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Measurements of X-Ray Emission from Laboratory Sparks and Upward Initiated Lightning
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In 1925 Nobel laureate R. C. Wilson predicted that high electric fields of thunderstorms could accelerate electrons to relativistic energies which are capable of generating high energetic radiation. The first detection of X-rays from lightning was made in 2001 and from long sparks in 2005. Still there are gaps in our knowledge concerning the production of X-rays from lightning and long sparks, and the motivation of this thesis was to rectify this situation by performing new experiments to gather data in this subject.

The first problem that we addressed in this thesis was to understand how the electrode geometry influences the generation of X-rays. The results showed that the electrode geometry affects the X-ray generation and this dependency could be explained using a model developed previously by scientists at Uppsala University. The other missing information was the distribution of energy. Using a series of attenuators, we observed how the X-ray photons were attenuated as a function of barrier thickness and using a simple model we obtained the average and the maximum energy of X-rays. 

All the studies conducted previously was based on the lightning impulses, but in switching impulses, the voltage waveform rises very slowly compared to lightning impulses, and according to some scientists the rate of rise is an important parameter in X-ray development. Our study showed that the switching impulses were as efficient as lightning impulses in generating X-rays even though the rate of rise of voltage in switching impulses was hundreds of times slower.

All the observations on X-ray generation from lightning by other scientists were based on either natural downward lightning flashes or triggered lightning in Florida. The first experiments to study the X-ray generation from upward lightning flashes systematically was conducted within this thesis work at Gaisberg Tower in Austria. The results showed that the X-ray emissions from these flashes were much weaker than the ones produced by either natural downward or triggered lightning. An attempt was made to explain this observation by invoking the possible differences in the charge distribution of leaders associated with the triggered lightning flashes in Florida and upward initiated lightning flashes at Gaisberg tower.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 58
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1618
Keywords [en]
X-ray, upward lighting, laboratory discharges, energy distribution
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-338158ISBN: 978-91-513-0204-1 (print)OAI: oai:DiVA.org:uu-338158DiVA, id: diva2:1171602
Public defence
2018-02-27, 80127, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2015-05026Available from: 2018-02-05 Created: 2018-01-08 Last updated: 2018-03-08
List of papers
1. X-rays from negative laboratory sparks in air: Influence of the anode geometry
Open this publication in new window or tab >>X-rays from negative laboratory sparks in air: Influence of the anode geometry
2017 (English)In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 190-194Article in journal (Refereed) Published
Abstract [en]

In this experimental work, the influence of the grounded anode geometry is studied on the X-ray production from the laboratory sparks in air at atmospheric pressure when a negative impulse voltage is applied to a high voltage rod which served as a cathode. The result shows that the smaller the diameter of the anode, the higher the energy of X-ray bursts. This observation can be explained by the mechanism that the encounter of negative and positive streamer fronts just before the final breakdown is the event that accelerates electrons to X-ray generating energies, but may not be the only mechanism that generates X-rays.

Keywords
X-rays, laboratory sparks, electrodes, runaway electrons
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-268859 (URN)10.1016/j.jastp.2016.07.012 (DOI)000395952000019 ()
Funder
Swedish Research Council, 621-2012-3300
Available from: 2015-12-10 Created: 2015-12-10 Last updated: 2018-01-08Bibliographically approved
2. Energy Distribution of X-rays Produced by Meter-long Negative Discharges in Air
Open this publication in new window or tab >>Energy Distribution of X-rays Produced by Meter-long Negative Discharges in Air
2017 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 8, no 12, article id 244Article in journal (Refereed) Published
Abstract [en]

The energy deposited from X-rays generated by 1 m long laboratory sparks in air created by 950 kV negative lightning impulses on scintillated detectors was measured. Assuming the X-ray energy detected in such sparks results from the accumulation of multiple photons at the detector having a certain energy distribution, an experiment was designed in such a way to characterize their distribution parameters. The detector was screened by a copper shield, and eight series of fifteen impulses were applied by stepwise increasing the copper shield thickness. The average deposited energy was calculated in each series and compared with the results from a model consisting of the attenuation of photons along their path and probable photon distributions. The results show that the energy distribution of X-ray bursts can be approximated by a bremsstrahlung spectrum of photons, having a maximum energy of 200 keV to 250 keV and a mean photon energy around 52 keV to 55 keV.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-335142 (URN)10.3390/atmos8120244 (DOI)000419179200014 ()
Available from: 2017-11-30 Created: 2017-11-30 Last updated: 2018-02-14Bibliographically approved
3. X-ray observations at Gaisberg Tower
Open this publication in new window or tab >>X-ray observations at Gaisberg Tower
Show others...
2018 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 9, no 1, article id 20Article in journal (Refereed) Published
Abstract [en]

We report the occurrence of X-rays at ground level due to cloud-to-ground flashes of upward initiated lightning from Gaisberg Tower in Austria which is located at a 1300 m altitude.  This is the first time that the X-rays from upward lightning from a tower top located in high altitude is observed. Measurement was carried out using scintillation detectors installed close to the tower top in two phases from 2011 to 2015. X-rays were recorded in three subsequent strokes of three flashes out of the total of 108 flashes recorded in the system during both phases. In contrast to the observations from downward natural or triggered lightning, X-rays were observed only within 10 µs before the subsequent return stroke. This shows that X-rays were emitted when the dart leader is in the vicinity of the tower top and hence during the most intense phase of the dart leader. Both the detected energy and the fluence of X-rays are far lower compared to X-rays from downward natural or rocket-triggered lightning. In addition to above 108 flashes, an interesting observation of X-rays produced by a nearby downward flash is also presented. The shorter dart-leader channels length in Gaisberg is suggested as a possible cause of this apparently weaker X-ray production.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338132 (URN)10.3390/atmos9010020 (DOI)000424095100019 ()
Funder
Swedish Research Council, 2015-05026
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-03-19Bibliographically approved
4. X-ray observations from laboratory sparks in air at atmospheric pressure under negative switching impulse voltages
Open this publication in new window or tab >>X-ray observations from laboratory sparks in air at atmospheric pressure under negative switching impulse voltages
Show others...
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present for the first time detection of X-rays from laboratory sparks created in air at atmospheric pressure by applying an impulse voltage with slow rise time. X-ray production from three different electrode configurations were studied. The results confirm, for the first time, the production of X-rays in gaps excited by switching impulses. Results also show that the slow rate of rise of the voltage from switching impulses does not have a significant influence on the production of X-rays. Additionally, the timing of the X-ray occurrence strengthens the possibility that the mechanism of X-ray production is related to the encounter between streamers of opposite polarity.

National Category
Meteorology and Atmospheric Sciences
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338135 (URN)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), IG2004-2031Swedish Research Council, 621-2009-2697Swedish Research Council, 621-2006-4299Swedish Research Council, 621-2012-3300
Available from: 2018-01-08 Created: 2018-01-08 Last updated: 2018-01-08

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