Study of the plasma near the plasma electrode by probes and photodetachment in ECR-driven negative ion source

Contributions to the conference will be published, following peer review, in the American Institute of Physics conference proceedings.International audienceThe effect of the plasma electrode bias on the plasma characteristics near the extraction aperture in a large volume hybrid multicusp negative ion source, driven by 2.45 GHz microwaves, is reported. Spatially resolved negative ion and electron density measurements were performed under various pressures (1-4 mTorr) by means of electrostatic probe and photodetachment technique

Dipolar plasma source modeling: a first approach

International audienceThe scaling up of conventional plasmas presents limitations in terms of plasma density, limited to the critical density, and of uniformity, due to the difficulty of achieving constant amplitude standing wave patterns along linear microwave applicators in the meter range. An alternative solution lies in the concept of distribution from one- to two-dimensional networks of elementary plasma. Each elementary plasma source consists in a permanent magnet on which microwaves are applied via an independent coaxial line [1]. The plasma is produced by the electrons accelerated at ECR (Electron Cyclotron Resonance) and trapped in the dipolar magnetic field. Large-size uniform plasmas can be obtained by assembling as many such elementary plasma sources as necessary, without any physical or technical limitations [2]. Simulation of the plasma produced by a dipolar source requires a global, self consistent, modeling of its functioning. In order to obtain results to lead a first optimization of the dipolar source, magnetostatics, microwave propagation and fast electrons trajectories (Particles in Cell (PIC) and Monte-Carlo hybrid method [3]) have been performed with Comsol Multiphysics and MatLab

Vibrationnally excited H2 formation on graphite surface

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Comparison between Langmuir probe and microwave autointerferometry measurements at intermediate pressure in an argon surface wave discharge

International audienceThis paper is devoted to the validation of Langmuir probe technique by microwave autointerferometry in a surface wave discharge at medium pressure (from 0.1 up to 10 Torr). Temperatures of neutrals, obtained from Rayleigh scattering, and electrons, given by double probe measurements, have been used to estimate the mean free path and the sheath length. Hence, the number of collisions in the sheath has been obtained. We have verified that two different phenomena occur in the sheath, while the pressure increases. These phenomena are depicted, in literature, as two different coefficients used to modify the value of the noncollisional current of Laframboise. Coefficients given by various authors have been investigated with accuracy knowing the number of collisions in the sheath. Very good agreements are obtained between Zakrzewski and Kopiczynski theory and autointerferometry measurements which are unaffected by collisional phenomena

Emission spectroscopy of a dipolar plasma source in hydrogen under low pressures

International audienceLow-temperature hydrogen plasma has been investigated under the conditions of electron cyclotronresonance by emission spectroscopy. The molecular distribution functions over the low rotational andvibrational levels of the hydrogen molecule in the triplet state have been measured. The translational,rotational, and vibrational temperatures of the ground and excited triplet states of the hydrogen molecule aredetermined. The obtained translational and vibrational temperatures indicate that low-temperature hydrogenplasma under the conditions of electron cyclotron resonance is a more efficient source of vibrationally excitedhydrogen molecules in comparison with the other gas discharges

Plasma processes controlled by the adjustment of particle and energy fluxes

International audienceAn electronic state sensitive semiempirical collision-radiative model of hydrogen plasma of ECR-discharge is used to analyze the applicability of emission of triplet states of molecular hydrogen for plasma diagnostics. It is shown that secondary processes make the greatest contribution to the kinetics of population-depopulation of triplet states ${a}^{3}{{\rm{\Sigma }}}_{g}^{+},{c}^{3}{{\rm{\Pi }}}_{u},{d}^{3}{{\rm{\Pi }}}_{u},{e}^{3}{{\rm{\Sigma }}}_{u}^{+},{g}^{3}{{\rm{\Sigma }}}_{g}^{+},{h}^{3}{{\rm{\Sigma }}}_{g}^{+}$, i 3Πg and r 3Πg. The secondary processes give the smallest contribution to the excitation and deactivation of triplet states {f}^{3}{{\rm{\Sigma }}}_{u}^{+}\,{\unicode{x00438;}}\,{k}^{3}{{\rm{\Pi }}}_{u}. Thus a simplified coronal model (electron impact excitation followed by radiative decay) can be used to process the intensities of the dipole allowed ${f}^{3}{{\rm{\Sigma }}}_{u}^{+}\,\to \,{a}^{3}{{\rm{\Sigma }}}_{g}^{+},{g}^{3}{{\rm{\Sigma }}}_{g}^{+}$ and ${k}^{3}{{\rm{\Pi }}}_{u}\,\to \,{a}^{3}{{\rm{\Sigma }}}_{g}^{+}$ transitions. The complicated collision-radiative model should be used for other transitions

Experimental and numerical simulation of the vibrational distribution function of the hydrogen molecule in the ground state X1Σ+g in gas discharges

International audienceThe comparison of the vibrational distribution functions obtained by experimental techniques andnumerical simulation in the different discharges was carried out. There are considered and discusseddifferent sets of level – to – level rate coefficients at which a good agreement is observed between theoryand experiment