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Rev Sci Instrum. 2010 Oct;81(10):10D710. doi: 10.1063/1.3475372.

Design of a cavity ring-down spectroscopy diagnostic for negative ion rf source SPIDER.

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  • 1Consorzio RFX-Associazione Euratom-Enea sulla Fusione, corso Stati Uniti 4, I-35127 Padova, Italy.


The rf source test facility SPIDER will test and optimize the source of the 1 MV neutral beam injection systems for ITER. Cavity ring-down spectroscopy (CRDS) will measure the absolute line-of-sight integrated density of negative (H(-) and D(-)) ions, produced in the extraction region of the source. CRDS takes advantage of the photodetachment process: negative ions are converted to neutral hydrogen atoms by electron stripping through absorption of a photon from a laser. The design of this diagnostic is presented with the corresponding simulation of the expected performance. A prototype operated without plasma has provided CRDS reference signals, design validation, and results concerning the signal-to-noise ratio.

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