Fast ions from graphene with potential application spanning fusion and oncology
Proton and heavier ion acceleration using ultra-intense lasers is being widely investigated for pure science, plasma diagnostics, medical as well as fusion engineering applications. One approach to achieving higher proton and ion energies is to use thin targets, and perhaps the thinner the better. However, thin targets are easily destroyed by the so-called laser prepulse which arrives prior to the main laser pulse on all intense laser systems. The maximum proton energy achieved so far has been limited to several tens of MeV when using relatively thick, of the order of a micrometer, targets. This has been the case even though there has been a successful decade long development of laser technologies which provide higher contrast, higher intensity and higher energy laser pulses. Very recently, the use of thin (10-100 nm) targets with ultra-intense lasers has shown promise by accelerating protons and carbons ions up to higher energies. This proposal pursues this approach through a collaboration with teams in Japan and Taiwan to the development and shoot the ‘ultimate target’; a large-area suspended graphene foil which is as thin as one atom (order of 1 nm) and suspended across holes of 100 μm in diameter. Graphene has several features that make this a particularly exciting material for laser ion acceleration. It is: 1) the thinnest material known, 2) mechanically strong, 3) formed from carbon which is a biologically compatible material and so suitable for ion oncology, and 4) transparent and unaffected by a laser prepulse below intensities of approximately 1011 W/cm2. Large-area suspended graphene foil is uniform and flat, thickness control is exquisite offering nm-order accuracy by building targets graphene layer by layer. Longer term, target manufacture is relatively straightforward and cheap target mass produce seems possible. Very little material is ablated in a laser shot, making the material suitable for future high repetition rate (e.g. many Hz). Perhaps it will be a magical material? This project will develop experimental and computational tools to study carbon (and proton) acceleration from graphene targets. The work will be carried out at the York Plasma Institute and at large facilities in the UK, Japan and elsewhere. The project provides an excellent opportunity for collaboration and for exploring new ideas.