Below is a list of DPhil projects for 2021 for R&D projects and the John Adams Institure; potential graduate students are encouraged to contact supervisors if they have any questions with regard to these projects.
John Adams Institute for Accelerator Science
The John Adams Institute was founded in April 2004 as one of two Institutes of Accelerator Science in the UK. The institute is a joint venture between Oxford University, Royal Holloway, University of London and Imperial College London. The current R&D projects are focused on the area of synergy between laser and plasma physics and accelerators; on research towards novel compact light sources and FELs; on design studies for future colliders and neutrino factories; on development of advanced beam instrumentation and diagnostics; on development of new accelerator techniques for applications in medicine, energy, and other fields of science; and research towards upgrades for existing facilities such as ISIS, Diamond, LHC, and new facilities such as ESS and Future Circular Collider. The institute is developing connections with industry, aiming to render the benefits of accelerator science and technology accessible to society. The Institute also has a vigorous outreach programme. Opportunities in a wide variety of research areas exist, as indicated below.
The sections shown below describe the thesis topics available at JAI in Oxford; for further information see this page: http://www.adams-institute.ac.uk/training/admissions/ and contact Professor Phillip Burrows.
The Rutherford-Appleton Laboratory may also offer joint RAL-Oxford Studentships in accelerator topics. For further information see this page http://www.stfc.ac.uk/ASTeC/Groups/Intense+Beams+Group/17527.aspx and contact Dr John Thomason (email@example.com).
Optimisation of support structures for future trackers
Future collider experiments will require support structures and services which will use significantly less material than current systems. This can only be achieved with modern engineering techniques using advanced composite materials (e.g. ultra-high modulus carbon fibre, high-thermal conductivity materials), state-of-the art fabrication techniques (e.g. 3d printing) and a high level of integration (e.g. co-curing).
After design the performance of the solutions developed to meet this challenge needs to be verified. This comprises measurements of mechanical stability under various thermal and mechanical loads at the sub-μm level and verification of the thermal performance. Because of the unique requirements for HEP experiments a mix of existing state-of-the-art and to-be-developed measurement techniques are required for this task.
While these R&D activities have a strong connection to mechanical engineering they require a good understanding of topics across many fields of physics (mechanics, thermodynamics, and optics) and are a great opportunity to unleash all the things you suffered through in your undergraduate years to enable future breakthroughs in particle physics.
Next-generation high-energy colliders, beam feedback, instrumentation and control
The FONT group http://www-pnp.physics.ox.ac.uk/~font/ is the international leader in ultra-fast nanosecond timescale beam feedback systems for future high-energy electron-positron colliders. These feedbacks are mandatory for steering and maintaining colliding beams in all currently conceivable linear collider designs. They are also needed in single-pass electron linacs where a high degree of transverse beam stability is required, such as X-ray FELs. The key elements of the feedback are fast, precision Beam Position Monitor signal processing electronics, fast feedback processors, and ultra-fast high-power drive amplifiers. These components are designed, fabricated and bench-tested in Oxford, and subsequently deployed in beamlines for testing with real electron beams of the appropriate charge and time structure.
We work currently mainly at the Accelerator Test Facility in Tsukuba, Japan, and at the CLIC Test Facility (CTF3) at CERN. The group typically visits Japan 4 times per year, for the purpose of testing our novel feedback systems. We are developing a new phase feed-forward correction system at CTF3 and this is an exciting new project for us. Graduate students play a key role in these beam tests, and there are also opportunities to spend time in Japan, at CERN (Geneva) and SLAC (California), as well as to give posters and papers at international conferences.
We are a young and dynamic research team. 20 D. Phil. theses have been completed or are in progress and our graduates have moved on to jobs at CERN, SLAC (USA), Brookhaven (USA), DESY (Germany) and ESS (Sweden).
In a laser wakefield accelerator an intense laser pulse propagating through a plasma excites a trailing plasma wave via the action of the ponderomotive force, which acts to expel electrons from the region of the laser pulse. The longitudinal electric field in this plasma wakefield can be as high as 100 GV / m, more than three orders of magnitude larger than that found in conventional RF accelerators such as those used at CERN. Particles injected into the correct phase of the plasma wave can therefore be accelerated to energies of order 1 GeV in only a few tens of millimetres. Laser-driven plasma accelerators could therefore drive novel, very compact sources of particles and ultrafast radiation.
Theoretical and experimental work on plasma accelerators in Oxford is undertaken by a collaboration of research groups in the sub-departments of Particle Physics and Atomic & Laser Physics. For this reason applications to work in this area should be made to the sub-departments of Atomic & Laser physics AND to Particle Physics.
Our work in this area is undertaken in our new high-power laser lab in Oxford, and at national laser facilities in the UK and elsewhere. We have recently been awarded a £2M, 4-year grant from EPSRC to support our research programme. Further information on our research can be found on the laser-plasma accelerator group website
We are offering two DPhil projects to start in October 2021, as outlined below.
1. X-ray sources driven in all-optical plasma channels
Conventional electron-beam-driven light sources (i.e. synchrotrons and free-electron lasers) use electron bunches with energies of a few GeV. An Oxford-Berkeley collaboration were the first to generate electron beams with comparable energy from a laser-plasma accelerator. Reaching this energy requires the driving laser pulse, which has an intensity of around 10^18 W / cm^2, to be guided over several centimetres — well beyond the distance over which diffraction occurs.
In the first GeV-scale experiments, the laser pulse was guided in a plasma channel — a gradient refractive index waveguide made from plasma — generated by a capillary discharge. The drawback of this approach is that the discharge structure can be damaged by the driving laser pulse. The Oxford group has recently developed a new type of plasma channel generated by auxiliary laser pulses. Since they are free-standing, these channels are immune to laser damage, and hence they are very promising stages for future multi-GeV plasma accelerators operating at kilohertz pulse repetition rates.
In this project we will investigate further developments of these hydrodynamic optical-field-ionized (HOFI) plasma channels, and their application to the generation of incoherent keV X-rays via the transverse oscillation of the electron bunch in the plasma wakefield.
2. Multi-pulse laser wakefield accelerators
In a laser wakefield plasma accelerator, a short, intense laser pulse is used to drive a longitudinal density wave (a ‘plasma wave’) in a plasma. The electric fields (which constitute a ‘laser wakefield') within this wave are about 1000 times greater than the accelerating fields employed in a conventional, radio-frequency accelerator — and hence laser-plasma accelerators can generate high-energy beams from a very compact accelerator stage. Laser-driven plasma accelerators have already been demonstrated to generated electron beams with energies of several GeV.
To date, most work has been done with single driving pulses. These must have an energy of order 1 J and a duration shorter than the plasma period, which is around 100 fs. These demanding parameters can be generated by Ti:sapphire laser laser systems. However, Ti:sapphire lasers have very low efficiencies (< 0.1%) and (at these pulse energies) are limited to pulse repetition rates below 10 Hz.
Many potential applications of laser-plasma accelerators — such as light sources and future particle colliders — require operation at much higher pulse repetition rates (at least in the kilohertz range) and much higher ‘wall-plug’ efficiencies. New types of laser are becoming available which can meet these requirements, but they generate pulses in the picosecond range, which are too long to drive a plasma wave. If the output pulses of these lasers could be modulated, with a modulation spacing equal to the plasma period, then they could be used to resonantly excite the plasma wave in a plasma accelerator. We have recently shown that this is possible in a proof-of-principle experiment which employed temporally-stretched Ti:sapphire laser pulses.
In this project we will investigate methods for modulating long, high-energy laser pulses to form a train of short, low energy pulses. We will investigate multi-pulse laser wakefield accelerators (MP-LWFA) driven in this way, and will seek to demonstrate electron acceleration in a MP-LWFA for the first time.
The Diamond Light Source and its upgrade
A step-change in the design of electron storage-rings for synchrotron light sources is currently underway. The latest structures consist of cells of magnets with multiple bending magnets which reduce the electron beam emittance by an order of magnitude and provide a corresponding increase in the source brightness. One consequence of these designs is a substantial reduction in the electron beam lifetime. This is typically compensated for by using harmonic RF cavities to stretch the electron bunches and reduce the particle density. One drawback however is that the emitted x-ray pulses become longer than in previous designs, and the longitudinal dynamics of the circulating electron bunches become more complex. Within this context, the aim of the project is to study how best to meet the needs of timing-mode users, taking the Diamond-II storage ring as an example.
Three potential methods are proposed for study. The first is to use a hybrid filling pattern, in which the ring is filled with one long train of electron bunches to provide the light for the majority of users, and a single electron bunch in a gap for those studying time-dependent phenomenon. The second would be to use ‘pulse-picking by resonant excitation’, in which fast magnets are used to excite vertical oscillations in a single electron bunch. The light from this bunch can then be spatially separated from the remainder for use in timing experiments. The final method would be to use the harmonic cavity to compress the electron bunches rather than stretch them. This would reduce the x-ray pulse length, improving the temporal resolution for users. For each method, particle tracking studies are required to investigate how the electrons react to the applied conditions in order to determine the equilibrium bunch properties and maximum charge before it becomes unstable.
Intense hadron beams R&D
Collaborative projects between the John Adams Institute and ISIS Neutron and Muon Source may be available to interested applicants. The Intense Beams Group use a number of advanced accelerator physics methods in order to explore the ways to design high current and versatile proton accelerators for scientific, energy, medical or other applications. Existing PhD student projects include applications of the FFA (Fixed-Field Alternating Gradient) type of accelerator and the use of Paul traps to study dynamics in proton accelerators.
The dynamics of charged particle beam in accelerators is a highly interdisciplinary research area crossing electromagnetism, analytical mechanics, and accelerators technology. The application of advanced techniques in nonlinear dynamics opens a number of new applications that extend performance and capabilities of existing machines. The PhD programme focuses on the investigation of beam dynamics in proximity of nonlinear resonances to manipulate the beam phase space distribution and tailor it for new injection and extraction schemes, or novel concepts in advanced radiation sources.
The programme will develop solid theoretical framework as well as advanced computer simulations in nonlinear beam dynamics for leptons. The PhD programme based at CERN however it will have access to experimental shifts at the Diamond Light Source as well as at the European Synchrotron Radiation Facility.
Super-bright x-rays using plasma wigglers
Particle accelerators have made an enormous impact in all fields of natural sciences, from elementary particle physics, to the imaging of proteins and the development of new pharmaceuticals. Modern light sources have advanced many fields by providing extraordinarily bright, short X-ray pulses. Here we want the student to undertake a novel numerical study to characterise and optimise a plasma-based wiggler device.
Previous studies demonstrated that existing third generation light sources can significantly enhance the brightness and photon energy of their X-ray pulses by undulating their beams within plasma wakefields. This study showed that a three order of magnitude increase in X-ray brightness and over an order of magnitude increase in X-ray photon energy was achieved by passing a 3 GeV electron beam through a two-stage plasma insertion device. The production mechanism micro-bunches the electron beam and ensures the pulses are radially polarised on creation. We also demonstrated that the micro-bunched electron beam is itself an effective wakefield driver that can potentially accelerate a witness electron beam up to 6 GeV.
In this project, the student will simulate and help implement experimentally a novel extension to this concept, one where a single electron bunch experience the ponderomotive force of the X-rays and produces SASE radiation, ultimately leading to additional increases in brightness, into the XFEL regime.
Metrology At Selected Science/Industry Interfaces (MASSIF)
We work on selected world leading scientific projects from the accelerator, astro and particle physics fields and approach their extremely challenging metrology problems by developing commercially viable instruments that can help to solve them. We do this in close collaboration with both the relevant scientist to find an optimal solution for the science problem and with our industrial partners, Etalon (part of the Hexagon group) and VadaTech to ensure that the instruments we develop and they build achieve the biggest possible impact also in industrial applications.
Among the most challenging metrological problems in science is the alignment and stabilisation of next generation accelerator elements. These often guide or focus or otherwise manipulate nanometre sized beams over many kilometres. The future linear e+-e- colliders ILC, CLIC or FCCee even have to collide such beams after having travelled tens of kilometres requiring extremely precise alignment and nanometre level stabilisation of their elements. Many other accelerator physics project such as the HL-LHC, CEPC or certain medical accelerators face similarly formidable metrology challenges. Oxford Physics will play a leading role in developing metrology instruments that can solve these problems.
The next generation of particle physics detectors for these “Higss factories” will contain extremely low mass tracking detectors, spanning tens of cubic meters, which have to measure charged particle trajectories to micron accuracy. The development and assembly of these structures requires position survey and vibration sensing technology of very high performance which we develop at Oxford Physics.
In astrophysics, many of the next generation of large telescopes such as the GMTO (Giant Magellan Telescope), EELT (European Extremely Large Telescope, KECK, CCAT now called FYST (Fred Young Sub-millimeter Telescope), SRT (Sardina Radio Telescope), LMT (Large Millimetre Telescope) already decided to use the industrial version of Oxfords metrology instruments (Absolute Multiline™) to solve the survey and stabilisation problems of their very large mirrors.
Similarly, many large accelerator centres such as CERN, SLAC, GSI, PSI as well as national institutes of standards, among them (NPL, PTB, le cnam, INRiM), are already using our technology produced under license by Etalon.
A new DPhil student would work with us to understand the impact of metrology and stabilisation problems on the performance of scientific instruments (e.g. how does a future collider luminosity depend on the alignment and stabilisation of its elements), propose solutions to these problems and build and characterise prototype instruments that can deliver the proposed solution. This will involve computer simulations, optical design, DAQ software and finally prototype experiments and their data analysis. During all of this the student is in close collaboration with our industry partners, learning how to make these instruments and their related software and firmware producible, maintainable and commercially viable. The student will also learn about the specific additional requirement for our instruments when they are used in industrial applications where ease of operation, reliability, repairability, traceability, cost and many other factors play larger roles than they do in science applications.
Choosing which scientific problem to focus on is a complex task which will evolve during the first year of the DPhil. This happens by learning about the already existing capabilities of our instruments and the achievable improvements or additions in functionality while comparing these to the general range of problems present in specific science projects.
In any case, the science project ultimately chosen will be one in which Oxford's Department of Physics plays a leading role and is well equipped to make important contributions. The largest range of project clearly lies in accelerator physics (JAI) or the particle physics sub-department but collaborations with the astrophysics sub-department are also possible.
AWAKE experiment at CERN
The AWAKE experiment is a unique proton-driven plasma wakefield experiment, aiming to demonstrate acceleration of electrons to high energies (tens of GeV) via accelerating gradients in excess of 1GV/m. JAI/Oxford is leading the design of the electron injection beamline for AWAKE Run 2, as well as developing novel instrumentation systems for measuring co-propagating proton and electron beams. The latter are based on coherent Cherenkov diffraction radiation techniques. There is the opportunity to design and develop prototypes that can be tested with beams at AWAKE, as well as the CLEAR facility at CERN, and to contribute to advancement of AWAKE during Run 2.
Advances in particle-beam cancer therapy
STELLA (Smart Technologies to Extend Lives with Linear Accelerators), is a multidisciplinary effort to produce a comprehensive, linac-based, Radio Therapy system. The international STELLA collaboration, of which the JAI is a founder member, aims to transform the treatment of patients with cancer particularly in LMICs. It is apparent that linear accelerators in LMIC are down more often than those in wealthier countries. This is partly due to environmental factors, but also to lack of trained technical personnel, which increases not only the frequency of failures but the time to resolve them. To improve the recognition of problems and their nature, we aim to develop a system that uses machine learning and artificial intelligence to monitor the log files of a medical linac regularly to diagnose and predict issues, so that a warning system can be implemented. We have an extensive collaborative network in LMIC’s that would allow us eventually to implement such a system, enabling timely interventions.
Very High-Energy Electron (VHEE) beams with energies in the range 100–200 MeV offer several advantages over conventional beams. In contrast to photon beams, VHEE beams of small diameter can be scanned and focused to conform to the tumour, thereby producing finer resolution for intensity-modulated treatments. The VHEE beams can be operated at very high dose rates, allowing the generation of the “FLASH effect”. Moreover, compared to proton-beam therapy, VHEE could constitute a superior alternative in terms of compactness, simplicity and ultimately cost-effectiveness. Before VHEE and VHEE-FLASH can be adopted for cancer treatment, it will be necessary to: characterise experimentally the properties of VHEE beams; establish the degree to which the VHEE technique improves penetration, focusing, and scanning; and determine the radiobiological effectiveness of VHEE in vitro and in vivo over a range of beam configurations including the FLASH regime. We propose to study physical beam characteristics and beam dosimetry for feasibility in both VHEE and FLASH irradiation with electrons in collaboration with the CLEAR team at CERN.
The University of Oxford Radiation Oncology institute has developed a mathematical model to predict the biological effects of different modalities, including oxygen and FLASH effects, which depend on pulse height, length and overall dose delivered. This model will be tested by varying and refining the parameters to obtain a clinically usable model to predict effects in treatment. The model works for all charged particles (and by extension also for photons). Preliminary data have been obtained for lower-energy electrons (6MeV), at dose rates commensurate with the FLASH effect. Ideally the model will be tested at CERN. The CERN Linear Electron Accelerator for Research (CLEAR) test facility provides the 50-200MeV and high-charge beam necessary to deliver VHEE and FLASH therapy.