Levitated Dipole Experiment
Levitated Dipole Experiment | |
---|---|
Device type | Levitated dipole |
Location | Cambridge, Massachusetts, United States |
Affiliation | MIT Plasma Science and Fusion Center, Columbia University |
Technical specifications | |
Major radius | 0.34 m (1 ft 1 in) |
History | |
Year(s) of operation | 2004–2011 |
Related devices | Collisionless Terrella Experiment (CTX) |
Links | |
Website | The Levitated Dipole eXperiment website |
The Levitated Dipole Experiment (LDX) was an experiment investigating the generation of fusion power using the concept of a levitated dipole. The device was the first of its kind to test the levitated dipole concept and was funded by the US Department of Energy.[1] The machine was also part of a collaboration between the MIT Plasma Science and Fusion Center and Columbia University, where another (non-levitated) dipole experiment, the Collisionless Terrella Experiment (CTX), was located.[2]
LDX ceased operations in November 2011 when its funding from the Department of Energy ended as resources were being diverted to tokamak research.[3][4]
Concept and development
The concept of the levitated dipole as a
The Machine
The Dipole
This experiment needed a very special free-floating electromagnet, which created the unique "toilet-bowl" magnetic field. The magnetic field was originally made of three coils. Each coil contained a 19-strand
Chamber
The dipole was suspended inside a "squashed-pumpkin"-shaped vacuum chamber, which was about 5.2 meters in diameter and ~3 meters high.[15] At the base of the chamber was a charging coil. This coil is used to charge the dipole, using induction. Next, the dipole is raised into the center of the chamber using a launcher-rather system running through the bore of the dipole magnet. A copper magnet fixed on top of the chamber produced a magnetic field which attracted the floating dipole magnet. This external field would interact with the dipole field, suspending the dipole. The magnetic field produce by the floating dipole magnet is used to confine the plasma. The plasma forms around the dipole and inside the chamber. The plasma is formed by heating a low pressure gas using a radio frequency, essentially microwaving the plasma in a ~15-kilowatt field.[16]
The Diagnostics
The machine was monitored using diagnostics fairly standard to all of fusion. These included:
- A Flux loop. This is a loop of wire. The magnetic field passes through the wire loop. As the field varied inside the loop, it generated a current. This was measured and from the signal the magnetic flux was measured.
- An X-ray detector.[17] This diagnostic measured the X-rays emitted. From this, the plasmas' temperature was found. There were four of these inside the machine, each measuring along a cord (or line out) inside the machine.[17] This detector was good for measuring electrons, typically around 100 electron-volts. All plasma loses energy by emitting light. This covers the whole spectrum: visible, IR, UV, and X-rays. This occurs anytime a particle changes speed, for any reason.[18] If the reason is deflection by a magnetic field, the radiation is Cyclotron radiation at low speeds and Synchrotron radiation at high speeds. If the reason is deflection by another particle, plasma radiates X-rays, known as Bremsstrahlung radiation.
- An X-ray Camera.[19] This can read lower energy X-rays.
- A Conventional Video Camera [19]
- An emissive Langmuir probe. A Langmuir probe is a wire, stuck into a plasma, which absorbs the surrounding charged particles. You can vary the voltage on this wire. As the voltage changes, the charged particles absorbed change, making an IV curve. This can be read and used to measure the density and temperature of the nearby plasma.
- A triple Langmuir probe[19]
- A dozen Langmuir probes grouped together[19]
Behavior
The plasma is confined by the dipole magnetic field. Single particles corkscrew along the field lines of the dipole magnet at the cyclotron resonance frequency while completing poloidal orbits. The electron population was shown to have a peaked pressure and density profile as a result of the turbulent pinch phenomenon.[10]
Modes of Operation
There were two modes of operation observed:[21]
- Hot electron interchange: a lower density, mostly electron plasma, occurring when the dipole was operated in "supported" mode (not levitated).
- A more conventional Magnetohydrodynamicmode.
These had been proposed by Nicholas Krall in the 1960s.[22]
Tritium Suppression
In the case of deuterium fusion (the cheapest and most straightforward fusion fuel) the geometry of the LDX has the unique advantage over other concepts. Deuterium fusion makes two products, that occur with near equal probability:
In this machine, the secondary tritium could be partially removed, a unique property of the dipole.
References
- ^ "Levitated Dipole Experiment". www-internal.psfc.mit.edu. Retrieved 2020-06-22.
- ^ "CTX". sites.apam.columbia.edu. Retrieved 2020-06-22.
- ^ "LDX funding canceled". Archived from the original on 2013-01-17. Retrieved June 27, 2012.
- .
- ISSN 0374-2806.
- Bibcode:1997PlPhR..23..742K.
- ^ "LDX begins first plasma experiments". Levitated Dipole Experiment. 13 August 2004. Retrieved 7 August 2016.
- ^ "First flight and damaged L-coil". Levitated Dipole Experiment. 9 March 2009.
- ^ "Levitation coil replacement". Levitated Dipole Experiment. 21 May 2007.
- ^ .
- .
- ^ "The Levitated Dipole Experiment". MIT. Retrieved 7 August 2016.
- ^ a b "Design and Fabrication of the Cryostat for the Floating Coil of the Levitated Dipole Experiment (LDX)" A. Zhukovsky, M. Morgan, D. Garnier, A. Radovinsky, B. Smith, J. Schultz, L. Myatt, S. Pourrahimi, J. Minervini.
- ^ "Turbulent Transport in a Laboratory Magnetospheric Dipole" European Physical Society 38th Conference on Plasma Physics, Strasbourg, France June 28, 2011.
- ^ presentation"LDX Machine Design and Diagnostics" APS DPP meeting 1998, Garnier and Mauel
- ^ "Optimization of Hot Electron Diagnostics on LDX" Nogami, Woskov, Kesner, Garnier, Mauel, 2009
- ^ a b "X-Ray Diagnostics for the Levitated Dipole Experiment" Jennifer L. Ellsworth, Master's Thesis, MIT 2004
- ^ J. Larmor, "On a dynamical theory of the electric and luminiferous medium", Philosophical Transactions of the Royal Society 190, (1897) pp. 205–300 (Third and last in a series of papers with the same name).
- ^ a b c d "Diagnostic setup for spatial and temporal measurements of plasma fluctuations using electric probes in the LDX" E Ortiz, M Mauel, D Garnier, 45th DPP meeting, October 2003
- ^ "Overview of LDX Results" Jay Kesner, A. Boxer, J. Ellsworth, I. Karim, Presented at the APS Meeting, Philadelphia, November 2, 2006, Paper VP1.00020
- ^ "Helium Catalyzed D-D Fusion in a Levitated Dipole" Presentation Kesner, Catto, Krasheninnikova APS 2005 DPP Meeting, Denver
- ^ "Stabilization of Hot Electron Plasma by a Cold Background" N Krall, Phys. Fluids 9, 820 (1966)
- ^ "Fusion Technologies for Tritium-Suppressed D-D Fusion" White Paper prepared for FESAC Materials Science Subcommittee, M. E. Mauel and J. Kesner, December 19, 2011