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Publications (4)0.87 Total impact

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    ABSTRACT: Several experiments at the Nevada Terawatt Facility (NTF) study the interaction of laser-created plasmas with large external magnetic fields. Examples include a ldquosolar windrdquo experiment that studies the development of a shock when an ablation plasma flow interacts with a strong magnetic field, and an isochoric heating experiment, in which the effect of a confining external magnetic field on target heating will be investigated. The plasmas can be created with one of our two multiterawatt laser systems, namely, Tomcat (up to 10 TW) and Leopard (up to 100 TW). Analyzing the experiments requires a thorough understanding of the initial conditions of the laser plasma. The measurements performed with Faraday cups yield the hot-electron temperature, which is characteristic for electrons that directly absorb the laser energy. Energy spectrum measurements have been carried out with Tomcat pulses (1057 nm) with up to 4-J pulse energy and 4 ps/1 ps duration. For an optimized focal spot size, a hot-electron temperature of more than 2.6 keV was measured, which is consistent with a laser intensity between 10<sup>15</sup> and 10<sup>16</sup> W/cm<sup>2</sup>.
    IEEE Transactions on Plasma Science 11/2008; · 0.87 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Several experiments at the Nevada Terawatt Facility (NTF) study the interaction of laser-created plasmas with large external magnetic fields. Examples include a “solar wind” experiment that studies the development of a shock when an ablation plasma flow interacts with a strong magnetic field, and an isochoric heating experiment, in which the effect of a confining external magnetic field on target heating will be investigated. The plasmas can be created with one of our two multi-terawatt laser systems, Tomcat (up to 10TW) and Leopard (up to 100TW). Analyzing the experiments requires a thorough understanding of the initial conditions of the laser plasma. The laser absorption on target can be characterized by analyzing the energy spectrum of proton emitted from the target surface. The measurements, performed with Faraday cups, yield both the hot electron temperature (characteristic for electrons which directly absorb the laser energy) and the cold electron temperature (characteristic for the bulk of the target electrons, which are indirectly heated by the hot electrons). Energy spectrum measurements have been carried out with Tomcat pulses with up to 4J pulse energy and 4ps/1ps duration. For an optimized focal spot size, a hot electron temperature of more than 2.6keV was measured, corresponding to an absorbed laser intensity of 10<sup>16</sup> W/cm<sup>2</sup>.
    Pulsed Power Conference, 2007 16th IEEE International; 07/2007
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    ABSTRACT: Explosive plasma expansion in an external magnetic field occurs in a variety of space and astrophysical events that include supernova explosions in the interstellar magnetic field and the interaction of solar coronal mass ejections with planetary magnetospheres. Effects of the interaction of plasma winds with magnetic obstacles were investigated in the laboratory using a laser produced plasma plume and an external magnetic field created by a current driven through a metal rod by a pulsed power generator. Instabilities develop at the plasma-field boundary. In the frontal direction, along the normal to the target, flute-like instabilities grow and eventually lead to plasma penetration across the magnetic field with constant velocity. Along the lateral boundary, the plasma deceleration by the transverse magnetic field initiated a Kelvin-Helmholtz instability.
    Pulsed Power Conference, 2007 16th IEEE International; 07/2007
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    ABSTRACT: Summary form only given. Collisional particle-in-cell simulations predict that solid density matter irradiated with a short pulse high intensity laser can be heated to keV temperatures by applying an external magnetic field. The role of the magnetic field is to restrict the radial diffusion of the hot electrons accelerated by the laser field. The confinement can be effective if the gvro-period is less than the collision time. This reduces the radial diffusion of the hot electrons long enough so that they can couple to the cold electrons which in turn couple to the ions. To test these predictions, an experiment is being developed that takes advantage of the coupled Tomcat/Leopard -Zebra facility. According to simulations performed for achievable values of the parameters, with a laser intensity higher than 1017 W/cm2 and a magnetic field of the order of 1 MG material volumes of 105 mum can be heated for several ps to temperatures of several hundred eV. These parameters make this technique extremely appealing for fusion and opacity studies with numerous applications that include modeling the radiation transport in the interiors of stars. In preparation for the integrated experiment, magnetic fields higher than 1 MG were produced in vacuum with the pulsed power generator Zebra (0.6 MA, 200 ns) using horseshoe shaped coils. In the configuration used, no plasma was created on the surface of a CM laser target placed inside the coil. To date, the best parameters measured for the Tomcat compressed laser pulse are: energy 4 J, duration 0.8 ps, and focal spot FWHM 30 mum (measured with the unamplified beam), resulting in an irradiance on target around 1018 W/cm2. Higher irradiance will be soon available using the 100 TW laser Leopard, the pulse compression of which is currently under way. The jitter of Zebra was reduced to less than 15 ns rms assuring successful synchronization with the lasers. The goal of the experiment i- s to demonstrate enhanced heating of a solid target irradiated by an intense, short pulse laser in the presence of an external magnetic field. Several types of targets including homogeneous Si and CD targets, as well as layered targets CD-Si-CD will be used, and their heating compared. The electron temperature and ionization balance will be inferred from X-ray spectra. A von Hamos KAP crystal spectrograph was built and used to record single shot Al and Si spectra from laser irradiated targets. Neutron yield measurements with scintillator-photomultiplier detectors will be used to determine the deuteron temperature.
    IEEE International Conference on Plasma Science 01/2007;