Carbon plasma facing components

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

The relevance of chemical erosion became evident when introducing low Z elements, in particular carbon, for plasma facing components in tokamaks. The erosion yields of chemical processes and sputtering can be of the same order of up to a few percent but show significantly different dependencies physical sputtering has a strong j-dependence, whereas the yield Ych of chemical erosion varies with surface temperature Ts and flux density, as is shown in the following. 

In the fusion devices (tokamaks) using carbonaceous plasma facing components (PFC), erosion as well as re-deposition of carbon atoms have been observed. In the current configuration of Tore Supra (TS), the tokamak located in Cadarache, France, the largest part of PFCs is the toroidal pumped limiter, which is in close interaction with the plasma. It is composed of actively cooled (120°C) carbon fiber composites (CFC) tiles. Analysis of long plasma discharges has pointed out an abnormal deuterium retention which can be due to redeposited layers, as observed on several places on the PFCs [1]. These carbon layers (up to 800 micrometers thick) have been collected and their chemical analysis performed using nuclear reaction analysis shows a D/C deuterium concentration less than 10 % [2]. This low co-deposition rate makes difficult explanation of the particle retention and it is possible that porosity and structural properties of deposits play an important role in deuterimn retention. 

Ting J.-M., and Lake, M.I.. VGCF/carbon as plasma facing materials, Proc. DOE Plasma Facing Materials and Components Task Group Meeting, West Dennis, MA, Sept., 1992. 

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