The ultrahigh laser intensities enabled by high power lasers facilitate the generation of high energy ions using accelerating gradients many million times that of conventional accelerators. The maturation of these sources relies on breakthroughs in the generated beam parameters and improved reproducibility and repetition rate. We used two independent state-of-the-art femtosecond laser systems capable of repetitive operation to accelerate protons and carbons to high energies (>50 MeV and 30 MeV/nucleon respectively) in the relativistically induced transparency (RIT) regime. We demonstrate that acceleration is optimised for different laser prepulse levels by varying the initial target thickness, relaxing laser requirements for energetic ion generation. We elucidated the acceleration dynamics with cutting-edge 3D simulation, showing a) the role of the laser prepulse in pre-expanding the target, and b) radiation pressure assisted electron expulsion from the target during relativistically induced transparency, generating a strong space charge field which rapidly accelerates ions. Our demonstration of a robust acceleration mechanism that does not require complicated targetry nor a single-shot prepulse suppressing plasma mirror is an important step forward for developing high repetition rate applications of laser driven ion sources.
We review a number of instruments employed in a high-intensity J-KAREN-P laser-solid interaction experiment and discuss the applicability of the diagnostics to the best target position determination with a ~10 μm accuracy, while the focal spot size was ~1 μm and peak intensity was up to 7×1021 W/cm2. We discuss both front- and back-side diagnostics, some of them operated in the infrared, visible and ultraviolet ranges, while others in the extreme ultraviolet, soft X-ray and gamma-ray ranges. We found that the applicability of some of the instruments to the best at-focus target position determination depends on the thickness of the target.
We report on the J-KAREN-P laser facility at QST, which can provide PW peak power at 0.1 Hz on target. The system
can deliver short pulses with an energy of 30 J and pulse duration of 30 fs after compression with a contrast level of
better than 1012. Such performance in high field science will give rise to the birth of new applications and breakthroughs,
which include relativistic particle acceleration, bright x-ray source generation, and nuclear activation. The current
achieved laser intensity on target is up to > 9x1021 Wcm-2 with an energy of ~9 J on target. The interaction with a 3 to 5-
μm stainless steel tape target provides us electrons with a typical temperature of more than 10 MeV and energetic proton
beams with typical maximum energies of > 40 MeV with good reproducibility. The protons are accelerated in the Target
Normal Sheath Acceleration regime, which is suitable for many applications including as an injector into a beamline for
medical use, which is one of our objectives.
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