April 12, 2002

Jolt of energy for fusion research

In 20 to 30 years, the energy industry could start building heavy ion fusion power plants that would generate electricity from fusion energy.
A heavy ion fusion power plant uses intense ion beams focused on a small target to create a small thermonuclear reaction.

The Lab’s heavy ion fusion group, part of Fusion Energy Programs, is helping to develop the technology for heavy ion fusion. This effort recently reached a major milestone with the dedication of its injector test stand, otherwise known to the fusion energy physicists as STS-500, a 500-kilovolt ion source test stand in Bldg. 341.
The test stand can generate a 500-kilovolt pulse for 17 microseconds at a rate of once every two to three seconds. The stand uses 10 kilojoules of stored energy to generate the pulses. The goals are to develop ion sources through high voltage pulses and the flexibility to install a variety of sources and accelerating structures.

The first source experiments will begin in May, according to project manager Larry Ahle.

At first glance, the STS-500 looks like something out of a 1950s science fiction film. But to the trained eye, the machine consists of a high-voltage dome, insulator column, a diagnostic tank, a transformer and a pulse forming network tank.

Working with scientists from Lawrence Ber-keley and the Princeton Plasma Physics laboratories, LLNL physicists hope to test two sources with the new injector test stand: a surface ionization source and a gas plasma source.

"It will be 20 to 30 years before this technology is ready for a commercial application," Ahle said.

The STS-500 will allow experiments on aperturing high-current beams, high electric-field gradient insulators, beam-beam effects and merging, and long pulse width beam physics issues.

One experiment will involve a multiple beamlet source in which many miliamp beams are extracted and transported individually before being merged, creating a 1 amp beam.

A heavy ion fusion driver, necessary for a power plant, would require at least 100 beams to generate the amount of energy needed to run a plant. For now, Lab physicists are trying to provide a source for each beam.

Ahle said the test stand is unique because of the rise time and width of the pulse.