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Teramobile laser triggers lightning strikes

Posted: 21 Apr 2008     Print Version  Bookmark and Share

Keywords:plasma filaments  ground-based lasers 

Since Benjamin Franklin conducted his famous kite experiments, harnessing lightning strikes has been a fascination. Strikes have been deliberately conducted to the ground by rockets spooling long wires behind them, but that technique has only been successful about 50 percent of the time. Now a team of European scientists has triggered lightning strikes with ground-based lasers.

Lessons from lightning
The goal is to create miles-long plasma filaments that would extend from clouds to the ground, providing an economical conduit—akin to Franklin's kite string—to channel surefire strikes for the purpose of studying lightning's mechanisms and its effects on infrastructure.

According to researcher J�r�me Kasparian of the University of Lyon, the team's Teramobile laser is the first solid-state system to generate lightning successfully in thunderclouds. From a site atop New Mexico's South Baldy Peak, femtosecond laser pulses "seeded" storm clouds. As the lasers penetrated the atmosphere, they created plasma filaments along their path.

The lasers succeeded in triggering lightning discharges in the thunderclouds, though the pulses were too short-lived to provide a conduit all the way to the ground. Nonetheless, Kasparian said the test was an important first step toward triggering lightning strikes with laser beams.

Now the researchers are reprogramming their lasers with more-powerful pulse trains in a bid to create filaments that will conduct the lightning back to terra firma. The end goal is to expand scientists' understanding of lightning as well as test the lightning sensitivity of airplanes, powerlines and other critical infrastructure features and systems that are vulnerable to damage by strikes.

Plasma filaments
In the Teramobile experiments, lasers created plasma filaments by ionizing molecules of air as they passed through it, essentially yielding electrical conduits with similar conduction characteristics to wires. The concept itself was born more than 30 years ago, but not until recently have lasers become powerful enough to create the filaments. With lasers that can fire ultrashort, femtosecond pulses in series, Teramobile was designed specifically for generating long plasma channels. The test site—Langmuir Laboratory in the Magdalena Mountains of central New Mexico—was chosen because of its lofty location atop the 10,500-foot-high South Baldy Peak, as well as for the lab's ability to measure atmospheric electrical discharges.

The lab was able to confirm that Teramobile's lasers generated local electrical discharges in the clouds, but the plasma channels only persisted long enough for them to travel a distance of less than 10m. Now the researchers are reprogramming Teramobile to create bursts of femtosecond pulses at 10x higher power.

The Teramobile project is a collaborative effort of the National Center for Scientific Research (CNRS) in France and the German Research Foundation (DFG). Kasparian conducted the research with his colleagues at CNRS; the University of Lyon; the University of Geneva; �cole Polytechnique and ENSTA in Palaiseau, France; the Free University of Berlin; and the Dresden-Rossendorf Research Center. Funding was provided the CNRS, DFG, the French fand German ministries of foreign affairs and various European research agencies.

- R. Colin Johnson
EE Times





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