Migma
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Migma was a proposed inertial electrostatic confinement fusion reactor designed by Bogdan Maglich in the early 1970s.[1] Migma uses self-intersecting beams of ions from small particle accelerators to "force" the ions to fuse. It was an area of some research in the 1970s and early 1980s, but lack of funding precluded further development.
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[edit] Conventional fusion
In order to produce a fusion reaction, atoms of the fuel must be forced together to a very small distance from each other. In the conventional approach the fuel is heated, which results in the electrons disassociating from the nuclei, which are left as ions. The heat leaves some of these ions with very high energies (speeds), and on occasion two such high-speed ions could collide, and fuse. Counteracting this process is the fact that the ions are all positively charged, and thus repel each other due to the electrostatic force between each other. In order for fusion to occur, the ions must have enough energy to overcome this coulomb barrier, which is about 100 keV (see requirements for fusion).
Any particles in a gas, like the fuel in a conventional fusion reactor design, are distributed across a wide range of energies in a spectrum known as the Maxwell-Boltzmann distribution. At any given temperature the majority of the particles are at lower energies, with a "long tail" containing smaller numbers of particles at much higher energies. As the fuel is heated the number of particles in the tail with enough energy to undergo fusion increases, and the energy production rate increases along with it. In order to produce enough reactions for commercial energy production the fuel must be heated to very high temperatures, typically tens to hundreds of millions of degrees. Confining such a hot gas for a time period long enough for useful power generation has proven "difficult", to say the least.
[edit] Migma fusion
The Migma approach avoided the problem of heating the mass of fuel to these temperatures by accelerating the ions directly in a particle accelerator. Accelerators capable of 100 keV are fairly simple to build, although in order to make up for various losses the energy provided is generally higher. Later Migma testbed devices used accelerators of about 1 MeV,[2] fairly small compared to the large research reactors like Tevatron, which are a million times more powerful.
The original Migma concept used two small accelerators arranged in a collider arrangement, but this reaction proved to have fairly low cross-sections and most of the particles exited the experimental chamber without colliding. Maglich's concept modified the arrangement to include a powerful magnetic confinement system in the target area; ions injected into the center would orbit around the center for some time, thereby greatly increasing the chance that any given particle would undergo a collision given a long enough confinement time. It was not obvious that this approach could work, as positively charged ions would all orbit the magnetic field in the same direction. However, Maglich showed that it was nevertheless possible to produce self-intersecting orbital paths in such a system, and he was able to point to experimental results from the intersecting beams at CERN to back up the proposal with real-world numbers.
Several Migma experimental devices were built in the 1970s; the original in 1972, Migma II in 1975, Migma III in 1978, and eventually culminating with the Migma IV in 1982. These devices were relatively small, only a few meters long along the accelerator beamline with a disk-shaped target chamber about 2 m in diameter and 1 m "thick". This device achieved the record fusion triple product (density × energy-confinement-time × mean energy) of 4e14 keV sec cm-3 in 1982, a record that was not approached by a conventional tokamak until JET achieved 3e14 keV sec cm-3 in 1987.
Maglich has been attempting to secure funding for a follow-on version for some time now, unsuccessfully. According to an article in The Scientist, Maglich has been involved in an apparently acrimonious debate with the various funding agencies since the 1980s.
[edit] Migma drawbacks
One more recent concern with the Migma design is that the particles lose energy through collisions with other particles in the reaction area, and through other interactions that only become an issue at very high energies, notably bremsstrahlung. These processes remove energy from the "fast" particles being injected, lowering their temperature and feeding it into the surrounding fuel mass. It appears there is no obvious way to "fix" this problem.[3] Whether this concern applies to the Migma is not clear.
[edit] References
- ^ The Migma principle of controlled fusion, Bogdan C. Maglich, Nuclear Instruments and Methods III (1973), p 213-235
- ^ Migma IV High Energy Fusion Apperatus
- ^ Fundamental Limitations on Plasma Fusion Systems Not in Thermodynamic Equilibrium, MIT Department of Electrical Engineering and Computer Science, June 1995
[edit] External links
- Visionary Physicist's Crusade Serves As Lesson In Futility in The Scientist
- Bogdan Maglich- Migma Fusion
- HiEnergy Technologies, Inc.
- Letter: Migma Omissions By Bogdan Maglich cache of letter to The Scientist
