Kinetic simulations of fusion ignition with hot-spot ablator mix
James D. Sadler, Yingchao Lu, Benjamin Spiers, Marko W. Mayr, Alex Savin, Robin H. W. Wang, Ramy Aboushelbaya, Kevin Glize, Robert Bingham, Hui Li, Kirk A. Flippo, Peter A. Norreys
Inertial confinement fusion fuel suffers increased X-ray radiation losses when carbon from the capsule ablator mixes into the hot-spot. Here we present one and two-dimensional ion Vlasov-Fokker-Planck simulations that resolve hot-spot self heating in the presence of a localized spike of carbon mix, totalling 1.9% of the hot-spot mass. The mix region cools and contracts over tens of picoseconds, increasing its alpha particle stopping power and radiative losses. This makes a localized mix region more severe than an equal amount of uniformly distributed mix. There is also a purely kinetic effect that reduces fusion reactivity by several percent, since faster ions in the tail of the distribution are absorbed by the mix region. Radiative cooling and contraction of the spike induces fluid motion, causing neutron spectrum broadening. This artificially increases the inferred experimental ion temperatures and gives line of sight variations.
Hot Spot Evolution Measured by High-Resolution X-Ray Spectroscopy at the National Ignition Facility
Princeton Plasma Physics Laboratory, Princeton University（普林斯顿等离子体物理实验室，普林斯顿大学）；Lawrence Livermore National Laboratory（劳伦斯利弗莫尔国家实验室）；Laboratory for Laser Energetics, University of Rochester（罗切斯特大学激光能源实验室）
Inertical Confinement Fusion configuration model is analized for direct ignition without an ablator. The compression of the target pellet is neglected and rapid volume ignition is achieved by a laser pulse, which is as short as the penetraton time of the light across the pellet. The reflectivity of the target is assumed to be negligible, and the absorptivity is constant so that the light pulse can reach the opposite side of the pellet. The necessary pulse length and pulse strength is calculated.
In laser-drive ICF, hybrid drive (HD) combined direct drive (DD) and indirect drive (ID) offers a smoothed HD pressure $P_{HD}$, far higher than the ablation pressure in ID and DD, to suppress hydrodynamic instabilities. In this letter, simulations of a new robust HD ignition target show that maximal HD pressure as high as $P_{HD} \sim$ 650 Mbar driven by a novel "bulldozer" effect is achieved, resulting in nonstagnation hotspot ignition at the convergence ratio $C_r \sim $23, and finally, fusion energy gain $\sim$ 10 in total laser energy = 1.42 MJ. Two-dimensional simulations have confirmed …
A novel capsule target design to improve the hot-spot pressure in the high-adiabat implosion for inertial confinement fusion is proposed, where a layer of comparatively high-density material is used as a pusher between the fuel and the ablator. This design is based on our theoretical finding of the stagnation scaling laws, which indicates that the hot spot pressure can be improved by increasing the kinetic energy density $ρ_d V_{imp}^2/2$ ($ρ_d$ is the shell density when the maximum shell velocity is reached, $V_{imp}$ is the implosion velocity.) of the shell. The proposed design uses the high…
We report the first measurement of the $^{10}{\rm B}(α,n)^{13}{\rm N}$ reaction in a polar-direct-drive exploding pusher (PDXP) at the National Ignition Facility (NIF). This work is motivated by the need to develop alternative mix diagnostics, radiochemistry being the focus here. The target is composed of a $65/35\,\rm at.\,\%$ deuterium-tritium (DT) fill surrounded by a roughly $30\,μ\rm m$ thick beryllium ablator. The inner portion of the beryllium ablator is doped with $10\,\rm at.\,\%$ of $^{10}{\rm B}$. Radiation-hydrodynamics calculations were performed in 1D to optimize both the remaini…
The National Ignition Facility (NIF) technology is designed to drive deuterium-tritium (DT) internal confinement fusion (ICF) targets to ignition using indirect radiation from laser beam energy captured in a hohlraum. Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix between the DT fue l and the ablator shell material are of fundamental physical interest and can affect the performance characteristics of the capsule. In this Letter we describe new radiochemical diagnostics for mix processes in ICF capsules with plastic or Be (0.9%Cu) ablator shells. Reactions of high-…
We present analytic calculations and results from computational simulations showing that reaction-in-flight (RIF) neutrons act as a robust indicator for mixing of the ablator shell material into the fuel in DT capsules designed for the National Ignition Facility. The sensitivity of RIF neutrons to hydrodynamical mixing arises through the dependence of RIF production on charged-particle stopping lengths in the mixture of DT fuel and ablator material. Since the stopping power in the plasma is a sensitive function of the electron temperature and density, it is also sensitive to mix. RIF productio…
The National Ignition Facility(NIF) megajoule laser at the Lawrence Livermore National Laboratory(LLNL)\cite{moses} has produced a significant amount of useful physics results related to inertial confinement fusion since it began operating in 2010. However, achievement of its primary goal of generating ignition in a thermonuclear plasma has proven elusive, and measured yields were far below those expected from an ignited, and burning, plasma. The reason for the limited yields has not been explained in detail. This work proposes, and shows support for, the possibility that the low yields may be…
ELI ALPS, ELI-HU Non-Profit Ltd.（ELI ALPS，ELI-HU非营利有限公司）；HUN-REN Wigner Research Centre for Physics（匈牙利科学院维格纳物理研究中心）；Department of Optics and Quantum Electronics, University of Szeged（塞格德大学光学与量子电子学系）；Cyclotron Institute, Texas A&M University（德克萨斯农工大学回旋加速器研究所）；Laboratori Nazionali del Sud, INFN（意大利国家核物理研究所南部分实验室）；Budapest University of Technology and Economics（布达佩斯技术与经济大学）；Department of Physics and Technology, University of Bergen（卑尔根大学物理与技术系）；National Laser-Initiated Transmutation Laboratory, University of Szeged（塞格德大学国家激光诱导嬗变实验室）；King's College London（伦敦国王学院）；Csernai Consult Bergen（Csernai咨询（卑尔根））；Frankfurt Institute for Advanced Studies（法兰克福高等研究院）
Engineering features are known to cause jets of ablator material to enter the fuel hot-spot in inertial confinement fusion implosions. The Biermann battery mechanism wraps them in self-generated magnetic field. We show that higher-Z jets have an additional thermoelectric magnetic source term that is not present for hydrogen jets, verified here through a kinetic simulation. It has similar magnitude to the Biermann term. We then include this in an extended magneto-hydrodynamics approach to post-process an xRAGE radiation-hydrodynamic implosion simulation. The simulation includes an accurate mode…
Experimental asymmetries in fusion implosions can lead to magnetic field generation in the hot plasma core. For typical parameters, previous studies found that the magnetisation Hall parameter, given by the product of the electron gyro-frequency and Coulomb collision time, can exceed one. This will affect the hydrodynamics through inhibition and deflection of the electron heat flux. The magnetic field source is the collisionless Biermann term, which arises from the Debye shielding potential in electron pressure gradients. We show that there is an additional source term due to the Z dependence …
