An experimental fusion reactor at the Plasma Science and Fusion Center on the MIT campus called the Levitated Dipole Experiment, or LDX uses a half-ton donut-shaped magnet about the size and shape of a large truck tire, made of superconducting wire coiled inside a stainless steel vessel.

LDX Diagram. Click image for the largest view.

Used in a new experiment that reproduces the magnetic fields of planetary bodies has yielded its first significant results.  The results confirmed the theory that LDX’s unique approach has some potential to be developed into a new way of building a power-production plant based on nuclear fusion mimicking the process that generates the sun’s prodigious output of energy.

The theorizing began with observations in the way plasmas in space interact with the Earth and Jupiter magnetic fields.  The effect hasn’t before been achieved in a laboratory.  The experiment confirms the seeming counter-intuitive prediction that inside the device’s magnetic chamber, random turbulence causes the plasma to become more densely concentrated – crucial step to getting atoms to fuse together – instead of becoming more spread out, as usually happens during turbulence.  MIT is using the term “pinch effect” to describe the observation, a term we’ve heard before from other fusion developers.

MIT is touting LDX as a new approach.  MIT senior scientist Jay Kesner, MIT’s physics research group leader for LDX says, “It’s the first experiment of its kind.”  That is certainly so, but if the pinch effect is a functioning phenomena, MIT is late to the game following other pinch phenomena.  Yet every pathway to a fusion pinch is welcome and deserves intense study and development.

LDX Lab View with Legends. Click image for the largest view.

The superconducting LDX magnet is levitated by a powerful electromagnetic field, and is used to control the motion of the 10-million-degree-hot electrically charged gas, or plasma, contained within its 16-foot-diameter outer chamber.  When operating, the huge LDX magnet is supported by the magnetic field from an electromagnet positioned overhead.  The supporting magnet is controlled continuously by a computer control system acting on precision monitoring of the position using eight laser beams and detectors. The position of the half-ton magnet, which carries a current of one million amperes (compared to a typical home’s total capacity of 200 amperes) can be maintained this way to within half a millimeter. A cone-shaped support with springs is positioned under the magnet to catch it safely if anything goes wrong with the control system.

This is a link to an mp4 movie of the LDX in an operation cycle: starting, operating and returning to recharge.

“Levitation is crucial because the magnetic field used to confine the plasma would be disturbed by any objects in its way, such as any supports used to hold the magnet in place. In the experimental runs, they recreated the same conditions with and without the support system in place, and confirmed that the confinement of the plasma was dramatically increased in the levitated mode, with the supports removed. With the magnet levitated, the central peak of plasma density developed within a few hundredths of a second, and closely resembled those observed in planetary magnetospheres.”

Kesner summarizes the difference between the two approaches explaining, “(I)n a tokamak, the hot plasma is confined inside a huge magnet, but in the LDX the magnet is inside the plasma. The whole concept was inspired by observations of planetary magnetospheres made by interplanetary spacecraft. In turn for planetary research the experiments in LDX can yield “a lot more subtle detail than you can get by launching satellites, and more cheaply.””

Kesner and co-director the project Michael E. Mauel, professor of applied physics at Columbia University’s Fu Foundation School of Engineering and Applied Science published the results last week in the journal Nature Physics.

The team is saying say that if the turbulence-induced density enhancement exhibited by the LDX could be scaled up to larger devices, it might enable them to recreate the conditions necessary to sustain fusion reactions, and thus may point the way toward abundant and sustainable production of fusion energy.

Stewart Prager, director of the Princeton Plasma Physics Laboratory in observing the unique geometry of the system says, “LDX is one of the most novel fusion plasma physics experiments underway today.  Theoretical predictions indicate that the confinement of energy might be very favorable (for producing practical fusion power, but the theory needs to be confirmed in practice) For these benefits to be realized, the somewhat bold theoretical predictions must be realized experimentally.”

Prager is right, the LDX is one of several magnetic confining forms to hold fusion fuel and manipulate it.  The curiosity here is the magnet is in the plasma, which begs the question of its operating parameters during fusion events.  Tests of that nature will be intensely interesting.

Mauel and Kesner’s LDX project is now through more than 10 years of design, construction and testing.  The first experimental results in its levitated configuration occurred last year are being reported in the analysis published this week. A newly installed microwave interferometer array, developed by MIT PhD ’09 graduate student Alex Boxer was used to make the precision measurements of the plasma concentrations that were used to observe the turbulent pinch.

The team offers another pathway outside of the massively expensive and time-consuming tokamak system.  Add one more confinement idea.  Something is going to work.  What do you think?


7 Comments so far

  1. WPT on January 31, 2010 7:48 AM

    Fills people in on this and the post helped me a lot in my college assignment. Saying thank you for your information.

  2. kate sisco on May 11, 2010 7:20 AM

    Now there is a large star forming again against current theory. One wonders if the concept of an aether is correct and that the sun’s orbital bodies are super capacitors: two non reactive plates coated with carbon bathed in electrolyte. Seems to fit best as not a chemical reaction but holds a charge.

  3. Chet Pistilli on May 20, 2011 9:29 PM

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  4. Pete Widrick on August 29, 2011 2:13 AM

    I was just having a conversation over this I am glad I came across this it cleared some of the questions I had.

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  7. Dudley Codell on October 7, 2011 9:18 AM

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