You are currently browsing the tag archive for the ‘fusion’ tag.

apollo16_earth_northamerica

Many people complain that the news is all bad.  That is not true at all, but good news is sometimes harder to quantify or follow than bad tidings—plus human progress tends to be incremental.  I bring this up because this week did feature a good news story—and Ferrebeekeeper has been following along (as best we can) for years. The nuclear scientists at the National Ignition Facility (a part of Lawrence Livermore National Laboratory) have been attempting to use a vast laser array to heat/compress a deuterium and tritium fuel pellet to the extreme conditions necessary for nuclear fusion.

The container for the nuclear fuel

The container for the nuclear fuel

Nuclear fusion involves compressing/heating the elementary particles which make up atoms until the atoms fuse into new atoms.  Such a process releases outrageous amounts of energy but it does not start easily–indeed so much energy is required to begin the reaction that “hot” fusion typically requires a star or a nuclear fission detonator.  These items are dangerous and alarming to have lying around so scientists have been attempting to find a more controlled method of fusing atoms together.

The NIF Target Chamber

The NIF Target Chamber

Earlier this week the science journal Nature published a paper which details how NIF scientists finally managed to produce more energy than was initially put into the fuel pellet (albeit not into the overall system).  This does not sound overwhelmingly exciting—yet it is farther than nuclear engineers have got in 50 years.  To quote the amazingly named head scientist, Omar Hurricane, “We’ve assembled that stick of dynamite and we’ve gotten the fuse to light…If we can get that fuse to burn all the way to the dynamite, it’s going to pack a wallop.”

Just dream what we could accomplish with such energy!

Just dream what we could accomplish with such energy!

Abundant safe energy from nuclear fusion would be an astonishingly transformative innovation for humankind.  Immediately our principle economic and environmental problems would be forever altered.  Additionally having such a cosmic wellspring of energy available would allow us to embark on engineering works of a vastly greater scale than any known so far.

Planetary Engineering!

Planetary Engineering!

6299819

Between giant planets and small stars exists a bizarre class of heavenly objects known as brown dwarfs. Brown dwarfs are not massive enough to fuse hydrogen elements together as do main sequence stars like the sun, however brown dwarfs larger than 13 Jovian masses are believed to fuse deuterium atoms and large brown dwarfs (65 Jovian masses and up) are believed to fuse lithium.  Since brown dwarfs can be very much like planets or like stars, there is a specific definition to describe the objects: a brown dwarf must have experienced some sort of nuclear fusion as a result of mass and temperature, however it cannot have fused all of its lithium (or it is considered a star or stellar fragment).  A stellar physicist reading this blog might object that medium and large stars have some lithium present in their outer atmosphere, or that a very young white dwarf could still have some unused lithium present, or even that an old heavy brown dwarf could have fused all of its lithium.  That physicist would be correct: she deserves some cookies and a pat on the head for poking holes in unnecessarily simple definitions.

Various Classifications of Brown Dwarfs

Various Classifications of Brown Dwarfs

Brown dwarfs were theorized to exist in the 1960s, but no astronomer managed to discover one until 1988 when a team of University of California astronomers who were studying white dwarfs found a bizarrely cool red spectral signature for a faint companion to the star GD 165.  Since then many brown dwarfs have been discovered and sorted into the major types M, L, T, and Y.  They occupy a strange ambiguous area at the bottom of the Hertzsprung-Russell diagram—objects which are luminous and massive in comparison to everything else but tiny and dim compared to real stars.

450px-Relative_star_sizes.svg

There are some planets which are known to orbit brown dwarfs and there also brown dwarfs known to orbit true stars.  It is beginning to seem that there a great many brown dwarfs out there: perhaps they are as numerous as true stars (or maybe they are even more common than that).  Since they are hard to detect, scientists do not have a very accurate assay of their frequency in the universe.  The question bears somewhat on our understanding of the universe–since a great deal of matter is  not accounted for.

An artist's conception of a brown dwarf seem from a closely orbiting planet

An artist’s conception of a brown dwarf seem from a closely orbiting planet

My mind keeps returning to the fact that some brown dwarfs have planetary systems.  Imagine these melancholic twilight ice worlds forever orbiting a dim glow which will never blaze into a true sun.   It is a melancholy picture, but not without a certain beauty.

A Brown Dwarf with Planet and Moon (painting by Lynette Cook from fineartamerica.com)

A Brown Dwarf with Planet and Moon (painting by Lynette Cook from fineartamerica.com)

So, it is not easy to do what has never been done before. In October of 2010, I wrote about the National Ignition Facility, a joint scientific project run by Lawrence Livermore National Laboratory in Livermore California.  The National Ignition Facility aims to recreate the heat and pressure of stars and hydrogen bombs on a microscopic controlled scale.   The project is ostensibly designed as a United States defense project to model the nation’s next generation nuclear arsenal without use of (treaty-prohibited) nuclear testing, but cognoscenti have long suspected that it is a way that our country can pursue fundamental energy and physics research despite the apathy (or outright animosity) of a do-nothing congress and politically divided citizenry.

One of four banks of giant capacitors which power the laser microburst

Unfortunately the facility experienced a series of setbacks, and the massive laser array did not deliver the promised energy output.  However, this month all that changed!  On July 5th the facility briefly powered up its 192 lasers to deliver a 1.85-megajoule blast that released more than 500 trillion watts of power. Although the laser beam was only active for a miniscule fraction of a second, during that brief time it was focusing a thousand times more energy than the rest of the entire United States was actively using.  Remember Doc Brown from “Back to the Future” shouting about “1.21 gigawatts!” and desperately running his hands through his hair? Well, a gigawatt is a billion watts.  This laser beam produced a 500 terrawatt blast–500 trillion watts.  So just imagine Doc shouting “1.21 gigawatts!” four hundred thousand plus times!

The successful test firing brings the NIF within tantalizing reach of their desired ignition breakthrough—the glorious moment when scientists flip a switch and create a controlled, contained fusion reaction.  Building such a “star in a jar” is the first step on a road to titanic engineering and energy-creation achievements which could reshape humanity’s place in the universe.

Ye Olde Ferrebeekeeper Archives

November 2020
M T W T F S S
 1
2345678
9101112131415
16171819202122
23242526272829
30