Field Emission From Nanostructured Tendril Bundles

Enhancement of Arc Ignition on Tungsten in Helium Plasmas with Impurity Gases

“…Figure 4 shows the frequency of arcing, f arc , defined as the number of arc occurrence per an hour as a function of the bias voltage for different plasma conditions. When samples were exposed to a pure He plasma without any pre-treatment, f arc was always 0 at the bias voltage range of −150 to −250 V. When Ne was seeded, arcs were not detected at −150 V, but triggered at −200 V and f arc became greater as the bias voltage deepened to −250 V. It is thought that the field emission from the tip of NTBs was enhanced, hence increased chance in transit to breakdown [10]. When Ar was seeded, the arcing occurred at −150 V, likely due to the presence of NTBs on this condition.…”

“…Considering that no NTB formation is anticipated on a surface with a pure He plasma exposure, this also suggests that NTBs, which have already grown on the surface, trigger arcing with ease. It is known that the onset of field electron emission on NTBs is on the order of ∼1 kV/mm depending on their shapes [10], which is much lower than that on fuzzy surface (∼7 kV/mm) [13]. It implies that the breakdown could be initiated by the onset of field electron emission from the tip of NTBs and lead to arcing.…”

“…This implies that there is a possibility of NTBs formation on the ITER divertor. The field electron emission measurements from NTBs showed that the NTBs can be a trigger of arc ignition with greater possibility compared to fuzz [10], whereas detailed conditions for arc ignition on such NTBs surfaces have not been investigated.…”

Growth origin of large-scale fiberform nanostructures in He-W co-deposition environment

“…The necessary condition for fuzz growth could be satisfied around the strike point in the ITER divertor 7 . There are concerns about fuzz formation in fusion reactors, which leads to the significantly reduced thermal resistance 8 and increased field electron emission [9][10][11] , may lead to the initiation of arcing and the release of large amounts of W 5,[12][13][14] .…”

Growth origin of large-scale fiberform nanostructures in He–W co-deposition environment

“…The necessary condition for fuzz growth could be satisfied around the strike point in the ITER divertor 7 . There are concerns about fuzz formation in fusion reactors, which leads to the significantly reduced thermal resistance 8 and increased field electron emission [9][10][11] . This may lead to the initiation of arcing and the release of large amounts of W 5,[12][13][14] .…”