arXiv subjects

N. Chaturvedi

Publications and source records attributed to N. Chaturvedi.

4 recordsLinked to original sources

arXiv2025

Fusion alpha particle momentum deposition in thermonuclear burn dynamics

In inertial confinement fusion, the DT fusion alpha particles carry not only energy but also appreciable momentum that is typically neglected in models of thermonuclear burn. In the central hotspot ignition scheme, the hotspot must self-heat and propagate thermonuclear burn before disassembly. Using radiation hydrodynamics simulations with a Monte Carlo alpha particle transport model, we investigate the effect of alpha momentum deposition across sub-ignition to robustly igniting regimes by hydrodynamic scaling of current central hotspot ignition designs from the National Ignition Facility (NIF). We find that the effective alpha particle ram pressure accelerates the shell at burn, reducing hotspot compression, increasing the rate of disassembly and decreasing yield. This causes a notable (~ 30%) reduction in yield at current NIF scale, with a persistent (~ 10%) penalty at larger hydrodynamic scales. These results demonstrate that alpha momentum deposition is a significant effect for present ignition-scale implosions, necessitating its inclusion in ignition criteria, burn models, and designs for high-gain inertial confinement fusion.

physics.plasm-ph↗

arXiv2021

A preliminary assessment of the sensitivity of uniaxially-driven fusion targets to flux-limited thermal conduction modeling

The role of flux-limited thermal conduction on the fusion performance of the uniaxially-driven targets studied by Derentowicz et al.; Jour. Tech. Phys. 18, 465 (1977) and Jour. Tech. Phys. 25, 135 (1977), is explored as part of a wider effort to understand and quantify uncertainties in ICF systems sharing similarities with First Light Fusion's projectile-driven concept. We examine the role of uncertainties in plasma microphysics and different choices for the numerical implementation of the conduction operator on simple metrics encapsulating the target performance. The results indicate that choices which affect the description of ionic heat flow between the heated fusion fuel and the gold anvil used to contain it are the most important. The electronic contribution is found to be robustly described by local diffusion. The sensitivities found suggest a prevalent role for quasi-nonlocal ionic transport, especially in the treatment of conduction across material interfaces with strong gradients in temperature and conductivity. We note that none of the simulations produce neutron yields which substantiate those reported by Derentowicz et al. Jour. Tech. Phys. 25, 135 (1977), leaving open future studies aimed at more fully understanding this class of ICF systems.

physics.plasm-ph↗

arXiv2020

Gnomonious Projections for Bend-Free Textures: Thoughts on the Splay-Twist Phase

The Hopf fibration has inspired any number of geometric structures in physical systems, in particular in chiral liquid crystalline materials. Because the Hopf fibration lives on the three sphere, $\mathbb{S}^3$, some method of projection or distortion must be employed to realize textures in flat space. Here, we explore the geodesic-preserving gnomonic projection of the Hopf fibration, and show that this could be the basis for a new liquid crystalline texture with only splay and twist. We outline the structure and show that it is defined by the tangent vectors along the straight line rulings on a series of hyperboloids. The phase is defined by a lack of bend deformations in the texture, and is reminiscent of the splay-bend and twist-bend nematic phases. We show that domains of this phase may be stabilized through anchoring and saddle-splay.

cond-mat.soft↗

arXiv2019

Mechanisms to Splay-Bend Nematic Phases

While twist-bend nematic phases have been extensively studied, the experimental observation of two dimensional, oscillating splay-bend phases is recent. We consider two theoretical models that have been used to explain the formation of twist-bend phases -- flexoelectricity and bond orientational order -- as mechanisms to induce splay-bend phases. Flexoelectricity is a viable mechanism, and splay and bend flexoelectric couplings can lead to splay-bend phases with different modulations. We show that while bond orientational order circumvents the need for higher order terms in the free energy, the important role of nematic symmetry and phase chirality rules it out as a basic mechanism.

cond-mat.soft↗