Showing papers by "Angelo Schiavi published in 2002"

Electric field detection in laser-plasma interaction experiments via the proton imaging technique

Abstract: Due to their particular properties, the beams of the multi-MeV protons generated during the interaction of ultraintense (I>1019 W/cm2) short pulses with thin solid targets are most suited for use as a particle probe in laser-plasma experiments. The recently developed proton imaging technique employs the beams in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in laser-plasma interaction experiments. In recent investigations carried out at the Rutherford Appleton Laboratory (RAL, UK), a wide range of laser-plasma interaction conditions of relevance for inertial confinement fusion (ICF)/fast ignition has been explored. Among the results obtained will be discussed: the electric field distribution in laser-produced long-scale plasmas of ICF interest; the measurement of highly transient electric fields related to the generation and dynamics of hot electron currents following ultra-intense laser irradiation of targets; the observation in underdense plasmas, after the ...

Macroscopic evidence of soliton formation in multiterawatt laser-plasma interaction

Abstract: A novel physical phenomenon has been observed following the interaction of an intense $({10}^{19}\mathrm{W}/{\mathrm{cm}}^{2})$ laser pulse with an underdense plasma. Long-lived, macroscopic bubblelike structures have been detected through the deflection that the associated electric charge separation causes in a proton probe beam. These structures are interpreted as the remnants of a cloud of relativistic solitons generated in the plasma by the ultraintense laser pulse. This interpretation is supported by an analytical study of the soliton cloud evolution, by particle-in-cell simulations, and by a reconstruction of the proton-beam deflection.

Laser-produced protons and their application as a particle probe

Abstract: One of the most exciting results recently obtained in the ultraintense interaction research area is the observation of beams of protons with energies up to several tens of megaelectron volts, generated during the interaction of ultraintense picosecond pulses with solid targets. The particular properties of these beams (high brilliance, small source size, high degree of collimation, short duration) make them of exceptional interest in view of diagnostic applications. In a series of experiments carried out at the Rutherford Appleton Laboratory (RAL) and at the Lawrence Livermore National Laboratory (LLNL), the laser-produced proton beams have been characterized in view of their application as a particle probe for high-density matter, and applied to diagnose ultraintense laser-plasma interactions. In general, the intensity cross section of a proton beam traversing matter will be modified both by collisional stopping/scattering, and deflections caused by electric/magnetic fields. With a suitable choice of irradiation geometry and target parameters, the proton probe can be made mainly sensitive to the electric field distribution in the object probed. Therefore, point projection proton imaging appears as a powerful and unique technique for electric field detection in laser-irradiated targets and plasmas. The first measurements of transient electric fields in high-intensity laser-plasma interactions have been obtained with this technique.

Propagation issues and energetic particle production in laser-plasma interactions at intensities exceeding 1019 W/cm2

Abstract: A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser-plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 10 19 W/cm 2 . The transmission of laser energy through long-scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of collimated energy transport through the plasma. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-megaelectron volt protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.

Propagation issues and energetic particle production in laser-plasma interactions at intensities

Abstract: A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser‐plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 10 19 W0cm 2 . The transmission of laser energy through long-scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of collimated energy transport through the plasma. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-megaelectron volt protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary tests were carried out.

Imaging of Plasmas Using Proton Beams Generated by Ultra-Intense Laser Pulses

Abstract: During the interaction of ultraintense laser pulses with plasmas and solid targets, a considerable fraction of the laser energy is deposited into highly energetic charged particles One of the most exciting results recently obtained in this area of research is the observation of very energetic beams of protons, generated during the interaction of ultraintense short pulses with solid targets In a number of experiments, performed with different laser systems and in different interaction conditions, protons with energies up to several tens of MeV have been detected behind thin foils irradiated with high intensity pulses1 In these experiments it was seen that the particle beams are directed along the normal to the back surface of the target, and have a small angular aperture at the highest energies As proton beams are observed even using target which nominally do not contain hydrogen, protons are thought to originate from hydro-carbon impurities located on the target surfaces2 or from bulk contamination of the target Proposed theoretical models indicate that the protons gain their energy from the enormous electric field (∼MV/micron) set up by laser accelerated fast electrons via space-charge at the back target surface3 As protons are easier to accelerate than heavier ions, protons are the dominant component of the ion emission