D. Kato

H.A. Sakaue

L. Pichl

T. Kusakabe

National Institute for Fusion Science (NIFS-Repository)

Construction of the ITER (International Thermo-nuclear Experimental Reactor) which is a next day largenuclear fusion device is advancing by internationalcooperation. Tungsten (W) materials are planned to usetogether with carbon based materials at the divertor of theITER. For the modeling of ITER plasma, the cross-section data of charge-transfer processes of W ionscolliding with some kinds of hydrocarbon molecules arerequired. However, these cross section data are stillscarce in the low collision energy.1-3) In this research, theproducing method of W ions is established first, and wemeasure the charge-transfer cross sections of W ions incollisions with hydrocarbon molecules in the energy regionbelow 4 keV/q (q : the number of ionic charge).In the present experiment, as a first step of this study,tungsten ions were extracted from an electron impact ionsource (EIIS) with ion source test equipment as shown inFig. 1. Tungsten hex carbonyl W(CO)6 is widely used inelectron beam-induced deposition technique. Because itsvapor pressure is relatively high, it is easily vaporizedunder a high vacuum. In this experiment, the tungsten hexcarbonyl powder in a reservoir evaporates under a highvacuum, and is introduced into the EIIS. W(CO)6molecules were ionized and decomposed by 100eVelectron impact. Extracted ions were mass-separated withhomogeneous magnetic field in a 60 sector magnet, inwhich magnetic density can set to be up to about 6 k Gaussand its radius is 0.15 m, and were detected with a channelelectron multiplier (CEM) or a micro-channel plate detector(MCP). The front and main chambers were evacuateddown to the back pressure of less than about 1×10–4 Pa by50 l/s and 150 l/s turbo-molecular pumps (TMP).Figure 2 shows a typical mass spectrum of tungstenand their fragment ions generated from the tungsten hexcarbonyl extracted from the EIIS. The electric potentialfor acceleration of ions is 700 V. The net W(CO)6 gaspressure was about 1×10–3 Pa at outer region of the EIIS.It can be thought that some ions such as H+, H2+, H2O+, O2+,and so forth among the detected ions were produced fromH2O, and O2 molecules of residual gas. Singly and doublycharged tungsten ions, W+ and W2+, were clearly detectedand separated from many fragment W(CO)n+ and W(CO)n2+ions (n = 1 ~ 6). A large number of the ions correspond-ding to CO+, its dimmer (CO)2+, C+, O+, O2+, and so forthconsidered to originate in the carbonyl radical (-CO-) oftungsten hex carbonyl, were also identified.As mentioned above, singly and doubly chargedtungsten ions were separated and detected from manyfragment ions with the mass spectrometer by a uniformmagnetic field. However, a Wien filter is used to analyzethe mass and charge of extracted ions from the ion sourcein our current experimental apparatus for cross sectionmeasurement. At present, the mass resolution of thisWien filter is low, and these fragment ions cannot beseparated. In order to be able to perform cross sectionmeasurement, some improvements in the mass resolution ofthis Wien filter are under preparation.Fig. 1. Experimental apparatus for testing the ionsource.Fig. 2. Mass spectrum of tungsten and their fragmentions generated from tungsten hex carbonyl extractedfrom the EIIS. The electric potential for accelerationof ions is 700 V.1) Janev, R. K., Belić, D. S., Bransden, B. H.: Phys. Rev.A 28 (1983) 1293.2) Meyer, F. W. et al.: Phys. Rev. A 19 (1979) 515.3) Kheyrandish, H., Armour, D. G., and Jones, E. J.:Vacuum 34 (1984) 269.Countingrate（cps）50 l/s T MPMovable slit60゜sector magnetMovable slitFaraday cupChanneltron (CEM)Electron impaction source (EIIS)Valve150 l/s TMPW(CO)6to RotarypumpReservoir323§45. Cross Sections of Charge Transfer by Slow Tungsten Ions in Collisions with Hydrocarbon MoleculesKusakabe, T. (Dept. Phys. Kinki Univ.),  Pichl, L. (ICU),  Kato, D.,  Sakaue, H.A.

Cross Sections of Charge Transfer by Slow Tungsten Ions in Collisions with Hydrocarbon Molecules

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