The Laser Lightning Rod Project

Summary

This presentation details the Laser Lightning Rod (LLR) project, presented at UNIGE Physics Day 2024. It covers the history of lightning protection, principles of laser filamentation, experimental testing at the Mount Säntis research facility, and direct experimental evidence demonstrating laser-guided upward lightning discharges over 50 meters.

Title Page - UNIGE Physics Day 2024

Funded by the European Union Laser Lightning Rod UNIGE Physics Day 2024 THE LASER LIGHTNING ROD PROJECT Victor MORENO, Thomas PRODUIT, Ugo ANDRAL, Michel MORET, Jérôme KASPARIAN, Jean-Pierre WOLF - Université de Genève, Switzerland Pierre WALCH, Benoit MAHIEU, Magali LOZANO, Laurent BIZET, Yves-Bernard ANDRE, André MYSYROWICZ, Aurélien HOUARD - Laboratoire d’Optique Appliquée, CNRS - ENSTA Paris - Ecole polytechnique – IP Paris Clemens HERKOMMER, Robert BESSING, Thomas METZGER - TRUMPF Scientific Lasers, Unterföhring, Germany Antonio SUNJERGA, Amihossein MOSTAJABI, Farhad RACHIDI - EMC Laboratory, Swiss Federal Institute of Technology, Switzerland Mohamad Azadifar, Marcos Rubinstein - University of Applied Sciences and Arts Western Switzerland, Switzerland Olivier MAURICE, Gilles FOURNIER, Bruno ESMILLER - ArianeGroup, France Walter HAAS - Swisscom Broadcast AG, Switzerland

Background - Lightning Phenomena & History

BACKGROUND • Between 40 and 120 lightning flashes per second • Causing every year more than 4000 fatalities and damages amounting to billions of dollars • Protection: Lightning rod invented by Benjamin Franklin in the 18th century • Initiation demonstrated with rockets (Newman et al. 1965) Lightning triggered by a rocket trailing a conducting wire (USA)

Background - Charge Distribution & Types of Lightning

BACKGROUND • Stratification distribution of the electrical charges of a cumulonimbus • Apparent electric field between the ground and the bottom of the cloud a) Downward negative lightning b) Upward negative lightning c) Downward positive d) Upward positive

Lightning Protections - Classical Methods

LIGHTNING PROTECTIONS • Typical lightning rod protection area approximately equal to the height of the rod above the ground. Taller structures, the protective range extends only around 30m from the base. Reliable for small installation such but fails for large sensitive installations.

Lightning Protections - History of Laser Guidance

LIGHTNING PROTECTIONS • First demonstration in the 90’s in Japan • Idea emerged in the 70’s in Japan

Guiding Discharges with Laser Filamentation

GUIDING DISCHARGES WITH LASER FILAMENTATION • Demonstration of guiding with fs UV laser (J.-C. Diels 1994) • Meter scale discharges with TW lasers (IR, UV, Bessel beam, dual pulse) – INRS, Teramobile, Fujii et al., Ionin et al, Schwartz et al., Polynkin et al. • 2004: First campaign of lightning triggering with fs laser filament by the Teramobile group -> Observe corona initiation with TW filament in the clouds Rodriguez, OL 27, 772 (2002) D = 4 m, 1.4 MV

Background - Target Lightning Types

BACKGROUND Emphasis on upward lightning types: b) Upward negative lightning d) Upward positive

LLR Goal

LLR GOAL • Demonstrate the guiding of lightning flash over long distance with laser filamentation • Stimulate the number of lightning flashes in the presence of laser filaments • Final application: – Study of lightning – Lightning protection for airports, launchpads or large infrastructures

What Is a Laser Filament?

WHAT IS A LASER FILAMENT ? “In nonlinear optics, filament propagation is propagation of a beam of light through a medium without diffraction.” Kerr self-focusing -> Filament -> Plasma channel Nonlinear Schrödinger Equation (NLSE): ∂ℰ/∂z = (i / 2k₀) Δ_⊥ ℰ - i (k” / 2) (∂²ℰ / ∂t²) + i (k₀ / n₀) n₂ |ℰ|² ℰ - i (k₀ / (2 n₀² ρ_c)) ρ ℰ - (σ / 2) ρ ℰ - (β^(K) / 2) |ℰ|^(2K-2) ℰ

Laser Specifications (TRUMPF)

The LLR laser wavelength : 1030 nm pulse energy : 500 mJ pulse duration : 1 ps repetition rate : 1 kHz Final laser system delivered in January 2020 LLR laser inside the tent Modules: compressor, multipass, regen

Characterization of Long Range Filamentation

CHARACTERIZATION OF LONG RANGE FILAMENTATION • October 2020 March 2021 – Long distance propagation (>150 m) • Testing the laser • Characterize filament up to 110 m • Preparation of the final experiment Former linear accelerator of Orsay LAL (IJCLab)

Study of Filament Produced at Long Distance: First Test at LAL

STUDY OF FILAMENT PRODUCED AT LONG DISTANCE : FIRST TEST AT LAL IJCLab (Irène Joliot-Curie Laboratoire de Physique des 2 Infinis)

Outdoor Filament Characterization

OUTDOOR FILAMENT CHARACTERIZATION • Evidence of filamentation at long distance (> 110 m) • Guiding of discharges • Generation of strong SHG and THG Plasma filament at 55 m Guided discharge: 40 cm Input 500W @ 1030nm | Power @ 1ps | Efficiency @ 1ps SHG: ~ 300 W | ~60% THG: ~ 100 W | ~ 20%

Summer 2021: Lightning Campaign

SUMMER 2021: LIGHTNING CAMPAIGN Meteorological station of Mount Säntis (Switzerland) • Altitude 2 500 m • Fully instrumented for the detection of lightning • 100 lightning strikes every year • 97% of events are upward lightning leaders

Experimental Setup

EXPERIMENTAL SETUP A: Laser inside air-tight tent with air-conditioning in Radome Building, Focusing Telescope (distance 20 m to tower, angle α = 7°), Tower 124 m. B: Radome, Telescope, Säntis tower, Filamentation zone.

Real Conditions

REAL CONDITIONS Photographs of Mount Säntis installation in harsh alpine weather conditions (snow, ice, clear sky, installation via crane/helicopter).

Diagnostics: The Säntis Lightning Research Facility

DIAGNOSTICS: THE SÄNTIS LIGHTNING RESEARCH FACILITY EPFL / HES-SO Installation of different measuring equipments to characterize lightning:

Electric Field Mill
Current measurement (Rogowski coil / B-dot x4)
Slow and Fast Antennas (Radiowave)
VHF Time of Arrival and Interferometer
Weather Radar (Microwave)
High-speed Video Observations (Infrared / Visible)
Full HD camera x2 (Visible / Ultraviolet)
Scintillator x2 (X-ray / Gamma rays) Remote sites: Herisau, Albis (60km), Kronberg, Säntis - das Hotel, Säntis, Neudorf (380km).

Selected Data

SELECTED DATA Table of recorded events (Events, Date, UTC Time, Laser, Current, Flash polarity, HSC, INT, X-RAY, E(20m), E(15km)):

L1 | 24.7.2021 | 16:06:07 | ON | YES | POS | NO | YES | YES | YES | YES
L2 | 24.7.2021 | 16:24:03 | ON | YES | POS | YES | NO | YES | YES | YES
L3 | 30.7.2021 | 18:00:10 | ON | YES | POS | NO | YES | YES | YES | YES
L4 | 30.7.2021 | 18:02:40 | ON | YES | POS | NO | YES | NO | NO | YES
N01 | 30.7.2021 | 15:17:09 | OFF | YES | NEG | NO | YES | YES | YES | YES
N02 | 30.7.2021 | 15:22:29 | OFF | YES | NEG | NO | YES | NO | NO | NO
N03 | 30.7.2021 | 15:30:51 | OFF | YES | NEG | NO | YES | YES | YES | NO
N04 | 30.7.2021 | 15:35:41 | OFF | YES | NEG | NO | YES | YES | YES | YES
N05 | 30.7.2021 | 15:38:10 | OFF | YES | NEG | YES | YES | YES | YES | YES
N06 | 30.7.2021 | 18:04:53 | OFF | YES | POS | NO | YES | YES | YES | YES
N07 | 16.8.2021 | 02:00:27 | OFF | YES | NEG | NO | YES | NO | NO | NO
N08 | 16.8.2021 | 02:34:10 | OFF | YES | NEG | YES | YES | YES | YES | YES
N09 | 16.8.2021 | 05:53:24 | OFF | YES | NEG | NO | YES | YES | YES | YES
N10 | 16.8.2021 | 10:16:32 | OFF | YES | NEG | NO | YES | NO | NO | NO
N11 | 16.8.2021 | 15:06:45 | OFF | YES | NEG | NO | YES | YES | YES | NO
N12 | 16.8.2021 | 15:08:34 | OFF | YES | NEG | NO | YES | YES | YES | NO

Fast Cam Images Overlayed with Beam Pics

FAST CAM IMAGES OVERLAYED WITH BEAM PICS The lightning follows the laser path over 60 m Comparison of images a and b with 50 m scale bar.

High Speed Images of Upward Leaders

HIGH SPEED IMAGES OF UPWARD LEADERS a: with laser (t₁ = 250 µs, t₁ = 375 µs, t₁ = 915 µs, t₁ = 2750 µs) b: without laser (t₂ = 200 µs, t₂ = 400 µs, t₂ = 900 µs, t₂ = 3000 µs)

Measurement with the VHF Interferometer Imaging System

MEASUREMENT WITH THE VHF INTERFEROMETER IMAGING SYSTEM (LANGMUIR LABORATORY) With the laser on (L1) vs Without laser (N6) Average distance between the VHF emitting sources and the laser beam: Laser ON: 20.6 m Laser OFF: 28 m Reference: Stanley, M. A. et al. AGU Fall Meeting, December 1-17 2020

Measurement with the VHF Interferometer Imaging System - Detailed Analysis

MEASUREMENT WITH THE VHF INTERFEROMETER IMAGING SYSTEM (LANGMUIR LABORATORY) Height-resolved analysis comparing With the laser on (L1) and Without laser (N6) highlighting spatial confinement near the laser channel.

VHF Source Distance to Laser Filaments

VHF SOURCE DISTANCE TO LASER FILAMENTS • 0–60 m range above tower, the standard deviation of the distance of the sources to the laser is reduced by 45% when the laser is on. • Above 60 m, this reduction due to the laser filament is much weaker, as expected since the length of the filament is estimated to be 50–60 m. Histograms shown for intervals: 0-30 m (a), 30-60 m (b), 60-90 m (c) along beam propagation.

Conclusions

CONCLUSIONS • We study the effect of filaments formed by a TW laser working at kHz repetition rate on the initiation and propagation of upward lightning flashes above the Säntis tower • We observe evidence of laser guided lightning flashes over 50 m – One event recorded by 2 separate cameras and 3 events recorded by VHF interferometer • The fact that all laser events were of positive polarity can be explained by the stronger effect of filaments on the inception of positive lightning flash • These preliminary results should be confirmed by additional campaigns to obtain more statistics and test new configurations

Contact and References

Laser Lightning Rod Contact : [email protected] victor-moreno.com A. Houard, et al., “Laser Guided Lightning”, https://doi.org/10.48550/arXiv.2207.03769