Tiny target chambers may become rugby footballs. Will these save ICF/IFE?
During the early spring (2015), the National Ignition Facilty (NIF) at LLNL released/published several modifications to the target design that are worth mentioning.
- One is the realization that the gossamer tents used to hold the spherical targets in place actually cause detrimental asymmetry in the resulting implosions. Report
- One is the demonstration that thinner ablative shells around the targets implode faster, with better spherical symmetry and with no shell mixing into the fuel that that might poison ignition. Report ← most exciting of the three.
- One was the future shift to a new hohlraum chamber shape, changing the current (nearly) open cylinder to an egg shaped one with holes in the two ends.
These are all good steps forward; here we discuss the Third point, on the chamber that surrounds the target to be imploded.This is called the hohlraum (German for hollow cavity). Click any figure to see its full sized image.
Fig 1 shows both the old and newly proposed designs. The images are of the two assembled hohlraums in their mounting frames.
- Old: Standard style: cylinder with rounded end caps. 10 1/8 mm long by 5 3/4 mm inside diameter (ID), with rounded end caps and large hole for the laser beams. Images show the symmetry is damaged by very large diagnostic ports in the side.
- New: Proposed prolate spheroid rugby design: 11 mm long by 7 mm maximum ID (one published proposal). Diagnostic ports are not as visible – must be present!
For reasons we discuss here, cylinders have not worked very well. So NIF scientists propose replacing the standard shape with a larger and more interesting one. Continue reading