Source property demonstration

Proton source

           - M.Borghesi/M.Zepf, QUB

Ion source

           - P.McKenna, SUPA

Gamma source

           - D.Neely, RAL

Full characterization and optimization of the high-repetition radiation sources will be carried out, including : energy tuning and spectral tailoring of the particle beams; novel methods of beam transport and focusing; techniques for simultaneous delivery of different forms of high energy radiation. In particular, for Libra to successfully meet the end requirements for industrial, scientific and medical applications it is essential that we demonstrate the following properties:

High repetition rate (reliability, reproducibility and debris mitigation):  The production of high repetition rate, high energy laser-driven radiation sources suitable for application in a medical and technological context requires exacting reproducibility and reliability of better than 5%, ideally ~1% on a shot to shot (or integrated) basis depending on the exact application. We will investigate the laser reproducibility required to achieve stable beam characteristics. The particle beam performance will be monitored continuously with the ultrafast diagnostics developed within the programme to ensure that a knowledge base is built up on how to control Libra within application specific tolerance. This will be aided by an illumination uniformity control system which will be developed in the course of the project. We will use the high rep rate sources to develop the debris mitigation schemes discussed above and to demonstrate that we can meet and maintain the repetition rates necessary for delivery. High absorption coatings of materials suitable for use in debris mitigation schemes will also be developed and tested.

Tunability (Source control and purity): Proton therapy requires beams of narrow energy spread ~5-15% selectable over the energy range 50-250 MeV. Proton and ion beams must be made free of co-propagating γ-rays and electrons. Using ultra-thin structured targets coupled with beam separation hardware we will demonstrate (i) delivery of clean proton/ion beams and (ii) ion source spectral tunability. Application in radiography and tomography of large objects (e.g. container crates) requires 0.1-5 MeV γ-rays. Control of the γ beam spectral range will be achieved by irradiation and target parameter optimisation. Use of a dual injector/converter target will enable optimised conversion and γ beam purity control over the required energy range by reducing the impedance of the electron beam source. The use of circular polarisation, resulting in a radiation pressure driven acceleration regime, will be investigated as a route to proton beams with substantially reduced γ flux.

Flux delivery (high integrated flux and beam control): Many applications require high average fluxes of radiations to deliver the necessary flux/dose within an acceptable time frame (e.g. patient exposures below 15 mins). Laser-irradiation of solids currently produces 1011-12 ions per shot, with conversion efficiencies of up to 1% for sub 100 fs driven ion acceleration. We plan to demonstrate production of: (a) high total flux (20 seconds repetition sustainable for 1 hour) proton beams at 50MeV, with detailed investigation of beam quality and the ability to cover simulated complex-shaped cancers with high predictive accuracy. Dose deposition tests using human body phantoms will be carried out in conjunction with the medical and industrial partners (b) high rep rate (1 Hz sustainable for 15 mins) proton and ion beams at more moderate (few MeV per nucleon) energies for industrial and scientific application. We also aim to demonstrate: (i) beam focusing to µm-scale spots (reported emittances can in principle allow sub-µm performance) using ballistic and electrostatic techniques, (ii) beam emission control using optical levitation to achieve direction tuning.