Showing papers by "David Neely published in 2004"

Ion acceleration by collisionless shocks in high-intensity-laser-underdense-plasma interaction.

Abstract: e . Two-dimensional particle-in-cell simulations suggest that multiple collisionless shocks are formed at high density. The interaction of shocks is responsible for the observed plateau structure in the ion spectrum and leads to an enhanced ion acceleration beyond that possible by the ponderomotive potential of the laser alone.

Characterization of proton and heavier ion acceleration in ultrahigh-intensity laser interactions with heated target foils.

Abstract: Proton and heavy ion acceleration in ultrahigh intensity ( approximately 2 x 10(20) W cm(-2) ) laser plasma interactions has been investigated using the new petawatt arm of the VULCAN laser. Nuclear activation techniques have been applied to make the first spatially integrated measurements of both proton and heavy ion acceleration from the same laser shots with heated and unheated Fe foil targets. Fe ions with energies greater than 10 MeV per nucleon have been observed. Effects of target heating on the accelerated ion energy spectra and the laser-to-ion energy conversion efficiencies are discussed. The laser-driven production of the long-lived isotope (57 )Co (271 days) via a heavy ion induced reaction is demonstrated.

High power laser production of short-lived isotopes for positron emission tomography

Abstract: Positron emission tomography (PET) is a powerful diagnostic/imaging technique requiring the production of the short-lived positron emitting isotopes 11C, 13N, 15O and 18F by proton irradiation of natural/enriched targets using cyclotrons. The development of PET has been hampered due to the size and shielding requirements of nuclear installations. Recent results show that when an intense laser beam interacts with solid targets, megaelectronvolt (MeV) protons capable of producing PET isotopes are generated. This report describes how to generate intense PET sources of 11C and 18F using a petawatt laser beam. The work describing the laser production of 18F through a (p,n) 18O reaction, and the subsequent synthesis of 2-[18F] is reported for the first time. The potential for developing compact laser technology for this purpose is discussed.

Electronic conduction in shock-compressed water

Abstract: The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.

Neutron production by fast protons from ultraintense laser-plasma interactions

Abstract: Tens of MeV proton beams have been generated by interactions of the VULCAN petawatt laser with foil targets and used to induce nuclear reactions in zinc and boron samples. The numbers of C11, Ga66, Ga67, Ga68, Cu61, Zn62, Zn63, and Zn69m nuclei have been measured and used to determine the proton energy spectrum. It is known that (p,n) reactions provide an important method for producing neutron sources and in the present experiment up to ∼109neutronssr−1 have been generated via B11(p,n)C11 reactions. Using experimentally determined proton energy spectra, the production of neutrons via (p,n) reactions in various targets has been simulated, to quantify neutron pulse intensities and energy spectra. It has been shown that as high as 4×109neutronssr−1 per laser pulse can be generated via Li7(p,n)B7 reactions using the present VULCAN petawatt laser-pulse conditions.

Nuclear reactions in copper induced by protons from a petawatt laser-foil interaction

Abstract: High-intensity (>1019 W cm−2) laser-plasma interactions have been shown to produce large quantities of protons with energies up to several tens of MeV. A range of laser-driven proton-induced reactions in copper have been investigated and the observed reactions quantified. The energy spectrum of the accelerated protons was determined from the reactions in a single thin copper foil and found to be in agreement with that deduced from (p,n) reactions measured in a stack of copper foils. The potential applications of this diagnostic technique are discussed.

Progress towards Petawatt level OPCPA

Abstract: The technique of optical parametric chirped pulse amplification1/2(OPCPA) offers the possibility of generating powers and intensities much higher than is feasible with current CPA systems and provides a route to possible future upgrades for the 'Vulcan' Nd:glass laser at the Central Laser Facility. Earlier work3on this laser demonstrated feasibility up to the TW level. The current programme is aimed at fully assessing the technique to much higher powers with a view to including it in future upgrade plans for Vulcan and consists of a campaign of 2 experimental periods on Vulcan. The purpose of this article is to report on the results from the first of these experiments.

Laser acceleration and laser cooling for ion beams

Abstract: Cooling and acceleration of ions by lasers has gained increasing attention over the last years. The common interest is to further increase the luminosity of ion beams, either by shrinking the phase space occupied by the beam, or simply via increasing the number of particles. Recently, laser cooling has demonstrated ion beam crystallization as the ultimate reduction of the beam temperature. On the other hand, acceleration of ions by ultra-intense lasers resulted in the generation of ion beams of unprecedented quality, both in terms of beam power and beam emittance.