Effect of Strongly Magnetized Electrons and Ions on Heat Flow and Symmetry of Inertial Fusion Implosions

This Letter presents the first observation on how a strong, 500 kG, externally applied $B$ field increases the mode-two asymmetry in shock-heated inertial fusion implosions. Using a direct-drive implosion with polar illumination and imposed field, we observed that magnetization produces a significant increase in the implosion oblateness (a $2.5\times$ larger $P2$ amplitude in x-ray self-emission images) compared with reference experiments with identical drive but with no field applied. The implosions produce strongly magnetized electrons (${\omega }_e{\tau }_e\gg 1$) and ions (${\omega }_i{\tau }_i>1$) that, as shown using simulations, restrict the cross field heat flow necessary for lateral distribution of the laser and shock heating from the implosion pole to the waist, causing the enhanced mode-two shape.

Figure 1

(a) Schematic of the magnetized implosion experiment, (b) the current carrying coil producing the applied $B$ field, and (c) variation in intensity of laser drive with polar angle.

Figure 2

X-ray self emission images of the (a) unmagnetized and (b) magnetized implosions. The shot number, average radius of the marked contour (corresponding to 40% of peak intensity), and the oblateness parameter $a/b$ (ratio of major-to-minor axis) are listed below each image.

Figure 3

Density profile at bang time (a), and synthetic x-ray self emission images (b), from simulations with 0 kG (left) and 500 kG (right) applied $B$ field. The shorter curved arrows in (b) represent a reduced cross field heat flow ($q_{\perp }$).

Figure 4

Magnetized shock-driven implosion at $\approx 100\mathrm{ps}$ prior to shock rebound at the center. (a) Illustration showing magnetization (${\chi }_e>1$ using yellow) in the shocked fuel and the conduction zone. The applied $B$-field lines exit near the pole to close outside the implosion. Lineouts from the Gorgon simulation taken along the implosion waist (b) and pole (c). (d) Lineouts showing electron- and Triton- Hall parameters (${\omega }_e{\tau }_e$ and ${\omega }_i{\tau }_i$) along the pole and the waist.