7 Search Results

The majority of studies on laser-driven proton–boron nuclear reaction is based on the measurement of α-particles with solid-state nuclear tracks detector (Cr39). However, Cr39's interpretation is difficult due to the presence of several other accelerated particles which can bias the analysis. Furthermore, in some laser irradiation geometries, cross-checking measurements are almost impossible. In this case, numerical simulations can play a very important role in supporting the experimental analysis. In our work, we exploited different laser irradiation schemes (pitcher–catcher and direct irradiation) during the same experimental campaign, and we performed numerical analysis, allowing to obtain conclusive results on laser-driven proton–boron reactions.more » A direct comparison of the two laser irradiation schemes, using the same laser parameters is presented.« less

Ion acceleration from gaseous targets driven by relativistic-intensity lasers was demonstrated as early as the late 1990s, yet most of the experiments conducted to date have involved picosecond-duration, Nd:glass lasers operating at low repetition rate. Here, we present measurements on the interaction of ultraintense $(\approx {10}^{20}\mathrm{W}{\mathrm{cm}}^{-2}, 1 \mathrm{PW})$ , ultrashort $(\approx 70\mathrm{fs})$ Ti:Sa laser pulses with near-critical /> cm − 3 ) helium gas jets, a debris-free targetry with the potential for future compatibility with high $(\approx 1 \mathrm{Hz})$ repetition rate operation. We provide evidence of $\alpha$ particles being forward accelerated up to $\approx 2.7\text{−}\mathrm{MeV}$ energy with a total flux of $\approx {10}^{11}{\mathrm{sr}}^{-1}$ as integrated over $>0.1\text{−}\mathrm{MeV}$ energies and detected within a $0.5\text{−}\mathrm{mrad}$ solid angle. We also report on on-axis emission of relativistic electrons with an exponentially decaying spectrum characterized by a $\approx 10\text{−}\mathrm{MeV}$ slope, i.e., five times larger than the standard ponderomotive scaling. The total charge of these electrons with energy above 2 MeV is estimated to be of $\approx 1\mathrm{nC}$ , corresponding to $\approx 0.1\%$ of the laser drive energy. In addition, we observe the formation of a plasma channel, extending longitudinally across the gas density maximum and expanding radially with time. These results are well captured by large-scale particle-in-cell simulations, which reveal that the detected fast ions most likely originate from reflection off the rapidly expanding channel walls. The latter process is predicted to yield ion energies in the MeV range, which compare well with the measurements. Finally, direct laser acceleration is shown to be the dominant mechanism behind the observed electron energization. Published by the American Physical Society 2024« less

In inertial confinement fusion, electromagnetic pulses (EMPs) can be produced during high-power laser interacting with solid targets, which are intimately related to laser intensity and laser energy. In this study, EMPs generated by hybrid laser pulses coupling with targets are recorded and analyzed. The results indicate that a single picosecond laser gives birth to the most intense EMPs, but they are remarkably suppressed when a nanosecond laser-shooting target is triggered before the picosecond and femtosecond laser. One possible hypothesis is proposed based on x-rays inducing pre-ablation that generates pre-plasma at the surfaces of the picosecond target and femtosecond target, leadingmore » to a sharp drop both in the energy and number of the emitting hot electrons and protons. Here, the findings will deepen our understanding of the mechanism of EMPs' generation and will also open a new avenue to regulate EMPs by hybrid laser pulses.« less

A novel detector based on a polycrystalline diamond sensor is here employed in an advanced time-of-flight scheme for the characterization of energetic ions accelerated during laser-matter interactions. The optimization of the detector and of the advanced TOF methodology allow to obtain signals characterized by high signal-to-noise ratio and high dynamic range even in the most challenging experimental environments, where the interaction of high-intensity laser pulses with matter leads to effective ion acceleration, but also to the generation of strong Electromagnetic Pulses (EMPs) with intensities up to the MV/m order. These are known to be a serious threat for the fieldedmore » diagnostic systems. Here we report on the measurement performed with the PW-class laser system Vega 3 at CLPU (~30 J energy, ~10²¹ W/cm² intensity, ~30 fs pulses) irradiating solid targets, where both tens of MeV ions and intense EMP fields were generated. The data were analyzed to retrieve a calibrated proton spectrum and in particular we focus on the analysis of the most energetic portion (E > 5.8 MeV) of the spectrum showing a procedure to deal with the intrinsic lower sensitivity of the detector in the mentioned spectral-range.« less

This work describes the results of experiments performed at the femtosecond ECLIPSE laser facility at CELIA in Bordeaux. Targets constituted by aluminium foils of various thicknesses were irradiated with accelerated protons with energies in the range of interest for p+¹¹B nuclear fusion. Plasma formed in the laser-target interaction were detected using high temperature high radiation resistant diamonds. Time-of-flight measurements were performed by using Chemical Vapor Deposition (CVD) monocrystalline diamonds detectors, which are specifically designed to operate in harsh environments where large ElectroMagnetic Pulses (EMPs) are generated during laser-target interaction. The 1 Hz high repetition rate used for the ECLIPSE lasermore » allowed the collection of a large number of similar shots, giving therefore a large statistics to accurately characterize the energy spectrum of the laser-plasma accelerated protons. As a result, the laser repetitivity at a relatively small intensity permits to improve the signal-to-noise ratio of the detection of the products of low cross-section reactions, such as the p+¹¹B one, by their collection over a large number of similar shots.« less

In this paper, we present a new and general method for measuring the astrophysical S factor of nuclear reactions in laser-induced plasmas and we apply it to ²H(d,n)³He. The experiment was performed with the Texas Petawatt Laser, which delivered 150–270 fs pulses of energy ranging from 90 to 180 J to D₂ or CD₄ molecular clusters (where D denotes ²H). After removing the background noise, we used the measured time-of-flight data of energetic deuterium ions to obtain their energy distribution. We derive the S factor using the measured energy distribution of the ions, the measured volume of the fusion plasma,more » and the measured fusion yields. This method is model independent in the sense that no assumption on the state of the system is required, but it requires an accurate measurement of the ion energy distribution, especially at high energies, and of the relevant fusion yields. In the ²H(d,n)³He and ³He(d,p)⁴He cases discussed here, it is very important to apply the background subtraction for the energetic ions and to measure the fusion yields with high precision. While the available data on both ion distribution and fusion yields allow us to determine with good precision the S factor in the d+d case (lower Gamow energies), for the d+³He case the data are not precise enough to obtain the S factor using this method. Our results agree with other experiments within the experimental error, even though smaller values of the S factor were obtained. This might be due to the plasma environment differing from the beam target conditions in a conventional accelerator experiment.« less