Goals

Develop a new lightning protection

The LLR team aims to investigate and develop a new type of lightning protection based on the use of upward lightning discharges initiated through a high-repetition-rate multi-terawatt laser. A long-lasting, low-density air channel generated by laser filamentation at high repetition rate will stimulate upward lightning discharge initiation from an existing grounded tall object. A low-density channel created by the high-power, pulsed laser will operate by promoting the initiation of upward discharges to preemptively transfer cloud charges to the ground. A demonstration of laser-induced upward lightning will constitute a major breakthrough in lightning research with potentially profound impact on future lightning protection systems.

A timely and achievable project

It has been demonstrated recently by CNRS, AMC and AGI that it is possible to trigger electric discharges between charged electrodes at distances reaching 500 m by sending a multi-terawatt short laser pulse into the atmosphere. The laser intensity is maintained sufficiently high to ionize the air at such distances thanks to the process of filamentation. Only low-repetition-rate lasers (10 Hz) were available for such experiments a few years ago.

A second advance is the recent discovery that the filamentation process initiates a long-lasting low density channel along the filamentation path. For a low repetition rate multi TW laser, the air density is initially reduced by a factor 5, an effect that lasts for milliseconds with a density 15% below normal atmospheric pressure. The typical length of the channel is a few meters. It has also been demonstrated that these straight, low-density channels are the source of the triggering and guiding of electric discharges in the atmosphere at a 60% reduced voltage. At higher repetition rates, the decrease in the air density due to filamentation can be amplified by a cumulative effect A third development is the considerable recent progress in ultra short TW laser systems thanks to the diode pumped technology. One of the partners (TRUMPF) is committed to the development of a transportable multi TW laser system operating at 1 kHz for the project. This unique laser will constitute a major asset for its success, as it makes possible to realize the above-mentioned low density channel on a large scale.