ICCD camera images negative streamers
T.M.P. Briels et al., used the 4 Quik E intensified CCD camera from Stanford Computer Optics to study the phenomena of positive and negative steamers.
The progression of a negative streamer imaged with a 4 Quik E ICCD camera. The exposure time of each picture is about 5ns. The gate delay is rising from (a) 4.4ns, (b) 9.3ns, © 14.3ns, (d) 19.6ns, (e) 28.8ns. Reprinted figure with permission from T. M. P. Briels et al, J. Phys. D: Appl. Phys., 41, 23, 2008. Copyright (2008) by IOP Publishing Ltd.
High speed ICCD cameras image the temporal progress of lightning.
ICCD cameras with a high resolution in space and a wavelength range from 200 to 800nm are perfectly suited for investigations of high speed phenomena like streamers. The 4 Quik E intensified camera has a built-in delay generator to synchronize it with the event to be recorded. This enables reasearcher, at the Technische Universiteit Eindhoven, to image the development of positive and negative streamers. Streamers are an atmospheric electrical discharge which are colloquially described as lightning or flash phenomena. With the intensified ultra high speed camera system, instantaneous diameters and, in particular, velocities of streamers can be measured with high accuracy.
Images of Positive and negative streamers
In nature, streamers of both polarities appear in many phenomena. However, industrial applications have largely focused on positive streamers. These cathode directed streamers are easier to create around sharp tips than anode directed (negative) streamers. This even has lead to a tendency in the applied physics and electrical engineering literature to use the term "streamer" as equivalent to "positive streamer".
Increasing interest in negative streamer
Even though positive steamers are in the focus of most applications, recent publications show the possibilities of negative streamers. Investigations with a new generation of pulsed power supplies have shown that negative streamers can convert pulsed electric energy into ozone. Moreover, negative DC-corona is used in dust precipitators to charge small particles that they can be drawn out of a gas stream by an electric field.
Steamers imaged by fast gated ICCD camera
The 4 Quik E intensified CCD camera from Stanford Computer Optics with ultra high shutter speed and a gating time down to 1.2ns enables the study high speed phenomena like streamers. Even the progression of streamers can be imaged with a delay time freely adjustable in 10ps steps. This can be seen in the figure below which shows the evolution of a negative streamer. The time delay between the images is roughly 5ns. The individual images show the expansion and propagation of negative streamer. Therefore, the diameter, the velocity and the dissipated energy of the streamer can be detected.
Title: Positive and negative streamers in ambient air: measuring diameter, velocity and dissipated energy
Author: T M P Briels, J Kos, G J J Winands, E M van Veldhuizen and U Ebert
Institute: Department of Applied Physics and Department of Electrical Engineering,
Technische Universiteit Eindhoven