Understanding Fuel Magnetization and Mix Using Secondary Nuclear Reactions in Magneto-Inertial Fusion

Abstract

Magnetizing the fuel in inertial confinement fusion relaxes ignition requirements by reducing thermal conductivity and changing the physics of burn product confinement. Diagnosing the level of fuel magnetization during burn is critical to understanding target performance in magneto-inertial fusion (MIF) implosions. In pure deuterium fusion plasma, 1.01 MeV tritons are emitted during DD fusion and can undergo secondary DT reactions before exiting the fuel. Increasing the fuel magnetization elongates the path lengths through the fuel of some of the tritons, enhancing their probability of reaction. Based on this feature, a method to diagnose fuel magnetization using the ratio of overall DT to DD neutron yields is developed. Analysis of anisotropies in the secondary neutron energy spectra further constrain the measurement. Secondary reactions are also shown to provide an upper bound for volumetric fuel-pusher mix in MIF. The analysis is applied to recent MIF experiments [M. R. Gomez et al., to appear in PRL] on the Z Pulsed Power Facility, indicating that significant magnetic confinement of charged burn products was achieved and suggesting a relatively low-mix environment. Both of these are essential features of future ignition-scale MIF designs. PACS numbers:Introduction.-Magneto-inertial fusion (MIF) offers some key advantages over traditional inertial confinement fusion (ICF). In MIF, fuel magnetization relaxes the extreme pressure requirements characteristic of traditional ICF and enhances thermal insulation of the hot fuel from the colder pusher [1-10]. We consider paradigmatically the radial compression of a long, thin cylinder of fuel magnetized with a uniform, axial field prior to compression [11][12][13][14][15][16][17]. At stagnation, the compressed magnetic flux redirects charged burn products axially, increasing the effective fuel areal density from ρR to ρZ, where ρ is the fuel mass density, R is the fuel radius, Z is the fuel length, and A ≡ Z/R ≫ 1 is the aspect ratio.Sandia National Laboratories has fielded the first integrated experiments investigating Magnetized Liner I nertial F usion (MagLIF) [14][15][16][17], which involves direct compression of magnetized, preheated deuterium fuel by a solid metal (beryllium) liner, imploded on the 26 MA, 100 ns Z Pulsed Power Facility [18]. The imploding cylindrical liner compresses a pre-seeded axial magnetic field, B 0 (≈ 10 T in the first experiments), to high amplitude at stagnation, B, where perfect flux conservation would imply B = B 0 (R 0 /R) 2 , and R 0 = 2.325 mm is the initial fuel radius. However, detailed simulations suggest that multiple effects (e.g., resistive losses, Nerst effect) can lead to leakage of magnetic flux out of the hot fuel [14,17]. Thus, diagnosing the efficacy of flux compression in experiments is critical for understanding target performance and the viability of the concept.

Ab InitioThermodynamic Results for the Degenerate Electron Gas at Finite Temperature

“…We also present quantum statistical data within the e 4 -approximation that are in good agreement with the simulations at small to moderate rs. [11,12]. Besides, the electron component is of crucial importance for understanding the properties of atoms, molecules and existing and novel materials.…”

Ab initioquantum Monte Carlo simulations of the uniform electron gas without fixed nodes: The unpolarized case

“…In particular, recent experimental progress with highly compressed matter [1][2][3] such as plasmas in laser fusion experiments [4][5][6][7][8][9] and solids after laser irradiation [10], but also the need for an appropriate description of compact stars and planet cores [11][12][13], has lead to a high demand for accurate simulations of electrons in the warm dense matter (WDM) regime. Unfortunately, the application of all QMC methods to fermions is severely hampered by the fermion sign problem (FSP) [14,15].…”

Ab InitioQuantum Monte Carlo Simulation of the Warm Dense Electron Gas in the Thermodynamic Limit

“…However, the charged quantum matter in astrophysical systems such as planet cores and white dwarf atmospheres [4,5] is at temperatures way above the ground state, as are inertial confinement fusion targets [6][7][8], laser-excited solids [9], and pressure induced modifications of solids, such as insulator-metal transitions [10,11]. This unusual regime, in which strong ionic correlations coexist with electronic quantum effects and partial ionization, has been termed "warm dense matter" and is one of the most active frontiers in plasma physics and materials science.…”