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

R Agnello; M Barbisan; I Furno; Ph Guittienne; A A Howling; R Jacquier; R Pasqualotto; G Plyushchev; Y Andrebe; S Béchu; I Morgal; A Simonin

doi:10.1063/1.5044504

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

Rev Sci Instrum. 2018 Oct;89(10):103504. doi: 10.1063/1.5044504.

Authors

R Agnello¹, M Barbisan², I Furno¹, Ph Guittienne³, A A Howling¹, R Jacquier¹, R Pasqualotto², G Plyushchev¹, Y Andrebe¹, S Béchu⁴, I Morgal⁵, A Simonin⁵

Affiliations

¹ Ecole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC), CH-1015 Lausanne, Switzerland.
² Consorzio RFX, Corso Stati Uniti 4, I-35127 Padova, Italy.
³ Helyssen, Route de la Louche 31, CH-1092 Belmont-sur-Lausanne, Switzerland.
⁴ Université Grenoble-Alpes, CNRS, Grenoble INP, LPSC-INP23, 38000 Grenoble, France.
⁵ CEA, IRFM, F-13108 St-Paul-lez-Durance, France.

PMID: 30399701
DOI: 10.1063/1.5044504

Abstract

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 ≅ 1.5 × 10¹⁸ m^-3 in H₂ and D₂ 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 × 10¹⁶ 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.