"plasma bullets" imaged with ultra high speed photography

R. Bussiahn, et al., from the Leibniz Institute for Plasma Science and Technology (INP) used the 4 Quik E ICCD camera to investigate the propagation velocity of "plasma bullets" within the effluent of an atmospheric pressure plasma jet in argon atmosphere.

Image of the atmospheric pressure plasma jet with long integration

A photograph of the atmospheric pressure plasma jet in argon atmosphere, as it appears to the human eye. In this time integrated image the most intensive area of light emission appears in the interelectrode space where the active discharge occurs. Directly at the nozzle exit a bright channel follows. This is the visible effluent surrounded by a pale sheath. Reprinted figure with permission from R. Bussiahn, et al., J. Phys. D: Appl. Phys. 43 (2010) © IOP Publishing. All rights reserved.

The effluent of atmospheric pressure plasma jets show "plasma bullets"

Over the past years non-thermal atmospheric pressure plasma jets have attracted a wide range of applications. A few examples are plasma activation of surfaces for adhesion control, surface cleaning, deposition of functional coatings or biomedical appliances. With the increasing interest a growing number of publications deal with the temporal and spatial development of atmospheric pressure plasma jet effluents. Recent reports show, that the plasma in the effluent is formed by fast-moving "plasma bullets" with velocities of more than 10 km/s. In the present work, the simultaneous existence of plasma bullets and metastable argon atoms outside of an atmospheric pressure plasma jet is reported.

Experimental Setup of the atmospheric pressure plasma jet

The experimental setup consists of a central stainless steel rod electrode inside of a quartz capillary. The inner electrode is powered by a sinusoidal amplifier which also triggers the ICCD camera while the gas flows through the capillary. A laser atom absorption spectroscopy was used to determine relative particle number densities of excited species. Time resolved photographs of the effluent from the plasma jet were taken by the 4 Quik E ICCD camera applying an exposure time of 40ns. The delay time of the intensified CCD camera was related to the leading edge of the first current pulse. A step size of 40ns from pictrue to picture was chosen to image the emission processes in the effluent. The following pictures show the three current pulses which launch the atmosphere pressure plasma jets.

The current pulses of the atmospheric pressure plasma jet.

The three current pulses in the anode phase of the discharge and the related curve of the total discharge current with open squares, indicating the times to which the images below are taken by the 4 Quik E ICCD camera. Reprinted figure with permission from R. Bussiahn, et al., J. Phys. D: Appl. Phys. 43 (2010) © IOP Publishing. All rights reserved.

"plasma bullets" recorded with time resolved photography

At the beginning of the first current pulse a "plasma bullet" starts from the tip of the inner electrode. After 80ns a second bullet appear whereas the first one travels with a speed of 6 km/s out of the capillary and finally disappears. In below figures (b) the discharge activity during the second and largest current pulse is shown. Contrary to the pre-discharge phase a strong discharge develops between the two electrodes. No visible plasma exists outside of the capillary.

Time resolved images of the plasma bullet.

This is a sequence of images taken for each current pulse at different delay times from the start of the first discharge pulse. Reprinted figure with permission from R. Bussiahn, et al., J. Phys. D: Appl. Phys. 43 (2010) © IOP Publishing. All rights reserved.

The behaviour during the third current pulse seems to be similar to the results observed for the pre-discharge phase. A spatio-temporally extended plasma bullet comes of the tip of the inner electrode and leaves the quartz capillary. The more the plasma departs from the nozzle, the bullet gets compressed in axial direction. For the first 240ns the evaluation of the images provides a mean propagation velocity of 20 km/s and after that time a value of 5 km/s.

Conclusion of the atmospheric pressure plasma jet experiment

The time resolved photography using the 4 Quik E ICCD camera enables the demonstration and verification of luminous effects in the effluent of an atmospheric pressure plasma jet with an argon gas flow into ambient air, the so called "plasma bullets". R. Bussiahn, et al., showed the behaviour of such "plasma bullets" and determine the propagation velocity of the "plasma bullets" with up to 20km/s.

Title: Spatially and temporally resolved measurements of argon metastable atoms
in the effluent of a cold atmospheric pressure plasma jet
Author: R. Bussiahn, E. Kindel, H. Lange and K.-D. Weltmann
Institute: Leibniz Institute for Plasma Science and Technology (INP), Greifswald, Germany

Title: Back and forth directed plasma bullets in a helium atmospheric pressure
needle-to-plane discharge with oxygen admixtures
Author: T. Gerling, A. V. Nastuta, R. Bussiahn, E. Kindel and K.-D. Weltmann
Institute: Leibniz Institute for Plasma Science and Technology (INP), Greifswald, Germany