Laser acceleration of quasi-monoenergetic MeV ion beams

Abstract

Acceleration of particles by intense laser-plasma interactions represents a rapidly evolving field of interest, as highlighted by the recent demonstration of laser-driven relativistic beams of monoenergetic electrons. Ultrahigh-intensity lasers can produce accelerating fields of 10 TV m(-1) (1 TV = 10(12) V), surpassing those in conventional accelerators by six orders of magnitude. Laser-driven ions with energies of several MeV per nucleon have also been produced. Such ion beams exhibit unprecedented characteristics--short pulse lengths, high currents and low transverse emittance--but their exponential energy spectra have almost 100% energy spread. This large energy spread, which is a consequence of the experimental conditions used to date, remains the biggest impediment to the wider use of this technology. Here we report the production of quasi-monoenergetic laser-driven C5+ ions with a vastly reduced energy spread of 17%. The ions have a mean energy of 3 MeV per nucleon (full-width at half-maximum approximately 0.5 MeV per nucleon) and a longitudinal emittance of less than 2 x 10(-6) eV s for pulse durations shorter than 1 ps. Such laser-driven, high-current, quasi-monoenergetic ion sources may enable significant advances in the development of compact MeV ion accelerators, new diagnostics, medical physics, inertial confinement fusion and fast ignition.

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…The proton spectra are usually continuous up to a sharp cut-off representing the highest proton energies. However, for specific target types ion spectra with dips [91,92] or quasi-monoenergetic [13][14][15][16] features have been observed. Since the generation of monoenergetic ion beams is of high interest for many applications, it will be discussed shortly in the next section.…”

“…But also this feature is discussed controversy since a saturation of the used CR39-detector can explain this structure [75]. On the other hand experiments where the target is pre-heated and thus the contamination layers are removed show a reduced proton signal whereas the ion signal is enhanced [14,76]. A pre-heated target, coated with CaF 2 at the rear side only was used to identify the "rear-side" acceleration to be responsible for the ion acceleration [76].…”

“…The potential ϕ el can be determined using the Poisson equation: 14) where λ D is the electron Debye length defined by:…”

“…For instance, in reference [13] micro-structured targets were used. In reference [14] quasi-monoenergetic ions are accelerated by heating the target and thus manipulating the target surface. At the Max-BornInstitute it was shown for the first time that water-droplet targets can deliver nearly monoenergetic deuteron and proton beams [15,16].…”

“…Concave targets focus or collimate the whole ion beam [1,[10][11][12]. Manipulated target surfaces or microstructured targets can deliver quasi-monoenergetic ion and proton beams [13,14]. At the Max-Born-Institute it was shown for the first time that also water-droplet targets can deliver quasi-monoenergetic deuteron and proton beams [15,16] (see Chapter 5.2).…”