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

Designing a high resolution microcontroller-based electrostatic probe system for plasma characterization

International audienceIn this work, an automated system capable of biasing electrostatic probes in cold plasmas and acquiring the associated data is implemented. The step-by-step design, fabrication, and fine calibration of the entire system are presented. High resolution and accuracy, increased acquisition rate and high noise rejection, are the main claims for the system presented hereby. The device efficiency is eventually demonstrated through measurements in the negative ion H- source "Prometheus I"

Influence of a DC, point-to-plane, low-pressure discharge in nitrogen on polystyrene thin films

In the first part of this work the regime of the DC electrical discharge in nitrogen, in absence and in presence of polystyrene thin films in the cold plasma reactor, for a constant gap length d = 1 cm and for variable pressures ($1~{\rm~mbar} < p < 10~{\rm~mbar}$) is characterized, while the gas flow rate is maintained at Q = 1 sccm. V-I curves underline that in any case a “normal glow-like” discharge is established. Experimental results bring out that the presence of the films in the volume of the produced plasma seems to modify the structure and some of the discharge characteristics, like the cathode secondary emission effects. V-I curves ($I <200~\mu$A), discharge repetitive current impulses, discharge repetitive emitted light impulses along the discharge symmetry axis and photos of the discharge, in presence and in absence of the films, are presented. In the second part of this paper results of polystyrene thin films treatment under the above DC “normal glow-like” discharge regime in nitrogen for improving the wettability of the films are presented. The effect of discharge main parameters (pressure p and mean current I through the discharge) on the treatment is studied under certain experimental conditions. The wettability is characterized by contact angle measurements using deionized water drops and the evolution versus the treatment time ttr of the $\Delta \theta/\theta_{\rm i}=(\theta_{\rm i}-\theta_{\rm f})/\theta_{\rm i}$ ratio ($\theta_{\rm i}$: the contact angle before the treatment and $\theta_{\rm f}$: the contact angle after the treatment) is estimated. It is deduced that optimizing main parameters of the DC electrical discharge in nitrogen it is possible to obtain films with very good wettability (suggestively $\Delta\theta/\theta_{\rm i}=0.951$ corresponding to $\theta_{\rm f}=4^{\circ}$, at p = 4 mbar, $I=200~\mu$A, $t_{\rm tr}\cong 600$ s). A rapid change of the films surface nature ($0~{\rm s} < t_{\rm tr} < 60$ s, suggestively) seems to be followed by a slower one and finally by a saturation. The gas pressure and the discharge mean current seem to play a very important role for the treatment. The experimental results allow us to start a discussion about the possible role of some active particles produced in the plasma to the treatment of the films and especially the role of the neutrals and the metastables

Automated electrostatic probe device of high resolution and accuracy

International audienceIn this work, an automated apparatus for driving single electrostatic probes and acquiring the plasmarelateddata has been designed and fabricated. The voltage range of the present system is ±110 Vwith an adjustable voltage step as low as 3 mV. Voltage and current measurements are carried out withhigh resolution and high accuracy circuits, both based on 16 bit analog-to-digital converters. The codeembedded in a micro-controller, schedules the operation of the device and transfers the experimentaldata to a personal computer. The modular design of the system makes possible its modification andthus increases its adaptability to different plasma setups. Finally, the reliable operation of the entiredevice is confirmed by tests in Electron Cyclotron Resonance plasma. © 2014 AIP Publishing LLC

Laser-induced photodetachment diagnostic for interrogating pulsed ECR-driven plasmas: Application to H- and D- negative ions

Discharges sustained in the pulsed mode of operation are of great interest on a fundamental level as they may unveil important information on the plasma kinetics. The present work is devoted to an experimental setup tailored to study time-resolved processes relative to negative ion formation in ECR-driven plasmas. It refers to a laser-induced electron photo-detachment system synchronized with H 2 and D 2 ECR-plasmas, sustained by 2.45 GHz bursts in the kHz range. The system is combined with electrostatic probe time-resolved measurements and information is obtained both on the formation path and the yield enhancement of H − and D − negative ions

H−^{-} and D−^{-} production efficiency in a multi-dipole ECR-plasma source as a function of gas pressure

International audienceThe electron cyclotron resonance (ECR) negative ion source “Prometheus I” is operated either with high purity H2 (> 99.999%) or D2 (> 99.8%) to probe H$^{-}$ and D$^{-}$ ions, respectively, and examine the isotope effect within a wide range of gas pressure. These ions are predominantly formed in the bulk plasma by dissociative attachment (DA) of low-energy (cold) electrons to highly ro-vibrationally excited molecules. The latter result mainly from the radiative decay and excitation (EV) process sustained by high-energy (hot) electrons heated in the ECR zones. Langmuir probe and laser photo-detachment measurements are realized within the pressure range 0.27 to 2.67 Pa under constant microwave power (0.9 kW). It is revealed that: (i) the plasma potential, cold electron temperature, and cold electron density tend to be higher in deuterium; (ii) no pronounced difference in the hot electron density and temperature is found between the two plasmas; and (iii) overall a similar H$^{-}$ and D$^{-}$ negative ion yield (up to 6×10$^{9}$ cm$^{-3}$; under the present conditions) is achieved. However, for equal plasma densities an isotope effect is exhibited showing higher H$^{-}$ density over the entire pressure range. Finally, the n$_{H}$- / n ratio is constantly higher than the n$_{D}$- / n$_{e}$ one and they both peak around 1.33 Pa

Experimental study on dynamic effects of H and D negative ions in an ECR-plasma source

International audienceThe electrostatic probe-based photo-detachment technique with one or two laser beams can provide insight on the negative ion absolute densities and dynamics, respectively, in electronegative plasmas. In this work, this diagnostic is installed in the ECR-driven (2.45 GHz) negative ion source “Prometheus I” and details of the setup design along with main underlying physics are discussed. Potential origins of signal distortions and thus erroneous employment of this technique are demonstrated. Based on these observations, H$^{-}$ and D$^{-}$ negative ion densities and temperatures are measured in a reliable manner. The experiments are carried out for variable microwave power (2.45 GHz), at 1.33 Pa, unveiling two distinct kinetic equilibriums of the negative ions, in both gases, and an isotope effect