Pulsed-power-driven cylindrical liner implosions of laser preheated fuel magnetized with an axial field

Abstract

The radial convergence required to reach fusion conditions is considerably higher for cylindrical than for spherical implosions since the volume is proportional to r2 versus r3, respectively. Fuel magnetization and preheat significantly lowers the required radial convergence enabling cylindrical implosions to become an attractive path toward generating fusion conditions. Numerical simulations are presented indicating that significant fusion yields may be obtained by pulsed-power-driven implosions of cylindrical metal liners onto magnetized (>10 T) and preheated (100–500 eV) deuterium-tritium (DT) fuel. Yields exceeding 100 kJ could be possible on Z at 25 MA, while yields exceeding 50 MJ could be possible with a more advanced pulsed power machine delivering 60 MA. These implosions occur on a much shorter time scale than previously proposed implosions, about 100 ns as compared to about 10 μs for magnetic target fusion (MTF) [I. R. Lindemuth and R. C. Kirkpatrick, Nucl. Fusion 23, 263 (1983)]. Consequently the optimal initial fuel density (1–5 mg/cc) is considerably higher than for MTF (∼1 μg/cc). Thus the final fuel density is high enough to axially trap most of the α-particles for cylinders of approximately 1 cm in length with a purely axial magnetic field, i.e., no closed field configuration is required for ignition. According to the simulations, an initial axial magnetic field is partially frozen into the highly conducting preheated fuel and is compressed to more than 100 MG. This final field is strong enough to inhibit both electron thermal conduction and the escape of α-particles in the radial direction. Analytical and numerical calculations indicate that the DT can be heated to 200–500 eV with 5–10 kJ of green laser light, which could be provided by the Z-Beamlet laser. The magneto-Rayleigh-Taylor (MRT) instability poses the greatest threat to this approach to fusion. Two-dimensional Lasnex simulations indicate that the liner walls must have a substantial initial thickness (10–20% of the radius) so that they maintain integrity throughout the implosion. The Z and Z-Beamlet experiments are now being planned to test the various components of this concept, e.g., the laser heating of the fuel and the robustness of liner implosions to the MRT instability.

Neutron spectra from beam-target reactions in dense Z-pinches

“…Recent experimental results from the MagLIF project 49 have highlighted the importance of neutron spectroscopy diagnostics. In these experiments, DD spectra were used to measure the ion temperature 50 (there was no evidence of BT neutrons in this data), while the DT neutron spectra from secondary neutrons 32 were used to infer the level of magnetization of the deuterium plasma.…”

Magneto-Inertial Fusion

“…They have obtained record values of magnetic field and demonstrated increases in neutron yields [8][9][10]. Sandia is developing magnetized liner inertial fusion (MagLIF), in which a magnetically driven beryllium liner, imploded by the Z-machine, adiabatically compresses a laser-preheated magnetized DT target plasma [11][12][13][14]. In the very first series of integrated MagLIF shots last year, [10 11 -10 12 DD neutrons were observed, indicating significant improvement in target performance due to the presence of preheated and magnetized fuel in the target [15].…”

A systematic study of current flow and impedance behavior in the Z machine double post-hole convolute

“…The analysis described above was expanded to the cylindrical liner loads central to the Magnetized Liner Inertial Fusion concept [16]. Three types of cylindrical liner experiments were examined: the standard MagLIF design (high L 0 , low dL/dt), a pulse-shaped version (low dI/dt), and a low charge voltage version.…”