Abstract
Particle emittance quantifies the ability to focus and transport a beam, and is one of the most important parameters for a beamline. The emittance of a proton beam produced by ultraintense laser irradiation of a micron-thick flat solid target has been measured systematically for the first time, using three different methods at different positions along the transport beamline: pepper-pot method, quadrupole triplet scan technique, and single-shot emittance measurement. Emittance growth is shown both in experiments and in simulations using CST. An over 3-fold emittance growth was found for 5 MeV laser-driven protons with an energy spread of $\ifmmode\pm\else\textpm\fi{}2%$ and divergence of $\ifmmode\pm\else\textpm\fi{}20\text{ }\text{ }\mathrm{mrad}$ after being transported 5.9 m in the experiment, due to the energy spread and angular dispersion of the protons.
Highlights
The energy of protons accelerated by ultrahighintensity laser pulses irradiating solid ultrathin targets has reached nearly 100 MeV within acceleration distances of tens of micrometers [1]
The emittance of a proton beam produced by ultraintense laser irradiation of a micron-thick flat solid target has been measured systematically for the first time, using three different methods at different positions along the transport beamline: pepper-pot method, quadrupole triplet scan technique, and single-shot emittance measurement
We systematically study the emittance growth caused by the phase-space distribution diffusion of protons during the transport, and present the first experimental emittance measurement of a laser-accelerated proton beam through a beamline
Summary
The energy of protons accelerated by ultrahighintensity laser pulses irradiating solid ultrathin targets has reached nearly 100 MeV within acceleration distances of tens of micrometers [1]. The accelerated protons, which originate primarily from contaminant layers of water vapor or hydrocarbons on the target surface, have an exponentially decaying energy spectrum and a divergence angle of around 10° [19]. Microstructure targets have been used to image the initial accelerating sheath and to fully reconstruct the proton transverse phase space, showing that the normalized rootmean-square (rms) emittance from the target is as low as < 0.004 mm mrad for proton with energy > 10 MeV, which is 100 times smaller than typical rf accelerators [2]. We systematically study the emittance growth caused by the phase-space distribution diffusion of protons during the transport, and present the first experimental emittance measurement of a laser-accelerated proton beam through a beamline.
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