Cavity ring-down spectroscopy to measure negative ion density in a helicon plasma source for fusion neutral beams

Cavity Ring Down Spectroscopy (CRDS) is used to measure the D- absolute density produced in the helicon plasma reactor RAID (Resonant Antenna Ion Device) at the Swiss Plasma Center. The birdcage geometry of the helicon antenna produces a homogeneous, high-density plasma column (n(e) congruent to 1.5 x 10(18) m(-3) in H-2 and D-2 at 0.3 Pa and 3 kW of input power) 1.4 m long. We present the CRDS experimental setup, its positioning on the RAID reactor, and how the mechanical and thermal effects of the plasma affect the measurement. First results in deuterium plasma confirm the production of negative ions (D-) with a significant density: an average value of 3.0 x 10(16) m(-3) of D- is obtained at 0.3 Pa and 5 kW of power input in Cs-free plasma. This result is in good agreement with calculations performed with the collisional radiative code YACORA.

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Riccardo Agnello, Yanis Andrebe, Ivo Furno, Philippe Frédérique Bruno Guittienne, Alan Howling, Rémy Jacquier, Gennady Plyushchev
2018
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https://infoscience.epfl.ch/record/261834?ln=fr

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Negative ion characterization in a helicon plasma source for fusion neutral beams by cavity ring-down spectroscopy and Langmuir probe laser photodetachment

Riccardo Agnello, Ivo Furno, Philippe Frédérique Bruno Guittienne, Alan Howling, Rémy Jacquier, Gennady Plyushchev

Negative ions are characterized in the helicon plasma source resonant antenna ion device (RAID) at the Swiss plasma center by means of cavity ring-down spectroscopy (CRDS) and Langmuir probe (LP)-assisted laser photodetachment. A high density and axially homogeneous plasma column is produced via a RF antenna able to sustain the propagation of helicon waves in a steady state regime. An electron density n(e) congruent to 2.0 x 10(18) m(-3) in H-2 plasma at 0.3 Pa and 3 kW of input power is measured in the center of the plasma column by LP and microwave interferometry. The electron temperature profile is peaked on axis reaching T-e approximate to 5 eV and decreasing to 1.5 eV at r = 0.05 m. Thus, a hot core region forms where H2 molecules are rovibrationally excited (H-2(nu)), and a cold edge, where low energy electrons can attach to H-2(nu) and produce H- ions by dissociative attachment. In this work we use LP-assisted laser photodetachment and CRDS diagnostics to measure H- and D- radial density profiles and how they depend on source parameters. We show that negative ions are distributed on a shell of 0.06 m radius with a peak value of similar to 2.0 x 10(16) m(-3) in H-2 plasma. These results suggest that, although substantial technical development is needed, helicon plasmas could be considered as a possible candidate as sources of negative ions for future NBIs.

IOP PUBLISHING LTD2020

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Helicon wave-generated plasmas for negative ion beams for fusion

Riccardo Agnello, Ivo Furno, Philippe Frédérique Bruno Guittienne, Alan Howling, Rémy Jacquier, Claudio Marini, Gennady Plyushchev

In the next generation of fusion reactors, such as DEMO, neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atom swith high wall-plug efficiency (>50%) will be required to reach burning plasma conditions and to provide a significant amount of current drive.The present NBI system for DEMO assumes that 50 MW is delivered to the plasma by 3 NBIs. In the Siphore NBI concept, negative deuterium ions are extracted from a long, thin ion source 3 m high and 15 cm wide, accelerated and subsequently photo-neutralized. This requires the development of a new generation of negative ion sources. At the Swiss Plasma Center, a novel radio frequency helicon plasma source, based on a resonant network antenna source delivering up to 10 kW at 13.56 MHz, has been developed and is presently under study on the Resonant Antenna Ion Device (RAID). RAID is a linear device (1.9 m total length, 0.4 m diameter) and is equipped with an extensive set of diagnostics for full plasma characterization. In this work, the principles of operation of resonant antennas as helicon sources areintroduced. Wepresent absolute spectroscopy, Langmuir probe, and interferometry measurements on helicon plasmas. We characterize the performanceof the source in terms of hydrogen/deuterium dissociation and negative ion production as a function of the input power. Furthermore, first results with the helicon birdcage antenna installed on the Cybele negative ion source at CEA-IRFM arepresented, as a first step towards the validation of the Siphoreconcept.

2017

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Magnetic field configurational study on a helicon-based plasma source for future neutral beam systems

Riccardo Agnello, Ivo Furno, Philippe Frédérique Bruno Guittienne, Alan Howling, Rémy Jacquier

A helicon-based plasma source is under development and exploration at CEA-IRFM to produce an efficient and dense magnetized plasma column. The final objective of this development is the extraction and acceleration of a blade-like negative ion beam in view of future neutral beam injector systems for fusion reactors. The extraction of a negative ion beam from a magnetized plasma column requires a specific topology of the magnetic confinement, which significantly impacts the plasma parameters and wave propagation along the column. The magnetic confinement under investigation is based on water-cooled internal coils implemented under vacuum along the source (column) axis; these coils are supplied with a high DC current (similar to 1000 A), providing the axial magnetic field (B// similar to 10 mT). Different diagnostics developed in academic laboratories, such as 3D B-dot probes, optical emission spectroscopy and Langmuir probes, have been used for plasma characterization. The paper reports the experimental results obtained under different operating conditions of this particular magnetic confinement.

IOP PUBLISHING LTD2019

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État plasma

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Neutral-beam injection (NBI) is one method used to heat plasma inside a fusion device consisting in a beam of high-energy neutral particles that can enter the magnetic confinement field. When these ne

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