Dynamic Control of Laser-Produced Proton Beams

Abstract

The emission characteristics of intense laser driven protons are controlled using ultrastrong (of the order of 10(9) V/m) electrostatic fields varying on a few ps time scale. The field structures are achieved by exploiting the high potential of the target (reaching multi-MV during the laser interaction). Suitably shaped targets result in a reduction in the proton beam divergence, and hence an increase in proton flux while preserving the high beam quality. The peak focusing power and its temporal variation are shown to depend on the target characteristics, allowing for the collimation of the inherently highly divergent beam and the design of achromatic electrostatic lenses.

Dynamic control of laser driven proton beams by exploiting self-generated, ultrashort electromagnetic pulses

“…While some of the focussing techniques, such as laser-driven micro-lenses 6 , magnetic quadrupoles 7 , pulsed solenoids 8 , allow a degree of spectral tailoring in addition to the divergence control, they typically captures a small portion of the divergent proton beam. Other techniques such as ballistic focussing from curved targets 9 or self-driven quasi-electrostatic lenses 10 act on the full beam, but they either provide achromatic focussing or only partial reduction in divergence. Therefore innovative approaches are a) Electronic mail: s.kar@qub.ac.uk required to enable beam control and optimisation.…”

“…The EM pulse effectively carries a neutralizing current which attempts to restore charge neutrality in the irradiated region of the target, following its positive charge-up due to the prompt escape of a fraction of hot electrons produced during the interaction [10][11][12] . The experimental data characterising the propagation of the pulse is presented, followed by data showing chromatic focussing of the TNSA proton beam.…”

Temporal Narrowing of Neutrons Produced by High-Intensity Short-Pulse Lasers

“…Additionally, the upcoming increase in repetition rate of these lasers (now a few shots per hour) will soon increase with the development of fiber [41] or diode-pumped lasers [42,43]. The smooth electric field profiles [19] and the simple structure (potentially a single target [44]) of the microlens make this technique compatible with quick, repeatable lasers making laser-based short-pulse neutron sources even more attractive.…”

Ion beam requirements for fast ignition of inertial fusion targets

“…Kar et al [45] showed beam focusing by using rectangular or cylindrical hollow lens attached to a foil target. Offermann et al [46] found theoretically and experimentally that ion divergence depends on the thermal expansion of the co-moving hot electrons, resulting in a hyperbolic ion beam envelope.…”