15-20 October 2017
CERN
Europe/Zurich timezone

First Experimental Results of the Helicon Driver on Cybele

17 Oct 2017, 16:30
2h 30m
CERN

CERN

Centre international de Conférence Genève (CICG). http://www.cicg.ch/
Poster presentation Negative ion sources Poster Session 2

Speaker

Mr Iaroslav Morgal (CEA Cadarache, IRFM / AMU )

Description

Cybele machine which is directed to development of the future NBI system SIPHORE for the reactor DEMO [1] is assembled and operated at the IRFM in CEA Cadarache. The main purpose is to create a tall and narrow (blade-like) negative ion beam (H$^{-}$, D$^{-}$), for further neutralisation by laser photodetachment. The source has a high aspect ratio ($1.2\,$m $\times$ $0.15\,$m), which is particularly relevant to the SIPHORE concept and creation of the blade-like beam. In the top of the source a Helicon driver is installed, which currently operates with a $13.56\,$MHz $10\,$kW generator. A magnetic field parallel to the source vertical axis is generated by two lateral electric coils sitting on opposite sides of an iron rectangular frame which surrounds the source, to provide homogeneous vertical magnetic field.

The Cybele ion source has been tested with the Helicon driver to inject plasma particles in the direction parallel to $\vec{\mathbf{B}}$. The first experiments were carried out with $3\,$kW of RF power, in pure Argon or mixture of Argon and Hydrogen at the gas pressure ~$0.3\,$Pa (ITER and DEMO relevant).

Plasma propagates well in the source volume over $1$ to $1.2\,$m. The Langmuir probe diagnostics measured plasma density up to $4 x 10^{17}\,$m$^{-3}$ and temperature around $3$-$5\,$eV (pure Argon) at a distance of $10\,$cm from the center of plasma column and at a vertical position $60\,$cm from the output of the driver.

The experiments revealed a significant deviation of the plasma column from the vertical axis.

Modelling activities dedicated to the optimization of the Cybele source were performed. The simulation of 3D electron trajectories explained the reason of plasma deviation. The non-symmetrical magnetic field coils with respect to the Helicon driver cause plasma particle deflection from the main central axis of the NI source.

Further investigation and construction modification will be done in next few months, to make the plasma column well centered in the vertical direction. For this purpose a new flange is under manufacturing now. Also new extraction and acceleration grids in front of plasma source are manufactured in order to extract the negative ions from the plasma edge.

Finally, in this contribution we will present the first results obtained on the optimized Cybele machine. Also, the plans for the future are acceleration grids construction and negative ions extraction from the plasma.

References

[1] A. Simonin et. al., R&D around a photoneutralizer-based NBI system (Siphore) in view of a DEMO Tokamak steady state fusion reactor, Nucl. Fusion 55 (2015) 123020 (19pp).

Primary authors

Mr Iaroslav Morgal (CEA Cadarache, IRFM / AMU ) Dr Alain Simonin (CEA Cadarache, IRFM) Mr Christian Grand (CEA Cadarache, IRFM) Dr Gilles Cartry (Aix-Marseille Universite) Dr Hubert De Esch (CEA Cadarache, IRFM)

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