Abstract
A laser-driven, multi-MeV-range ion beamline has been installed at the GSI Helmholtz center for heavy ion research. The high-power laser PHELIX drives the very short (picosecond) ion acceleration on μm scale, with energies ranging up to 28.4 MeV for protons in a continuous spectrum. The necessary beam shaping behind the source is accomplished by applying magnetic ion lenses like solenoids and quadrupoles and a radiofrequency cavity. Based on the unique beam properties from the laser-driven source, high-current single bunches could be produced and characterized in a recent experiment: At a central energy of 7.8 MeV, up to 5 × 108 protons could be re-focused in time to a FWHM bunch length of τ = (462 ± 40) ps via phase focusing. The bunches show a moderate energy spread between 10% and 15% (ΔE/E0 at FWHM) and are available at 6 m distance to the source und thus separated from the harsh laser-matter interaction environment. These successful experiments represent the basis for developing novel laser-driven ion beamlines and accessing highest peak intensities for ultra-short MeV-range ion bunches.
Highlights
The possibility of efficient acceleration of these ion species has already been demonstrated within the TNSA regime[13]
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Summary
The mechanism of phase rotation for temporal bunch compression essentially relies on the quite large energy spread of the bunch. Our simulations predict this focal position to be at 3.45 m behind the cavity (6 m to source) for protons of 7.8 MeV energy and a total applied gap voltage of 0.96 MV This position was chosen as diagnostic position in the performed experiments and the rf power varied to scan the bunch length at this specific position. A direct comparison of the response of both detectors is given, showing the measured signal at the optimum temporal compression parameters While both show a rapid signal rise time, the signal decay is dominated for the streak camera by the slow scintillator decay time and the diamond shows an undershoot oscillation due to intrinsic detector characteristics. The oscillating behavior could be identified as an artefact of a resonant circuit within the detector electronics
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