Creating metallic under-dense radiators by electron beam heating prior to laser impact

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A pulsed, relativistic electron beam can heat a metal foil to a plasma state, and initiate an expanding flow into vacuum. At a given time in its evolution, this flow fills a nearly spherical volume with nearly uniform density, assuming a rapid expansion prior to any condensation. A metal cloud produced in this way can serve as a target of intense laser illumination to create an under-dense radiator of x-rays. The phrase ''under-dense radiator'' means that the cloud, assumed ionized, has a plasma density that is less than the critical density for the wavelength of the laser light. The example ... continued below

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303 Kilobytes pages

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Garcia, M December 15, 1998.

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Description

A pulsed, relativistic electron beam can heat a metal foil to a plasma state, and initiate an expanding flow into vacuum. At a given time in its evolution, this flow fills a nearly spherical volume with nearly uniform density, assuming a rapid expansion prior to any condensation. A metal cloud produced in this way can serve as a target of intense laser illumination to create an under-dense radiator of x-rays. The phrase ''under-dense radiator'' means that the cloud, assumed ionized, has a plasma density that is less than the critical density for the wavelength of the laser light. The example described here is of a 2 {micro}g copper foil 23 {micro}m thick and 0.16 mm in diameter, heated by 8 mJ of electron beam energy in as short a time as possible, perhaps under 50 ns. The electron beam pulse must be at least 140 nC at 100 keV in order to transit the foil and deposit 8 mJ. A 50 ns pulse focused on the target would have a current of 2.8 A, and a current density of 14 kA/cm{sup 2}. The initial plasma temperature is 0.5 eV. After 300 ns, the flow has expanded to fill a nearly spherical volume of 1 mm diameter, with a nearly uniform copper density of 1.5 x 10{sup 20} cm{sup {minus}3}. The leading edge of the cloud is expanding at 1700 m/s, while flow at the original position of the foil surface expands at 150 m/s. This cloud is nearly stationary during the short time of a laser pulse at the National Ignition Facility (NIF).

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303 Kilobytes pages

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  • Other Information: PBD: 15 Dec 1998

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  • Report No.: UCRL-ID-134255
  • Report No.: YN0100000
  • Grant Number: W-7405-ENG-48
  • DOI: 10.2172/14753 | External Link
  • Office of Scientific & Technical Information Report Number: 14753
  • Archival Resource Key: ark:/67531/metadc622633

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  • December 15, 1998

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • May 6, 2016, 2:20 p.m.

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Garcia, M. Creating metallic under-dense radiators by electron beam heating prior to laser impact, report, December 15, 1998; California. (digital.library.unt.edu/ark:/67531/metadc622633/: accessed July 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.