3 November 2005
Study Of Runaway Breakdown Set For Lab
by Kate Melville
In recent experiments, researchers from the Florida Institute of Technology found that sparks generated in their laboratory produced x-ray bursts that were very similar to those created by lightning. High voltage sparks like lightning are known to emit x-rays and gamma ray bursts, although the mechanisms behind these emissions are still not clearly understood. Now, however, researcher Dr. Joseph Dwyer's experiments demonstrate that x-ray emissions can occur from relatively low-energy sparks in the laboratory, which should open the door to further research into the poorly understood relationship between lightning and terrestrial gamma ray bursts.
"We know that x-rays are made in exotic places� but we didn't think they could be made so easily in the air," remarked Dwyer. "The results should allow for the detailed laboratory study of runaway breakdown, a mechanism that may play a role in thunderstorm electrification, lightning initiation and propagation, and terrestrial gamma-ray flashes."
Runaway breakdown is a controversial phenomenon believed to be associated with lightning and high energy bursts. Scientists speculate that runaway breakdown occurs when the electric force experienced by electrons exceeds the effective frictional force due to collisions with air molecules, allowing the electrons to "run away" and gain very large energies. The only mechanism that can account for the creation of the high-energy electrons that make x-rays is the runaway breakdown of air.
Dwyer's team used a Marx spark generator to create the sparks that yielded the x-ray bursts. Their study, in Geophysical Research Letters, noted that 1.5- 2.0 million-volt sparks in the air produced the x-ray burstsand that the bursts were remarkably similar to the x-ray bursts previously observed from lightning. "This amazed us. It opens the door to answering really big questions about lightning by generating it in the lab," said co-researcher Dr. Hamid Rassoul. "It also tells us that we have a lot to learn about how even small sparks work."
Source: Florida Institute of Technology