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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 × 10 8 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/E 0 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.

We report on the development of an ultrafast optical parametric amplifier front-end for the Petawatt High Energy Laser for heavy Ion eXperiments (PHELIX) and the Petawatt ENergy-Efficient Laser for Optical Plasma Experiments (PEnELOPE) facilities. This front-end delivers broadband and stable amplification up to 1 mJ per pulse while maintaining a high beam quality. Its implementation at PHELIX allowed one to bypass the front-end amplifier, which is known to be a source of pre-pulses. With the bypass, an amplified spontaneous emission contrast of $4.9\\times {10}^{-13}$ and a pre-pulse contrast of $6.2\\times {10}^{-11}$ could be realized. Due to its high stability, high beam quality and its versatile pump amplifier, the system offers an alternative for high-gain regenerative amplifiers in the front-end of various laser systems.

In this work, we propose and verify experimentally a model that describes the concomitant influence of the beam size and optical roughness on the temporal contrast of optical pulses passing through a pulse stretcher in chirped-pulse amplification laser systems. We develop an analytical model that is capable of predicting the rising edge caused by the reflection from an optical element in a pulse stretcher, based on the power spectral density of the surface and the spatial beam profile on the surface. In an experimental campaign, we characterize the temporal contrast of a laser pulse that passed through either a folded or an unfolded stretcher design and compare these results with the analytical model. By varying the beam size for both setups, we verify that optical elements in the near- and the far-field act opposed to each with respect to the temporal contrast and that the rising edge caused by a surface benefits from a larger spatial beam size on that surface.

The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi- MeV photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around 100 MeV , the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of 200 J at ≈ 500 fs duration from the PHELIX laser produced more than 10 12 protons with energies above 15 MeV in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the γ -rays were registered. The identified nuclides include those that have half-lives down to 39 s . These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities.

Abstract The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi- $$\\hbox {MeV}$$ MeV photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around $$100 \\, \\hbox {MeV}$$ 100 MeV , the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of $$200 \\, \\hbox {J}$$ 200 J at $$\\approx \\, 500 \\, \\hbox {fs}$$ ≈ 500 fs duration from the PHELIX laser produced more than $$10^{12}$$ 10 12 protons with energies above $$15 \\, \\hbox {MeV}$$ 15 MeV in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the $$\\upgamma$$ γ -rays were registered. The identified nuclides include those that have half-lives down to $$39 \\, \\hbox {s}$$ 39 s . These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities.

In the frame of this thesis laser-driven proton acceleration was studied within the target normal sheath acceleration (TNSA) regime with focus on control of the laser beam parameters to manipulate the generated proton beam. The experiments for this thesis were conducted at the PHELIX laser facility at the GSI Helmholtzzentrum fur Schwerionenforschung GmbH. High intensity laser beams ionize atoms of the target, produce a plasma, and accelerate electrons through the target. On the rear side a strong electric field is generated and the strong charge separation leads to an acceleration of ions, mostly protons. The ions and electrons expand into the vacuum behind the target as a quasineutral plasma cloud. Such particle beams, originating from the target rear side contamination layer, have outstanding properties like ultra-low emittance and a pulse duration in the range of the laser pulse duration.The goal of this work at hand was to change the initial conditions of the emitted ion beam from the TNSA source. The accelerated proton beam exhibit a large divergence angle. To reduce this up to 60◦ opening angle this work aims at shaping the rear side electron sheath using specially shaped laser beams. This can be done using specially designed helical phase plates. The result is a hollow focal spot on the target with an intensity minimum in the center. Therefore it was necessary to study and control the propagation of such a special laser beam through a complete laser amplification beam line. Numerical simulations were developed to assist identifying limitations on the laser beam quality and find possibilities for improvement.Two successful experimental campaigns on laser-driven ion acceleration as well as one dedicated beam time for laser wave-front improvements were carried out during this thesis. The main diagnostic for generated protons within the conducted experiments were the radiochromic films (RCF). The analysis software for these films was improved and new functions were developed to obtain two-dimensional energy-wise resolved particle numbers. Up to now it was assumed to have the same laser intensity distribution on the target as it was measured before a high-energy shot. Therefore, a new imaging system was implemented to image the real laser focal spot on target during the laser-matter interaction with a reasonable quality.It was the first time that laser-driven ion acceleration with a hollow laser beam was experimentally demonstrated. The experimental data are in agreement with the simulations. Improvements on the laser-driven ion acceleration with shaped laser beams were demonstrated and compared to laser-driven ion acceleration with Gaussian focal spots. The initial proton beam parameter, the envelope divergence, was reduced by (3.07 ± 0.42)◦ or roughly 10 %. The scaling of the maximum proton energy Eprotons,max with the square root of the laser intensity √ Ilaser was experimentally verified for experiments with a hollow laser focus. It appeared that the highest proton energies were achieved with the hollow laser beam exceeding 34.6 MeV. Also the dependency of the proton energy as well as the divergence angle on the target thickness was demonstrated within the thickness range of 5 µm to 20 µm. The study of the laser beam aberrations and the improvements made on it, resulted in the best ever achieved wave-front of the laser system, deduced from the reached maximum proton energies.

The thermal behavior of wires within the electrical distribution system (EDS) has a strong impact on the conductor cross section, the type of insulation, the derating, and the fusing system, and therefore on weight, cost, and reliability. Consequently, significant efforts have been made to develop sound static and dynamic thermal models for single wires and wire bundles. However, these models are based on the simplifying assumption that the object is completely surrounded by air, where, with the exception of free convection, airflow can be neglected, and where no interaction with other objects is considered. The approach presented in this paper takes into account the actual environment and routing within a vehicle, where some objects such as metal sheets can be considered as heat sinks and other objects, e.g. a motor block, as heat sources. For this reason, measurements were performed using an experimental set-up that allows any desired positioning and alignment of the DuT (device under test, here: wire, cable, bundle) and of two temperature-controlled heat source/sink objects. These objects are a large rectangular surface and a small sphere, in order to be able to emulate as many spatial configurations as possible. The overall set-up is protected against externally-induced airflows. Because the exact modelling of the heat transfer processes (radiation, conduction, and free/forced convection) would require time-consuming FEM calculations for the investigated complex geometries, a simplified and partially data-driven model is proposed. The paper describes the theory and the modeling approach, and presents initial simulation and measurement results.