scholarship report milenka_andjelic 03/2014

8/15/2019 Scholarship Report Milenka_Andjelic 03/2014

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Regionalbüro | Regional OfficeInnsbruck

Zl.: ICM-2013-05166

CEEPUS, CIII-AT-0063

SCHOLARSHIP R EPORT

Name Milenka ANDJELIC

Nationality MONTENEGRO

Date of birth 09.10.1992

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During my stay I have been working on the hollow cathode (HC) device which creates plasma

with many applications, such as: intensive light and spectroscopic light sources, electron beam

sources for the laboratory and space applications. One of the most important technological applica-

tions is producing thin films.

The main work consisted in the characterization of this type of plasma by two methods: opti-

cal and electrical. In first experiment, I observed the difference between the HC discharge in Ar and in

He as working gases by identifying the atomic lines using NIST Atomic Spectra Database, and the

evolution of those lines according to the intensity of the applied current.

For those experiments we used a hollow cathode system (Figure 1.) which consists of one ti-

tanium HC with a length of 30 mm, the inner diameter of 5mm and an outer diameter of 10 mm. The

cathode is covered by a ceramic cylinder in order to isolate it. We worked at a constant flow of gas (Ar

or He). The HC was connected to a high voltage power supply while the anode was connected to the

ground. (Figure 1.a.) With this configuration we obtained a high density plasma which is shown in

Figure 1 b.

a) b)Fig. 1. a) Experimental setup of hollow cathode discharge, b)the picture of HC plasma

For the optical diagnostics of plasma we used an optical fibre, and in order to acquire the

global spectra we used an Ocean optic spectrometer. In Figure 2 we present two optical spectra of

the HC discharges with the Ti cathode in Ar working gas in the first case, and in He working gas in the

second case (experiment). The lines were identified using NIST Atomic Spectra Database.

01.03.2014 31.03.2014

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a) b)Fig. 2. Typical optical spectrum of hollow cathode discharges with Ti cathode in a) Ar and b) He work-

ing gas.

These experiments were performed for the same pressure (6,4∙10

–2

mbar) and for the same inten-sity of the current (45 mA) for both Ar and He working gases.

To see the evolution of those line intensities with respect to the applied current, we kept the pres-

sure constant at a value of 6,4∙10 –2 mbar and we changed the current from 10 mA to 45 mA for both

working gases Ar and He.

a) b)

Fig. 3. Intensity of the light emitted by plasma function of the current discharge in a) Ar and b) Heworking gas.

In Figure 3 can be seen that the intensity of the light emitted by the plasma increases when

we raise the value of the current intensity.

To make electrical diagnostics of plasma I built a Langmuir probe which we inserted in plasma

to acquire the current-voltage characteristic using a Keithley sourcemeter.





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Fig.4. I-V characteristic of the hollow cathode plasma

The discharge current was 30 mA and the working pressure was 2,3∙10 –1mbar. We worked ata constant flow of Ar gas. From the first derivative of the plasma I-V characteristic we find the plasma

potential V p = –0,64 V and from the slope of the semi-logarithmic representation of the I-V character-istic, i.e. ln(I )=f(V ), we find the electron temperature to be T e = 1,43 eV.

Innsbruck, 27.03.2014

Confirmed by Confirmed by

_______________________________________________ ______________________________________________(Univ.Prof.i.R.Dr. Roman SCHRITTWIESER)Datum, Unterschrift, Stempel des Instituts

(Milenka ANDJELIC)date, signature


scholarship report milenka_andjelic 03/2014

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