E. Asano

K. Ikeda

K. Tsumori

L." Grisham

M. Osakabe

M. Sato

O. Kaneko

T. Kawamoto

Y. "Oka

Y. Takeiri

National Institute for Fusion Science (NIFS-Repository)

§25. Filament Lifetime and Doppler-Shift Spectrum in LHD-NBI Negative Ion Source Oka, Y., Tsumori, K., Takeiri, Y., Ikeda, K., Osakabe, M., Kaneko, 0., Asano, E., Kawamoto, T., Sato, M., Grisham, L. (PPPL, USA) Firstly" in FY 2001~ filament lifetime, which brings inevitably an interruption of NBI experiments, de-conditioning of high -voltage, Cs deterioration et al, was evaluated in Negative Ion _ Source of Large Helical Device-Neutral Beam Injectorl). Secondly, energy spectrum of negative ion beam was measured with Doppler-shift spectrometry to study the stripping loss and put more of the power into the full energy component. H- iOn source consists ofCs seeded external filtermulti-cusp plasma source and a 25x125cm2 multi-aperture accelerator. H:. current of -25A was demonstrated in every six ion sources for 3 - Beam-Lines. Each plasma source contains 24 filaments of 1.8 mm diam tungsten wire. Table I lists the filament weight loss (in column 3), total shots (in colwnn 4), and others dwing the LHD experimental cycles. It is found that the filaments have to be exchanged in general every 10,000 shots, which occurs approximately every 1~3 months. The loss rate in BL-2 is increased by about 30 % compared to that in previous cycle due to increased total shots for a IQllger pulse duration of 3$$. Filament life time in BL-I increases drastically in this cycle due to improvement in the source plasma confinement It was also observed that the filament location of high loss rate corresponded to a position of higher H- production and plasma density. TABLE I Ion source Run No. Weight loss (gr/filament) (max) IS-lA 4 0.571 5 0.081 8 IS-18 3 0.18 4 0.115 IS-2A 4 0.085 0.142 (S-2B 3 0.103 IS-3A 0.18 IS-3B 5 0.12 138 Experimentally-guided improvements were made to the Doppler-shift spectroscopy system~ which consisted of GratinglCCD spectrometer. These enabled us to get the first measurements of the preliminary spectrum of the LHD beams, as sho\Vll in Fig.I. It appears that the energy distribution is peaked at the full acceleration energy, but looks as if may have a significant lower energy continmnn of beam arising from stripping of negative ions during the acceleration process. As the instrumentation does not permit a qualitative analysis, a much better measurement is needed for the next step of investigation. - - -~ ....... ~ ~A 1,;".' 6.AA.J. •• /II. ~". ..... " ... .Ni\, ." ... , V -.. I It I I" f • I •• • ••• I •• I I r • I •• I I ••••• I , • • •••• , I ••. Wave length (pixel) Shifted peak H(alpha) Fig. 1 The first measurements of the Doppler-shift spectrum of the LHD beams Reference 1) Oka, Y., et aI., Rev. Sci. lnstrum. 73, 1054(2002) total shots Loss rate total loss (mgr/shot (gr/one source) lfilament) 5536 0.103 (-'3.7 ) 2458 0.033 9953 -0.01 6536 0.028 3801 0.03 8580 0.01 1.17 6884 0.013 6874 0.015 1.23 8229 0.022 8432 0.014 

Filament Lifetime and Doppler-Shift Spectrum in LHD-NBI Negative Ion Source

Filament Lifetime and Doppler-Shift Spectrum in LHD-NBI Negative Ion Source

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