High-temperature dynamic hohlraums on the pulsed power driver Z

Abstract

In the concept of the dynamic hohlraum an imploding Z pinch is optically thick to its own radiation. Radiation may be trapped inside the pinch to give a radiation temperature inside the pinch greater than that outside the pinch. The radiation is typically produced by colliding an outer Z-pinch liner onto an inner liner. The collision generates a strongly radiating shock, and the radiation is trapped by the outer liner. As the implosion continues after the collision, the radiation temperature may continue to increase due to ongoing PdV (pressure times change in volume) work done by the implosion. In principal, the radiation temperature may increase to the point at which the outer liner burns through, becomes optically thin, and no longer traps the radiation. One application of the dynamic hohlraum is to drive an ICF (inertial confinement fusion) pellet with the trapped radiation field. Members of the dynamic hohlraum team at Sandia National Labs have used the pulsed power driver Z (20 MA, 100 ns) to create a dynamic hohlraum with temperature linearly ramping from 100 to 180 eV over 5 ns. On this shot zp214 a nested tungsten wire array of 4 and 2 cm diam with masses of 2 and 1 mg imploded onto a 2.5 mg plastic annulus at 5 mm diam. The current return can on this shot was slotted. It is likely the radiation temperature may be increased to over 200 eV by stabilizing the pinch with a solid current return can. A current return can with nine slots imprints nine filaments onto the imploding pinch. This degrades the optical trapping and the quality of the liner collision. A 1.6 mm diam capsule situated inside this dynamic hohlraum of zp214 would see 15 kJ of radiation impinging on its surface before the pinch itself collapses to a 1.6 mm diam. Dynamic hohlraum shots including pellets were scheduled to take place on Z in September of 1998.

Wire array Z-pinch insights for enhanced x-ray production

“…The imprint of such an azimuthal structure has been observed from the radiation field generated from foam targets placed interior to the wire array by , Derzon et al [32]. Nash et al [33] have shown by replacing the posts with an azimuthally continuous shell that the on-axis radiation generated from a dynamic hohiraum configuration is doubled, again illustrating the importance ojmaintairzing azh.m.h-d symmetry throughout the entire ioad region for producing high radia!ion yields.…”

Dynamics of a Z-pinch x-ray source for heating inertial-confinement-fusion relevant hohlraums to 120–160 eV

“…These diagnostics included a total-energy bolometer, a faltered XRD set, and faltered fast-framing pin-hole cameras. Additionally, on some shots the hohlraum was removed and the power exiting the REH was measured by a further suite of on-axis diagnostics [22,25,48]. For these measurements, Lambertian emission at the REH was assumed.…”

“…At Sandia National Laboratories, for example, three hohlraum concepts that take advantage of the high x-ray powers generated with thk new pulsed-power capability are under development to investigate the feasibility of z-pinches to drive ICF targets [18][19][20][21][22]. They are referred to as the z-pinch driven [23,24], the dynamic [25,26], and the static-wall hohlraum [27]. To date, the large-volume z-pinch driven hohlraum has developed a temperature of 95*5 eV in a 17-mm diameter by 15-mm high hohlraum, when heated by radiation generated external to a single pinch [28], The energy-efficient dynamic hohlraum, which uses radiation generated internal to a radially converging target heated by the imploding wire array, has developed temperatures ranging from 80 to 180 eV as the diameter of a 10-mm high hohlraum compresses from 5 to 1.6 mm [22].…”

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

“…Implicit in these applications is the assumption that the axial radiation produced is top-bottom symmetric [18]. Sandia's initial DH configuration was developed by Nash and colleagues [3], after it was established that a high x-ray power could be generated by a wire-array z-pinch if a large number of wires were used in the array [19][20].…”

“…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).…”