Quantitatively measuring the influence of helium in plasma-exposed tungsten

Tungsten samples are exposed to 3He plasma to quantify their helium retention behavior. The retention saturates quickly with helium fluence and increases only slightly from 4.3 × 1019 He/m2 at 773 K, to 7.5 × 1019 He/m2 at 973 K. The helium content increases dramatically to 6.8 × 1020 He/m2 when fuzz is formed on the surface of a sample exposed at 1173 K, but the majority of the retained helium (5.1 × 1020 He/m2) is found to reside below the layer of fuzz tendrils. Additional tungsten samples were exposed to either simultaneous, or sequential, D/He plasma, followed by TDS. Measurements show the majority of the D retained during simultaneous exposures is located in the near surface region of helium nano-bubbles. No deuterium was detected in any of the samples after the heating to 1273 K, but 67% of the helium was released from simultaneously exposed samples, and only 23% of the helium was released from the sequentially exposed samples.