Abstract
In the next generation of fusion reactors, such as DEMO, neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atoms with 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 are introduced. We present absolute spectroscopy, Langmuir probe, and interferometry measurements on helicon plasmas. We characterize the performance of 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 are presented, as a first step towards the validation of the Siphore concept.
Highlights
The generation of fusion reactors, such as DEMO, will require neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atoms with high wall-plug efficiency (>50%) to reach burning plasma conditions and 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
The present NBI system for DEMO assumes that 50 MW is delivered to the plasma by 3 NBIs, which can only be obtained using a negative ion-based NBI system
Summary
The generation of fusion reactors, such as DEMO, will require neutral beam injectors (NBIs) of high energy (0.8-1 MeV) deuterium atoms with high wall-plug efficiency (>50%) to reach burning plasma conditions and provide a significant amount of current drive. Since the first experiments performed by Boswell [3], helicon sources have been extensively studied and they are proven to be very efficient for high-density 10181019 m-3 plasma production (in noble gases, typically argon) with moderate injection power at low pressure. They have found applications in semiconductor manufacturing and ion thruster systems.
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