Diagnostics and modelling of ECRH microwave discharges

Behringer, K.

doi:10.1088/0741-3335/33/9/001

Cited by 89 publications

(89 citation statements)

References 33 publications

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“…It has been shown elsewhere that the rotational temperature of the N 2 C 3 Π u state is equal to the gas temperature 56,57 . The result of Fantz 55 is that the temperature in the vibronic band V 2 of the Fulcher-α transition matches best with the nitrogen rotational temperature.…”

Section: Gas Temperaturementioning

confidence: 93%

Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

Sode

Schwarz-Selinger

Jacob

2013

Journal of Applied Physics

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Inductively coupled H 2 -Ar plasmas are characterized by an energy-dispersive mass spectrometer (plasma monitor), a retarding field analyzer, optical emission spectroscopy and a Langmuir probe. A procedure is presented that allows determining quantitatively the absolute ion densities of Ar + , H + , H + 2 , H + 3 and ArH + from the plasma monitor raw signals. The calibration procedure considers the energy and mass-dependent transmission of the plasma monitor. It is shown that an additional diagnostic like a Langmuir probe or a retarding field analyzer is necessary to derive absolute fluxes with the plasma monitor. The conversion from fluxes into densities is based on a sheath and density profile model.Measurements were conducted for a total gas pressure of 1.0 Pa. For pure H 2 plasmas the dominant ion is H + 3 . For mixed H 2 -Ar plasmas the ArH + molecular ion is the most dominant ion species in a wide parameter range. The electron density n e is around 3 × 10 16 m −3 and the electron temperature T e decreases from 5 to 3 eV with increasing Ar content. The dissociation degree was measured by actinometry. It is around 1.7 % nearly independent on Ar content. The gas temperature, estimated by the rotational distribution of the Q-branch lines of the H 2 Fulcher-α diagonal band (v' = v" = 2) is estimated to (540±50) K.

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Section: Gas Temperaturementioning

confidence: 93%

Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

Sode

Schwarz-Selinger

Jacob

2013

Journal of Applied Physics

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“…The line of sight was directed radially through the discharge and located in the middle of the RF antenna position. The electron density has been obtained via the line ratio evaluation of argon ion lines (480.6 & 488.0 nm) [5] and the electron temperature has been evaluated from the absolute emission of the 750.4 nm argon line [6]. However, in hydrogen or deuterium only density ratios can be obtained since a similar diagnostic like in argon which does not require additional plasma parameters is not available.…”

Section: Experimental Setup and Diagnostic Methodsmentioning

confidence: 99%

Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Briefi

Fantz

2013

AIP Conference Proceedings

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Abstract. The ITER reference source for H − and D − requires a high RF input power (up to 90 kW per driver). To reduce the demands on the RF circuit, it is highly desirable to reduce the power consumption while retaining the values of the relevant plasma parameters namely the positive ion density and the atomic hydrogen density. Helicon plasmas are a promising alternative RF coupling concept but they are typically generated in long thin discharge tubes using rare gases and an RF frequency of 13.56 MHz. Hence the applicability to the ITER reference source geometry, frequency and the utilization of hydrogen/deuterium has to be proved. In this paper the strategy of the approach for using Helicon discharges for ITER reference source parameters is introduced and the first promising measurements which were carried out at a small laboratory experiment are presented. With increasing RF power a mode transition to the Helicon regime was observed for argon and argon/hydrogen mixtures. In pure hydrogen/deuterium the mode transition could not yet be achieved as the available RF power is too low. In deuterium a special feature of Helicon discharges, the socalled low field peak, could be observed at a moderate B-field of 3 mT.

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“…Therefore, a method for determining the gas temperature in low-temperature nitrogen plasmas will be presented in the following. A frequently used method is the measurement of the rotational temperature of the excited state C 3 Π u of the N 2 molecule [20][21][22][23][24][25] . In the following the correlation between T N 2 rot and T g as well as the determination of T N 2 rot from the line intensity of the rotational spectrum will be presented.…”

mentioning

confidence: 99%

“…The translational energy of N 2 molecules is determined by collisions with gas molecules as well as with the plasma-surrounding wall. A fast thermalization between translation and rotation occurs due to collisions so that T N 2 rot ≈ T g [22][23][24]26 . By electron impact excitation of the ground state, the rotational population distribution is directly transferred to the excited state since the electron is too light to change the rotational momentum.…”

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confidence: 99%

Wall loss of atomic nitrogen determined by ionization threshold mass spectrometry

Sode

Schwarz-Selinger

Jacob

et al. 2014

Journal of Applied Physics

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In the afterglow of an inductively coupled N 2 plasma relative N atom densities are measured by ionization threshold mass spectrometry (ITMS) as a function of time in order to determine the wall loss time t wN from the exponential decay curves. The procedure is performed with two mass spectrometers on different positions in the plasma chamber. t wN is determined for various pressures, i.e., for 3.0, 5.0, 7.5, and 10 Pa. For this conditions also the internal plasma parameters electron density n e and electron temperature T e are determined with the Langmuir probe and the rotational temperature T N 2 rot of N 2 is determined with the optical emission spectroscopy. For T N 2 rot a procedure is presented to evaluate the spectrum of the transition v' = 0 → v" = 2 of the second positive system (C 3 Π u → B 3 Π g ) of N 2 . With this method a gas temperature of 610 K is determined. For both mass spectrometers an increase of the wall loss times of atomic nitrogen with increasing pressure is observed. The wall loss time measured with the first mass spectrometer in the radial center of the cylindrical plasma vessel increases linearly from 0.31 ms for 3 Pa to 0.82 ms for 10 Pa. The wall loss time measured with the second mass spectrometer (further away from the discharge) is about 4 times higher. A model is applied to describe the measured t wN .The main loss mechanism of atomic nitrogen for the considered pressure is diffusion to the wall. The surface loss probability β N of atomic nitrogen on stainless steel was derived from t wN and is found to be 1 for the present conditions. The difference in wall loss times measured with the mass spectrometers on different positions in the plasma chamber is attributed to the different diffusion lengths.

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Diagnostics and modelling of ECRH microwave discharges

Cited by 89 publications

References 33 publications

Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

Investigation of Helicon discharges as RF coupling concept of negative hydrogen ion sources

Wall loss of atomic nitrogen determined by ionization threshold mass spectrometry

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