Extended Interview with Tom Ligon (6 of 8)

The Polywell™ is a concept for a fusion reactor that creates fusion through electrostatically accelerating ions. Ions, like deuterium, can be "heated" by accelerating them across a voltage. "Heated" ions can slam head onto one another and fuse. The device consists of six electromagnets, spaced apart in a cube. The cube is contained inside a vacuum chamber. Each electromagnet creates a magnetic field which interferes with one another in the center, where there is no field. Electrons are injected into this void. Electrons re-circulate into and out of the center, but effectively there is a huge mass of them in the center. This acts like a big point charge. It is theorized that with so many electrons together; the cloud could behave diamagnetically. This behavior is referred to as the "whifle ball" and it helps trap electrons. Once the point charge is established, ions are injected. The ions are attracted by the electrons. They fall towards the center, slam into one another, and fuse. Many different interactions occur inside the center. The most common event is ion-ion collisions which do not result in fusion. Ideally, these collisions would be elastic enough to conserve the energy of the system. Electron-ion collisions generally do not result in recombination because the ions are at too high of an energy. There is also X-rays being generated, as well as a glow discharge which cools the plasma. The major argument against the polywell working is that the device will thermalize. Thermalization is when the cloud of ions in the center assumes a bell energy curve. The work mainly referred to in the film which discusses this, is that of Dr. Todd Rider. Aside from thermalization, some other research challenges include:

1. X-ray Cooling
2. Arching inside the device
3. Firing in the ions at the correct electric potential. If the polywell can be kept from thermalizing; is a question which lies at the heart of its viability.

Category:

Science & Technology

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• Steven Chu
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