Title of Thesis

Investigation of Plasma Parameteers in Ne-N2 Mixture Discharge with 13.56 MH2RF Generator

Author(s)

Najeeb-ur-Rehman

Abstract
Non-LTE Ne-N2 (Local thermal equilibrium) mixture plasma is characterized to evaluate the electron temperature (Te) and Excitation temperature (Texc). The investigated plasma is of density range (109 to 1010 cm-3), thus it belongs to corona balance. Optical emission spectroscopy (OES) is used to calculate the electron temperature and excitation temperature. Ne-I lines are employed to calculate the electron temperature and excitation temperature. The effective principal quantum numbers ‘ k p ’ of the selected Ne-I lines, are less than 7 for the above mentioned density range, which confirm that the corona balance is the most probable balance. Modified Boltzmann plot is employed to estimate the electron temperature, whereas simple Boltzmann plot is used to calculate the excitation temperature. Langmuir probe has also been used to measure the plasma parameters e.g., electron temperature (Te), electron number density (ne), plasma potential (Vp) and electron energy distribution function (EEDF).
Electron temperature (Te) measured from Ne-I lines, by employing modified Boltzmann plot technique, is also compared with Langmuir probe results. In both techniques the trend is same i.e., electron temperature increases with increase in Ne % and RF power in the mixture and it decreases with increase in filling pressure. It is also observed that electron temperature (Te) measured with Langmuir probe is slightly greater than electron temperature (Te) measured with modified Boltzmann plot method. Generally, excitation temperature (Texc) is greater than electron temperature (Te).This fact is also observed in the characterization of the Ne-N2 mixture plasma.
EEDFs in Ne-N2 mixture plasma are measured as a function of Ne %, filling pressure and RF power. It is observed that the tails of the EEDF gain height and extend towards the higher energy with increase in Ne %, which confirms that population of high energy electrons increases with increase in Ne % in the mixture. Electron number density (ne) is also calculated and results show that ‘ne’ decreases with Ne %. Optical emission spectroscopy (OES) is used to investigate the effect of neon mixing on the vibrational temperature of second positive ( 3 ,ν ′→ 3 ,ν ′′) 2 u g N C Π B Π and first negative ( Σ+ ν ′→ Σ+ ν ′′) + 2 , 2 , 2 u g N B X system of nitrogen plasma generated by 13.56 MHz RF generator. The relative changes in vibrational population of ( 3 ) 2 u N C Π and Σ+ + N (B 2 u ) 2 states with neon mixing are monitored by measuring the emission intensities of second positive and first negative system of nitrogen molecules. Vibrational temperature is calculated for the sequences Δν = 0, -1 and -2, that follows the Boltzmann distribution. It is found that electron temperature as well as vibrational temperature of second positive and first negative system can be raised significantly by mixing of neon in the nitrogen plasma.Vibrational temperature of second positive system is raised up to 0.67 eV at 90 % neo whereas for first negative system it is raised up to 0.78 eV at 0.5 mbar pressure and 250 watt RF power. It is also found that vibrational temperature increases with the gas pressure up to 0.5 mbar.The over population of the levels of ( 3 , ) N2 C Πu ν ′ states with neon mixing are monitored by measuring the emission intensities of second positive system of nitrogen molecules. Since, over populations of levels of ( 3 , ) N2 C Πu ν ′ e.g., 1 and 4, effect the calculus of vibrational temperature of ( 3 , ) N2 C Πu ν ′ state, therefore, a linearization process is employed to such distributions allowing us to calculate the vibrational temperature of the ( 3 , ) N2 C Πu ν ′ state. Vibration temperature ( ν T ) measured from different linear adjust gives different value of ‘ ν T ’, which in turns reflects the effect of over population of levels of ( 3 , ) N2 C Πu ν ′ state.

1

1.1 The plasma state
1.2 The basic plasma parameters
1.3 Thermodynamic equilibrium
1.4 Equilibrium departure; proper and improper balances
1.5 Plasma temperature
1.6 Survey of glow discharge plasma
1.7 Glow discharge sources

2.1 The principle of detailed balancing
2.2 Elastic collision; Maxwell distribution
2.3 Excitation and de-excitation; Boltzmann distribution
2.4 Ionization and three body recombination; Saha distribution
2.5 Matter-radiation interaction; Planck’s distribution
2.6 Deviation from the Boltzmann distribution
2.7 Deviation from Saha distribution
2.8 Properties of atomic states
2.9 The oscillator strength

3.1 Introduction
3.2 Collision Radiative Model
3.3 Classification of domains in atomic system
3.4 Validity conditions for LTE and CE

4.1 Introduction
4.2 Plasma spectroscopy
4.3 Molecular spectroscopy
4.4 Diatomic molecules
4.5 Line Broadening
4.6 Natural line broadening
4.7 Doppler broadening
4.8 Electric probe diagnostic

5.1 Introduction
5.2 Experimental setup
5.3 Optical emission spectroscopy
5.4 Langmuir probe measurements
5.5 Results and discussions
5.6 Errors
5.7 Conclusions

6.1 Introduction
6.2 Experimental setup
6.3 Vibrational temperature
6.3.1 Second positive system
6.3.2 First negative system
6.4 Conclusions

7.1 Introduction
7.2 Experimental setup
7.3 Excitation temperature
7.4 Vibrational Analysis of ( 3 , )N2 C Πu ν ′ State
7.5 Conclusions

8.1 Conclusions
8.2 Suggestions for future work