Redeposition Characteristics of Heavy Hydrocarbon Molecules on a Divertor Plate

Abstract

In this study, local redeposition characteristics of hydrocarbon molecules from the ethane family are investigated using Monte Carlo simulation. Information about redeposition characteristics is required to estimate tritium retention via redeposition with chemically eroded hydrocarbon molecules. For the condition of multiple reflections at divertor surface and a plasma density of 1.0 × 10 19 m −3 , the local redeposition characteristics for injection of ethane family (C 2 H 2 , C 2 H 4 , C 2 H 6 ) have been investigated for plasma temperatures ranging from 1 to 100 eV. The number of redeposited hydrocarbon molecules increases with plasma temperature because of the increase in impinging particle energy. The increase in sheath potential results in the increase in particle energy. For plasma temperatures lower than 5 eV, there is a sudden increase in the number of redeposited particles with plasma temperature because of the increase in the number of impinging molecular ions. Sheath field acceleration is the main mechanism that causes the ions to move to the divertor plate, and the exponential increase in the number of redeposited particles results from the increase in hydrocarbon break-up products in the sheath potential region.

Effects of fibre-form nanostructures on particle emissions from a tungsten surface in plasmas

“…It is quite reasonable since the secondary electrons cannot come out to the sheath region through a forest of fibre-form nanostructures because of the much higher likelihood of collisions with the surfaces of the fibres if deep troughs are present. A similar situation has already been analysed numerically by Ohya's group, in which a deep trough prevents the emission of secondary electrons [18]. The final sheath voltage of 65 V is still smaller than the theoretical value obtained from figure 3.…”