Simulation and experimental research of Langmuir probe operation in electro-negative plasma

The mathematical model of single cylindrical Langmuir probe describing dependence of positive ion current gathered by the probe on the basic parameters of electronegative plasma, such as probe potential, densities of electrons, positive and negative ions, relation between ion and electron temperatures is built. The model is based on the theory of the radial motion of charged particles. The model covers wide parameters domain of the electronegative plasma, particularly the whole range typical for technological systems. The experimental measurements, confirming the high reliability of the model are reported. The model can be used in probe measurements of electronegative plasma parameters in laboratory and technological systems, as well as for further theories perfection of surface layers in gas-discharge plasma.Построена математическая модель работы одиночного цилиндрического зонда Ленгмюра, описывающая взаимосвязь собираемого зондом тока положительных ионов с основными параметрами электроотрицательной плазмы, такими как: потенциал зонда, плотности электронов, положительных и отрицательных ионов, отношение температур электронов и ионов. Модель основывается на теории радиального движения заряженных частиц. Она перекрывает широкую область параметров электроотрицательной плазмы, в частности, весь диапазон, характерный для технологических систем. Проведены экспериментальные измерения, подтверждающие высокую достоверность модели. Модель может быть использована при проведении зондовых исследований в электроотрицательной плазме в лабораторных и технологических системах, а также для дальнейшего совершенствования теорий приповерхностных слоев в газоразрядной плазме.Побудовано математичну модель роботи одиночного циліндричного зонда Ленгмюра, яка описує взаємозв'язок струму позитивних іонів, що збирається зондом, з основними параметрами електронегативної плазми, такими як: потенціал зонда, густина електронів, позитивних та негативних іонів, співвідношення температур електронів та іонів. Модель грунтується на теорії радіального руху заряджених частинок. Вона перекриває широку область параметрів електронегативної плазми, зокрема, весь діапазон, характерний для технологічних систем. Проведено експериментальні вимірювання, які підтверджують високу достовірність моделі. Модель може бути використана під час проведення зондових досліджень електронегативної плазми в лабораторних і технологічних системах, а також для подальшого вдосконалення теорій приповерхневих шарів в газорозрядній плазмі

Hysteresis effects in the formation of a neutralizing beam plasma at low ion energy

International audienceIn this paper, the PEGASES II thruster prototype is used as an ion source generating low-energy positive Ar ion beam, extracted without an external neutralizer. The ions are extracted and accelerated from the source using a two-grid system. The extracted positive ion beam current is measured on a large beam target that can be translated along the acceleration axis. The ion beam current shows a stepwise transition from a low-current to a high-current extraction regime with hysteresis. The hysteresis region depends strongly upon the beam target position. Langmuir probe measurements in the plume show high plasma potentials and low plasma densities in the low-current mode, while the plasma potential drops and the density increases in the high-current mode. The ion energy distribution functions of the beam are measured for different regimes of ion extraction. The ion beam extracted in the high-current mode is indicated by the presence of an additional low-energy peak corresponding to ions from an ion-beam plasma created in the downstream chamber, as well as 1020 times higher intensity of the primary ion beam peak. The hysteresis behavior is explained by the formation of a downstream neutralizing beam plasma, that depends on the target position and pressure in agreement with a Paschen-like breakdown by secondary electrons. The obtained results are of high relevance for further development of the PEGASES thruster, as well as for improving existing neutralizer-free concepts of the broad-beam ion sources

Using the DC self-bias effect for simultaneous ion-electron beam generation in space thruster applications

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Plasma acceleration using a radio frequency self-bias effect

International audienceIn this work plasma acceleration using a RF self-bias effect is experimentally studied. The experiments are conducted using a novel plasma accelerator system, called Neptune, consisting of an inductively coupled plasma source and a RF-biased set of grids. The plasma accelerator can operate in a steady state mode, producing a plasma flow with separately controlled plasma flux and velocity without any magnetic configuration. The operating pressure at the source output is as low as 0.2 mTorr and can further be decreased. The ion and electron flows are investigated by measuring the ion and electron energy distribution functions both space resolved and with different orientations with respect to the flow direction. It is found that the flow of electrons from the source is highly anisotropic and directed along the ion flow and this global flow of accelerated plasma is well localized in the plasma transport chamber. The maximum flux is about 7.5·1015 ions s−1 m−2 (at standard conditions) on the axis and decreasing to almost zero at a radial distances of more than 15 cm from the flow axis. Varying the RF acceleration voltage in the range 20350 V, the plasma flow velocity can be changed between 10 and 35 km/s. The system is prospective for different technology such as space propulsion and surface modification and also interesting for fundamental studies for space-related plasma simulations and investigation of the dynamo effect using accelerated rotating plasmas. I. INTRODUC

Electron-less negative ion extraction from ion-ion plasmas

International audienceThis paper presents experimental results showing that continuous negative ion extraction, without co-extracted electrons, is possible from highly electronegative SF6 ion-ion plasma at low gas pressure (1 mTorr). The ratio between the negative ion and electron densities is more than 3000 in the vicinity of the two-grid extraction and acceleration system. The measurements are conducted by both magnetized and non-magnetized energy analyzers attached to the external grid. With these two analyzers, we show that the extracted negative ion flux is almost electron-free and has the same magnitude as the positive ion flux extracted and accelerated when the grids are biased oppositely. The results presented here can be used for validation of numerical and analytical models of ion extraction from ion-ion plasma

The NEPTUNE Bipolar Source: A New Instrument for Surface Treatment Applications

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Ion-ion plasma potential control at alternate ion-ion beam extraction

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Deposition of semiconductive films in SF6 ion-ion plasma

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Development of plasma and beam diagnostics for the PEGASES thruster experiment

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A Neutralizer-Free Gridded Ion Thruster Embedded Into A 1U Cubesat Module

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