Ultralow Emittance, Multi-MeV Proton Beams from a Laser Virtual-Cathode Plasma Accelerator

Abstract

The laminarity of high-current multi-MeV proton beams produced by irradiating thin metallic foils with ultraintense lasers has been measured. For proton energies >10 MeV, the transverse and longitudinal emittance are, respectively, <0.004 mm mrad and <10(-4) eV s, i.e., at least 100-fold and may be as much as 10(4)-fold better than conventional accelerator beams. The fast acceleration being electrostatic from an initially cold surface, only collisions with the accelerating fast electrons appear to limit the beam laminarity. The ion beam source size is measured to be <15 microm (FWHM) for proton energies >10 MeV.

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…The result is similar to estimations applied in reference [3,99]. In comparison to conventional proton accelerators with an usual emittance in the order of 1 π mm mrad [100] laser generated proton beams have tenfold up to hundredfold lower emittance.…”

“…The temporal characteristics of the proton emission have been discussed theoretically and are supported by experimentally gained arguments in several publications [1,3,93,101,102]. The acceleration of the protons takes place on a picosecond timescale.…”

“…Although the energy spread of laser accelerated proton beams is large (e.g. 0-10 MeV), the short acceleration time (at least < 10 ps) leads to a longitudinal emittance of less than 10 −4 eV s. In [3] the longitudinal emittance was estimated by PIC-simulations being < 10 −7 eV s. This is several orders of magnitudes smaller compared to typical values of 0.5 eVs (CERN SPS) [98] for conventional accelerators. Thus, laser accelerated proton beams can be used for time resolved measurements.…”

“…The transversal emittance delivers a value for the spread in angle, relative to the axes of propagation, caused by random components of transverse velocities [97]. On the other hand the longitudinal emittance considers the "velocity chirp" [3] of the proton beam and is defined by the energy-time product of the beam envelope. Although the energy spread of laser accelerated proton beams is large (e.g.…”

“…They could be injected into common accelerators, benefitting from the unique attributes of the beams [2,3]. Further on, the advantages of laser induced proton beams are discussed in the scope of cancer therapy [4,5].…”