Comparison of wall/divertor deuterium retention and plasma fueling requirements on the DIII-D, TdeV, and ASDEX-upgrade tokamaks

The authors present a comparison of the wall deuterium retention and plasma fueling requirements of three diverted tokamaks, DIII-D, TdeV, and ASDEX-Upgrade, with different fractions of graphite coverage of stainless steel or Inconel outer walls and different heating modes. Data from particle balance experiments on each tokamak demonstrate well-defined differences in wall retention of deuterium gas, even though all three tokamaks have complete graphite coverage of divertor components and all three are routinely boronized. This paper compares the evolution of the change in wall loading and net fueling efficiency for gas during dedicated experiments without Helium Glow Discharge Cleaning on the DIII-D and TdeV tokamaks. On the DIII-D tokamak, it was demonstrated that the wall loading could be increased by > 1,250 Torr-1 (equivalent to 150 {times} plasma particle content) plasma inventories resulting in an increase in fueling efficiency from 0.08 to 0.25, whereas the wall loading on the TdeV tokamak could only be increased by < 35 Torr-{ell} (equivalent to 50{times} plasma particle content) plasma inventories at a maximum fueling efficiency {approximately} 1. Data from the ASDEX-Upgrade tokamak suggests qualitative behavior of wall retention and fueling efficiency similar to DIII-D

Layer Splitting by H-Ion Implantation in Silicon: Lower Limit on Layer Thickness?

AbstractThe Smart-Cut™ process and its variants involve H and/or He ion implantation and annealing to neatly exfoliate a layer of material as thin as the ion range. At low ion energy, as required for further miniaturisation, several effects may inhibit the process. We implanted undoped Si (100), (110) and (111) with 5 keV H or D ions at doses below (3–4×1016/cm2) or above (5.5×1016/cm2) the critical dose for blistering. The samples were either isochronally annealed for 1h or 2h in three steps at 500, 550 and 600°C, or subjected to thermal desorption spectroscopy (TDS) with linear ramps of 7.5 K/min up to 500, 550 or 600°C. The surface morphology was observed at each step by scanning electron or atomic force microscopy. Below the critical blistering dose, TDS only shows a broad high temperature (∼525°C) peak, while above that dose, a low temperature peak (∼360°C) also appears, though weakly in the case of (110) samples. The exfoliated area (as % of total surface) increases with temperature, and also varies with wafer orientation, being minimum for (110) samples and maximum for (111) samples. This orientation effect is much more pronounced for H-implants than for D-implants. All these trends indicate that ion channelling leads to an inhibition of exfoliation.</jats:p

Surface Microstructure of High Temperature Beryllium Implanted with Deuterium

ABSTRACTWe have investigated implantation temperature effects on the formation of blisters on the surface of Be foils implanted with low energy, 1.5 keV, deuterium ions to doses ranging from 3×1016 to 1.2×1018 ions cm-2, a dose exceeding by far the saturation (≈1.8×1017 ions cm-2: 30% at.). The implantation temperature was varied from 293 K (RT) to 983 K. The samples have been characterized by scanning electron microscopy (SEM). For saturated samples, blisters were present even at high temperatures, viz 983 K, and no blisters were found for samples implanted below 20% at.. However, on samples in which a dramatic grain growth has been observed, blisters were found to decorate the grain boundaries and to interconnect with each other. The average blister diameter increases with increasing temperature, thus indicating the thermodynamical aspect of blister formation and coalescence. On the other hand, for low temperature (473 K), the surface structure that has developed is similar to that at RT, except for an increased most probable blister diameter and blister density, and there was no indication that the blisters ruptured. The blister skin thickness agrees well with the projected range of the implanted ions. Over-saturated samples at RT retained only ≈30% at., corroborating the observations that some blisters formed on already ruptured ones.</jats:p