Ebert, U. (Ute)

Nijdam, S. (Sander)

Takahashi, E.

Trienekens, D.J.M. (Dirk)

English

Nijdam, Sander

Trienekens, Dirk

Ebert, Ute

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Multi-dimensional experimental studies on streamers

Nijdam, S.

Trienekens, D.J.M.

Ebert, U.M.

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CWI's Institutional Repository

ESCAMPIG XXII, Greifswald, Germany, July 15-19, 2014 Topic number: 6Multi-dimensional experimental studies on streamersS. Nijdam(∗)1, D.J.M. Trienekens1, E. Takahashi2, U. Ebert1,31 Eindhoven University of Technology, Dept. Applied PhysicsP.O. Box 513, 5600 MB Eindhoven, The Netherlands2 National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan3 Centrum Wiskunde & Informatica, Amsterdam, The Netherlands(∗) s.nijdam@tue.nlAbstractPrecise space and time resolved imaging of propagating streamers can be very challenging due theirstochastic nature and high propagation velocities. I will discuss two techniques to improve streamerimaging above what can be achieved with the ubiquitous standard ICCD method. The first of thesetechniques is stereo imaging with one ICCD-camera. This method can image the three-dimensionalpath of streamers in great detail. The second technique that I will discuss is stroboscopic imagingwhere the gate of an ICCD camera is repeatedly opened and closed with a frequency up to 110MHz.Together these techniques can give a complete insight in the time-dependent position of a propagat-ing streamer head. This is a valuable tool to understand the physics governing the propagation ofstreamers and their interaction with each other, background ionization density or dielectric surfaces.In nearly all streamer discharges the streamers are following complex paths, while the duration ofpropagation is generally in the order of a few hundred nanoseconds or less. Advanced diagnostic methodsare required to capture all details of such fast three-dimensional phenomena. One of these methods isstereo-photography with one ICCD-camera. This technique was first employed by us to measure thebranching angle of streamers in air [1]. Recently this technique has been used by others as well [2, 3].(a) (b)Figure 1: (a) Stereo photography set-up as used in [1]. It contains, from left to right, the vacuum vessel withpointed tip above the plate, the stereo-photography set-up and the ICCD camera. The approximate center lines ofboth optical paths are also shown. (b) Stereo image of a streamer discharge as imaged by this set-up. Settings:positive voltage on tip, Vmax =+47 kV, p= 200mbar, point-plane gap of 140mm. Images from [1].The stereo-photography set-up used by us is shown in figure 1a. With it, streamer discharges in airat pressures between 200 and 1000mbar were imaged. This was achieved by placing a combination oftwo prisms and two mirrors between the discharge and the ICCD camera. This allowed us to capture twoimages from slightly different directions at once, as is shown in figure 1b. This image shows two nearidentical views from which we can reconstruct the full three-dimensional structure of the discharge. Anexample of such a reconstructed image is given in figure 2.Stereo-photography can also be used to check if phenomena that are observed in 2D streamer imagesactually occur or are artefacts caused by the projection. An example of this is visible in figures 1b and 2.In figure 1b two streamer sections are marked with a white line. It appears that this section is makes acurve and then reconnects with the ’main branch’ of the discharge. However, the reconstruction shown inESCAMPIG XXII, Greifswald, Germany, July 15-19, 2014Figure 2: Orthogonal views of the 3D reconstruction of streamer structure shown in figure 1. The section origi-nally marked with the white line is now marked with an arrow in both views. Image from [1].Figure 3: Schematic overview of the set-up including, from left to right, the ICCD camera, stereoscopic set-upand vacuum vessel with indication of laser beam path. In the presented images the recorded images are rotatedanti-clockwise by 90◦ so that the electrode tip is shown on top.figure 2 reveals that this apparent reconnection is caused by the image projection and in fact is a streamermoving almost perpendicular to the image plane.Recently we have used stereo-photography to test the effects of low levels of pre-ionization on thepropagation of streamers [4]. Here we have used a KrF excimer laser to create a trail of increased back-ground ionization in oxygen-nitrogen mixtures. The estimated density of background ionization pro-duced by the laser is about 8 ·108 cm−3 in 133mbar pure nitrogen. The size of the trail is approximately9 by 10mm2.For this experiment we have used a similar stereo-photography set-up as is described above, but nowrotated 90◦ with respect to the point-plane geometry (see figure 3). This allows us to accurately determinethe position of streamers that run horizontally (i.e., parallel to the plane) in contrast to the original set-upwhich can better determine the positions of streamers that roughly run in the vertical direction.1234a−5 0 50510z (mm)y (mm)124 3bFigure 4: (a) Example of stereo-photography image with the laser trail indicated by the purple lines and the anodetip indicated in green. Experimental settings: gas fill: 133mbar pure nitrogen; 103mm point plane geometry;Vmax = +5.9 kV. Measured parts of the streamer trails are indicated by numbers. b) Plot of the position of thenumbered streamer trails with respect to the laser beam position (marked by the purple rectangle). The marker sizeindicates their x-position.An example of a streamer of which the path is deflected by the laser beam is shown in figure 4a. ThisESCAMPIG XXII, Greifswald, Germany, July 15-19, 2014image is a composite of the two original image parts (looking slightly from above and below) which arerepresented in red and cyan respectively. Streamers that appear at the same position in both images arerepresented in white and move in the plane of the image. The figure shows that the streamers are indeedaffected by the pre-ionization trail left by the laser. In fact, many of the channels follow this trail insteadof taking a more direct route towards the plane electrode below. The position of the numbered sectionswith respect to the laser beam in figure 4a is plotted in figure 4b. Together, these two figures showthe strength of stereo-photography by clearly proving that the numbered streamer sections are actuallyguided by the laser pre-ionization.Even though all experiments discussed above do give the exact positions of streamer trails, they giveno information about the development of streamer velocity or other time-resolved properties. Unfortu-nately, no practical and affordable camera is fast enough to shoot multiple frames during the propagationof a streamer as this would require a frame-rate of at least 20 million frames per second (and preferablymore). This can be partly remedied by using multiple image paths [5, section 2.3.3] or multiple cameras.Both methods have the disadvantage that only a very small number of frames (4) can be used. Alterna-tively, it is possible to measure the development by acquiring many images of different discharge events.This method was recently employed by Clevis et al. [6] and improved by Heijmans et al. [7]. However, itonly works for very reproducible discharges or to investigate reproducible phenomena in more stochasticdischarges.A technique that can give direct insight into the time and space resolved velocity distribution ofpropagating streamers is stroboscopic imaging. This can be achieved with an ICCD camera of which thegate can be opened and closed at high repetition rates. This technique has been first used by Pancheshnyiet al. [8] and has recently been used more extensively by us [9]. We use a LaVision PicoStar HR12camera that can be gated with a maximum frequency of 110MHz. Because the propagating streamers inair and other nitrogen-oxygen mixtures only emit radiation from the streamer head and decay times areshort, images made in this way will look like a string of beads. An example of such an image is shownin figure 5.Figure 5: Stroboscopic image of streamer discharge with a surface component in 60mbar ambient air with a10 kV positive voltage pulse imaged with a gating frequency of 50MHz at a 50% duty cycle. The anode tip andthe dielectric rod are shown in white. Image from [9].Here a streamer discharge in the vicinity of an epoxy rod is imaged. The relative velocity of eachstreamer section can be easily deduced from this image. This shows that the streamers propagate fasteralong the dielectric rod than through the bulk gas.The present stroboscopic images are made without a stereo-photography set-up. Therefore veloc-ities of streamers which are propagating out of the image plane will be underestimated. This can beremedied by combining stroboscopic imaging with stereo-photography. Together this can give a fullthree-dimensional, time-resolved image of streamer propagation in a single discharge.Figure 6 contains such a combined stereoscopic stroboscopic image. In this experiment a dielectricplate with dimensions 150× 30× 2mm3 is placed nearly vertical below and to the side of the tip. Theleft part of the stereoscopic image is directed at the side of the plate while the right part is looking slantedonto the surface of the plate. The angle between both views is approximately 20◦.ESCAMPIG XXII, Greifswald, Germany, July 15-19, 2014Figure 6: Stroboscopic stereo image of streamer discharge with a surface component in 200mbar ambient air withabout 21 kV positive voltage pulse imaged with a gating frequency of 50MHz at a 50% duty cycle. A dielectricplate with dimensions 150× 30× 2mm3 is placed below and to the side of the tip. The approximate location ofthis plate is shown in white in the left side view. Image from [9].In this figure some of the most prominent streamers propagate over the surface of the dielectric plate.These streamers show branching with some of the branches continuing on the surface itself while other,shorter, branches propagate away from the surface. Again the streamers on the surface have a higherpropagation velocity than the bulk gas streamers.Even without detailed three-dimensional reconstruction or exact velocity measurements this imageshows the potential of the combination of imaging techniques.This research is supported by the Dutch Technology Foundation STW, which is part of the Nether-lands Organisation for Scientific Research (NWO), and which is partly funded by the Ministry of Eco-nomic Affairs and for this project is partly funded by ABB Corporate Research.References[1] S. Nijdam, J. S. Moerman, T. M. P. Briels, E. M. van Veldhuizen, and U. Ebert. Stereo-photography ofstreamers in air. Appl. Phys. Lett., 92:101502, 2008.[2] M. Kocik, M. Tan´ski, J. Mizeraczyk, R. Ichiki, S. Kanazawa, and J. Dembski. Reconstruction of 3D structureof positive corona streamer by local methods. In Hakone XII, 12th International Symposium on High PressureLow Temperature Plasma Chemistry, 2010.[3] Ryuta Ichiki, Seiji Kanazawa, Kosuke Tomokiyo, Shuichi Akamine, Marek Kocik, and Jerzy Mizeraczyk.Investigation of three-dimensional characteristics of underwater streamer discharges. Japanese Journal ofApplied Physics, 51(10R):106101, 2012.[4] S. Nijdam, E. Takahashi, J.. Teunissen, and U. Ebert. Laser guiding of streamers by extremely weakly ionizedchannels. 2014. In preparation.[5] S. J. Voeten. Matching high voltage pulsed power technologies. PhD thesis, Eindhoven University of Techno-logy, 2013. Available online at http://alexandria.tue.nl/extra2/750268.pdf.[6] T.T.J. Clevis, S. Nijdam, and U. Ebert. Inception and propagation of positive streamers in high-purity nitrogen:effects of the voltage rise rate. Journal of Physics D: Applied Physics, 46(4):045202, 2013.[7] L.C.J. Heijmans, S. Nijdam, E.M. van Veldhuizen, and U. Ebert. Investigation of the inception cloud ofpositive streamers in air. In Proceedings of the 31st International Conference on Phenomena in Ionized Gases(ICPIG 2013), 14 - 19 July 2013, Granada, Spain, 2013.[8] S. Pancheshnyi, M. Nudnova, and A. Starikovskii. Development of a cathode-directed streamer discharge in airat different pressures: Experiment and comparison with direct numerical simulation. Phys. Rev. E, 71:016407,2005.[9] D.J.M. Trienekens, S. Nijdam, and U. Ebert. Stroboscopic imaging of streamer discharges with a surfacecomponent. IEEE T. Plasma. Sci., 2014. Revision submitted.

Multi-dimensional experimental studies on streamers

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