EPJ D Colloquium - Overview of photo-neutralization techniques for negative ion-based neutral beam injectors in future fusion reactors

The need for safe, carbon-free and abundant sources of energy is becoming more and more pressing. While still under development, nuclear fusion can play a key role in a medium term, decarbonized energy scenario. However, in order for fusion to be commercially competitive, many sub-systems constituting the current experimental reactors need to be optimized in terms of their efficiency: in particular, DEMO and future fusion energy plants will require a substantial increase in the energy performances of the plasma heating systems.

In a new Colloquium paper published in EPJD, authors from Consorzio RFX, Padova and from CNR, Consiglio Nazionale delle Ricerche, Padova, consider the neutral beam injector system, a device whose aim is to warm up the plasma particles through collisions with neutral particles. One of the most challenging aspects of this system is to realize a high efficiency neutralizer of negative ions accelerated at around 1 MV. In this paper, the authors address the most promising technique for the realization of such a high efficiency neutralizer, namely photo-neutralization. The aim of the paper is to present an overview of the state-of-the-art in photo-neutralization configurations and compare their relative merits. Furthermore, possible future developments are investigated, such as the implementation of an ad-hoc free electron laser to help attain the required system performances.

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