We report on investigations of gas metal arc welding plasma operated in pure argon and in a mixture of argon and CO 2 at a dc current of 326 A. The spatially resolved electron densities and temperatures were directly obtained by measuring the Stark widths of the Ar I 695.5 nm and Fe I 538.3 nm spectral lines. Our experimental results show a reduction of the plasma conductivity and transfer from spray arc to globular arc operation with increasing CO 2 concentration. Although the electron density n e increases while approaching the core of the plasma in the spray-arc mode, a drop in the electron temperature T e is observed. Moreover, the maximum T e that we measure is about 13 000 K. Our experimental results differ from the Haidar model where T e is always maximum on the arc axis and its values exceed 20 000 K. These discrepancies can be explained as a result of underestimation of the amount of metal vapours in the plasma core and of the assumption of local thermal equilibrium plasma in the model.
Doppler-broadened Ha emission (656.28 nm) detected from a 13.56 MHz, parallel-plate, radio-frequency discharge in hydrogen indicates the presence of fast excited H atoms throughout the discharge volume. Time and spatially resolved measurements of the Doppler-broadened emission indicate that the fast H atoms are formed primarily at the surface of the powered electrode with kinetic energies exceeding 120 eV. Energetic neutrals produced in radio-frequency (rt) discharges used in the production of microelectronic devices can influence etching rates, the quality of diamond deposition, and plasma cleaning mechanisms. While the anticipated energies of these neutrals have been calculated,1 almost no experimental data exist. In this paper we present a new technique that allows the determination of fast atom velocities parallel to the electrode axis in a parallel-plate rf reactor by. measuring the time-resolved Doppler-shifted optical emission perpendicular to the electrode axis. We apply the technique to the detection of fast H atoms in a 13.56-MHz hydrogen discharge because of the interest2-4in the production and transport of fast H. Doppler-broadened Balmer-alpha (Ha) emission from excited fast hydrogen atoms has been previously observed from dc and low frequency rf discharges (... 300 kHz) in pure hydrogen.2.3.5The fast atoms observed in dc and low frequency discharges have kinetic energies of hundreds of electron volts, far in excess of the kinetic energies (up to approximately 8 eV) that have been reported due to electronimpact dissociative ionization of hydrogen.6 Recent work2 suggests that there are two sources of these fast atoms in dc discharges. The first is charge-exchange collisions between fast ions and the background H2 gas, producing fast atoms moving towards the cathode. The second is the formation of fast H atoms at the cathode surface due to bombardment by fast ions and neutrals formed in the discharge. This produces '
The plasma column in the metal inert gas welding process is investigated by optical emission spectroscopy and high-speed imaging. The concentration and repartition of iron vapours are measured and correlated to the plasma and electrode geometric configuration. Plasma temperatures and electron densities were also measured for each studied position in the plasma. The temperatures are calculated using two different methods, allowing validation of the local thermodynamic equilibrium state of the plasma. The results show a maximum temperature of 12500 K on the arc upper part, away from the arc axis. The iron concentration reaches a maximum of 0.3% close to the anode and strongly decreases along both the vertical and the radial directions. The plasma thermophysical properties, calculated from this plasma composition, are then discussed regarding the metal transfer mode.
Laser-collision induced fluorescence (LCIF) is the emission of light from states that have been populated by laser excitation and a subsequent collision. By simultaneously measuring the LCIF from two different states, it is possible to determine both the electron density and temperature of the low energy bulk electrons within a plasma. This method is described in detail and has been applied in the determination of the total, temporally averaged, and spatially resolved electron density in a rf (13.56 MHz) helium discharge in the Gaseous Electronics Conference reference cell. The rf discharge was operated at pressures P=33.3–133.3 Pa (0.25–1.0 Torr) and peak-to-peak voltages of Vpp=75–300 V were applied. We found the total electron density varied from 1.8×108 cm−3 at P=33.3 Pa and Vpp=75 V to 4.0×1010 cm−3 at P=133.3 Pa and Vpp=300 V. A comparison of results from different experiments has been made.
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