Periodic Reporting for period 3 - LLR (Laser Lightning Rod) Reporting period: 2021-01-01 to 2021-12-31 Summary of the context and overall objectives of the project Lightning is a fascinating albeit destructive manifestation of nature. Estimates on the average number of persons killed by lightning every year range from 6000 to as many as 24000 worldwide. Lightning is also the cause of power outages, forest fires and damages to electronics and infrastructure amounting to billions of euros each year, making it a major societal concern. Although lightning protection techniques have seen considerable progress in the past, the best external lightning protection to date is still based on the concept of the lightning rod, invented by Benjamin Franklin almost 300 years ago. The present project proposes to use a laser-based technique to stimulate the number of upward lightning flashes with the aim of transferring cloud charges to the ground and thus to influence the incidence of downward natural lightning. The laser-based system could be easily deployable for the protection of especially vulnerable installations on a temporary or a permanent basis. Examples are large crowds gathering at events, rockets on their launching pad, storage or transport of hazardous materials from industrial, nuclear, chemical, electrical plants, etc. Another important issue is the protection of airplanes in airports prone to thunderstorms. It is foreseen that this last issue represent the first wide-scale industrial application of the laser lightning project. Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far The LLR project started in 2017. The first year was dedicated to the development of the instruments, the telescope, and the first stage of the laser, and to the preparation of the two main experimental campaigns of WP3 and WP4, including the study of the research on the conditions conducive to the initiation of lightning to enhance the probability of laser triggering. In 2018 the first filamentation experiments were performed by the partners at the premise of Trumpf Scientific Laser with the 200 mJ laser amplifier. The results obtained confirmed the efficiency of the laser. The LLR laser system was finalized by the beginning of January 2020 at the labs of Trumpf Scientific Lasers. A compressed pulse energy of 720 mJ could be achieved at the repetition rate of 1 kHz, with a pulse duration of < 1 ps, leading to a peak power as high as 720 GW. An horizontal campaign to characterize the filament produced by the laser has been realized in Orsay in 2020 and early 2021. Studies of the laser beam propagation with a telescope have shown that it is possible to generate filaments starting at a distance exceeding 110 m, which corresponds to the height of the Saentis tower. Finally, during the Summer of 2021, the developed high-power 720 mJ, 1 kHz laser was installed near the Säntis Tower at the top of the 2504-m tall Säntis mountain. During this campaign the influence of the laser and filament to trigger and guide lightning was analyzed. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by VHF interferometric measurements, and the number of X-ray bursts detected during guided lightning events was significantly increased. While this research field has been very active for more than 20 years with many research groups around the world working to achieve this goal, this result demonstrates lightning guiding by lasers, which may lead to the development of a laser lightning rod. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Lightning can have a considerable influence on the environment and on the economy since it causes energy supply outages, forest fires, damages, injury and death of humans and livestock worldwide. The risk of adverse effects from lightning is likely to increase as a consequence of climate change, since storms may become more severe and the lightning itself could become more energetic. In addition, human activity, spurred in large part by efforts to curb climate change, is already influencing lightning incidence as the number of installed wind turbines and telecommunication towers increases. Thanks to the development of such a lightning protection technology, safer air transport is expected, with reduced flight delays and congestion of airports during intense thunderstorms activity. Also expected is a significant reduction of maintenance costs due to lightning strike either on airport assets or aircraft. This could be a showcase for airport technological modernity, in case of regional competition.More generally, the target is the protection of industrial sites, chemical and nuclear power plants. It will more specifically concern the Space Industry (protection of launch pad and launcher/satellite integration buildings), airport (protection of aircraft during the take-off, landing and taxiing phases, protection of radars), wind turbines (for French, German, Danish, British, and Dutch offshore windfarms). Picture of the LLR laser generating filaments above the Saentis tower Picture of the Saentis tower (experimental site) Picture of the LLR laser system built by Trumpf Scientifc Laser
