NIF Notes_Hohlraum Spring-2015

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!
Holhraums cylinder + rugby NIF

FIg 1  NIF hohlraum designs.  Left– standard cylinder, 5.75 mm ID.   Right– new rugby, 7 mm max ID.  Top– concept designs for the two types, with 2.2 mm capsule located at center of cavities.  Bottom– images of actual chambers. Hohlraum photos:  LLNL

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

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Physics – Science or Ideology?

Should physics theories be tested – or just accepted?  So asks essay the in New York Times

Adam Frank  and Marcelo Gleiser discuss whether Physics has moved beyond the need to be checked.  Their essay (Sunday New York Times 2015-Jun-7) is on science vs empirical evidence (experimental verification)

“Today our most ambitious science can seem at odds with the empirical methodology that has historically given the field its credibility”

2015 Marcelo Gleiser 450x450

Fig 1B  Marcelo Gleiser, physicist

Frank Adams, astrophysicist

Fig 1A  Adam Frank, astrophysicist

“How did we get to this impasse?” they ask.  Then they discuss the Higgs particle that generates a core part of any particle’s mass.  It was predicted 50 years ago and measured last year.

The Higgs is the “lynchpin of … the Standard Model” of particle physics, a powerful mathematical theory that is known to contain problems, but can not be extended.  New theories have elegant math, are each hailed as “the” organizing principle of the universe, but have not predicted anything new.  Are our standards for science changing? Continue reading

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NIF Notes_tents Spring 2015

The NIF fusion lab reports that their target support structure could hurt implosion results – our discussion.

During the early spring (2015), the National Ignition Facility (NIF) at LLNL released/published several modifications to the target 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 implosion.
  • One is the demonstration that thinner ablative shells around the targets implode faster, with better symmetry and with no shell mixing into the fuel that could 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. Report

These are all good steps forward. Here, we discuss the First result on tents.  All our links are to no-charge reports from phys.org, an important source of physics updates, out of the U.K.

Gossamer Tents

Support Tent

Fig 1  Support Tent

A tent is the support structure that holds the spherical target capsule in place. Made of 2 very thin plastic membranes that encapsulate the target.  You can see for yourself how this works using a ping-pong ball and sheets from a roll of kitchen plastic wrap.

Fig 1 is my (very slight) markup of an image LLNL makes available.  Tent sheeting has been tested with thicknesses from 12 to 300 nm. Very fragile since a molecule of “plastic” might be only 10 nm in mean diameter — sheets 1 to 30 molecules thick!  They mention that the thicker ones are more reliable with heavy targets. Continue reading

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NIF Notes_shells Spring-2015

NIF reports tests with capsule designs that illuminate the path toward great results

During the early spring (2015), the National Ignition Facility (NIF) at LLNL released/published several modifications to the targets worth discussing.

  • 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.   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. Report

These are all good steps forward; here we discuss the Second point, on target shell thickness.  A test of the survivability of a thin walled capsule is important because of worries that if the wall is too thin, it will break up during the  implosion and poison the resulting core.

T Ma PhD

FIg 1  Tammy Ma, NIF Scientist

We are discussing the April 2015 published paper with  Dr. Tammy Ma as its lead author.

As with most facility physics work, 74 authors are listed, including Drs. Hurricane and Edwards. Many of these 74 were not involved in writing the paper, but were deeply involved in capsule issues, diagnostic operations and analysis, computational analysis, and other such activities very necessary for success.

The investigators fired NIF beams with the same power level into 3 different targets with different ablative shell thicknesses. Only one “popular press” source, phys.org, has taken notice of these data.

So, though not much other notice has been made, these results are extremely important.  Here’s hoping that NIF leadership pays attention! Continue reading

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Fortunetelling killed by Time’s arrow

Precognition / clairvoyance / prescience?  Not in our universe!

The gypsy soothsayer says “Cross my hand with silver and I will tell you your true future.”

If such actions could be possible, over our past 70,000 years, the soothsayer’s guild should have become the absolute monarchs of the world.  Ms. Soothsayer must be a charlatan!

Future sight cannot happen – time flow will not let it.

Precognition, and other psychic magic

James Randi skeptic

Fig 1 A  James Randi (1928-…)

The Randi Challenge    James Randi (“The Amazing”), stage magician and skeptic of psychic adepts, offers a $ 1M  prize to anyone who can demonstrate psychic mind-over-matter abilities that he can neither duplicate nor explain.

Many candidates have attempted his challenge for the big prize – not one was psychokinetic, not one was telepathic, not one was clairvoyant.  Not one verifiable psychic seer, ever!  Losers, all.

Figs 1  shows Mr. Randi who is also founder of the James Randi Education Foundation, the group working to bring rationality into our society.  For many years, Randi has ranked as one of my top intellectual heroes! Continue reading

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KMS Fusion – an addendum

KMS Fusion, an early ICF group mostly remembered for its mashup of good science and bad politics. This is our historical addendum.

An excellent article on the beginning of ICF (inertial confinement fusion) was posted on January 28th by ScienceLine’s Chelsey Coombes.  This is a summary of Alex Wellerstein‘s presentation at the October 2014 meeting of the New York Academy of Science.

Wellerstein is a respected science historian specializing in American Classified research, and is located at Stevens Institute of Technology.

LLNL KMS_Fusion LANL

Fig 1    Early ICF labs cited in this report

Coombes’ (and Wellerstein’s) good discussion of the early days of inertial confinement fusion traces development of the LLNL  indirect drive approach and the KMS fusion direct drive alternative (see Fig 1).  We also discuss, in passing, ICF efforts at LANL.

We add a missing link to the KMSf  story, one that I have never seen mention in any published description of the early days of fusion energy research.  This small band of researchers produced some of the best results in ICF physics in the 1970s and even the ’80s, but their leadership made stunningly bad political mistakes that got themselves ignored by history. Continue reading

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KXL threatens US environment -Not energy -Not climate

Keystone XL is is a threat to US environmental integrity. Its Senate vote is near.

The bill forcing development of the Keystone XL (KXL) pipeline build is about to be set before the president.   The proponents say it is about (A) permanent jobs and lots of them, and (B) oil independence for good ol’ U.S. of A.   It is about neither.

Bridger Poplar System kills life

Fig 1  Fish kill in Yellowstone River from 2015  leak of Bridger Pipeline’s Poplar System

The American issue is truly about the transport of dangerous but profitable product through delicate environmental structures.

Pipelines leak.

Here is a good discussion about a very recent demonstration:   Does the Yellowstone River Oil Spill Foreshadow The Future… ?   Posted by , care2.com.   Fig 1 shows a bit of its toll.

The issue as a bullet list –

  • Transport of processed tar sands involves solvents to keep the stuff fluid (dilbit, see our Index for other KXL discussions)
  • These solvents are chemically active hydrocarbons, they attack most things.
  • These are things that would destroy you, were you to drink some.
  • When oil pipelines break, solvents are the first things locals have to deal with, the tar-like residue is another, either to be cleaned up later, or labeled “unimportant.”
  • Sometimes consequences extend far beyond the folks initially bothered by the issue.

Fig 2 shows the location of this month’s (2015 Jan 17) Leakage. Bridger Pipeline’s Poplar System 83 is near the route for KXL, it dumped into Montana’s Yellowstone River.  Continue reading

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