Advanced laser-ion acceleration strategies towards next generation healthcare

The interaction of intense laser pulses with matter is opening up new frontiers in physics via the production of extreme pressures, temperatures and intense electric and magnetic fields. This is leading to the use of high power laser radiation for exploring the properties of hot dense matter, the production of high energy particles and radiation, and the development of schemes to generate energy by inertial confinement fusion. These advances are driven by rapid developments in ultrashort pulse laser technology which have enabled new regimes in laser power and intensity to be reached. With the advent of multi-petawatt power lasers (e.g. the upgrade project to the Vulcan laser at the UK's Central Laser Facility will deliver 10 petawatt pulses by 2013-2014) exotic new plasmas with unique properties are accessible, including strongly relativistic dense plasma. The principal aims of this proposed project are to investigate the fundamentals of laser-solid interactions in strongly relativistic plasmas - a regime of laser-plasma interactions not previously accessible - and to harness predicted promising new ion acceleration schemes achievable with ultrahigh intensity laser pulses. This will advance our understanding of ultrahigh intensity laser solid interactions and may lead to new applications of laser-plasma-based particle and radiation sources. The proposal involves the development and application of new techniques on experiments using some of the highest power laser systems available.

"This fellowship research project aims to investigate the physics of strongly relativistic plasmas produced at the focus of ultra-intense laser pulses. This includes investigation of fundamental laser-plasma interaction physics and the use of this new knowledge in the exploration of new frontiers in laser-driven ion acceleration. The project is on-going and has, to date, resulted in 42 publications in leading peer-review journals, including a paper in Nature Physics and 5 papers in Physical Review Letters.

One of the highlights of this research project was the discovery that in the interaction of an ultraintense laser pulse with an ultra-thin foil target a 'relativistic plasma aperture' is produced in the region of the peak laser intensity, leading to diffraction of the laser light. It was discovered that the diffraction pattern is mapped into the beam of fast electrons accelerated from the target and can be used to control the collective motion of the electrons. The results, which were published in Nature Physics in January 2016, have potentially important implications for the development of laser-driven particle accelerators and radiation sources (which rely on controlling the motion of plasma electrons displaced by the intense laser fields) and for the investigation of aspects of laboratory astrophysics.

Other pioneering work resulting from this research programme includes demonstration that in the interaction of an intense laser pulse with a thin foil undergoing transparency, a plasma jet is formed which couples additional energy into the beam of protons accelerated from the foil. It was demonstrated that techniques based on controlling the properties of the jet could be used to control the maximum energy of the proton beam. This work produced significant new insight into the physics underpinning laser-driven ion acceleration in an important parameter regime.

Other highlights include important new understanding of the effects of self-generated magnetic fields on the propagation of energetic electron beams in homogeneous solids and a new technique for guiding energetic electrons in layered solid targets irradiated by ultra-intense laser pulses.

This research project is on-going and so the research findings are not yet complete. A full description of the research findings will be provided at the end of the grant."