High Temperatures in Inertial Confinement Fusion Radiation Cavities Heated with 0.35μmLight

Abstract

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].

Study of shockwave method for diagnosing the radiation fields of laser-driven gold hohlraums

“…Considering the influence of the equation of state (EOS) and reradiation of Aluminum, the radiative ablation process is no longer stationary, but a similar relation may be expressed as T R = × D s , where the parameters and can be determined via numerical simulation and fitting. Kauffman et al [2] proposed the following scaling relation…”

“…4 in Ref. [2]) used to derive formula (1) ablates more Aluminum plasmas before the arrival of the main pulse, which absorbs and reemits backward more x-ray flux, therefore little x-ray flux arrives at the ablation front and produces a smaller ablation pressure and a slower shock wave. That means the scaling relation of the peak radiation temperature T R with the ablation shock velocity D s in Aluminum plates can be affected, to some extent, by the temporal profile of x-ray sources, i.e.…”

“…So, accurate measurements of the peak temperature, the pulse shape and the high energy x-ray amount of the hohlraums radiation fields are of great importance. Currently, there are two independent experimental approaches [1][2][3] to diagnose the hohlraums radiation field: (1) direct measurement of the radiation flux with broad-band x-ray spectrometer (Dante [4] or SXS [5] and (2) observing the velocity D s of the shock wave in an Al witness plate driven by hohlraums radiation field, where the radiation temperature is inferred via a scaling relation [2] of T R with D s .…”

Progress toward the Laboratory Simulation of Young Supernova Remnants

“…The basic structure of the target was developed over a period of several years (Glendinning et al 1992 ;Kau †man et al 1994 ;Louis et al 1995 ;Peyser et al 1995 ;Remington et al 1995 ;Dimonte et al 1996). It has been used successfully for many hydrodynamic experiments.…”

X-ray spectroscopy from fusion plasmas

“…This correction, called albedo correction, is performed on calculational basis [40] and corroborated by witness plate measurements [44] and xray emission measurements through the laser entrance hole [6,45,46]. Simultaneously, three independent detection systems have been applied for a complete measurement of the scattering losses.…”