Reduced scale National Ignition Facility capsule design

Abstract

In this article we describe the design and simulated performance characteristics of an indirectly-driven inertial confinement fusion capsule which utilizes only 900 kJ of laser energy and 250 TW of laser power from the National Ignition Facility (NIF) [Paisner et al., Laser Focus World 30, 75 (1994)]. This intentional reduction in laser performance from the nominal NIF specifications of 1.8 MJ and 500 TW results in lowering the hohlraum x-ray drive temperature from 300 eV to 250 eV. These energy and radiation temperature reductions are believed to define a “lower bound” on the successful implosion of an ignition capsule. This reduced scale capsule has a beryllium ablator containing a radially varying copper dopant, and a cryogenic solid deuterium–tritium fuel layer surrounding a cavity filled with equilibrium vapor pressure gaseous deuterium and tritium. Two-dimensional simulations predict ignition and propagated burn from this capsule when either Rayleigh–Taylor instability or time-dependent drive asymmetry effects are included.

Increasing robustness of indirect drive capsule designs against short wavelength hydrodynamic instabilities

“…Multimode simulations have been done for the capsules described here, using the spectrum of initial perturbations described in Ref. [10]. When the rms is 10 nm, this spectrum corresponds to the high-mode part of the "NIF standard" spectrum used by the target fabrication community as a roughness goal [27].…”

“…The scans used for optimization were expanded to scans over one parameter, [10] and then the two parameters of ablator and fuel thickness [12]. As described in more detail below, the optimization process has now been automated by one of us (Herrmann) allowing for much more detailed scans over the parameter spaces of possible designs.…”

“…Concurrently, some work was done with radially graded dopants. Dittrich [10] described a 250 eV Be(graded Cu) design, implementing a scheme attributed to Hatchett (unpublished) and considered in more detail below. Another graded dopant approach, with a layer of clean Be inside of an otherwise uniformly doped Be(Cu) shell, was considered in a 350 eV Be(Cu) design by Hinkel [11].…”

“…One such design from Ref. [10] was meant to explore the limits of extremely small size and low temperature, to see whether such a design might feasibly work. Hence it very small, and driven at low temperature (250 eV).…”

Dynamics of a Z-pinch x-ray source for heating inertial-confinement-fusion relevant hohlraums to 120–160 eV

“…The hohlraum walls are heated in an ever increasing mdti-phuse drive to a temperature of up to 300 eV [1,2], which emit soft x-rays that freely traverse the region between the walls and capsule. The early three phases of the drive consist approximately of a -85 eV foot pulse having a -10 ns duration, followed by a first-step pulse at -120 eV for -2 ns and a second-step puke at -155 eV for -1 ns [3,4]. The x-rays are absorbed by the low-Z material of the capsule shell (the ablator).…”