A 1.5D fluid-Monte Carlo model of a hydrogen helicon plasma

Helicon plasma sources operating with hydrogen or deuterium might be attractive for fusion applications due to their higher power efficiency compared to inductive radiofrequency plasma sources. In recent years, the resonant antenna ion device (RAID) has been investigating the physics of helicon plasmas and the possibility of employing them to produce negative ions for heating neutral beam injectors (HNBs). Herein, we present a fluid Monte Carlo (MC) model that describes plasma species transport in a typical helicon hydrogen plasma discharge. This work is motivated by an interest in better understanding the basic physics of helicon plasma devices operating in hydrogen and, in particular, the volume production of negative ions. This model is based on the synergy between two separate self-consistent approaches: a plasma fluid model that calculates ion transport and an MC model that determines the neutral and rovibrational density profiles of H-2. By introducing the electron density and the temperature profiles measured by Langmuir probes as model constraints, the densities of ion species (H+, H-2(+), H-3(+), H-) are computed in a 1.5D (dimensional) geometry. The estimate of the negative ion density profile represents a useful benchmark that is comparable with dedicated diagnostics, such as cavity ring-down spectroscopy and Langmuir probe laser photodetachment. Neutral gas particles (atoms and molecules) are calculated assuming a fixed plasma background. This gas-plasma decoupling is necessary due to the different timescales of plasma (microseconds) and gas kinetics (milliseconds).

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

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

A novel helicon plasma source for negative ion beams for fusion

Riccardo Agnello, Basil Duval, Ivo Furno, Philippe Frédérique Bruno Guittienne, Alan Howling, Rémy Jacquier, Claudio Marini

In DEMO reactor to produce electricity, a total installed power up to 150 MW is considered. In the heating mix, neutral beam (NB) injectors of high neutral particle energy (0.8-1 MeV) with high wall-plug efficiency (η in the range of 50% to 60%) will be required. Present design considered a NB system delivering in total 50 MW. In the Siphore NB concept [1], one of the promising candidates to meet these challenging requirements, negative ions will be 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 (SPC), a novel helicon plasma source, based on a resonant network antenna, is currently under study. The source delivers up to 10 kW at 13.56 MHz, and is installed on a linear (1.8 m long, 0.4 m diameter) vacuum vessel, allowing for full plasma characterization. In this work, the principles of operation of resonant antennas as helicon sources will be introduced, and absolute spectroscopic, Langmuir probe and interferometry measurements will be presented to characterize the performance of the source in terms of hydrogen/deuterium dissociation and negative ion production as a function of the input power at low gas pressure (0.3 Pa) and moderate magnetic field (~100 Gauss), as required by Siphore.

2016