Dynamics and characteristics of a 215-eV dynamic-hohlraum x-ray source on Z

Abstract

A radiation source has been developed on the 20-MA Z facility that produces a high-power x-ray pulse, generated in the axial direction primarily from the interior of a collapsing dynamic hohlraum (DH). The hohlraum is created from a solid cylindrical CH2 target centered within an imploding tungsten wire-array Z pinch. Analyses and interpretation of measurements made of the x-ray generation within and radiated from the hohlraum target have been done using radiation-magnetohydrodynamic-code simulations in the r-z plane that take account of the magnetic Rayleigh–Taylor (RT) instability. These analyses suggest that a significantly reduced RT seed (relative to that used to explain targetless Z-pinch data on Z) is required to explain the observations. Although some quantitative and qualitative agreement with the measurements is obtained with the reduced RT seed, differences remain. Initial attempts to include into the simulations a precursor plasma, arising from wire material driven ahead of the main implosion, did not ameliorate the differences. Modification of the simulated W/CH2 interface may be required to properly explain the measured axial radiation pulse. This pulse, which exits a 4.5-mm2 hole centered above the target, begins ∼5 ns prior to stagnation (as defined by peak radial radiation power). The 5-ns interval leading to stagnation represents the duration when the imploding tungsten plasma acts as a hohlraum wall, trapping radiation within the interior of the foam target. The hohlraum radiation exiting the hole at 6 degrees to the z-axis reaches a maximum intensity of 3.1±0.6 TW/str (associated with an average hohlraum temperature of 215±10 eV), 1.4±0.4 ns prior to stagnation. (The uncertainties represent rms shot-to-shot variations.) This radiation pulse, characterized here, is useful for performing radiation-transport experiments with drive temperatures in excess of 200 eV.

Overview of the dynamic-hohlraum x-ray source at Sandia National Laboratories.

“…For the baseline configuration (Φ = 40 mm and N = 240) with a simple target (Fig. 2C), the outer array O collides with the inner I at -23 ns, which produces the radial radiation peak [10] at -23 ns shown in Fig. 1B.…”

“…This configuration, like the present arrangements [10,[14][15], consisted of two coaxial nested arrays (Fig. 2) where the diameter Φ and wire number N of the outer array were 40 mm and 240 wires, respectively.…”

“…Dynamic-hohlraums (DHs) [1][2][3][4] driven by a wire-array z-pinch are being developed and used as intense blackbody x-ray sources for inertialconfinement-fusion (ICF) [5][6][7][8][9] and hightemperature radiation-flow experiments [10][11] (Fig. 1).…”

“…In radiation-transport experiments, x-rays exiting a top radiation-exit-hole (REH) (Fig. 1C) are used to study radiation flow at temperatures exceeding 200 eV [10]. X-rays exiting a bottom REH are used to monitor the radiation exiting the top when diagnostic access to the top is not available [11].…”

Blast wave energy diagnostic

“…6,7 A target is located above a 4 mm diameter radiation exit hole on the axial end of the DH, see of the cylindrical section. This platform supports a 56Ϯ 0.9 mg/ cm 3 , 4 mm diameter, 4 mm high silica aerogel, as well as a spatial fiducial grid that will be used as a spatial calibration reference for radiography.…”