Method for Recording Broadband High Resolution Emission Spectra of Laboratory Lightning Arcs
August 27th, 2019
Emission spectroscopy techniques have traditionally been used to analyze inherently random lightning arcs occurring in nature. In this paper, a method developed to obtain the emission spectroscopy from reproducible lightning arcs generated within a laboratory environment is described.
The overall goal of this experiment is to acquire the emission spectrum of a generated lightning arc. This method can help understand underlying lightning mechanisms, its interaction with the air, and its interaction with other elements within the surrounding environment. The main advantage of this technique is that it is non-intrusive and does not interfere with the lightning arc.
Helping me to demonstrate the procedure will be Chris Stone, the Lightning Laboratory manager. This experiment uses the lightning generator in the Morgan-Botti Lightning Lab of Cardiff University. The lightning is generated within an electromagnetic impulse-shielded chamber.
Inside the chamber, there is a lightning rig. The rig has supports for arc-generating electrodes. Two meters from the rig is a tripod supporting a small fiber optic.
The fiber is collimated and directed toward the discharge region. The fiber optic conducts light to a second chamber on top of the first;inside the chamber is a computer-controlled spectrograph system. The fiber optic terminates on the system's light-tight chassis.
The two chambers, the apparatus associated with each of them, and the connecting fiber are depicted in this schematic. The spectrograph system is based on a Czerny-Turner configuration with a focal length of 30 centimeters. Light from the fiber passes through an adjustable 100-micrometer slit.
Three mirrors and a rotatable grating reflect light into a digital camera operating at minus 70 degrees Celsius. The spectral resolution is 0.6 nanometers in a 140-nanometer subrange. Prepare electrodes made of an appropriate material.
This experiment uses a pair of tungsten hemispheres with a diameter of 60 millimeters. Preparing the electrodes requires lint-free cloths, a sonic water bath, and a range of sandpaper and polishing cloth grades. Clean one electrode at a time;begin with coarse sandpaper and rub the electrode for five minutes.
When done, place the hemisphere into a room-temperature sonic bath. After 10 minutes, wear clean gloves and remove the hemisphere. Wipe it off with a lint-free cloth.
Repeat the rub-and-clean process with finer grades of sandpaper. The aim is to remove contaminants and achieve a good polish for the experiment. When both electrodes are clean, take them to the chamber for mounting.
In this experiment, when mounted, the electrodes are separated by 14 millimeters. In the electrode chamber, position the fiber optic to view the center of the electrode gap. Via a control computer, start the spectrograph system and move its grating to the starting position of 450 nanometers, then place a calibration source at the open end of the fiber optic and turn it on.
On the control computer, optimize the signal and record the spectra. Turn off and remove the calibration source. Find the wavelengths for source's known peaks for calibration, in this case on the back of the device.
Enter these values into the spectrograph control software for automatic calibration. Continue by positioning the grating for its next subrange, which should overlap the first, then return the calibration source to the front of the fiber optic to calibrate this range. Repeat the calibration steps over the desired wavelength range.
For the experiment, close the electrode chamber door and ensure it is light tight. Next, go to the lightning generator control room. Make sure the door is secured.
Inside, switch on the lightning generator, then turn to the computers to control and monitor the experiment. Use software on the control computer to move the spectrograph grating to its start position of 450 nanometers, then use the camera to take a background image. Next select the waveform, in this case one with a 100-kilo-amp peak.
After ensuring the spectrograph will be triggered by the lightning event, start charging the system and monitor the charge level. When the charging is complete, the system is ready. Put on ear protection before starting a countdown.
Press the button to trigger the lightning. Soon after the arc, the lightning waveform will appear in the lightning generator control software. In addition, the spectra will appear in the spectrograph software.
Continue by taking three more measurements with the grating at 450 nanometers, then move the grating to its next position, 550 nanometers. Repeat measurements at this position and at each of the others in the desired range of wavelengths. These data are from a 100-kilo-amp laboratory-generated lightning arc.
It is the result of averaging the measured spectra of each subrange and stitching the subranges together. Here is the same data shown as an intensity plot with the prominent peaks identified through comparison to a database. Nitrogen, oxygen, argon, and helium lines appear due to their presence in the atmosphere.
Tungsten appears due to the electrode. Though this method can provide insight into generated lightning arcs, it can also be applied to other fast electrical discharges such as high-voltage partial discharge and sparking. After watching this video, you should have a good understanding of how to record lightning spectra from generated lightning arcs or from any other fast electrical discharge.
Overview
This study presents a method for acquiring the emission spectrum of laboratory-generated lightning arcs. The technique is non-intrusive and allows for detailed analysis of the lightning's interaction with the surrounding environment.
Key Study Components
Area of Science
- Emission spectroscopy
- Lightning phenomena
- Laboratory experimentation
Background
- Emission spectroscopy has been used to analyze natural lightning.
- Laboratory-generated lightning arcs provide reproducible conditions for study.
- The method allows for insights into the mechanisms of lightning.
- Non-intrusive techniques are essential for accurate measurements.
Purpose of Study
- To acquire the emission spectrum of generated lightning arcs.
- To understand the interaction of lightning with air and other elements.
- To develop a reliable laboratory method for studying lightning.
Methods Used
- Use of a lightning generator in a controlled environment.
- Fiber optic system to capture light from the discharge region.
- Calibration of the spectrograph system for accurate measurements.
- Data collection through multiple measurements across a range of wavelengths.
Main Results
- Emission spectra were successfully recorded from the lightning arcs.
- Identified spectral lines from nitrogen, oxygen, argon, and tungsten.
- Data showed the presence of atmospheric elements in the spectra.
- The method can be applied to other fast electrical discharges.
Conclusions
- The developed method provides valuable insights into lightning behavior.
- It can enhance understanding of fast electrical discharges.
- Future applications may extend beyond lightning to other phenomena.
Frequently Asked Questions
Executive Industry Relevance
This method enables reproducible, non-intrusive spectral analysis of high-energy electrical discharges, providing a controlled platform for studying plasma-material interactions relevant to electrical system reliability and failure analysis. By capturing broadband emission spectra with sub-nanometer resolution, it supports mechanistic de-risking in the design and validation of high-voltage components, insulation systems, and surge protection devices. The approach enhances predictive confidence in preclinical and translational evaluation of electrical stress models by delivering quantitative, database-verifiable elemental emission data.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of plasma chemistry and electrode material interactions under controlled, repeatable high-current discharge conditions.
- Operational Value: Provides a standardized, non-invasive optical method for real-time monitoring of arc dynamics without perturbing the discharge.
Screening & Assay Development
- Scientific Value: Generates quantitative, wavelength-resolved emission profiles that serve as fingerprint-like readouts for elemental composition and excitation states.
- Operational Value: Supports assay standardization through calibrated, stitchable subrange spectra with traceable resolution (<1 nm) and reproducibility across multiple arcs.
Translational & Preclinical Research
- Scientific Value: Facilitates continuity from bench-scale discharge modeling to real-world electrical stress scenarios by identifying atmospheric and electrode-derived emission signatures.
- Operational Value: Enables cross-platform validation of spectral databases and diagnostic algorithms for partial discharge monitoring in electrical apparatus.
Pipeline & Workflow Integration
The method integrates into electrical safety and materials testing workflows as a frontline diagnostic tool for characterizing discharge phenomena prior to mechanistic modeling or accelerated aging studies.
- Discovery Biology: Supports hypothesis testing of plasma-mediated material degradation pathways through direct optical emission readouts.
- Screening: Delivers reproducible, high-resolution spectral outputs suitable for automated peak identification and library matching.
- Analytics: Enables quantitative comparison of discharge conditions via intensity-calibrated spectral stitching and background subtraction.
- Translational Research: Connects laboratory arc characterization to field-relevant partial discharge and sparking phenomena in electrical systems.
- Enterprise Reuse: Establishes a reusable spectroscopic platform for evaluating multiple electrode materials, gap distances, and waveform profiles across test campaigns.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity in plasma-surface interactions by providing element-specific emission data validated against reference databases.
- Operational Value: Ensures standardization and scalability through fiber-coupled, computer-controlled spectrograph operation with automated grating positioning.
- Strategic Value: Improves go/no-go decisions in high-voltage system design by enabling early detection of undesirable electrode vaporization or insulation breakdown signatures.
- Portfolio Impact: Supports risk-adjusted advancement of insulation materials and surge protection components through objective, spectrally resolved failure mode discrimination.
Implementation Considerations
- Requires expertise in optical spectroscopy, plasma diagnostics, and high-voltage safety protocols.
- Dependent on Czerny-Turner spectrograph with UV-enhanced digital camera and sub-micron slit control.
- Necessitates electromagnetic shielding and light-tight enclosure to prevent signal contamination.
- Involves wavelength-stitching protocols requiring overlapping subrange calibration and intensity normalization.
- Limited to line-of-sight optical access; performance may be affected by particulate occlusion or window degradation in long-term use.
