, Coleman, Court, Grover, Palta, Van Dyk and Zubizarreta).

A study of coherent and incoherent resonances in high intensity beams using a linear Paul trap

New Journal of Physics IOP Publishing 21 (2019)

L Martin, S Machida, D Kelliher, S Sheehy

In this paper we present a quantitative measurement of the change in frequency (tune) with intensity of four transverse resonances in a high intensity Gaussian beam. Due to the non-linear space charge forces present in high intensity beams, particle motion cannot be analytically described. Instead we use the Simulator of Particle Orbit Dynamics (S-POD) and the Intense Beam Experiment (IBEX), two linear Paul traps, to experimentally replicate the system. In high intensity beams a coherent resonant response to both space charge and external field driven perturbations is possible, these coherent resonances are excited at a tune that differs by a factor $C_{m}$ from that of the incoherent resonance. By increasing the number of ions stored in the linear Paul trap and studying the location of four different resonances we extract provisional values describing the change in tune of the resonance with intensity. These values are then compared to the $C_{m}$ factors for coherent resonances. We find that the $C_{m}$ factors do not accurately predict the location of resonances in high intensity Gaussian beams. Further insight into the experiment is gained through simulation using Warp, a particle-in-cell code.

A new method to measure the beta function in a Paul trap

Joint Accelerator Conferences Website Joint Accelerator Conferences Website (2018) 3262-3265
Part of a series from 9th International Particle Accelerator Conference 2018 Vancouver, British Columbia, Canada, April 29 to May 4, 2018

L Martin, K Ito, DJ Kelliher, S Machida, H Okamoto, S Sheehy

The Simulator of Particle Orbit Dynamics (S-POD) is a linear Paul trap at Hiroshima University, Japan, used to study beam physics. S-POD has so far been used to study resonances in high intensity beams, predominantly using a simple alternating gradient lattice configuration. Recently a similar apparatus, the Intense Beam Experiment (IBEX), has been constructed at the Rutherford Appleton Lab in the UK. To use either of these experiments to study beam dynamics in more complex lattice configurations in the future, further diagnostic techniques must be developed for Paul traps. Here we describe a new method to measure the beta function and emittance in a Paul trap.

Commissioning and first results of the IBEX Paul Trap

Journal of Physics: Conference Series Institute of Physics 874 (2017) 012067-

S Sheehy, EJ Carr, LK Martin, K Budzik, DJ Kelliher, S Machida, CR Prior

The Intense Beam Experiment (IBEX) is a linear Paul trap designed to replicate the dynamics of intense particle beams in accelerators. Similar to the S-POD apparatus at Hiroshima University, IBEX is a small scale experiment which has been constructed and recently commissioned at the STFC Rutherford Appleton Laboratory in the UK. The aim of the experiment is to support theoretical studies of next-generation high intensity proton and ion accelerators, complementing existing computer simulation approaches. Here we report on the status of commissioning and first results obtained.

Fixed field alternating gradient accelerators

Proceedings of the CAS-CERN Accelerator School on Accelerators for Medical Applications CERN 2017 (2017) 321-335

S Sheehy

These notes provide an overview of Fixed-Field Alternating-Gradient (FFAG) accelerators for medical applications. We begin with a review of the basic principles of this type of accelerator, including the scaling and non-scaling types, highlighting beam dynamics issues that are of relevance to hadron accelerators. The potential of FFAG accelerators in the field of hadron therapy is discussed in detail, including an overview of existing medical FFAG designs. The options for FFAG treatment gantries are also considered.

Characterization techniques for fixed-field alternating gradient accelerators and beam studies using the KURRI 150 MeV proton FFAG

Progress of Theoretical and Experimental Physics Oxford University Press (2016)

S Sheehy, DJ Kelliher, S Machida, C Rogers, CR Prior, L Volat, M Haj Tahar, Y Ishi, Y Kuriyama, M Sakamoto, T Uesugi, Y Mori

In this paper we describe the methods and tools used to characterize a 150 MeV proton scaling Fixed Field Alternating Gradient (FFAG) accelerator at Kyoto University Research Reactor Institute. Many of the techniques used are unique to this class of machine and are thus of relevance to any future FFAG accelerator. For the first time we detail systematic studies under- taken to improve the beam quality of the FFAG. The control of beam quality in this manner is crucial to demonstrating high power operation of FFAG accelerators in future.

Studies of ultimate intensity limits for high power proton linacs

IPAC 2016 - Proceedings of the 7th International Particle Accelerator Conference (2016) 951-954

C Plostinar, CR Prior, GH Rees, SL Sheehy, IV Konoplev, A Seryi, MO Boenig, A Geisler, O Heid

Copyright © 2016 CC-BY-3.0 and by the respective authors. Although modern high power proton machines can now routinely deliver MW level operating powers, the next generation accelerators will be required to reach powers orders of magnitude higher [1,2]. Significant developments will be needed both in technology and in understanding the limits of high intensity operation. The present study investigates the beam dynamics in three experimental linac designs when the beam intensity is increased above current levels such that for CW regimes, beam powers of up to 400 MW can be attained. In the first, a 1 A proton beam is accelerated to 400 MeV using normal conducting structures. In the second, a comparison is made when two front ends accelerate 0.5 A beams to ∼20 MeV where they are funnelled to 1 A and accelerated to 400 MeV. Similarly, in the third, two 0.25 A beams are funnelled to 0.5 A and then accelerated in superconducting structures to 800 MeV. In addition, alternative unconventional methods of generating high current beams are also discussed. The further studies that are needed to be undertaken in the future are outlined, but it is considered that the three linac configurations found are sufficiently promising for detailed technical designs to follow.

Overview of the design of the IBEX linear Paul trap

IPAC 2016 - Proceedings of the 7th International Particle Accelerator Conference (2016) 3104-3106

SL Sheehy, DJ Kelliher, S Machida, C Plostinar, CR Prior

Copyright © 2016 CC-BY-3.0 and by the respective authors. We report on the status and design of the Intense Beam Experiment (IBEX) at RAL. This small experiment consists of a linear Paul trap apparatus similar to the S-POD system at Hiroshima University, confining non-neutral Argon plasma in an rf quadrupole field. The physical equivalence between this device and a beam in a linear focusing channel makes it suitable for accelerator physics studies including resonances and high intensity effects. We give an overview of the design and construction of IBEX and outline plans for commissioning and the future experimental programme.

Experimental study of integer resonance crossing in a nonscaling fixed field alternating gradient accelerator with a Paul ion trap


K Moriya, K Fukushima, K Ito, T Okano, H Okamoto, SL Sheehy, DJ Kelliher, S Machida, CR Prior

The PyZgoubi framework and the simulation of dynamic aperture in fixed-field alternating-gradient accelerators


S Tygier, RB Appleby, JM Garland, K Hock, H Owen, DJ Kelliher, SL Sheehy

Progress on simulation of fixed field alternating gradient accelerators

6th International Particle Accelerator Conference, IPAC 2015 (2015) 495-498

SL Sheehy, DJ Kelliher, S Machida, CR Prior, C Rogers, M Haj Tahar, F Meot, Y Ishi, T Uesugi, Y Kuriyama, M Sakamoto, Y Mori, A Adelmann

Copyright © 2015 CC-BY-3.0 and by the respective authors. Fixed Field Alternating Gradient accelerators have been realised in recent decades thanks partly to computational power, enabling detailed design and simulation prior to construction. We review the specific challenges of these machines and the range of different codes used to model them including ZGOUBI, OPAL, SCODE and a number of inhouse codes from different institutes. The current status of benchmarking between codes is presented and compared to the results of recent characterisation experiments with a 150 MeV FFAG at KURRI in Japan. Finally, we outline plans toward ever more realistic simulations including space charge, material interactions and more detailed models of various components.

Fixed points in presence of space charge in circular particle accelerators

6th International Particle Accelerator Conference, IPAC 2015 (2015) 389-391

SS Gilardoni, M Giovannozzi, A Huschauer, S Machida, CR Prior, SL Sheehy

Copyright © 2015 CC-BY-3.0 and by the respective authors. Recent measurements performed in the framework of the multi-turn extraction (MTE) studies at the CERN Proton Synchrotron showed a dependence of the position of beamlets obtained by crossing a stable transverse resonance on the total beam intensity. This novel observation has triggered a number of studies aiming at understanding the source of the observed effect. In this paper the results of numerical simulations performed in different conditions are discussed in detail.

Plans for a Linear Paul Trap at Rutherford Appleton Laboratory

6th International Particle Accelerator Conference, IPAC 2015 (2015) 2590-2593

DJ Kelliher, S Machida, C Plostinar, CR Prior, SL Sheehy

Copyright © 2015 CC-BY-3.0 and by the respective authors. For over a decade, Linear Paul Traps (LPT) have been used in the study of accelerator beam dynamics. LPT studies exploit the similarity of the Hamiltonian with that of a beam in a quadrupole channel while having advantages in the flexibility of parameter choice, compactness and low cost. In collaboration with Hiroshima University, LPT research planned at STFC Rutherford Appleton Laboratory (RAL) in the UK aims to investigate a range of topics including resonance crossing, halo formation, long-term stability studies and space charge effects. Initially, a conventional quadrupole-based LPT will be built at RAL and used for a variety of experiments. In parallel, a design for a more advanced LPT that incorporates higher order multipoles will be pursued and later constructed. This multipole trap will allow non-linear lattice elements to be simulated and so broaden considerably the range of experiments that can be conducted. These will include the investigation of resonance crossing in non-linear lattices, a more detailed study of halo formation and the effect of detuning with amplitude. In this paper we report on progress made in the project to date and future plans.

Study of resonance crossing in non-scaling FFAGS using the S-POD linear Paul trap

IPAC 2014: Proceedings of the 5th International Particle Accelerator Conference (2014) 1571-1573

DJ Kelliher, S Machida, CR Prior, SL Sheehy, K Fukushima, K Ito, K Moriya, H Okamoto, T Okano

Copyright © 2014 CC-BY-3.0 and by the respective authors. Experiments on EMMA have shown that with rapid acceleration a linear non-scaling FFAG can accelerate through several integer tunes without detrimental effects on the beam [1]. Proton and ion applications such as hadron therapy will necessarily have a slower acceleration rate, so their feasibility depends on how harmful resonance crossing is in this regime. A simple and useful tool to answer such fundamental questions is the Simulator of Particle Orbit Dynamics (S-POD) linear Paul trap (LPT) at Hiroshima University, which can be set up to simulate the dynamics of a beam in an FFAG. We report here results of experiments to explore different resonance crossing speeds, quantify beam loss and study nonlinear effects. We also discuss the implications of these experimental results in terms of limits on acceptable acceleration rates and alignment errors.

PIP: A low energy recycling non-scaling ffag for security and medicine

IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference (2013) 3711-3713

RJ Barlow, TR Edgecock, C Johnstone, H Owen, SL Sheehy

PIP, the Proton Isotope Production accelerator, is a low energy (6-10 MeV) proton nsFFAG design that uses a simple 4-cell lattice. Low energy reactions involving the creation of specific nuclear states can be used for neutron production and for the manufacture of various medical isotopes. Unfortunately a beam rapidly loses energy in a target and falls below the resonant energy. A recycling ring with a thin internal target enables the particles that did not interact to be re-accelerated and used for subsequent cycles. The increase in emittance due to scattering in the target is partially countered by the re-acceleration, and accommodated by the large acceptance of the nsFFAG. The ring is essentially isochronous, the fields provide strong focussing so that losses are small, the components are simple, and it could be built at low cost with existing technology.

Experimental studies of resonance crossing in linear non-scaling ffags with the S-POD plasma trap

IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference (2013) 2675-2677

SL Sheehy, DJ Kelliher, S Machida, CR Prior, K Fukushima, K Ito, K Moriya, T Okano, H Okamoto

In a linear non-scaling FFAG the betatron tunes vary over a wide range during acceleration. This naturally leads to multiple resonance crossing including first order integer resonances. The S-POD (Simulator for Particle Orbit Dynamics) plasma trap apparatus at Hiroshima University represents a physically equivalent system to a charged particle beam travelling in a strong focusing accelerator lattice. The S-POD system can be used as an experimental simulation to investigate the effects of resonance crossing and its dependence on dipole errors, tune crossing speed and other factors. Recent developments and experiments are discussed. Copyright © 2013 by JACoW- cc Creative Commons Attribution 3.0 (CC-BY-3.0).

Conceptual design of a nonscaling fixed field alternating gradient accelerator for protons and carbon ions for charged particle therapy


KJ Peach, M Aslaninejad, RJ Barlow, CD Beard, N Bliss, JH Cobb, MJ Easton, TR Edgecock, R Fenning, ISK Gardner, MA Hill, HL Owen, CJ Johnstone, B Jones, T Jones, DJ Kelliher, A Khan, S Machida, PA McIntosh, S Pattalwar, J Pasternak, J Pozimski, CR Prior, J Rochford, CT Rogers, R Seviour, SL Sheehy, SL Smith, J Strachan, S Tygier, B Vojnovic, P Wilson, H Witte, T Yokoi

The potential for a high power FFAG proton driver for ADS

11th International Topical Meeting on Nuclear Applications of Accelerators, AccApp 2013 (2013) 261-265

SL Sheehy, C Johnstone, R Barlow, A Adelmann

Fixed-field alternating gradient accelerators are promising candidates for next-generation 10 MW-class high power proton drivers. Recent advances in lattice design of non-scaling FFAGs have progressed toward both isochronicity and chromatic correction. The resulting 1 GeV non-scaling FFAG design may be able to support a continuous (CW) beam with far lower peak current than the pulsed alternative. A 6-cell non-scaling FFAG design is described and recent work in modeling 3D space charge using the OPAL framework is presented, including fixed energy studies and beam dynamics with fast acceleration in the so-called serpentine channel.

Orbit correction in the emma non-scaling ffag simulation and experimental results

IPAC 2012 - International Particle Accelerator Conference 2012 (2012) 1455-1457

DJ Kelliher, S Machida, SL Sheehy, JS Berg, E Keil, JK Jones, BD Muratori, IW Kirkman

The non-scaling FFAG EMMA (Electron Model for Many Applications) is currently inoperation at Daresbury Laboratory, UK. Since the lattice is made up solely of linearelements, the betatron tune varies strongly over the momentum range according to thenatural chromaticity. Orbit correction is complicated by the resulting variation inresponse to corrector magnet settings. We consider a method to optimise correction over arange of fixed momenta and discuss experimental results. Measurements of the closed orbitand response matrix are included. Copyright © 2012 by IEEE.

A 1 gev cw ffag high intensity proton driver

IPAC 2012 - International Particle Accelerator Conference 2012 (2012) 3234-3236

SL Sheehy, C Johnstone

The drive for high beam power, high duty cycle, and reliable beams at reasonable cost has focused world attention on fixed-field accelerators, notably Fixed-Field Alternating Gradient accelerators (FFAGs). High-intensity GeV proton drivers are of particular interest, as these encounter duty cycle and space-charge limits in the synchrotron and machine size concerns in the weaker-focusing cyclotron. Recently, the concept of isochronous orbits has been explored and developed for non-scaling FFAGs using powerful new methodologies in FFAG accelerator design. These new breeds of FFAGs have been identified by international collaborations for serious study thanks to their potential applications including Accelerator Driven Subcritical Reactors (ADS) and Accelerator Transmutation of Waste. The extreme reliability requirements for ADS mandate CW operation capability and the FFAGs strong focusing, particularly in the vertical, will serve to mitigate the effect of space charge (as compared with the weak-focusing cyclotron). This paper reports on these new advances in FFAG accelerator technology and presents a stable, 0.25- 1GeV isochronous FFAG for an accelerator driven subcritical reactor. Copyright © 2012 by IEEE.