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Hettiarachchi, PasanORCID iD iconorcid.org/0000-0003-1377-1923
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Publications (10 of 27) Show all publications
Rahman, M., Hettiarachchi, P., Cooray, V., Dwyer, J., Rakov, V. & Rassoul, H. (2019). Observations of X-rays from Laboratory Sparks in Air at Atmospheric Pressure under Negative Switching Impulse Voltages. Atmosphere, 10(4), Article ID 169.
Open this publication in new window or tab >>Observations of X-rays from Laboratory Sparks in Air at Atmospheric Pressure under Negative Switching Impulse Voltages
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2019 (English)In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 10, no 4, article id 169Article in journal (Refereed) Published
Abstract [en]

We present observations of X-rays from laboratory sparks created in the air at atmospheric pressure by applying an impulse voltage with long (250 µs) rise-time. X-ray production in 35 and 46 cm gaps for three different electrode configurations was studied. The results demonstrate, for the first time, the production of X-rays in gaps subjected to switching impulses. The low rate of rise of the voltage in switching impulses does not significantly reduce the production of X-rays. Additionally, the timing of the X-ray occurrence suggests the possibility that the mechanism of X-ray production by sparks is related to the collision of streamers of opposite polarity.

Keywords
X-rays, high energy radiation, laboratory sparks, switching impulse
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-338135 (URN)10.3390/atmos10040169 (DOI)000467313400008 ()
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: 2020-01-08Bibliographically approved
Chandimal, L., Hettiarachchi, P., Nanayakkara, S., Sapumanage, N., Fernando, M., Cooray, V. & Rahman, M. (2018). Impedance behaviour of earth enhancing compound under lightning transient conditions. In: : . Paper presented at 34th International Conference on Lightning Protection, 2-7 Sept., 2018, Rzeszow, Poland.
Open this publication in new window or tab >>Impedance behaviour of earth enhancing compound under lightning transient conditions
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-368793 (URN)
Conference
34th International Conference on Lightning Protection, 2-7 Sept., 2018, Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-07Bibliographically approved
Hettiarachchi, P. (2018). Measurements of X-Ray Emission from Laboratory Sparks and Upward Initiated Lightning. (Doctoral dissertation). Uppsala: Acta Universitatis Upsaliensis
Open this publication in new window or tab >>Measurements of X-Ray Emission from Laboratory Sparks and Upward Initiated Lightning
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
X-ray, upward lighting, laboratory discharges, energy distribution
National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-338158 (URN)978-91-513-0204-1 (ISBN)
Public defence
2018-02-27, 80127, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2015-05026
Available from: 2018-02-05 Created: 2018-01-08 Last updated: 2018-03-08
Sapumanage, N., Nanayakkara, S., Abeygunawardena, S., Chandimal, L., Hettiarachchi, P., Fernando, M. & Cooray, V. (2018). Study on responses of SPDs against the transient voltages generated by CG flashes. In: : . Paper presented at 34th International Conference on Lightning Protection,Rzeszow, Poland, 2-7 Sept, 2018.
Open this publication in new window or tab >>Study on responses of SPDs against the transient voltages generated by CG flashes
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368799 (URN)
Conference
34th International Conference on Lightning Protection,Rzeszow, Poland, 2-7 Sept, 2018
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-14Bibliographically approved
Arevalo, L., Wu, D., Hettiarachchi, P., Cooray, V., Lobato, A., Rahman, M. & Wooi, C.-L. (2018). The leader propagation velocity in long air gaps. In: : . Paper presented at 34th International Conference on Lightning Protection, 2-7 Sept, 2018,Rzeszow, Poland.
Open this publication in new window or tab >>The leader propagation velocity in long air gaps
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2018 (English)Conference paper, Published paper (Refereed)
National Category
Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:uu:diva-368783 (URN)10.1109/ICLP.2018.8503329 (DOI)
Conference
34th International Conference on Lightning Protection, 2-7 Sept, 2018,Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-14Bibliographically approved
Hettiarachchi, P., Lobato, A., Cooray, V. & Leijon, M. (2018). Time Domain Analysis of the Lightning Interaction with Wave Energy Converters. In: : . Paper presented at 34th International Conference on Lightning Protection, 2-7 Sept, 2018,Rzeszow, Poland.
Open this publication in new window or tab >>Time Domain Analysis of the Lightning Interaction with Wave Energy Converters
2018 (English)Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-368794 (URN)
Conference
34th International Conference on Lightning Protection, 2-7 Sept, 2018,Rzeszow, Poland
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2019-03-14Bibliographically approved
Hettiarachchi, P., Cooray, V., Diendorfer, G., Pichler, H., Dwyer, J. & Rahman, M. (2018). X-ray observations at Gaisberg Tower. Atmosphere, 9(1), Article ID 20.
Open this publication in new window or tab >>X-ray observations at Gaisberg Tower
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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
Johari, D., Cooray, V., Rahman, M., Hettiarachchi, P. & Ismail, M. M. (2017). Characteristics of leader pulses in positive ground flashes in Sweden. Electric power systems research, 153, 3-9
Open this publication in new window or tab >>Characteristics of leader pulses in positive ground flashes in Sweden
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2017 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 153, p. 3-9Article in journal (Refereed) Published
Abstract [en]

This paper presents the characteristics of the electric field pulses observed during leader propagation in positive ground flashes. We analysed in detail the electric field changes occurring just before the first return stroke in 51 positive ground flashes during 2014 summer thunderstorms in Uppsala, Sweden. Pronounced leader pulses (having the same polarity as the return stroke) were observed in 22% of the cases. They were observed to occur within 1.4 ms before the first return stroke. Interpulse duration ranged from 13.3 to 50.3 μs with a mean value of 24.7 μs. The peak amplitude of the leader pulses relative to the return stroke peak ranged from 2.7 to 17.8%. The presence of these pulses shows that the leaders propagate in a stepped manner. Based on the leader pulses’ time of initiation and average speed of the leader, the distance travelled by the leader was also estimated. One case of positive ground flash preceded by opposite polarity leader pulses just before the return stroke is also reported. To the best of our knowledge, this is the first time that such a case in positive ground flashes is reported. We suggest that these opposite polarity leader pulses are due to the negatively-charged leader branch of a bi-directional leader inside the cloud that propagates towards observation point.

National Category
Meteorology and Atmospheric Sciences Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-293059 (URN)10.1016/j.epsr.2016.11.026 (DOI)000413380500002 ()
Available from: 2016-05-11 Created: 2016-05-11 Last updated: 2019-07-16Bibliographically approved
Hettiarachchi, P., Cooray, V., Rahman, M. & Dwyer, J. (2017). Energy Distribution of X-rays Produced by Meter-long Negative Discharges in Air. Atmosphere, 8(12), Article ID 244.
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
Johari, D., Cooray, V., Rahman, M., Hettiarachchi, P. & Ismail, M. M. (2017). Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements. Electric power systems research, 150, 55-62
Open this publication in new window or tab >>Features of the First and Subsequent Return Strokes in Positive Ground Flashes based on Electric Field Measurements
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2017 (English)In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 150, p. 55-62Article in journal (Refereed) Published
Abstract [en]

This paper presents the characteristics of the electric fields produced by the first and the subsequent return strokes observed in positive ground flashes in Sweden. Fifty one positive ground flashes containing 60 return strokes recorded during 2014 summer thunderstorms were analyzed. In our analysis, only 12% of the cases were multiple-stroke while 88% were single-stroke. On average, the number of strokes per flash was 1.20 and the highest number of strokes per flash recorded was four. The geometric mean (GM) value of the interstroke interval was 60 ms while the distance between the first and the subsequent strokes ranged between 4.9 and 46.4km. We found that the average duration of the subsequent strokes parameters were smaller than that of the first strokes. For the first strokes, the GM values of the slow front duration, the fast transition 10-to-90% risetime, the zero crossing time, the zero-to-peak risetime and the 10-to-90% risetime were 8.7 mu s, 1.4 mu s, 29 mu s, 11 mu s and 5.7 mu s, respectively while for the subsequent strokes, the values were 4.0 mu s 0.91 mu s, 11 mu s 5.8 mu s and 3.2 mu s, respectively. Possible reasons for the shorter duration of the subsequent return strokes parameters were discussed.

National Category
Meteorology and Atmospheric Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Atmospheric Discharges
Identifiers
urn:nbn:se:uu:diva-317450 (URN)10.1016/j.epsr.2017.04.031 (DOI)000403744100006 ()
Available from: 2017-03-14 Created: 2017-03-14 Last updated: 2017-10-20Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1377-1923

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