Showing papers by "Angelo Schiavi published in 2006"

Quantum regime of free electron lasers starting from noise

Abstract: We investigate the quantum regime of a high-gain free-electron laser starting from noise. In the first part, we neglect the radiation propagation and we formulate a quantum linear theory of the N-particle free-electron laser Hamiltonian model, quantizing both the radiation field and the electron motion. Quantum effects such as frequency shift, line narrowing, quantum limitation for bunching and energy spread, and minimum uncertainty states are described. Using a second-quantization formalism, we demonstrate quantum entanglement between the recoiling electrons and the radiation field. In the second part, we describe the field classically but we include propagation effects (i.e. slippage) and we demonstrate the novel regime of quantum SASE with high temporal coherence and discrete spectrum. Furthermore, we describe "quantum purification'' of SASE: the classical chaotic spiking behavior disappears and the spectrum becomes a series of discrete very narrow lines which correspond to transitions between discrete momentum eigenstates ( which originate high temporal coherence).

Radiative shocks : An opportunity to study laboratory astrophysics

Abstract: In this paper, experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Two sets of experiments have been performed at the Laser pour l'Utilisation des Lasers Intenses (LULI) laboratory. Several shock parameters were simultaneously measured: shock temperature and velocities, the precursor two-dimensional (2D) time evolution, its electron density, density gradient, and temperature. Data were obtained varying initial conditions for different laser intensities and gas pressures. Comparisons with 1D and 2D radiative hydrodynamic simulations are shown for all measured parameters (shock velocity, shape, radial expansion, and temperature as well as precursor velocity and electron density).

Laser-driven shock waves for the study of extreme matter states

Abstract: During the last ten years, the ability of high power lasers to generate high energy density shocks has made them a reliable tool to study extreme states of matter. These states of matter are relevant in many important physics areas such as astrophysics, planetology and ICF physics. Here, we present some representative studies performed by using a driven laser shock: melting of iron at pressures relevant for geophysics, developments of new techniques to measure the density of highly compressed matter and a study of a radiative shock.

Isochoric heating of matter by laser-accelerated high-energy protons

Abstract: We describe an experiment on isochoric heating of matter by intense laser-accelerated protons. The experiment was performed using the LULI 100 TW facility with 15-20 J on target energy and > 10 19 W.cm -2 maximum focused intensity. Focusing the laser on a 10 micron thick Au foil, we accelerated forward a laminar proton beam with a maximum energy of 16 MeV. This proton beam irradiated and heated a secondary target positioned after a variable vacuum gap. The heating was diagnosed by ID and 2D time-resolved measurements of the optical self-emission of the heated target rear-surface. Detailed results as a function of the Z and the thickness of the secondary target as well as analysis, including a full modelling of the target heating with a 2D hydro-code (DUED) coupled to a proton energy deposition code, were obtained. We have also studied the efficiency of heating as a function of the primary target topology, i.e. either flat, which results in a diverging proton beam, or curved, which has the ability of focusing partly the proton beam.

Isochoric heating of matter by laser-accelerated high-energy protons

Abstract: We describe an experiment on isochoric heating of matter by intense laser-accelerated protons. The experiment was performed using the LULI 100 TW facility with 15-20 J on target energy and > 10 19 W.cm -2 maximum focused intensity. Focusing the laser on a 10 micron thick Au foil, we accelerated forward a laminar proton beam with a maximum energy of 16 MeV. This proton beam irradiated and heated a secondary target positioned after a variable vacuum gap. The heating was diagnosed by ID and 2D time-resolved measurements of the optical self-emission of the heated target rear-surface. Detailed results as a function of the Z and the thickness of the secondary target as well as analysis, including a full modelling of the target heating with a 2D hydro-code (DUED) coupled to a proton energy deposition code, were obtained. We have also studied the efficiency of heating as a function of the primary target topology, i.e. either flat, which results in a diverging proton beam, or curved, which has the ability of focusing partly the proton beam.

Dynamics of electric fields driving the laser acceleration of multi-MeV protons

Abstract: The acceleration of multi-MeV protons from the rear surface of thin solid foils irradiated by an intense (approximately 10(18) W/cm2) and short (approximately 1.5 ps) laser pulse has been investigated using transverse proton probing. The structure of the electric field driving the expansion of the proton beam has been resolved with high spatial and temporal resolution. The main features of the experimental observations, namely, an initial intense sheath field and a late time field peaking at the beam front, are consistent with the results from particle-in-cell and fluid simulations of thin plasma expansion into a vacuum.

Radiative shocks: New results for laboratory astrophysics

Abstract: In the framework of the Laboratory Astrophysics, we present new radiative shocks experiments performed using the LULI2000 facility. A strong shock is driven in a multi-layered solid target (CH-Ti-CH) which accelerates into a gas cell (∼ 60 km/s) filled with Xenon at low pressure (0.1 - 0.3 bar) and produces a radiative supercritical shock [4, 8]. A low power laser beam (8 ns - 532 nm) probes the Xenon gas in the transverse direction and is injected into a VISAR and on two optical framing cameras (GOI). These diagnostics allow to determine electron density variation, to measure both precursor and shock velocities along the shock propagation axis [3, 5] as well as the 2D shape of the shock. On rear side, the light emitted from the shocked Xenon is imaged onto the slit of a streak camera. An absolute calibration of the optical system allows to determine the brightness temperature [8]. Data were obtained for different laser intensities and gas pressures. Two VISARs on rear side allowed an accurate measurement of the shock conditions in the pusher before the breakout in the Xenon. Comparison between I D (MULTI) and 2D (DUED [1, 2]) radiative hydrodynamic codes and measured quantities (shock velocity, shape, radial expansion, and temperature as well as precursor velocity and precursor electron density) are presented.

Ultrafast charge dynamics initiated by high-intensity, ultrashort laser-matter interaction

Abstract: The interaction of high‐intensity laser pulses with matter releases instantaneously ultra‐large currents of highly energetic electrons, leading to the generation of highly‐transient, large‐amplitude electric and magnetic fields. We report results of recent experiment in which such charge dynamics have been studied by using proton probing techniques able to provide maps of the electrostatic fields with high spatial and temporal resolution. The dynamics of ponderomotive channelling in underdense plasmas have been studied in this way, as also the processes of Debye sheath formation and MeV ion front expansion at the rear of laser‐irradiated thin metallic foils. An application employing laser‐driven impulsive fields for energy‐selective ion beam focusing is also presented.

Laser-driven target for fast-ignition demonstration

Abstract: The basis for the design of a direct-drive target for demonstrating inertial fusion fast ignition and burn propagation is discussed. A preliminary design of a target driven by a pulse of about 300 kJ and ignited by an ultraintense pulse of about 100 kJ is presented and illustrated by 1-D simulations of the implosion stage and 2-D simulations of ignition and burn.

Modeling high-current instabilities in particle accelerators ∗

Abstract: Methods exploiting integration techniques of Lie algebraic nature have been successfully employed in the past to develop charged beam transport codes, for different types of accelerators. These methods have been so far applied to the transverse motion dynamics, while the longitudinal part has been treated using standard tracking codes. In this contribution we extend the symplectic technique to the analysis of longitudinal and coupled longitudinal and transverse motion in charged beam transport with the inclusion of the non linear dynamics due to the wake field effects. We use this method to model different types of instabilities due to high current. We consider in particular the case of coherent synchrotron radiation instabilities and their implication in the design and performances of high current accelerators. We discuss either single pass and recirculated devices. As to this last case, we also include the effect due to quantum noise and damping.