Abstract
Many experiments on Sandia National Laboratories' Z Pulsed Power Facility-a 30 MA, 100 ns rise-time, pulsed-power driver-use a monochromatic quartz crystal backlighter system at 1.865 keV (Si Heα) or 6.151 keV (Mn Heα) x-ray energy to radiograph an imploding liner (cylindrical tube) or wire array z-pinch. The x-ray source is generated by the Z-Beamlet laser, which provides two 527-nm, 1 kJ, 1-ns laser pulses. Radiographs of imploding, thick-walled beryllium liners at convergence ratios CR above 15 [CR=ri(0)/ri(t)] using the 6.151-keV backlighter system were too opaque to identify the inner radius ri of the liner with high confidence, demonstrating the need for a higher-energy x-ray radiography system. Here, we present a 7.242 keV backlighter system using a Ge(335) spherical crystal with the Co Heα resonance line. This system operates at a similar Bragg angle as the existing 1.865 keV and 6.151 keV backlighters, enhancing our capabilities for two-color, two-frame radiography without modifying the system integration at Z. The first data taken at Z include 6.2-keV and 7.2-keV two-color radiographs as well as radiographs of low-convergence (CR about 4-5), high-areal-density liner implosions.
Highlights
For more than three decades, spherical crystal based, monochromatic x-ray backlighter radiography[1,2,3,4,5,6,7,8] has been an essential probe for high-energy density physics (HEDP) experiments
We present a 7.242 keV backlighter system using a Ge(335) spherical crystal with the Co Heα resonance line. This system operates at a similar Bragg angle as the existing 1.865 keV and 6.151 keV backlighters, enhancing our capabilities for two-color, two-frame radiography without modifying the system integration at Z
Understanding and mitigating these instabilities is important for the Magnetized Liner Inertial Fusion (MagLIF) concept,[16,17] where fusion fuel is magnetized with an external field coil, preheated with a multi-kJ laser pulse, and compressed using Z to achieve thermonuclear conditions.[18]
Summary
For more than three decades, spherical crystal based, monochromatic x-ray backlighter radiography[1,2,3,4,5,6,7,8] has been an essential probe for high-energy density physics (HEDP) experiments. Bent-crystal microscopes can provide high spatial resolution over a centimeter-size field of view. They operate within a narrow spectral bandwidth (∆E/E ≈ 10−3 − 10−4), which results in nearly monochromatic images that allow for an easier interpretation compared to broadband images, for example, from point-projection backlighter systems. The strongest absorption of x-rays penetrating the liner occurs along the inner wall surface This limb thickness is a function of CR as well and can be calculated as. II–V, we describe these requirements in more detail, determine potential candidates for above 6-keV backlighting, present the chosen 7.2 keV backlighter system as well as laseronly tests to determine image brightness and spatial resolution, and we show examples of 7.2 keV radiographs at the Z Pulsed Power Facility
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