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Conference: Bucharest University Faculty of Physics 2008 Meeting

Section: Optics, Spectroscopy, Plasma and Lasers

Title:

Determination of “true values” of dissipated power and other electrical parameters in radiofrequency expanding plasma discharges

Authors:

E. R. Ionita1, T. Acsente1, G. Dinescu1, E. Amanatides2, D. Mataras2

Affiliation:

1National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Street, Magurele MG-36, RO 77125, Bucharest, Romania

2Laboratory of Plasma Chemistry, Department of Chemical Engineering, University of Patras, P.O. Box 1407, 26500 Patras, Greece

E-mail

dinescug@infim.ro

Keywords:

radio-frequency plasma jets, plasma sources, atmospheric pressure plasmas, electrical measurements

Abstract:

Radio-Frequency discharges are widely used in plasma processing technologies. It is very important for this kind of plasmas to have correct electrical measurements at least for two reasons: i) for investigation of fundamental plasma processes; and ii) for monitoring the plasma processing (deposition, etching, treatment, etc.). The control of discharge reproducibility is based on measurement of power dissipated in plasma, this parameter being a critical one. Moreover, the impedance measurements can be used to optimize the power transfer. Other useful parameters which can be evaluated are: the electron density, dark region width, ion energy, ion current. However, in spite of all advantages and a low cost the electrical measurements are invasive and affected by errors (at 13.56 MHz the stray impedance may be large, the signals are delayed and the phase shifts due to the probes and cables are important). The goal of this work was to find the value of dissipated power and other electrical parameters in an atmospheric pressure radiofrequency expanding plasma source. The plasma source has shown its potential in cleaning carbon films from surfaces, and is prospective tools for removal of co-deposited layers and de-tritiation of fusion machines. To eliminate errors as has been stated above and to increase the accuracy in measuring of current and voltage waveform we used the so named “shunt method” which was already used in low pressure discharges. The method consists in a tunable LC shunt circuit connected parallel with discharge to minimize the displacement current. As a result of the shunt method we have found that the power dissipated in plasma is about 70% from the forwarded power. The total impedance decreases with the power increase from 45 Ohm at dissipated power of 20 Watts to 10 Ohm at a dissipated power of 120 Watts.