Investigating the possibility of a monitoring fast ion diagnostic for ITER

In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information...

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Bibliographic Details
Published in:Review of scientific instruments 2008-10, Vol.79 (10), p.10E517-10E517-3
Main Authors: De Angelis, R., von Hellermann, M. G., Orsitto, F. P., Tugarinov, S.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALFVEN WAVES
ALPHA PARTICLES
CHARGE EXCHANGE
DISTRIBUTION FUNCTIONS
FIRST WALL
ICR HEATING
IONS
ITER TOKAMAK
LINE BROADENING
MEV RANGE
MONITORING
PARAMETRIC INSTABILITIES
PARTICLES
PLASMA
PLASMA BEAM INJECTION
SIGNAL-TO-NOISE RATIO
SPATIAL RESOLUTION
SPECTROMETERS
TIME RESOLUTION
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Summary:In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information for safe and reliable plasma operations. In this paper, we examine the feasibility of a monitoring system based on active charge exchange recombination spectroscopy making use of the 0.5 MeV ∕ amu ITER heating neutral beams for detecting fast He + 2 4 (alphas) particles in ITER plasmas. There are two time scales relevant to fast ion dynamics: the first is the slowing down time of the distribution function which is of the order of 1 s , and the second is the time scale of burstlike transport events such as collective Alfvén mode excitations, which-for typical ITER plasma parameters-can be as low as 0.2 - 1 ms . To detect such fast events a broadband high-throughput spectrometer is needed, while for the reconstruction of the alpha velocity distribution function a higher resolution spectrometer and longer integration time are necessary. To monitor a spatial redistribution of fast particles due to the propagation of the instability, it is proposed to use a limited number of spatial channels, looking at the charge exchange He II spectra induced by the heating beams, whose energy matches the slowing down energies of fast particles. The proposal is to share the motional stark effect periscope on equatorial port 3 [ A. Malaquias , Rev. Sci. Instrum . 75 , 3393 ( 2004 ) ] adding additional fibers and suitable instruments. A signal to noise ratio of 5 could be achieved with a spatial resolution of a ∕ 15 and a time resolution of 5 ms , in a broad spectral band of 100 Å , corresponding to the spectral broadening of the line emitted by alpha particles with energies Δ E ⩽ 1.5 MeV . Fast H and D ion populations created by heating neutral beam or ion cyclotron resonance heating are expected to produce significantly lower charge exchange signal levels and can only be monitored on substantially longer time scales as it is expected because of the strong energy difference with respect to the heating neutral beam and the consequently low charge exchange cross sections.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.2965003