Double layer formation in the expanding region of an inductively coupled electronegative plasma

Double-layers (DLs) were observed in the expanding region of an inductively coupled plasma with $\text{Ar}/\text{SF}\_6$ gas mixtures. No DL was observed in pure argon or $\text{SF}\_6$ fractions below few percent. They exist over a wide range of power and pressure although they are only stable for a small window of electronegativity (typically between 8\% and 13\% of $\text{SF}\_6$ at 1mTorr), becoming unstable at higher electronegativity. They seem to be formed at the boundary between the source tube and the diffusion chamber and act as an internal boundary (the amplitude being roughly 1.5$\frac{kT\_e}{e}$)between a high electron density, high electron temperature, low electronegativity plasma upstream (in the source), and a low electron density, low electron temperature, high electronegativity plasma downstream

Experimental investigation of double layers in expanding plasmas

Double layers (DLs) have been observed in a plasma reactor composed of a source chamber attached to a larger expanding chamber. Positive ion beams generated across the DL were characterized in the low plasma potential region using retarding field energy analyzers. In electropositive gases, DLs were formed at very low pressures between 0.1 and 1 mTorr with the plasma expansion forced by a strongly diverging magnetic field. The DL remains static, robust to changes in boundary conditions, and its position is related to the magnetic field lines. The voltage drop across the DL increases with decreasing pressure, i.e., with increasing electron temperature around 20 V at 0.17 mTorr. DLs were also observed in electronegative gases without a magnetic field over a greater range of pressure 0.5 to 10 mTorr. The actual profile of the electronegative DL is very sensitive to external parameters and intrusive elements, and they propagate at high negative ion fraction. Electrostatic probes measurements and laser-induced photodetachment show discontinuities in all plasma parameters electron density, electron temperature, negative ion fraction at the DL position. The voltage drop across the electronegative DL is about 8 V, is independent of the gas pressure and therefore of the electron temperature

Electron heating mechanisms in dual frequency capacitive discharges

We discuss electron heating mechanisms in the sheath regions of dual-frequency capacitive discharges, with the twin aims of identifying the dominant mechanisms and supplying closed-form expressions from which the heating power can be estimated. We show that the heating effect produced by either Ohmic or collisionless heating is much larger when the discharge is excited by a superposition of currents at two frequencies than if either current had acted alone. This coupling effect occurs because the lower frequency current, while not directly heating the electrons to any great extent, strongly affects the spatial structure of the discharge in the sheath regions

Evaluation of fatigue life of recycled opaque PET from household milk bottle wastes

Polyethylene terephthalate (PET) is among the most used thermoplastic polymers in large scale manufacturing. Opaque PET is increasingly used in milk bottles to save weight and to bring a glossy white aspect due to TiO2 nanoparticles. The recyclability of opaque PET is an issue: whereas the recycling channels are well established for transparent PET, the presence of opaque PET in household wastes weakens those channels: opaque bottles cannot be mixed with transparent ones because the resulting blend is not transparent anymore. Many research efforts focus on the possibility to turn opaque PET into resources, as one key to a more circular economy. A recent study has demonstrated the improvement of the mechanical properties of recycled PET through reactive extrusion. In the present work, the lifespan of recycled opaque PET has been evaluated throughout tensile–tensile fatigue loading cycles at various steps of the recycling process: The specimens are obtained from flakes after grinding PET wastes (F-r-OPET), from a subsequent homogenization step (r-OPET-hom) and after reactive extrusion (Rex-r-OPET). Virgin PET is also considered as a comparison. First, tensile tests monitored by digital image correlation have been carried out to obtain the elastic modulus and ultimate tensile stress of each type of PET. The fatigue properties of reactive REx-r-OPET increase, probably associated with the rise of cross-linking and branching rates. The fatigue lifespan increases with the macromolecular weight. The fracture surface analysis of specimens brings new insight regarding the factors governing the fatigue behavior and the damaging mode of recycled PET. TiO2 nanoparticles act as stress concentrators, contributing to void formation at multiple sites and thus promoting the fracture process. Finally, the fatigue life of REx-r-OPET is comparable to those of virgin PET. Upcycling opaque PET by reactive extrusion may be a relevant new route to absorb some of the growing amounts of PET worldwide

Periodic formation and propagation of double layers in the expanding chamber of an inductive discharge operating in Ar/SF₆ mixtures

It has previously been shown [Tuszewski et al., Plasma Sources Sci. Technol.12, 396 (2003)] that inductive discharges in electronegative gases are subject to two types of instability: the sourceinstability related to the E to H transition and a transport instability, occurring downstream when an expanding chamber is present. These two types of instability are observed in our “helicon” reactor operated without a static magnetic field in low-pressure Ar∕SF6 mixtures. Temporally and spatially resolved measurements show that, in our experiment, the downstream instability is a periodic formation and propagation of a double layer. The double layer is born at the end of the source tube and propagates slowly to the end of the expansion region with a velocity of 150ms⁻¹

High intensity and space charge problems at GANIL

http://accelconf.web.cern.ch/AccelConf/c86/papers/g-04.pdfInternational audienceWe routinely accelerate up to micro-amperes of ionsat energies ranging from 25 to 95 MeV / A. Already atthese levels, space charge (S.C) problems drasticallyaffect the bunching efficiency between the ECRexternal ion-source and our Co compact injector.Moreover in the "2.5" version of GANIL we expectcurrents above 50 e\l A (Ar+6 for instance) and S.Ceffects will be of prime importance during accelerationin the injector and even in our first SSC. Wepresent our computer codes and our first results

Equilibrium model for two low-pressure electronegative plasmas connected by a double layer

Plihon et al. [J. Appl. Phys.98, 023306 (2005)] have recently shown that double layers usually form during the expansion of a low pressure electronegative plasma. These double layers act as permeable internal boundaries between the source (upstream) plasma and the downstream expanding plasma; positive ions flow from upstream to downstream whereas negative ions flow in the opposite direction. So far, the detailed physical mechanisms leading to their formation have not been identified. In this paper, we develop a model for the two plasma equilibria, upstream and downstream, assuming that the double layer exists and couples the two plasmas. At very low pressure, typically 0.5mTorr, the coupling is strong and acts both ways. The negative ions created downstream contributes to the upstream equilibrium as well as the upstream positive ions contribute to the downstream equilibrium. As the pressure increases, the situation becomes asymmetric. The sourceplasma is not affected by the negative ions flowing from downstream, whereas the positive ions coming from the source control the downstream plasma equilibrium, where local ionization is negligible.This work has been supported by the European Space Agency, under Ariadna Study Contract No. ACT-04-3101. One of the authors A.J.L. acknowledges the hospitality of the LPTP, where the collaboration was begun

In Vitro Stability of Low-Concentration Ziconotide Alone or in Admixtures in Intrathecal Pumps

ObjectivesZiconotide is often administered in combination with other analgesics via an intrathecal pump. Studies have established that ziconotide is stable when delivered alone in high concentrations. No stability data are available, however, for ziconotide given in low concentrations and/or with other analgesics as usually occurs in clinical oncology practice. The objective of this study was to assess the in vitro stability of ziconotide alone and combined with other analgesics in intrathecal pumps at 37°C, as well as in syringes at 5°C, to evaluate conditions for storing and transporting preparations. Materials and Methods Various ziconotide concentrations (0.1, 0.25, 0.5, and 0.75 μg/mL) were combined with an admixture of ropivacaine (7.5 mg/mL), morphine (7.5 mg/mL), and clonidine (15 μg/mL) in 20-mL intrathecal pumps at 37°C and in syringes at 5°C. Solutions of ziconotide alone in concentrations of 0.25, 0.5, 0.75, and 1 μg/mL were introduced into pumps at 37°C and syringes at 5°C. Assays were performed using ultra high pressure liquid chromatography. Results In admixtures, mean ziconotide concentrations decreased linearly to 53.4% (±3.33%) of baseline after 35 days. When ziconotide was introduced alone in pumps at 37°C, the residual concentration on day 31 was 35.54% (±0.04%) with 0.25 μg/mL, 39.37% (±0.15%) with 0.5 μg/mL, and 44.49% (±0.18%) with 1 μg/mL. Ziconotide alone or combined with the other analgesics was stable in syringes stored at 5°C. The preparations complied with the prescriptions, with a mean error of less than 10%, except with the lowest ziconotide concentration (0.1 μg/mL). Conclusions At the low ziconotide concentrations studied, the degradation of ziconotide admixed with other drugs was linear and only weakly influenced by the baseline concentration. Linear regression with intrapolation to 30 days showed that the degradation of ziconotide admixed with other drugs was consistent with previously published data