Increased Ion Temperature and Neutron Yield Observed in Magnetized Indirectly Driven ${\mathrm{D}}_2$-Filled Capsule Implosions on the National Ignition Facility

The application of an external 26 Tesla axial magnetic field to a ${\mathrm{D}}_2$ gas-filled capsule indirectly driven on the National Ignition Facility is observed to increase the ion temperature by 40% and the neutron yield by a factor of 3.2 in a hot spot with areal density and temperature approaching what is required for fusion ignition [1]. The improvements are determined from energy spectral measurements of the 2.45 MeV neutrons from the $\mathrm{D}(d,n){}^3\mathrm{He}$ reaction, and the compressed central core $B$ field is estimated to be $\sim 4.9\mathrm{k}\mathrm{T}$ using the 14.1 MeV secondary neutrons from the $\mathrm{D}(\mathrm{T},n){}^4\mathrm{He}$ reactions. The experiments use a 30 kV pulsed-power system to deliver a $\sim 3\mu \mathrm{s}$ current pulse to a solenoidal coil wrapped around a novel high-electrical-resistivity ${\mathrm{AuTa}}_4$ hohlraum. Radiation magnetohydrodynamic simulations are consistent with the experiment.

Figure 1

(a) Sketch of the magnetized NIF hohlraum constructed from ${\mathrm{AuTa}}_4$ with solenoidal coil to carry current. (b) X-ray drive measured through one of the LEHs and the incident laser powers for a magnetized and unmagnetized ${\mathrm{AuTa}}_4$ hohlraum and two unmagnetized Au hohlraums. “BF” refers to “BigFoot,” the name of the previous ignition design [38].

Figure 2

(a) Plot shows that $T_{\mathrm{ion}}$ increases about 1.1 keV when adding a 26 T $B$ field to a ${\mathrm{D}}_2$ gas capsule implosion. Also shown in the plot are the simulation results. (b)–(d) Equatorial shapes of the implosions.