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, γ 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 γ. Within the admittedly rather large uncertainty, L-mode values of γ are found to be consistent with simple sheath theory.