A collisional radiative model for low-pressure hydrogen–caesium plasmas and its application to an RF source for negative hydrogen ions

Wünderlich, D.; Wimmer, Christian; Friedl, R.

doi:10.1016/j.jqsrt.2014.09.002

Cited by 12 publications

(10 citation statements)

References 66 publications

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“…In addition to the excitation caused by collisions with electrons, the Cs excited states are populated by the mutual neutralization of Cs + and H − , especially when 𝑛 𝐻 − reaches values similar or greater than 𝑛 𝑒 [13]. The importance of this channel is well documented, but including it requires assumptions on both 𝑛 𝐻 − and 𝑛 Cs + .…”

Section: Spidermentioning

confidence: 99%

Characterization of plasmas in negative ion sources using a Cs-H Collisional Radiative model

Pouradier Duteil,

Barbisan,

Milazzo

et al. 2024

J. Inst.

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SPIDER, hosted at the Neutral Beam Test Facility (NBTF) in Padova, Italy, is the full scale prototype for the ITER Heating Neutral Beam (HNB) source. Another smaller compact RF ion source, NIO1, hosted by Consorzio RFX, was built to study the production and acceleration of H- ions in continuous operation. Both machines operate with the evaporation of caesium in order to enhance the production of negative ions. A collisional radiative model for caesium-hydrogen plasmas was recently developed. When used in conjunction with measurements from Optical Emission Spectroscopy, Laser Absorption Spectroscopy and electrostatic probes, the model can provide estimates of the plasma parameters with a good spatial resolution thanks to the many lines of sight available. This work presents a characterization of the plasma in SPIDER and NIO1 using this method. In particular, we investigate the influence of the RF power and the magnetic filter field on the plasma properties, and compare the results with those of other source and beam diagnostics.

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Section: Spidermentioning

confidence: 99%

Characterization of plasmas in negative ion sources using a Cs-H Collisional Radiative model

Pouradier Duteil,

Barbisan,

Milazzo

et al. 2024

J. Inst.

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“…The caesium emission is correlated to plasma parameters like the caesium density, the electron density and the electron temperature. For quantitative statements absolutely calibrated measurements as well as the application of an appropriate population model are necessary [21]. During each of the four pulses a continuous slope of the Cs emission is seen, with two phases of slightly increased emission during the two beam blips, correlated with the increased caesium release from the back plate caused by the back streaming ions, i.e.…”

Section: Caesium Conditioning For Long Pulsesmentioning

confidence: 99%

Long pulse, high power operation of the ELISE test facility

Wünderlich¹,

Kraus²,

Fröschle³

et al. 2017

AIP Conference Proceedings

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Abstract. The ion source of the ELISE test facility (0.9×1.0 m 2 with an extraction area of 0.1 m 2 ) has half the size of the ion source foreseen for the ITER NBI beam lines. Aim of ELISE is to demonstrate that such large RF driven negative ion sources can achieve the following parameters at a filling pressure of 0.3 Pa and for pulse lengths of up to one hour: extracted current densities of 28.5 mA/cm 2 in deuterium and 33.0 mA/cm 2 in hydrogen, a ratio of co-extracted electrons to extracted ions below one and deviations in the uniformity of the extracted beam of less than 10 %. From the results obtained at ELISE so far it can be deduced that for demonstrating the ITER parameters, an RF power of 80 kW/driver will be necessary, i.e. final aim is to demonstrate long pulses (up to one hour) at this power level and a stable source performance. The most crucial factor limiting the source performance during such pulses -in particular in deuterium -is a steady increase in the co-extracted electron current. This paper reports measures that counteract this steady increase, namely applying a dedicated long pulse caesium conditioning technique and modifying the filter field topology by adding strengthening external permanent magnets. Additionally, RF issues are discussed that prevented increasing the RF power towards the target value. Although it was not possible up to now to perform long pulses at 80 kW/driver, a significant improvement of the source performance and its stability are demonstrated. The latter allowed performing the very first 1 h deuterium pulse in ELISE.

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“…For the determination of the neutral Cs density in the ground state close to the convertor surface, a tunable diode laser spectroscopy (TDLAS) at the resonant Cs 852 nm trans ition (6 2 S 1/2 → 6 2 P 3/2 , named Cs-D2) is applied at ELISE, measuring the hyperfine spectrum. The density of Cs 0 in the ground state reflects the total density of neutral Cs, because the densities in the excited states contribute with less than 1% to the total population [13,14]. Significant broadening and dist ortion of the lines result from the Doppler effect as well as from the Zeeman effect; further broadening mech anisms as the pressure or Stark broadening are of no relevance in the ion sources.…”

Section: Introductionmentioning

confidence: 99%

Determination of the Cs distribution along a line of sight by the Zeeman splitting in an inhomogeneous magnetic field

Wimmer

Lindauer

Fantz

2018

J. Phys. D: Appl. Phys.

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Large-scale sources for negative hydrogen ions are required for the neutral beam injection of the ITER fusion device. Caesium is used for the conversion of hydrogen atoms into negative ions. The combination of moderate background vacuum conditions (10−7–10−6 mbar), the high reactivity of Cs, continuous evaporation of Cs and plasma-enabled redistribution of Cs and Cs+ forms a complex dynamics. ELISE (extraction from a large ion source experiment) is a half ITER-source scale experiment. A tunable diode laser absorption spectroscopy (TDLAS) diagnostic at the resonant Cs 62S1/2–62P3/2 transition (852 nm) has been applied to the source in order to measure the density of neutral Cs close to the conversion surface and thus gaining a better insight into the Cs dynamics. An inhomogeneous magnetic field created by permanent magnets (≈25–320 G) is located along the line-of-sight (LOS) of the TDLAS, leading to a varying effect of the Zeeman splitting of the concerning Cs states and thus the absorption line profile along the LOS. In long plasma pulses at ELISE, a change of the Cs absorption line profile takes place, which can be attributed to a variation of the Cs density profile along the LOS. In order to attribute a measured line profile to a certain magnetic field strength and thus a certain position along the LOS, absorption spectra with a defined B-field at a Cs vapor cell using the same diagnostic system have been measured. The strong broadening of the measured line profile at ELISE after several 10 s of plasma indicates that neutral Cs is mainly located in the area of high magnetic field strength, i.e. close to the side wall. A correlation between the measured Cs density and the source performance exists during the beginning of the pulse and is lost in this later phase.

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A collisional radiative model for low-pressure hydrogen–caesium plasmas and its application to an RF source for negative hydrogen ions

Cited by 12 publications

References 66 publications

Characterization of plasmas in negative ion sources using a Cs-H Collisional Radiative model

Characterization of plasmas in negative ion sources using a Cs-H Collisional Radiative model

Long pulse, high power operation of the ELISE test facility

Determination of the Cs distribution along a line of sight by the Zeeman splitting in an inhomogeneous magnetic field

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