Magnetized Target Fusion

Posted by Rezwan on Jan 27, 2011 at 01:21 PM
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Discover Magazine’s Oct. 2010 issue (now online:  The Dark-Horse Lab That Just Might Figure Out Fusion) explains the project this way:

The technical term for what Wurden and his colleagues at Los Alamos do is “magnetized target fusion.” One component of their experimental device is a hollow aluminum cylinder, 30 centimeters tall and 10 centimeters in diameter, with walls 1 millimeter thick. “It’s the size of an extra-big beer can—Australian size” Wurden tells me as we approach his lab, which occupies all of a hangar-size building next door to his office.

The “beer can” is a larger container/shell/target than a hohlram.  And rather than use lasers to implode the plasma within the container as NIF does with their hohlram, Shiva “crushes the can” with powerful currents of electricity.  (This sounds like an extreme Australian drinking game.)

Banks of refrigerator-size capacitors, devices for storing and releasing electrical energy, take up most of the lab’s floor space, all linked by thick colored cables. But it is the can that will be the center of the action. That is where the fusion will happen—assuming the absence of short circuits and explosions.  With those caveats, canned fusion is supposed to work like this:

1. Switch on powerful magnetic fields to create and control a hot plasma (ionized gas) of deuterium.
2. Trap the plasma inside the aluminum can, again using magnetic fields; if the plasma physically touched the can, the aluminum would vaporize almost instantly.
3. Apply a quick burst of current to crush the can in a few millionths of a second, heating the confined deuterium to millions of degrees and compressing it to such an extreme that fusion occurs.
4. Harness the released energy and change the world.

At the stillpoint (well, 24 microseconds) of destruction the magnetic fields are out of this world:

“We crush the can in 24 microseconds with 12 million amps of current,” Wurden says. “The magnetic fields are held inside and go up by a factor of 100. There are no magnetic fields like that in our solar system, not even in this corner of the galaxy. The pressure inside equals a million atmospheres; the temperature goes up by a factor of 30 to 100.”

Taking a closer look at the beer can:

Wurden’s plasma-holding apparatus is a quartz tube, 40 centimeters in diameter and 150 centimeters long, mounted on a table and partially wrapped in the aluminum coils of an electromagnet. Pumps for evacuating the tube and diagnostic equipment for studying the plasma surround the table. Three computers control it all from a small room at the other end of the lab, which is sealed off by blast doors whenever the experiment runs.

We’re not sure how they’ll do #4 above (“Harness the released energy”).  Before they get to that, here are some of the other challenges:

The computer-controlled electromagnets are designed to generate potent electromagnetic fields inside the quartz tube. Those fields are supposed to ionize the deuterium and form it into a football-shaped plasma, a geometry that would prevent it from squirting out of the collapsing can. Maintaining that exact geometry is crucial to the experiment’s success, because leaks would rob the plasma of the pressure and energy needed for fusion. Wurden’s efforts now focus on carefully measuring the plasma in the quartz tube to check for the right density, temperature, and stability to make fusion possible.

This and other worthy challenges face the Shiva Star team.  Note that their budget is around 4 million, compared to NIF’s 5 billion or ITER’s 20 billion.  A bargain contender - this would be a good one for private investors.

Where does this approach fit on our handy parameter space chart? 

*Shiva