THz driven acceleration and deflection of relativistic beams.

THz driven modulation of relativistic beams has been previously demonstrated by the supervisors and CI colleagues, students and post-docs. These achievements and similar work coming from competitor groups in Beijing, Shanghai and in SLAC, have led to significant interest in the capability for THZ-driven acceleration, compression and deflection of high energy beams. The concepts offer unique approaches to control of the longitudinal phase space of beams, of driving synchronisation of beams to temporal-locked to external laser beams, and for ultrafast beams diagnostics.

This project will build on our previous work where observations indicated a significant degree of transverse and longitudinal coupling in THZ-driven acceleration process. The project will be a combination of simulation, modelling of beam dynamics, and experimental investigations into the transverse-longitudinal coupling in the THZ-driven interaction within dielectric lined waveguides.

The student will investigate through simulation the effects of transverse and longitudinal variation of acceleration acceleration, together with the interlinked transverse focusing/defocusing effects. They will examine both rectangular and cylindrical waveguide structures, allowing an understanding of our previous structure concepts and approaches taken by competitor groups.

Having examined waveguide geometries and structural parameterisation, they will seek an optimised structure choice for maintaining low energy spread and limiting emittance degradation for situations such as THZ-driven chirping for compression of beams to femtosecond time scale.

Modelling into the effects of beam-loading and of structure-wakefield effects will also be a significant part of the scope of work.

Beamtime will be sought on CLARA, either directly through exploitation calls or in conjunction with the H3Beams programme. An experimental investigation of modelled structure(s) will be undertaken to observe the transverse effects. The measurements will focus on energy resolved imaging of the electron beams, as function of electron beams and THZ properties. The experiments will be analysed using the prior modelling work to confirm the emittance and energy spread characteristics of the interaction. The experimental work will be undertaken together with other CI PhD and PDRA researchers working in the field. Project contingency for the experimental work, should CLARA beamtime become unavailable, will be through seeking time at other facilities such as CLEAR at CERN, or SPARC in Frascati. Further contingency will be available in the THZ bunker facility, where the same traverse-longitudinal coupling effects can be explored with lower energy electron beams. The THZ bunker is a stand-alone lab that is under the operation and discretion of the supervisors.

Project Outline

In year 1, October 2025-October 2026:

– Study the physics of sub- and relativistic acceleration and beam transport.

– Simulation of the beam interaction using Elegant, CST, and self-written code.

– Develop a report on the longitudinal-transverse coupling and emittance degradation effects.

– Study and gain experimental capabilities in the principles and techniques of THz generation and detection, in preparation and training for the experimental elements of the study

Year 2 October 2026-October 2027

– Extend the modelling simulations to space-charge, Wakefield and beam loading effects.

– Potential 3-month student placement at LCLS UED facility, or SPARC.

Year 3 October 2027-October 2028

– Design of experimental systems, including relevant control and in-experiment analysis software. Off-line construction and testing of the experimental systems. Undertake experiments on CLARA, or the contingency facilities. Experiments to be targeted at observation of the transverse-longitudinal coupling. Stretch-goal in the experiments will be characterisation of beams-loading and/or Wakefield effects within the THZ structures.

– Analysis of experiments

Year 4 October 2028-march 2029

– Time dedicated to thesis and publication preparation (publications also to be sought in years 2 and 3).