77 research outputs found
X-Rays from long laboratory sparks in air
This collective book provides a review of research concentrated on runaway electron beams and X-rays in an inhomogeneous electric field with different gases at increased pressure. Attention is also given to supershort avalanche electron beam (SAEB) in the optimal conditions. New experimental techniques and equipment, including those with picosecond time resolutions, were required for diagnostics of electrical and optical signals. The book consists of twenty-four chapters, some of which were written jointly by researchers of different teams. Some chapters consider the range of SAEB applications.Postprint (published version
High-speed videos of laboratory leaders emerging from wind turbine blade tips
This paper presents some observation results of the
attachment test of a wind turbine blade as described in the
upgrade of the IEC-61400-24. The optical observations were
performed by means of high-speed video and UV-sensitive
photo camera. This study investigates the effects on the
leaders emerging from the blade comparing three different
air-terminals: discrete receptors, discrete receptors with
diverter strips and metallic tip. In the first two types, salt
mist pollution was applied to the blade. For non polluted
tips positive leaders appeared from receptors towards the
ground avoiding the blade surface. When the blade was
polluted additional leaders emerged moving horizontally.
Moreover, in this situation the leader progressed on the
blade surface. Pollution also produced the inception of more
leaders when the blade was equipped with discrete
receptors and diverter strips.Preprin
X-rays and microwave RF power from high voltage laboratory sparks
Lightning flashes involve high energy processes that still are not well understood. In the laboratory, high voltage pulses are used to produce long sparks in open air allowing the production of energetic radiation. In this paper X-rays emitted by long sparks in air are simultaneously measured with the RF power radiation at 2.4 GHz. The experiment showed that the measured RF power systematically peaks at the time of the X-rays generation (in the microsecond time scale). All of the triggered sparks present peaks of RF radiation before the breakdown of the gap. The RF peaks are related to the applied voltage to the gap. RF peaks are also detected in discharges without breakdown. Cases where X-rays are detected presented higher RF power. The results indicate that at some stage of the discharge, before the breakdown, electrons are very fast accelerated letting in some cases to produce X-rays. Microwave radiation and X-rays may come from the same process.Preprin
High-speed video recordings of lightning, electric fields and high-energy detections during thunderstorms in Catalonia Spain
High-speed video recordings of natural lightning flashes
show amazing details of this phenomenon. The paper
summarizes the results of the 2009 measurement campaign
where the combination of electric fields, total lightning,
high-energy detections and high-speed videos provided a
valuable data. The paper describes the visible differences
between the recorded negative, positive and upward cloudto-
ground flashes. Thanks to the precise time
synchronization of each video frame we investigated which
processes are detected by the lightning location networks
(VHF and VLF). We suggest that the VHF interferometer
network detects mostly those processes of intra-cloud
flashes where substantial charge is transferred during few
milliseconds. The study of the detections of intra-cloud
events provided by the VLF network were related to high
and fast (less than a millisecond) charge transfers within the
cloud that saturated the camera in the same manner as
return strokes in cloud-to-ground flashes. In other hand, the
paper discusses the high-energy detections related to a very
close cloud-to-ground lightning flash.Preprin
Winter lightning activity in specific global regions and implications to wind turbines and tall structures
The paper presents winter lightning maps on specific regions in the northern hemisphere. Four different degrees of winter lightning activity are defined based on information derived from Japanese case. Based on this reference case it is possible to determine regions where winter lightning can be a threat to specific structures. Guidance on risk assessment to tall structures and wind turbines are described as well.Preprin
Global distribution of winter lightning: a threat to wind turbines and aircraft
Lightning is one of the major threats to multi-megawatt wind turbines and a concern for modern aircraft due to the use of lightweight composite materials. Both wind turbines and aircraft can initiate lightning, and very favorable conditions for lightning initiation occur in winter thunderstorms. Moreover, winter thunderstorms are characterized by a relatively high production of very energetic lightning. This paper reviews the different types of lightning interactions and summarizes the well-known winter thunderstorm areas. Until now comprehensive maps of global distribution of winter lightning prevalence to be used for risk assessment have been unavailable. In this paper we present the global winter lightning activity for a period of 5 years. Using lightning location data and meteorological re-analysis data, six maps are created: annual winter lightning stroke density, seasonal variation of the winter lightning and the annual number of winter thunderstorm days. In the Northern Hemisphere, the maps confirmed Japan to be one of the most active regions but other areas such as the Mediterranean and the USA are active as well. In the Southern Hemisphere, Uruguay and surrounding area, the southwestern Indian Ocean and the Tasman Sea experience the highest activity. The maps provided here can be used in the development of a risk assessment.Peer ReviewedPostprint (published version
High-speed observations of transient luminous events and lightning (The 2008/2009 Ebro Valley campaign)
Preprin
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