High-density carbon capsule experiments on the national ignition facility

Indirect-drive implosions with a high-density carbon (HDC) capsule were conducted on the National Ignition Facility (NIF) to test HDC properties as an ablator material for inertial confinement fusion. A series of five experiments were completed with $76\text{−}\mu \mathrm{m}$-thick HDC capsules using a four-shock laser pulse optimized for HDC. The pulse delivered a total energy of $1.3$ MJ with a peak power of 360 TW. The experiment demonstrated good laser to target coupling $\left(\sim 90\%\right)$ and excellent nuclear performance. A deuterium and tritium gas-filled HDC capsule implosion produced a neutron yield of $1.6\times {10}^{15}\pm 3\times {10}^{13}$, a yield over simulated in one dimension of $70\%$.

Figure 1

The target configuration is shown. The hohlraum is $9.425$ mm in length and $5.75$ mm in diameter. The 192 laser beams enter the hohlraum through two laser entrance holes $3.101$ mm in diameter. The high-density carbon capsule is located at the center of the hohlraum and has a shell thickness of $76\mu \mathrm{m}$.

Figure 2

The laser pulse shape for the HDC capsule (solid line) is compared to the high-foot CH pulse shape (dotted line) and the low-foot CH pulse (dashed line). All three laser pulses have a total energy of $1.3$ MJ and powers between 350 and 360 TW.

Figure 3

(a) VISAR streaked interferometry image with the shock breakout from the HDC ablator into the liquid deuterium and shock mergers 2, 3, and 4 are shown. (b) The measured shock velocity (black lines) compared to simulations (gray lines) is shown for the pole and equator views. Due to the opacity of the HDC, VISAR is unable to measure the velocity of the shock until it breaks out of the ablator at $5.2$ ns.

Figure 4

The time integrated x-ray emission from the hot spot is shown for the two deuterium-filled ConA experiments and the DT-filled symcap experiment. (a) With a wavelength separation of $+2.83\AA (+2.43\AA )$ between the ${30}^{\circ }\left({23}^{\circ }\right)$ beams and the outer beams, a prolate core image was observed. (b) After reducing the wavelength separation between the cones to $+1.73\AA$ and $+1.33\AA$, respectively, a nearly round core was produced. (c) This wavelength separation was then used for the DT symcap experiment producing a slightly prolate core.

Figure 5

(a) The x-ray radiograph of the imploding HDC capsule is shown for shot N130621. Late in time the capsule self-emission dominates the recorded signal. (b) The measured center of mass radius for shots N130408 (black circles) and N130621 (blue squares) is compared to a postshot simulation (red line) using drive multipliers to match the measured bang time.

Figure 6

The measured experimental yield is compared to the 1D simulated yield for a collection of NIF experiments (DT and Symcap shots between N111103 and N130812) with different convergence ratios (CR). The HDC DT symcap experiment (purple diamond) is close to 1D performance with a yield over simulated of $70\%$. The remaining points are CH capsule experiments with DT ice layers using the high-foot pulse [37] (green square, $\text{CR}\sim 30)$ and low-foot pulse [38] (blue squares, $\text{CR}\sim 40)$, low-foot DT symcaps (yellow squares, $\text{CR}\sim 20)$ and an exploding pusher [39] (pink square, $\text{CR}\sim 5)$. The typical convergence ratio for each experiment type is shown ranging from 5 for the exploding pusher to 40 for the layered DT shots.