Publications: Articles

Resume: The origin of differences in the rotational temperatures of various molecules and ions (N-2(+)(B), OH(A) and N-2(C)) is studied in helium atmospheric-pressure guided streamers. The rotational temperature of N-2(+)(B) is room temperature. It is estimated from the emission band of the first negative system at 391.4 nm, and it is governed by the temperature of N-2(X) in the surrounding air. N-2(X) is ionized by direct electron impact in the outer part of the plasma. N-2(+)(B) is deactivated by collisions with N-2 and O-2. The rotational temperature of OH(A), estimated from the OH band at 306.4 nm, is slightly higher than that of N-2(+)(B). OH(A) is excited by electron impact with H2O during the first 100 ns of the applied voltage pulse. Next, OH(A) is produced by electron impact with OH(X) created by the quenching of OH(A) by N-2 and O-2. H2O diffuses deeper than N-2 into the plasma ring and the rotational temperature of OH(A) is slightly higher than that of N-2(+)(B). The rotational temperature of N-2(C), estimated from the emission of the second positive system at 315.9 nm, is governed by its collisions with helium. The gas temperature of helium at the beginning of the pulse is predicted to be several hundred kelvin higher than room temperature.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Resume: In this paper, an experimental investigation of dust particle agglomeration in a capacitively coupled RF discharge is reported. Carbonaceous particles are produced in an argon plasma using acetylene. As soon as the particle density becomes sufficient, dust density waves (DDWs) are spontaneously excited within the cathode sheath. Recently, it was proven that DDWs can significantly enhance the agglomeration rate between particles by transferring them a significant kinetic energy. Thus, it helps them to overcome Coulomb repulsion. The influence of this mechanism is studied from acetylene injection to the formation of very large agglomerates forming an organized structure after a few dozens of seconds. For this purpose, three diagnostic tools are used: extinction measurements to probe nanometer-sized particles, fast imaging for large agglomerates and a dust extraction technique developed for ex-situ analysis. (C) 2013 American Institute of Physics.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Equipe: Centre de Compétences : X-Gamma rayons X et spectroscopie

Resume: This paper deals with pure argon plasma studied in a magnetically enhanced inductively coupled reactor. Laser induced fluorescence technique was performed with an optical parametric oscillator laser on the 3d4F7/2 and 3d2G9/2 Ar+ metastable levels and on the (2P03/2)4s2 neutral metastable state to determine their relative densities. Langmuir probe was used as a complementary diagnostic to measure the electron energy distribution functions. When increasing the confinement magnetic field, the metastable state density collapses for all cited levels, by contrast with ne which is continuously growing. Calculations were carried out for neutral argon to explain this behaviour. The results show that the metastable population is depleted by electron-impact excitation and ionization, these loss processes becoming dominant compared to the metastable state creation term.

Equipe: Département CP2S : Expériences et Simulations des Plasmas Réactifs - Interaction plasma-surface et Traitement des Surfaces ESPRITS

Equipe: Centre de Compétences : X-Gamma rayons X et spectroscopie