Effects of front surface plasma expansion on proton acceleration driven by the Vulcan Petawatt laser

Multi-MeV ion acceleration driven by high power laser irradiation of thin foil targets continues to attract considerable international interest . At the laser intensities presently available, ions are accelerated by the Target Normal Sheath Acceleration mechanism . The proton, due to its high charge-to-mass ratio, is the most efficiently accelerated ion species, and is sourced from hydrogenated layers on the target surfaces. A number of potential applications, including proton oncology, radiography, lithography and proton based fast ignition have been suggested for this novel and potentially compact laserdriven source. The challenge now is to develop techniques to enhance and control the source and beam properties. In particular, the development of techniques based on optical control of the acceleration would enable applications requiring the delivery of proton pulses at high repletion rate.