Terahertz driven dielectric linacs

Lead Research Organisation: Lancaster University
Department Name: Engineering

Abstract

In particle physics, future linear colliders such as CLIC or ILC require ultra-short, sub-picosecond, bunches to obtain the luminosity necessary for the particle physics science exploration. In accelerator based X-Ray sources, sub 10fs bunches are highly sought after, opening new windows on material science. Going beyond these massive accelerators will require higher gradient structures to shrink the size and cost of future high energy colliders. Current metallic microwave structures are limited by electric breakdown to around 100 MV/m.
In the drive to obtain every shorter particle bunches, the synchronization of the bunches, both to each other and to facility infrastructure (RF, drive lasers, facility clocks, diagnostic systems) is crucial for the facility optimization, and yet continues to present unsolved problems. Both generation and synchronization of such ultra-short particle beams presents a subsequent problem for the measurement of the ultra-short bunches; only two technologies exist that approach the requirements of future linear colliders and accelerator light sources; laser based 'electro-optic' detection and transverse deflecting cavities. However, EO detection is not currently able to address the few-fs regime, while the gradient requirements make RF (Transverse deflecting cavity) TDC's infeasible for sub-ps measurements on high energy particle physics machines. A high gradient, high frequency (>300 GHz) TDC would allow the same technique to be applied to ultra-short, high energy colliders.
Here we propose to develop a blue-skies approach to these problems, using laser generated THz radiation to be coupled to dielectric lined waveguide for acceleration and manipulation of those beams. In extending the GHz-RF techniques into the picosecond/THz regime we gain in time resolution for manipulation and detection; we gain orders of magnitude in the temporal gradient necessary for manipulation on the sub-picosecond time scale; we gain orders of magnitude in energy efficiency, through only generating the accelerating and deflecting fields over a time window matched to the beams to be accelerated (rather than matched to microsecond cavity filling times). Similar high profile research at Stanford has demonstrated gradients in excess of 250 MV/m using laser pulses at much shorter wavelengths. The short timescales involved and the lack of metallic-vacuum transitions prevents the breakdown in the structure up to the dielectric strength of the lining or grating. However in contrast to a wide body of research into optical acceleration methods, the THz approach allows complete trapping of 'conventional' picosecond bunches rather than the high frequency optical smearing associated with the <3fs periods of laser-acceleration concepts. By using THz the electron bunch can occupy a small range of phases producing a far higher quality bunch consistent with requirements from accelerator applications such as colliders and FELs.
One of the first steps towards this goal is the demonstration of laser-based schemes for the acceleration and deflection of relativistic electron beams. We propose to take preliminary simulations and experiments to the next stage of proof-of-concept demonstration on STFC's test accelerator, VELA. Our approach is a melding of concepts in electro-optic detection and THz generation (areas of expertise for Jamison and Graham) and particle physics cavity design (expertise of Burt). By using an integrated team the structure and source can be developed in tandem to provide a technology ideally suited to accelerator development. While other experiments have taken place with sub-relativistic particles this would be the first acceleration of fully relativistic particles by a THz structure and would be the first transverse deflecting cavity operating in the THz regime.

Planned Impact

The main beneficiaries of this research are the users of HEP colliders but they will not be the only beneficiaries. The development of high gradient accelerating structures and deflecting cavities for high resolution bunch length will have major implications on the many communities using accelerators. This would also extend to the users of FELs. The reduction in the size and hence cost of particle accelerators will have major effects on

1) Radiotherapy and future liancs for very high energy electron therapy and proton therapy allowing compact machines with much smaller gantries and the use of linacs in surgery
2) High energy cheap electrons would open up the possibility of deep electron beam curing. At present the limited energy of compact machines limit the technique to only a shallow layer from the surface.
3) Security cargo scanning linacs would benefit from compact high energy machine as it would allow nuclear resonance to produce reactions that could be used for material discrimination. The large size and cost of current rhodotron based systems is a major limitation in the current exploitation of this method.
4) If the size and cost can be sufficiently reduced then it may be possible for there to be many more accelerators such that every hospital and university would eventually have one.

It is likely that a high energy accelerator the size of a pencil could eventually be developed opening the possibility of novel industrial and medical uses that have not be considered before.

Publications

10 25 50
 
Description We have achieved the worlds first linear acceleration of relativistic electrons using Thz radiation, paving the way to future compact particle accelerators with high quality beams. We have no had our 2nd run where we increased the acceleration by a factor of 20, and demonstrated staged acceleration
Exploitation Route This is just the first step, next we need to demonstrate gradients in excess of traditional Rf accelerators, and synchronisation of multiple structures. The outcomes of this project show the flexibility of dielectric lined rectangular waveguide for these purposes and we have systematic studies of phase velocity matching and beam dynamics.
Sectors Chemicals,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Security and Diplomacy

 
Description Cockcroft Institute Capital bid 2018
Amount £174,000 (GBP)
Funding ID ST/S002200/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 08/2018 
End 03/2019
 
Description THz driven injection for high-quality high-gradient novel acceleration
Amount £126,658 (GBP)
Funding ID ST/T002735/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Public
Country United Kingdom
Start 08/2019 
End 05/2021
 
Title Acceleration of relativistic beams using laser-generated terahertz pulses 
Description Dataset for the figures contained in the manuscript entitled "Acceleration of relativistic beams using laser-generated terahertz pulses". 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL https://zenodo.org/record/3903506
 
Title Acceleration of relativistic beams using laser-generated terahertz pulses 
Description Dataset for the figures contained in the manuscript entitled "Acceleration of relativistic beams using laser-generated terahertz pulses". 
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL https://zenodo.org/record/3903505
 
Description PSI collaboration on THz linacs at CLARA 
Organisation Paul Scherrer Institute
Country Switzerland 
Sector Academic/University 
PI Contribution We helped run an experiment on our CLARA accelerator to test their Thz structures and made the THz sources
Collaborator Contribution They designed and built the structure to be tested
Impact We are producting a journal publication
Start Year 2019
 
Description IMAEGMOOH 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Schools
Results and Impact I participated in the STFC sponsored I'm an engineer get me out of here competition, where I did live webchats with several schools all over the UK answering questions over a two week period.
Year(s) Of Engagement Activity 2019
URL https://energym19.imanengineer.org.uk/