Dynamic stabilization of Rayleigh-Taylor instability of ablation fronts in inertial confinement fusion

One of the most important problems in inertial confinement fusion is how to find a way to mitigate the onset of the Rayleigh-Taylor instability which arises in the ablation front during the compression. In this thesis it is studied in detail the possibility of using for such a purpose the well-known mechanism of dynamic stabilization, already applied to other dynamical systems such as the inverted pendulum. In this context, a periodic acceleration superposed to the background gravity generates a vertical vibration of the ablation front itself. The effects of different driving modulations (Dirac deltas and square waves) are analyzed from a theoretical point of view, with a focus on stabilization of ion beam driven ablation fronts, and a comparison is made, in order to look for optimization

Relativistic attosecond electron bunch emission from few-cycle laser irradiated nanoscale droplets

Attosecond electron bunches produced at the surface of nanometer-scale droplets illuminated by a two-cycle laser pulse are investigated for the purpose of determining their optimal emission characteristics. Significant departures from Mie theory are found for electron bunch emission from droplets whose radii satisfy the condition δr<R<10δr, where δr=γ1/2c/ωp is the plasma relativistic skin depth; an effect which can be accounted for by induced transparency. Scattering from such droplets is subject to a transitional regime which is neither accounted for by optical Mie theory valid for R≫δ, where δ is the usual plasma skin depth, nor with the Rayleigh regime (R<δ≪λ). Instead the angular emission of the bunches is to a good approximation described by the nonlinear ponderomotive scattering model. Subsequently, the bunches are subject to further deflection by the ponderomotive pressure of the copropagating laser field in vacuum, depending on the initial droplet parameters. Final emission angles are estimated, together with the energy spectrum of the bunches

Post-acceleration of electron bunches from laser-irradiated nanoclusters

In this paper the energy gain of attosecond electron bunches emitted during the interaction of intense, few-cycle linearly polarized lasers with nanoscale spherical clusters is determined. In this case electron bunches are emitted from the rear side of the cluster and are then further accelerated while co-propagating with the laser. A previous study has shown how this two-stage process readily occurs for clusters whose radii lie between the relativistic skin depth, δr = γ1/2c/ωp, and the laser spot size σL (Di Lucchio & Gibbon, Phys. Rev. STAB 18, 2015). An analytical model for focused light waves interacting with compact, overdense electron bunches in vacuum is derived heuristically from world-line equations of motion of an electron. The functional integral approach is followed under the mathematical point of view of integration with respect to a stochastic variable. The resulting picture of the laser wave crossing the electron's trajectory leads to a finite energy gain of the electron in light–matter interaction in vacuum. The analytical theory is compared with three-dimensional PIC simulations from which trajectories of the electron bunches can be extracted. The effective increase in bunch energy is determined under realistic conditions both for the peak (mode) and the cutoff energy of the emitted bunch, in order to make quantitative comparisons with theory and the experimental findings of Cardenas et al , Nature Sci. Reports 9 (2019)

Ion acceleration by intense, few-cycle laser pulses with nanodroplets

The energy distribution of electrons and ions emerging from the interaction of a few-cycle Gaussian laserpulse with spherical nanoclusters is investigated with the aim of determining prospects for acceleratingions in this regime. It is found that the direct conversion of laser energy into dense attosecond electronnanobunches results in rapid charge separation and early onset of Coulomb-explosion-dominated ion dynamics.The ion core of the cluster starts to expand soon after the laser has crossed the droplet, the fastestions attaining 10 s of MeV at relativistic intensities. The current investigation should serve as a guide forcontemporary experiments, i.e., using state-of-the-art few-cycle ultraintense lasers and nanoclusters ofsolid densit

Sub-5-fs laser-driven nanophotonics in the relativistic intensity regime

We investigated the interaction of nanometric tungsten targets with ultra-relativistic-intensity sub-5-fs laser pulses. Electrons accelerated to multi-MeV energy with electric fields exceeding the TV/m range and dependence on the laser waveform (carrier-envelope phase) were observed

Towards a Laser-driven polarized 3He Ion-Beam Source

In order to investigate the polarization degree of laser-accelerated 3He ions from a pre-polarized 3He gas-jet target, several challenges have to be overcome beforehand. One of these includes the demonstration of the feasibility of laser-induced ion acceleration out of gas-jet targets. In particular, the ion-emission angles as well as the ion-energy spectra have to be determined for future polarization measurements. Such an experiment was performed at the PHELIX Petawatt Laser Facility, GSI Darmstadt. As laser target, both 4He, and in a second step, unpolarized 3He gas were applied

Simulations of Inverse Compton Scattering as a Diagnostic for Plasma Wakefield Electrons at FLASHForward

FLASHForward is a beam-driven plasma wakefield accelerator located at Deutsches Elektronen Synchrotron (DESY) in Hamburg, Germany. Within the FLASHForward project, laser-driven as well as beam-driven plasma waves enable acceleration of electron beams with energies from tens of MeV to a few GeV. The characterization of these electrons is important to control and improve this acceleration technique.The production of inverse Compton scattering (ICS) offers a possibility to measure electron beam parameters due to the dependence of the produced photons on the electron parameters. A numerical study of ICS radiation produced in experiments at FLASHForward was performed, using an ICS simulation code and the results from particle-in-cell simulations. The possibility of determining electron beam properties from measurements of the x-ray source was explored for a wide range of experimental conditions.The simulations show that the measurement of electron spectrum and divergence is in principle possible with the detection of ICS photons. In addition, transverse probing of the electron beam using ultra-short laser pulses allows to obtain longitudinal information about the electron beam in multi shot experiments. However, the detection of the produced ICS radiation, with photon energies of several MeV for the electron beams of interest, remains challenging.1. A. Aschikhin et al. “The FLASHForward facility at DESY,” Nucl. Instruments Methods Phys. Res. Sect. A Accel. Spectrometers, Detect. Assoc. Equip. 806 (2016).2. W. J. Brown and F. V. Hartemann, “Three-dimensional time and frequency-domain theory of femtosecond x-ray pulse generation through Thomson scattering,” Phys. Rev. Spec. Top. - Accel. Beams, 7, 060703 (2004).3. R. A. Fonseca et al., “OSIRIS: A Three-Dimensional, Fully Relativistic Particle in Cell Code for Modeling Plasma Based Accelerators,” Computational Science — ICCS 2002, 2331 (2002).4. T. Mehrling et al., “HiPACE: a quasi-static particle-in-cell code,” Plasma Phys. Control. Fusion 56, 8 (2014)

Simulation studies of injection techniques for Flashforward laser wakefield test beam line

In the context of FLASHForward laser wakefield tests, 2D simulations have been carried on with OSIRIS PIC code. Ionization injection with a gas jet doped with 1% Nitrogen and gaussian density downramp injection have been simulated. We present therefore the working points obtained for BOND laser from the collaboration between simulation group and laser wakefield beam line people