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Bernard Reman (Toulouse): Modelling of the beam-driven plasma neutraliser

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In the International Thermonuclear Experimental Reactor (ITER), the two neutral-beam in-

jectors (NBI) are designed to deliver a joint power of 33MW by injecting deuterium at 1 MeV.

The neutralisation of positively charged deuterium is inefficient at such energies which requires

to generate, to accelerate and to neutralise negatively charged deuterium ions. The magnetised plasma column source is a serious candidate for the generation of negative ions and different

schemes of neutralisation have been proposed including gas, plasma and photo-neutralisation

[1]. We focus on the plasma neutraliser [2] which appears to be the ideal trade-off between gas

neutralisation, limited to a neutralisation yield of ∼ 50%, and photoneutralisation which would

increase this beyond 90% although not ready technologically. Recent modelling work suggests

that the plasma could be sustained by the negative ion beam itself, alleviating the operation

of an external plasma source [3, 4] and it could reach a neutralisation efficiency ∼ 80% with

ne > 5 × 10^18 m−3 . The stripped electrons and the electrons created by beam ionisation of the

background gas must be magnetically confined. We conduct particle test calculations in a mag-

netic bottle, adding ionisation, to assess the electrons residence time before studying the plasma

neutraliser by means of fully self-consistent particle-in-cell (PIC) simulations [5]. In a second time, we address the stability of these linear plasma devices in the plane perpendicular to the magnetic field as it affects plasma transport and eventually their performance.



[1] J. Pamela, Plasma Phys. Control. Fusion 37 A325 (1995)

[2] K. H. Berkner et al., 2nd Int. Symp Prod. and Neutr. of Neg. Ions and Beams, Upton, NY (1980)

[3] E. Surrey and A.J.T. Holmes, AIP Conf. Proc. 1515 532 (2013)

[4] I. Turner and A.J.T. Holmes, Fusion Eng. Des. 149 111327 (2019)

[5] G. Fubiani et al., New J. Phys. 19 015002 (2017)

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