The enhancement of fusion reaction rates in a thermonuclear plasma by electron screening of the Coulomb barrier is an important plasma-nuclear effect that is present in stellar models but has not ...been experimentally observed. Experiments using inertial confinement fusion (ICF) implosions may provide a unique opportunity to observe this important plasma-nuclear effect. Herein, we show that experiments at the National Ignition Facility (NIF) have reached the relevant physical regime, with respect to the density and temperature conditions, but the estimated impacts of plasma screening on nuclear reaction rates are currently too small and need to be increased to lower the expected measurement uncertainty. Detailed radiation hydrodynamics simulations show that practical target changes, like adding readily available high-Z gases, and significantly slowing the inflight implosion velocity, while maintaining inflight kinetic energy, might be able to push these conditions to those where plasma screening effects may be measurable. We also perform synthetic data exercises to help understand where the anticipated experimental uncertainties will become important. But challenges remain, such as the detectability of the reaction products, non-thermal plasma effects, species separation, and impacts of spatial and temporal gradients. This work lays the foundation for future efforts to develop an important platform capable of the first plasma electron screening observation.
The impact of fuel-ion diffusion in inertial confinement fusion implosions is assessed using nuclear reaction yield ratios and reaction histories. In T3He-gas-filled (with trace D) shock-driven ...implosions, the observed TT/T3He yield ratio is ∼2× lower than expected from temperature scaling. In D3He-gas-filled (with trace T) shock-driven implosions, the timing of the D3He reaction history is ∼50 ps earlier than those of the DT reaction histories, and average-ion hydrodynamic simulations cannot reconcile this timing difference. Both experimental observations are consistent with reduced T ions in the burn region as predicted by multi-ion diffusion theory and particle-in-cell simulations.
In conventional gases and plasmas, it is known that heat fluxes are proportional to temperature gradients, with collisions between particles mediating energy flow from hotter to colder regions and ...the coefficient of thermal conduction given by Spitzer's theory. However, this theory breaks down in magnetized, turbulent, weakly collisional plasmas, although modifications are difficult to predict from first principles due to the complex, multiscale nature of the problem. Understanding heat transport is important in astrophysical plasmas such as those in galaxy clusters, where observed temperature profiles are explicable only in the presence of a strong suppression of heat conduction compared to Spitzer's theory. To address this problem, we have created a replica of such a system in a laser laboratory experiment. Our data show a reduction of heat transport by two orders of magnitude or more, leading to large temperature variations on small spatial scales (as is seen in cluster plasmas).
The impact of fuel-ion diffusion in inertial confinement fusion implosions is assessed using nuclear reaction yield ratios and reaction histories. In T3He-gas-filled (with trace D) shock-driven ...implosions, the observed TT/T3He yield ratio is ~2× lower than expected from temperature scaling. In D3He-gas-filled (with trace T) shock-driven implosions, the timing of the D3He reaction history is ~50 ps earlier than those of the DT reaction histories, and average-ion hydrodynamic simulations cannot reconcile this timing difference. Both experimental observations are consistent with reduced T ions in the burn region as predicted by multi-ion diffusion theory and particle-in-cell simulations.
We examine the performance of pure boron, boron carbide, high density carbon, and boron nitride ablators in the polar direct drive exploding pusher (PDXP) platform. The platform uses the polar direct ...drive configuration at the National Ignition Facility to drive high ion temperatures in a room temperature capsule and has potential applications for plasma physics studies and as a neutron source. The higher tensile strength of these materials compared to plastic enables a thinner ablator to support higher gas pressures, which could help optimize its performance for plasma physics experiments, while ablators containing boron enable the possibility of collecting additional data to constrain models of the platform. Applying recently developed and experimentally validated equation of state models for the boron materials, we examine the performance of these materials as ablators in 2D simulations, with particular focus on changes to the ablator and gas areal density, as well as the predicted symmetry of the inherently 2D implosion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, we examine the performance of pure boron, boron carbide, high density carbon, and boron nitride ablators in the polar direct drive exploding pusher (PDXP) platform. The platform uses ...the polar direct drive configuration at the National Ignition Facility to drive high ion temperatures in a room temperature capsule and has potential applications for plasma physics studies and as a neutron source. The higher tensile strength of these materials compared to plastic enables a thinner ablator to support higher gas pressures, which could help optimize its performance for plasma physics experiments, while ablators containing boron enable the possibility of collecting additional data to constrain models of the platform. Applying recently developed and experimentally validated equation of state models for the boron materials, we examine the performance of these materials as ablators in 2D simulations, with particular focus on changes to the ablator and gas areal density, as well as the predicted symmetry of the inherently 2D implosion.
Full text
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A feasibility study of a two-fluid small modular molten salt reactor (MSR) with in core heat removal was performed. The initial fuel block dimension for the configuration was based on the Fuji MSR. ...The fuel was a mixed fluoride salt of density 3.25 g/cc, composed of 71 LiF – 16 BeF 2 – 12 ThF4 – 1 233UF4 molar percentages. The coolant salt was Li2BeF4 (FLiBe) of density 1.94 g/cc. The work set out to establish whether or not such a reactor is thermodynamically feasible when optimized for various neutronics parameters. A Java based API was developed to facilitate the neutronics optimization of the reactor concept. In the simulation studies that followed (performed in MCNP), it was established that the optimal block dimension and fuel volume fraction to support under-moderation requirements are 20 cm across flats and 0.15 respectively. Fuel channel diameters varied from 12 cm to 9 cm such that neutron leakage could be suppressed while maintaining a radial power peaking factor of 2.20. In all the simulations except for temperature reactivity calculations, the reactor was assumed isothermal at 900 K. The average temperature coefficient of reactivity was calculated as -5.87E-5 Δk/k-K. Thermo hydraulic studies performed in STAR CCM+ revealed that complete in core heat removal cannot practically be achieved in a design purely optimized for neutronics. However, it was found that fractional heat removal ranging from 15% - 85% can be achieved with sufficient mass flow rates. Potential improvements necessary for complete in core heat removal are theorized and briefly discussed.
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