We have demonstrated efficient coupling of 0.35 p, m laser light for radiation production in inertial confinement fusion (ICF) cavity targets. Temperatures of 270 eV are measured in cavities used for implosions and 300 eV in smaller cavities, significantly extending the temperature range attained in the laboratory to those required for high-gain indirect drive ICF. High-contrast, shaped drive pulses required for implosion experiments have also been demonstrated for the first time. Low levels of scattered light and fast electrons are observed, indicating that plasma instability production is not significant.PACS numbers: 52.50.Jm, 52.40.Nk, 52.70.La Inertial confinement fusion (ICF) uses high powered laser or particle beams to compress and heat capsules containing fusion fuel with the goal of producing thermonuclear energy [1,2]. One proposed method for ICF is x-ray drive where high powered beams heat high-Z cavities, or Hohlraums, converting the driver energy to x rays which implode the capsule [3]. Present indirect drive target designs predict ignition, and gain can be attained with a 1-2 MJ laser for radiation drive temperatures on the order of 300 eV [4]. In this Letter we report experiments using the Nova laser that demonstrate efficient cavity heating with 0.35 p, m light to the temperatures required for these ignition target designs. Radiation temperatures in excess of 270 eV have been obtained in cavities used for implosions [5], while 300 eV temperatures have been obtained in smaller cavities. These radiation cavities are the highest thermal sources measured in the laboratory. The temperature scaling is consistent with a simple power balance model successfully used to model previous experiments at lower temperatures [6,7], extending its proven range of validity. We have demonstrated that shaped radiation drive pulses required to control shock preheat can easily be attained by varying the incident laser power. Laserplasma instabilities [8] that could reduce coupling efficiency and produce superthermal electrons appear not to be significant. Fast electrons are low, typically less than a few percent, indicating superthermal electron preheat is small. In addition to high density implosion experiments [9,10], these cavities have been used for a variety of radiation heating experiments including hydrodynamic instability studies of radiatively accelerated material both in planar [11,12] and convergent systems [13] and opacity experiments of radiatively heated material [14].
Aims. LYRA, the Large Yield Radiometer, is a vacuum ultraviolet (VUV) solar radiometer, planned to be launched in November 2009 on the European Space Agency PROBA2, the Project for On-Board Autonomy spacecraft. Methods. The instrument was radiometrically calibrated in the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) at the Berlin Electron Storage ring for SYnchroton radiation (BESSY II). The calibration was done using monochromatized synchrotron radiation at PTB's VUV and soft X-ray radiometry beamlines using reference detectors calibrated with the help of an electrical substitution radiometer as the primary detector standard. Results. A total relative uncertainty of the radiometric calibration of the LYRA instrument between 1% and 11% was achieved. LYRA will provide irradiance data of the Sun in four UV passbands and with high temporal resolution down to 10 ms. The present state of the LYRA pre-flight calibration is presented as well as the expected instrument performance.
The indirect drive method of inertial confinement fusion uses a high-Z radiation case to convert energy from high-powered laser beams to x rays which implode fusion capsules. Experiments have been performed on the Nova laser to characterize the x-ray production in high-Z cavities for studying the efficiency for x-ray production using two methods for characterization. One method measures the shock velocity produced in low-Z materials by the radiation. The shock velocity is measured by observing the optical signal from the rear of a stepped or continuously varying thickness of Al placed over a hole in the cavity wall. The other method measures the reradiated x-ray flux from the cavity wall viewing through a hole in the cavity. Both methods have been shown to provide a consistent characterization of the x-ray drive in the cavity target.
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