The hydrogen and deuterium inventories of the ASDEX Upgrade divertor tiles were measured after the experimental period from December 1994 to July 1995 by thermal desorption spectroscopy (TDS) of samples cut out of the divertor tiles. The samples were heated by electron bombardment up to 2100 K; the released gases were measured by means of a calibrated quadrupole mass spectrometer. The measured hydrogen or deuterium inventories are of the order of loz3 m-'. They are larger for samples of the inner divertor than of the outer divertor by a factor of about 2. The largest inventory was found at the separatrix position of the inner divertor. Most of the released hydrogen (H) can be attributed to water adsorbed in the near surface region during the air exposure prior to the TDS measurements. The total inventories measured by TDS exceed the inventories in the near surface region (< 25 pm) measured by ion beam analysis methods by a factor of up to 10. Hence, the total hydrogen retention is governed by the diffusion out of the near surface region deep into the material. The hydrogen and deuterium inventories decrease with increasing surface temperature.

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We study the interplay between crystal orientation and confinement in diffusion-limited growth. Growth of the overall morphology in the direction of minimal surface stiffness has been investigated in some detail by various authors, the most recent advances being summarized by Brener et al (Brener E, Müller-Krumbhaar H and Temkin D 1996 Phys. Rev. E 54 2714). Here, we consider competing influences, each trying to impose a different growth direction. The simplest possible situation giving rise to such a competition is growth in a channel with a mismatch between the orientation of the channel walls and surface tension anisotropy. Analysing this situation, we find a new structure and gain further insight into the problem of morphological stability. Another case is that of periodic boundary conditions, where the same angle of misorientation can be used to describe growth of a tilted array of finger-shaped crystals. It is found that the transition between dendritic and doublonic structures is affected by the tilt.