is it breakeven yet?

About a week ago news spread through the Internet and conventional media that scientists at the National Ignition Facility.  It surprised me, but I wrote it off to poor reporting.  Yesterday someone asked me about this "huge energy breakthrough", so a bit of where things stand...

 

Breakeven is the point where the energy output of a power station is greater than the energy necessary to operate it.  Scientists usually speak in terms of gain - energy output divided by energy input.  Breakeven comes when the gain is equal to or greater than 1.0.

 

In nuclear fusion two atoms come together to form one.  In the process energy is liberated.  Many fusion reactions involve isotopes of hydrogen - deuterium or tritium.  Bringing them together is difficult as the protons in each nucleus are all positively charged and want to repel each other.  Fusion doesn't happen until the nuclei are under great temperature and pressure to force them together.  Stars do this with their mass and the force of gravity. 

 

On earth we can achieve controlled fusion by confining its fuel of deuterium and tritium under extreme temperature and pressure.  The two main approaches are magnetic and inertial confinement.  Both are incredibly challenging.

 

The NIF is an inertial confinement experiment that uses 192 enormous lasers that ultimately crunch a two illimeter pellet filled with liquid deuterium and tritium raising its temperature and pressure to the point where fusion occurs. There are lots of gee whiz statistics - during the laser pulsing the power is about five hundred times more than the total electric power generation capacity of the United States. This is exotic stuff and has sparked a good deal of invention and spin-off technologies.¹

 

What took place at the end of September was a  record shot that produced 5*10¹⁵ neutrons carrying a total of about 13.5 kilojoules of energy - about the same amount of energy as a baseball traveling about 40 miles an hour.  Unfortunately this is only about 0.7% of the energy of the laser pulse.  While it wasn't close to a practical breakeven,  the energy of the X-ray blast was a bit less than 13.5 kJ so that part of the experiment achieved a technical breakeven.  A big deal and celebration worthy.

 

It will take a lot of work to go from 0.7 to over 100 percent to achieve real breakeven, but practical reactor is even farther down the road.  The energy required to fire the lasers is much greater than what they emit and you have to catch the neutrons and turn their kinetic energy into electricity somehow ..  the conventional way would boil water making steam to run a generator.³

 

It would be great to have terrestrial fusion - there is an enormous supply of deuterium and it should be easy enough to find enough tritium to supply enough energy to the world.  At the same time the Sun has been doing it for over four billion years - it cheats by using a reaction that requires a much lower temperature.  Unfortunately its power density is far too low to be practical so we are forced to use reactions that require higher temperatures and pressures.⁴

 

Researchers started serious work on fusion reactors in the 1950s it has always been said practical power stations are at least several decades away.  Currently people talk about 2050, but history suggests that  expect that might slip for technical and practical reasons. Renewable energy sources that are basically solar power (solar and wind) are becoming much less expensive and it is likely that progress in energy storage may make tapping the sun practical long before we get a fusion reactor.  

 

The Sun is about 500 light seconds away you might say fusion is 50 years in the future or 500 seconds in the past.⁵

 

And this post from phdcomics pretty much sums up the sciences news cycle...

 

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¹ To call the facility sophisticated is total understatement.  Amazing precision is required - much of the facility had to be invented and custom built for the task.

The lasers are fired simultaneously in a 20 nanosecond pulse (light travels about 20 feet in that time).  The combined energy is about  1.8 megajoules (about the same kinetic energy of a large family car traveling at 70 mph) and goes into a special spherical vessel called the hohlraum, heating it to give off X-rays which strike and crush a plastic capsule surrounding the fuel pellet.  The fuel pellet heats to about 100 million °K (six times the core temperature of the Sun) and a pressure of 100 billion atmospheres.

It should be noted magnetic confinement is closer to being practical than inertial confinement, but both are problematic.

² More properly ²H + ³H -> ⁴He + n where the neutron carries off about 17 MeV (17 MeV is about 2.7 * 10^-12 joules, but there can be a lot of nuclei. Also note chemical bonds are in the single eV range.)

³ The lasers are about 10% efficient and are followed by a step that converts their infrared output to ultraviolet that is about 30% efficient -- overall efficiency generating the light pulses is about 3%.  A steam turbine power generator is about 40% efficient, so the breakeven is farther off than the 0.7% figure suggests.

It is interesting to note that plants average a few tenths of a percent efficiency turning solar energy into chemical energy.  The process of making fossil fuels is enormously inefficient - tens or even hundreds of thousand times worse.  But that doesn't matter to us as we mine what required millennia to produce at no cost to us.

⁴ The Sun's reaction is non-trivial and parts of it proceed very slowly.  If you work out the energy density of the core of the Sun you find it is much less than the energy use density of a human - in fact it is roughly about the same as a lizard.

⁵ An astrophysicist would point out that energy produced by fusion in the core of the Sun takes a long time - something like 100,000 years - to migrate to the surface where it then travels at the speed of light.

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Recipe corner

tips rather than recipes this time...

Halloween approaches.  The large pumpkins suitable for carving taste awful - don't even think about it.  Compost everything but the seeds. The seeds are wonderful when you roast them.  Don't worry about separating the glop.  Put them on a cookie sheet (you may want to cover it with foil first) and toss them in oil and sea salt.  Pop 'em into an oven at 325°F and wait until they begin to brown around the edges.  The relatively cool oven lets them cook to their core and they will be wonderful.  The glop will dry out and is very easy to separate at this point.

And that brings us to pumpkin pie.   Use butternut squash (acorn squash isn't bad either) instead for a much better pie.  Don't bother with condensed milk - it was a WWII substitute for heavy cream.  Try using whole milk, half and half or even heavy cream depending on how rich you want the pie to be.  Remember the ginger and nutmeg are best if very fresh.  You'll be surprised how much better a pie with great ingredients is than the traditional canned pumpkin and condensed milk variety of the 1940s...  and you can make great ones will less sugar than you might think (just the thing for Jeri)