A strategy for reducing stagnation phase hydrodynamic instability growth in inertial confinement fusion implosions

Abstract

Encouraging progress is being made in demonstrating control of ablation front hydrodynamic instability growth in inertial confinement fusion implosion experiments on the National Ignition Facility [E. I. Moses, R. N. Boyd, B. A. Remington, C. J. Keane, and R. Al-Ayat, Phys. Plasmas 16, 041006 (2009)]. Even once ablation front stabilities are controlled, however, instability during the stagnation phase of the implosion can still quench ignition. A scheme is proposed to reduce the growth of stagnation phase instabilities through the reverse of the "adiabat shaping" mechanism proposed to control ablation front growth. Two-dimensional radiation hydrodynamics simulations confirm that improved stagnation phase stability should be possible without compromising fuel compression. V C 2015 AIP Publishing LLC. [http://dx.

Yield reduction via the Knudsen layer effect in a mixture of fuel and pusher material

“…The two distinct kinetic effects, Knudsen layer and diffusive tunneling, primarily concern the yield from the burn-up of DT ice that is mixed with CH pusher. In the central hot spot, which must form for ignition to occur, ablation at the mixing front due to the thermal conduction from the hot spot would turn any pusher material arriving there into higher temperature plasma [3,4] that would diffusively mix [31,32,[47][48][49] with the hot DT gas. The existence of a central hot spot (in approximately spherical shape) is further aided by ablative [41] and viscous stabilization [42] at its outer edge.…”

“…The existence of a central hot spot (in approximately spherical shape) is further aided by ablative [41] and viscous stabilization [42] at its outer edge. The path to ignition is thus essentially concerned with controlling the thermal loss through the inner ablation surface between the hot spot and ice/pusher mixture [3], which has the effect of lowering the temperature of the central hot spot while increasing its mass [3,4]. Magnetic fields, self-generated [50] or more interestingly, externally imposed [51], through their dynamic aligment with the interfacial mixing interface [50,51], offer a rare control knob that could significantly reduce hot spot thermal conduction loss via localized electron magnetization (even when ions remain unmagnetized) at the mixing interface, and hence aid in enabling a hot enough central hot spot under hydrodynamic mix scenario [42].…”

“…A well known example is through enhanced conductive (e.g. [3,4]) and radiative (e.g. [5]) cooling of the hot spot.…”

Reduction of the deceleration phase to mitigate the negative effect of hydrodynamic instabilities in direct-drive ICF implosions

“…The thickness of this region grows during the deceleration phase leading to the mixing of the low-density hot spot and the surrounding cold and dense fuel. An option for reducing the deleterious effects of this mixing layer is to reduce the deceleration time t d and different strategies have been recently proposed to mitigate the RT growth of the mixing layer volume [32][33][34][35].…”

Late-Time Mixing Sensitivity to Initial Broadband Surface Roughness in High-Energy-Density Shear Layers

“…Varying the initial roughness on otherwise identical aluminum foils, we have observed a change in the behavior of the mixing layer as it is forced from typical Kelvin-Helmholtz (KH) coherent features [6,7], corresponding to an initial Reynolds number of ∼10 3 , to an increasingly turbulent behavior with highly stochastic features at an initial Reynolds number of > 10 5 . Such a system has relevance to astronomical plasma shear flows, spanning the values thought to be present in protoplanetary accretion disks (Re ∼ 10 3 ) to protostellar accretion disks Re ≳ 10 10 [9], and has implications for the persistence of initial conditions through instabilities in inertial confinement fusion research [10].…”