K. "Nagaoka

K.Y. Watanabe

M. Osakabe

R." Seki

National Institute for Fusion Science (NIFS-Repository)

Measurement of Re-Entering Fast Ion Fluxat Outboard Side of LHD PlasmasNagaoka K., Watanabe K.Y., Osakabe M., Seki R.Estimation of energetic ion population is very im-portant to evaluate accurate heating power in neutralbeam injection (NBI) heated plasmas and for construc-tion of MHD equilibrium. Averaged orbit of co-directedfast ions shifts outwardly in major radial direction anddeviates from ﬂux surface of magnetic ﬁeld line. Dueto the orbit deviation, a part of co-directed fast ionstravel outside of the outboard-side last closed ﬂux surface(LCFS) and re-enters into the LCFS, which are called asre-entering fast ions. The numerical calculation of fastion population in the plasma region including the re-entering fast ions is not so simple because it is requiredthe full-orbit calculation and an adequate loss bound-ary. In order to experimentally estimate the re-enteringfast ions, a hybrid directional probe (HDLP) has beeninstalled in LHD, and the measurement of absolute fastion power ﬂux has been carried out1). The power ﬂuxwas evaluated from temperature increase of each probechannel, which has a thermocouple, and the calibrationwas carried out using laser injection onto the surface ofprobe channel1). In 11th and 12th campaign of LHDexperiments, the fast ion proﬁles were observed at theoutside of the LCFS, and the eﬀect of ICRF antenna onthe re-entering fast ion proﬁle was revealed.In the 13th campaign of LHD experiment, theHDLP was reconstructed to improve signal noise ratio forfast ion measurement. The probe head shape was modi-ﬁed and a pair of probe channels were arranged along themagnetic ﬁeld line for construct a directional probe andlocated near a corner of the probe head where the max-imum heat ﬂux deposits the probe surface. The fast ionmeasurement was carried out with the same condition asthat in the 11th and 12th campaign, and the comparisonbetween their results was summarized in Fig.1, in whichthe HDLP position was aligned to coincide each other.The diﬀerence between 11th and 12th is the eﬀect ofICRF antenna. In 13th campaign, the scan of magneticﬁeld strength from Bt = −0.6 T to −2.0 T was carriedout with the condition of Rax = 3.6 m, which is shown inFig. 2. The proﬁle of fast ions at the outside of the LCFSis wider for lower magnetic ﬁeld strength. The diﬀerenceof fast ion proﬁle is estimated at the 6 cm far from theLCFS and it is almost 14 mm between Bt = −0.6 T and−0.75 T, and is almost 50 mm between Bt = −0.6 T and−2.0 T, where the fast ion proﬁle with Bt = −2.0 T isextrapolated. Here the comparison with Larmor radiusis discussed. The Larmor radius of the typical fast ionwith the energy of 180 keV and pitch angle of 40 degreeis 64 mm for Bt = −0.6 T, 50 mm for Bt = −0.75 T and10 mm for Bt = −2.0 T. The scale length of diﬀerenceof fast ion proﬁles on the scan of magnetic ﬁeld strengthis almost same scale with the Larmor radius of fast ionswith the energy of 180 keV and pitch angle of 40 de-gree. For the further understanding of fast ion proﬁle atthe outside of the LCFS, the comparison with full-orbitnumerical simulation with real coordinates is required,which is now in progress and will be reported in nearfuture.Fig. 1: The proﬁle of fast ion power ﬂux normalized bythe deposition power of NBI measured by HDLP at theoutboard side of the LCFS. In the 11th campaign, theICRF anntenas exist, while it did not in 12th and 13thcampaigns.Fig. 2: The proﬁle of fast ion power ﬂux normalizedby the deposition power of NBI. The results with themagnetic ﬁeld strength of Bt = −0.6 T, Bt = −0.75 Tand Bt = −2.0 T are compared in the magnetic axisposition of Rax = 3.60 m.1) K. Nagaoka, K.Y. Watanabe, M. Osakabe, et al., Rev.Sci. Instrum. 79, (2008) 10E523.80§56. eas  f     at Outboard Side of L  Plas asNagaoka, K., Watanabe, K.Y., Osakabe, M., Seki, R.

Measurement of Re-Entering Fast Ion Flux at Outboard Side of LHD Plasmas

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)