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

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.

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

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

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.

2018

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

Negative ion source development for a photoneutralization based neutral beam system for future fusion reactors

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

In parallel to the developments dedicated to the ITER neutral beam (NB) system, CEA-IRFM with laboratories in France and Switzerland are studying the feasibility of a new generation of NB system able to provide heating and current drive for the future DEMOnstration fusion reactor. For the steady-state scenario, the NB system will have to provide a high NB power level with a high wall-plug efficiency (eta similar to 60%). Neutralization of the energetic negative ions by photodetachment (so called photoneutralization), if feasible, appears to be the ideal solution to meet these performances, in the sense that it could offer a high beam neutralization rate (>80%) and a wall-plug efficiency higher than 60%. The main challenge of this new injector concept is the achievement of a very high power photon flux which could be provided by 3 MW Fabry-Perot optical cavities implanted along the 1 MeVD- beam in the neutralizer stage. The beamline topology is tall and narrow to provide laminar ion beam sheets, which will be entirely illuminated by the intra-cavity photon beams propagating along the vertical axis. The paper describes the present R&D (experiments and modelling) addressing the development of a new ion source concept (Cybele source) which is based on a magnetized plasma column. Parametric studies of the source are performed using Langmuir probes in order to characterize and compare the plasma parameters in the source column with different plasma generators, such as filamented cathodes, radio-frequency driver and a helicon antenna specifically developed at SPC-EPFL satisfying the requirements for the Cybele (axial magnetic field of 10 mT, source operating pressure: 0.3 Pa in hydrogen or deuterium). The paper compares the performances of the three plasma generators. It is shown that the helicon plasma generator is a very promising candidate to provide an intense and uniform negative ion beam sheet.

Iop Publishing Ltd2016

Negative ion source development for a photoneutralization based neutral beam system for future fusion reactors

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

Iop Publishing Ltd2016