H. Funaba

National Institute for Fusion Science (NIFS-Repository)

The partial pressures of neutral gases in LHD are mea-sured by the penning gauge spectroscopy diagnostics whichwas developed at TEXTOR in order to distinguish the partialpressures of deuterium and helium [1]. Three penning gaugespectroscopy systems were operated on LHD in 2013. One islocated at the upper port (2.5U) and the other two are locatedat the inner ports. The inner port gauges are located at thedivertor regions with the bafﬂe structure (9I) and without thebafﬂe structure (3I). In this experimental campaign, the pre-cise calibration of helium partial pressure was made. Then,the partial pressures at three different positions are compared.The behavior of the neutral partial pressures during and be-tween the long pulse plasmas is also studied.Figure 1 shows the calibration result of the partial pres-sure with helium gas for the gauges at (a) 2.5U, (b) 3I and (c)9I. The signal sensitivity of the 2.5U gauge is high becausethe Alcatel gauge is used here. The sensitivity at 3I is betterthan that at 9I since the anode of the 3I gauge is improved forthe observing the penning discharge. As the calibration wasmade after the long pulse plasma experiment with helium, thecalibration with hydrogen gas was difﬁcult due to the build upof helium pressure. Therefore, the hydrogen gas pressure iscalibrated by subtracting the calibrated helium pressure.The helium and hydrogen pressure at the end of a longpulse discharge #124576, which had the duration of about2676 sec., at 2.5U is shown in Fig. 2 (a). The abscissa showsthe time of the data acquisition. For this long pulse discharge,the penning gauge spectroscopy was operated for 7200 sec.in order to measure between plasmas. The neutral pressure at2.5U reduced during the plasma discharge. The helium pres-sure increased at the and of the long pulse discharge. As thisplasma was operated with only the helium gas-puff, the hydro-gen pressure increased slightly later than the end timing of theplasma. Fig. 2 (b) shows the helium and hydrogen pressuresat 3I and 9I during another long pulse discharge (#122263),which had the duration of about 350 sec. Both the neutralpressures at 3I and 9I became high during the plasma dis-charge. The neutral pressure at the divertor region with thebafﬂe is higher than that at the divertor region without thebafﬂe by about one order.(a)(b) (c)Fig. 1: Results of helium partial pressure calibration at(a) 2.5U, (b) 3I and (c) 9I.(a)(b)heatingLHD #122263ECHICRF02×1019<ne>[m−3 ]<ne>05.0×10−51.0×10−41.5×10−42.0×10−4P [Pa]Neutral Pressure (with baffle)H20.0000.0010.0020.0030.004time [s]P [Pa]Neutral Pressure (with baffle)He01.0×10−52.0×10−53.0×10−54.0×10−5P [Pa]Neutral Pressure (w/o baffle)H26626.0 6706.0 6786.0 6866.0 6946.0 7026.00.00000.00020.00040.00060.0008time [s]P [Pa]Neutral Pressure (w/o baffle)HeFig. 2: Signals of ECH, ICRF, electron density and hydrogenand helium partial pressures in (a) the end of #124576at 2.5U and (b) #122263 at 3I and 9I.1) K.H. Finken, et al., Rev. Sci. Instrum. 63 (1992) 1.32§27. Hydrogen and Helium Partial Pressure Measurement by the Penning Gauge SpectroscopyFunaba, H.

Hydrogen and Helium Partial Pressure Measurement by the Penning Gauge Spectroscopy

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