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'Surgical' microwaves suppress plasma islands, up fusion rates. (Tokamaks).

Recent U.S. and German experiments have shown that fusion reaction rates and other properties in magnetically confined plasmas can be significantly improved by a relatively small amount of microwave power, applied at precisely the right location in the plasma.

Tokamak plasmas, and indeed most magnetically trapped plasmas, are subject to the growth of "magnetic islands," which break up the smooth magnetic field surfaces that confine the plasma. This leads to rapid loss of heat from the plasma and makes it more difficult to reach the high temperatures and pressures needed for nuclear fusion.

ASDEX Hosted Early Experiments

Experiments first carried out on the ASDEXUpgrade tokamak at Germany's Max-Planck Institute, and, more recently, on General Atomics' DIII-D tokamak in San Diego, confirmed theoretical predictions that islands, due to high plasma pressure, can be eliminated by adding a small amount of added electrical current at the island location.

A narrow beam of microwaves can drive the desired current, with surgical precision, by interacting with electrons at the appropriate location.

In experiments a magnetic island degraded plasma pressure by about 20 percent. Ad ding one megawatt of microwave power, about one-tenth of the total power needed to heat the plasma, drove enough current to suppress the island.

This allowed the plasma pressure to recover, resulting in a 35 percent increase in the fusion reaction rate on DIII-D.

These pioneering experiments show the feasibility of improving the performance of fusion plasmas by small, precisely controlled modifications of their internal structure.

Similar experiments also have been carried out in tokamaks in the United Kingdom and Japan.

Contacts: Hartmut Zohm, Max Planck Institut 011-49-89-3299-1925, e-mail: haz@ipp.mpg.de; or Robert La Haye, General Atomics, (858) 455-3134, e-mail: lahaye@fusion. gat.com.
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Publication:Fusion Power Report
Article Type:Brief Article
Geographic Code:1USA
Date:Nov 1, 2000
Words:287
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