Beam collimation and transport of quasineutral laser-accelerated protons by a solenoid field

This article reports about controlling laser-accelerated proton beams with respect to beam divergenceand energy. The particles are captured by a pulsed high field solenoidwith a magnetic field strength of 8.6 T directly behind a flat target foil that is irradiated by a high intensity laser pulse. Proton beams with energies around 2.3 MeV and particle numbersof 1012 could be collimatedand transported over a distance of more than 300 mm. In contrast to the protons the comoving electrons are strongly deflected by the solenoidfield. They propagate at a submillimeter gyroradiusaround the solenoid’s axis which could be experimentally verified. The originated high flux electron beam produces a high space chargeresulting in a stronger focusing of the proton beam than expected by tracking results. Leadoff particle-in- cellsimulations show qualitatively that this effect is caused by space chargeattraction due to the comoving electrons. The collimationand transport of laser-accelerated protons is the first ...