Sheath heat transmission factors on TCV

Despite its importance in determining the calculated surface power flux predicted, for example, by scrape-off layer simulation codes, the sheath heat transmission factor, gamma remains a quantity whose theoretically predicted value has rarely been tested experimentally. This contribution attempts such a test by comparing direct, infra-red measurements of the outer divertor target power fluxes in single null lower discharges on the TCV tokamak with tile embedded Langmuir probe data. A selection of L-mode plasmas have been used, including varying outer target flux expansion and a pair of matched D-He pulses. Particular care is taken to identify all possible sources of error and estimate their effect on the derived values of gamma. Within the admittedly rather large uncertainty, L-mode values of gamma are found to be consistent with simple sheath theory. (c) 2007 Elsevier B.V. All rights reserved.