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  THz-driven multi-stage relativistic beam facility design and beam dynamics

   Cockcroft Institute

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  Dr Robert Appleby  Applications accepted all year round  Awaiting Funding Decision/Possible External Funding

About the Project

Terahertz-driven acceleration and manipulation of non-relativistic and relativistic particle beams is rapidly evolving to centre-stage in the drive to novel accelerator methods. In the Cockcroft Institute (and supported by CI core and quota PhD students) we performed [1] the first proof-of-principle THz-driven phase-velocity-matched interaction in a dielectric-lined waveguide, with acceleration up to 10 keV. In the most recent CLARA run we demonstrated [2] record THz-driven linear acceleration of relativistic 35.5 MeV, 20-100 pC electron beams, and advanced manipulation of the bunch to show de-chirping and the modulation necessary for the generation of micro-bunches. In parallel we have shown how chained waveguides in the MeV regime can be used to maintain bunch quality in staged accelerator [3]. We are also exploring non-relativistic beams, focused around our 100 keV non-relativistic experimental rig in a purpose-built bunker at Daresbury Laboratory and recently demonstrated electron bunch deflection using THz-driven structures, where we observe the streaking on the screen of electron bunches. We are aiming to demonstrate that acceleration to MeV beam energies can be achieved with THz acceleration, and beam control can be achieved with synchronised THz compression. Our work is showing rapid progress but now we need to demonstrate the capability of these advances to deliver a larger energy facility, and solve the problems that using multi-stage THz-driven structures will present.

The aim of this PhD position is to demonstrate that a THz-driven high energy and high quality beam is possible, assessing the beam dynamics challenges, facility concept and the resulting beam quality and parameters.

This 3.5-year project will start October 2023, and will i) contribute to our existing experiments to obtain MeV scale beams, and ii) use this understanding to demonstrate the full facility design and beam quality using these techniques. This requires solving problems of multi-stage THz interactions to accelerate and manipulate the beam, whilst preserving the electron beam quality, and addressing the impact of beam-loading and wake fields on the accelerated beam. The project will explore the concept of THz-structure units, larger scale structures built of multiple waveguides that preserve beam quality, which are used to build the larger facility. The researcher will join our running experimental programme of compressing, accelerate and deflect the 100 keV bunches using high field THz sources in dielectric lined waveguides, and will have the opportunity to test the ideas generated during the PhD with beam in our bunker.

Objectives of the PhD:

1.      Demonstrate that acceleration to MeV beam energies can be realised with THz acceleration, and beam control can be realised with synchronised THz compression.

2.      Explore the concept and design of a higher energy THz facility, specifically addressing the issue of beam quality preservation through multi-stage THz-driven structures.

3.      Address the role of synchronisation, beam loading and wakefields in the facility dynamics.

The studentship is available in the THz group at the Cockcroft Institute, and the researcher will join the University of Manchester. The project is computational in nature, involving work on developing simulation codes, using codes such as CST and GPT. There will also be the opportunity to join our experimental team and perform experimental work at Daresbury Laboratory in our purpose-built bunker. The applicant will be expected to have a first or upper second-class degree in physics or other appropriate qualification. Computational experience is desirable but not essential, as is experience in accelerator physics. A full graduate programme of training and development is provided by the Cockcroft Institute. The student will be based primarily at the Institute at Daresbury, with some work at the University of Manchester. A willingness to travel to international conferences is desirable.

Plan for the 3.5 years:

In the 1st year the student will explore beam dynamics and particle tracking through multiple acceleration and compression structures. This includes large scale beam-quality-maintaining THz structure building block design and defining facility goals and parameters. The student will also work in the bunker on MeV experiment. Time will be spent on training, both in beam dynamics and novel accelerators, and practical based training in the lab.

In the 2nd year, a first pass at a facility design, combining self-contained THz structures which maintain beam quality. Start to end modelling will be performed, as well as experimental bunker work to test building block ideas.

The 3rd year will be focused on assessment of beam loading and synchronisation errors across multiple cavities, wakefields and final assessments of beam quality

The 4th year will be devoted to writing up the PhD thesis and submitting both the thesis and journal papers.

Supervisors involved and their background:

The project will involve two primary supervisors, and a strong wider supervision team. The supervision team contains world leading expertise in THz sources, beam dynamics and experimental physics and there is considerable PhD supervision experience in the team.

For more information, please contact Prof. Rob Appleby ([Email Address Removed])


[1] M. T. Hibberd et al., “Acceleration of relativistic beams using laser-generated terahertz pulses,” Nat. Photonics, 14, 755-760 (2020).

[2] To be submitted to Nature Photonics

[3] “6D phase space preservation in a terahertz-driven multi-stage dielectric-lined rectangular waveguide accelerator”, O, Apsimon, R.B. Appleby et al, Accepted by Phys. Rev. Accel. Beams (October 2021)

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