Collisionless shock acceleration of protons in a plasma slab produced in a gas jet by the collision of two laser-driven hydrodynamic shockwaves

We have recently proposed a new technique of plasma tailoring by laser-driven hydrodynamic shockwaves generated on both sides of a gas jet[Marquès et al.,Phys.Plasmas 28,023103(2021)].In a continuation of this numerical work,we study experimentally the influence of the tailoring on proton acceleration driven by a high-intensity picosecond laser in three cases:without tailoring,by tailoring only the entrance side of the picosecond laser,and by tailoring both sides of the gas jet.Without tailoring,the acceleration is transverse to the laser axis,with a low-energy exponential spectrum,produced by Coulomb explosion.When the front side of the gas jet is tailored,a forward acceleration appears,which is significantly enhanced when both the front and back sides of the plasma are tailored.This forward acceleration produces higher-energy protons,with a peaked spectrum,and is in good agreement with the mechanism of collisionless shock acceleration(CSA).The spatiotemporal evolution of the plasma profile is characterized by optical shadowgraphy of a probe beam.The refraction and absorption of this beam are simulated by post-processing 3D hydrodynamic simulations of the plasma tailoring.Comparison with the experimental results allows estimation of the thickness and near-critical density of the plasma slab produced by tailoring both sides of the gas jet.These parameters are in good agreement with those required for CSA.

Characterization and performance of the Apollon short-focal-area facility following its commissioning at 1 PW level

We present the results of the first commissioning phase of the short-focal-length area of the Apollon laser facility(located in Saclay,France),which was performed with the first available laser beam(F2),scaled to a nominal power of 1 PW.Under the conditions that were tested,this beam delivered on-target pulses of 10 J average energy and 24 fs duration.Several diagnostics were fielded to assess the performance of the facility.The on-target focal spot and its spatial stability,the temporal intensity profile prior to the main pulse,and the resulting density gradient formed at the irradiated side of solid targets have been thoroughly characterized,with the goal of helping users design future experiments.Emissions of energetic electrons,ions,and electromagnetic radiation were recorded,showing good laser-to-target coupling efficiency and an overall performance comparable to that of similar international facilities.This will be followed in 2022 by a further commissioning stage at the multipetawatt level.

EMP control and characterization on high-power laser systems

Giant electromagnetic pulses(EMP) generated during the interaction of high-power lasers with solid targets can seriously degrade electrical measurements and equipment. EMP emission is caused by the acceleration of hot electrons inside the target, which produce radiation across a wide band from DC to terahertz frequencies. Improved understanding and control of EMP is vital as we enter a new era of high repetition rate, high intensity lasers(e.g. the Extreme Light Infrastructure).We present recent data from the VULCAN laser facility that demonstrates how EMP can be readily and effectively reduced. Characterization of the EMP was achieved using B-dot and D-dot probes that took measurements for a range of different target and laser parameters. We demonstrate that target stalk geometry, material composition, geodesic path length and foil surface area can all play a significant role in the reduction of EMP. A combination of electromagnetic wave and 3 D particle-in-cell simulations is used to inform our conclusions about the effects of stalk geometry on EMP,providing an opportunity for comparison with existing charge separation models.

Time-dependent measurement of high-power laser light reflection by low-Z foam plasma

Porous materials have many applications for laser–matter interaction experiments related to inertial confinement fusion.Obtaining new knowledge about the properties of the laser-produced plasma of porous media is a challenging task.In this work,we report,for the first time to the best of our knowledge,the time-dependent measurement of the reflected light of a terawatt laser pulse from the laser-produced plasma of low-Z foam material of overcritical density.The experiments have been performed with the ABC laser,with targets constituted by foam of overcritical density and by solid media of the same chemical composition.We implemented in the MULTI-FM code a model for the light reflection to reproduce and interpret the experimental results.Using the simulations together with the experimental results,we indicate a criterion for estimating the homogenization time of the laser-produced plasma,whose measurement is challenging with direct diagnostic techniques and still not achieved.

Transient electromagnetic fields generated in experiments at the PHELIX laser facility

Large-amplitude electromagnetic radiofrequency fields are created by the charge-separation induced in interactions of high-intensity,short-pulse lasers with solid targets and have intensity that decreases with the distance from the target.Alternatively,it was experimentally proved very recently that charged particles emitted by petawatt laser±target interactions can be deposited on a capacitor-collector structure,far away from the target,and lead to the rapid(nanosecond-scale)generation of large quasi-static electric fields(MV/m),over wide regions.We demonstrate here the generation of both these fields in experiments at the PHELIX laser facility,with approximately 20 J energy and approximately 10^(19)W/cm^(2)intensity,for picoseconds laser pulses,interacting with pre-ionized polymer foams of near critical density.Quasi-static fields,up to tens of k V/m,were here observed at distances larger than 1 m from the target,with results much higher than the radiofrequency component.This is of primary importance for inertial-confinement fusion and laser±plasma acceleration and also for promising applications in different scenarios.

Time-of-flight methodologies with large-area diamond detectors for ion characterization in laser-driven experiments

The time-of-flight technique coupled with semiconductor detectors is a powerful instrument to provide real-time characterization of ions accelerated because of laser-matter interactions.Nevertheless,the presence of strong electromagnetic pulses(EMPs)generated during the interactions can severely hinder its employment.For this reason,the diagnostic system must be designed to have high EMP shielding.Here we present a new advanced prototype of detector,developed at ENEA-Centro Ricerche Frascati(Italy),with a large-area(15 mm×15 mm)polycrystalline diamond sensor having 150 μm thickness.The tailored detector design and testing ensure high sensitivity and,thanks to the fast temporal response,high-energy resolution of the reconstructed ion spectrum.The detector was offline calibrated and then successfully tested during an experimental campaign carried out at the PHELIX laser facility(E_(L)~100 J,τ_(L)=750 fs,I_(L)(1-2.5)×10^(19)W/cm^(2))at GSI(Germany).The high rejection to EMP fields was demonstrated and suitable calibrated spectra of the accelerated protons were obtained.

MS-ECRIS离子源进展报告(英文)

The design of each component of the Multipurpose Superconducting ECR Ion Source(MS-ECRIS) has been completed and some items are ready.The magnets and the cryostat are under construction at ACCEL and the commissioning is scheduled for March 2007.The mechanical have been optimized and their construction is under way;the microwave system is under refurbishment and the 65kV power supply is available and upgraded for afterglow operations.Pumping and extraction system were adapted to the EIS testbench of GSI Darmstadt.The description of each part will be given in the paper along with a schedule of the forthcoming development and experiments.

Single-shot electrons and protons time-resolved detection from high-intensity laser–solid matter interactions at SPARC LAB

Laser–plasma interactions have been studied in detail over the past twenty years,as they show great potential for the next generation of particle accelerators.The interaction between an ultra-intense laser and a solid-state target produces a huge amount of particles:electrons and photons(X-rays andγ-rays)at early stages of the process,with protons and ions following them.At SPARC LAB Test Facility we have set up two diagnostic lines to perform simultaneous temporally resolved measurements on both electrons and protons.

微波技术对ECR离子源性能的影响(英文)

The coupling between microwave generators and ECR ion sources(ECRIS)is a key point for the design of the new generation ECRIS as well as for the optimization of the existing ones.The electromagnetic characterization of the plasma chamber where the ionization phenomena take place is a fundamental starting point to understand and model such process.In such effort the complex structures of the injection and extraction flanges together with the large dimensions of the chamber and the high frequencies that are typically used make impossible an analytical solution and also create great difficulties in the modelling even with state-of- art electromagnetic simulators(CST,HFSS),In the following paper the results of some numerical calculations for the optimum plasma chamber excitation will be presented along with the experimental measurements carried out with the SERSE ion source at INFN-LNS.A campaign of measurements is also planned to further investigate the microwave coupling and the mode excitation,which determines the efficiency of the ECR plasma heating.