Hot Dense Capsule-Implosion Cores Produced byZ-Pinch Dynamic Hohlraum Radiation

Abstract

Hot dense capsule implosions driven by z-pinch x-rays have been measured for the first time. A ~220 eV dynamic hohlraum imploded 1.7-2.1 mm diameter gas-filled CH capsules which absorbed up to ~20 kJ of x-rays. Argon tracer atom spectra were used to measure the T e ~1 keV electron temperature and the n e ~1-4 x 10 23 cm -3 electron density. Spectra from multiple directions provide core symmetry estimates. Computer simulations agree well with the peak compression values of T e , n e , and symmetry, indicating reasonable understanding of the hohlraum and implosion physics.Implosion of spherical capsules by x-rays contained in an enclosure known as a hohlraum is the baseline approach for achieving inertial confinement fusion (ICF) [1]. These implosions provide a platform for high energy density physics investigations and may enable studies of matter at conditions similar to stellar interiors. One method for generating the required high energy density x-rays is the z-pinch dynamic hohlraum (ZPDH) [2][3][4]. Accelerating an annular high-atomic-number zpinch plasma onto a low-atomic-number low-density cylindrical foam creates this type of hohlraum. The z-pinch plasma impact onto the foam launches a radiating shock that propagates toward the cylinder axis and heats the hohlraum. The z-pinch plasma traps the radiation, improving the symmetry for driving capsule implosions at the center of the hohlraum. In this Letter we describe the first x-ray measurements of hot dense implosion cores produced using z-pinch radiation drive.ICF requires highly-symmetric capsule implosions. Absorption of 150 kJ of x-ray energy in a carefully-shaped pulse with ~1-3 % spatial symmetry is estimated to be sufficient for ignition [1].The appeal of the ZPDH approach is efficient generation and delivery of x-rays to the capsule. Indeed, the capsules in the experiments reported here absorbed up to 20 kJ of x-rays, about 1/8 of the estimated ignition requirement. However, it remains to be seen whether adequate symmetry and temporal pulse shaping control can be obtained. The experiments reported here represent an important step toward ZPDH symmetry control.Recent work [5][6] demonstrated reasonable ZPDH performance understanding. The effect of random z-pinch non-uniformities on the shock radiation source was found very small. The systematic asymmetries must now be addressed. The cylindrical ZPDH tends to drive the spherical capsule with equator-hot radiation that, if uncorrected, will produce an implosion elongated along the cylinder axis. Symmetry corrections, including radiation shields, non-cylindrical foams, and local foam dopants, require diagnostics capable of measuring the alteration's effect. Published laser driven implosions [7] showed that x-ray core imaging measurements of the equatorial plane radius (a) compared to the polar radius (b) reflected the x-ray drive asymmetry. Applying this method to the ZPDH is complicated by the difficulty of viewing the implosion through the luminous highopacity z-pinch plasma (Fig. 1). We consequently em...

Integration of MHD load models with circuit representations the Z generator.

“…These experiments were fielded by James Bailey [15]. These experiments used nested wire arrays that are 1.2cm in height, with a 2:1 mass ratio between the outer and inner wire arrays.…”

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

“…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).…”

Direct asymmetry measurement of temperature and density spatial distributions in inertial confinement fusion plasmas from pinhole space-resolved spectra

“…K-shell line emission spectroscopy using Ar as a tracer has proved to be a powerful tool to extract spaceaveraged electron temperature, T e , and density, n e [3][4][5]. However, two-dimensional (2-D) space-resolved spectra have never been extracted to study the asymmetries of T e and n e structures in the implosion core.…”

“…Thus, a tracer amount of Ar (0.18 % atomic concentration) was mixed into the fuel to infer the implosion core plasma conditions. Previous observations of spaceintegrated Ar K-shell spectra have uniquely determined T e and n e of implosion core plasmas by fitting the data with detailed spectral models [3][4][5]. In order to investigate the asymmetry in T e and n e spatial distributions, the challenge is to record Ar line emission not just with spectral resolution, but also with 2-D spatial resolution.…”

“…LILAC 1-D [8] hydrodynamic simulations predict that the implosion core plasma conditions would range 1-3 keV in T e and 1 − 4 × 10 24 cm −3 in n e around the collapse of the implosion. Ar K-shell spectroscopy is appropriate to diagnose these conditions [3][4][5]. Spectral line broadening of the Ar Lyβ and Heβ (i.e., n=3 to 1 transitions in H-like and He-like Ar, respectively) is dominated by the Stark effect, which is sensitive to n e .…”