H-mode scrape-off layer power width in the TCV tokamak

Obtaining acceptable conditions at the divertor targets of a next-step fusion experiment based on the tokamak concept is expected to be particularly challenging because of the small predicted value of the plasma power exhaust channel width. An increased confidence in this prediction is important to forestall any power exhaust issue and in developing corresponding divertor solutions. With the present prediction relying on empirical scaling laws based on data from six tokamaks, this letter tests these scaling laws on an additional device, the TCV tokamak. Estimates of the exhaust channel width, lambda(q), based on Thomson scattering measurements of the electron temperature and density profiles, correlate well with outer target infrared thermography. Reasonable agreement with multi-device scaling laws is found only when including both the power crossing the separatrix and the Greenwald density fraction as regression parameters. TCV's lambda(q) is 2 to 3 times smaller than in spherical tokamaks for the same value of the poloidal field. The inclusion of TCV data in the scaling laws would, therefore, require the retention of an explicit aspect ratio dependence, with consequences for all other dependencies.