Quartz micro-balance results of pulse-resolved erosion/deposition in the JET-ILW divertor. (August 2017) - Sergienko, G.
Highlights: Sensitivity of quartz crystal microbalances (QMB) used at JET has been improved by a factor of 10 up to 1.4 ng/cm 2 (about 0.05 Be monolayer). The stable deposition with average rate between 1.2 and 3 ng cm −2 s −1 was observed in inner divertor QMB when the strike point position is close to the bottom edge of the vertical target. Net erosion was found on both the inner and outer divertor QMBs for strike points on the horizontal targets by pulse based measurements. Observed net erosion signals can be explained by desorption-adsorption of the vacuum background gases on the deposited layer. Abstract: A set of quartz crystal microbalances (QMB) was used at JET with full carbon wall to monitor mass erosion/deposition rates in the remote areas of the divertor. After introduction of the ITER- like wall (ILW) in JET with beryllium main wall and tungsten divertor, strong reduction of the material deposition and accompanied fuel retention was observed. Therefore the existing QMB electronics have been modified to improve the accuracy of frequency measurements by a factor of ten down to 0.1 Hz which corresponds to 1.4 ng cm −2 . The averaged deposition rates of 1.2–3 ng cm −2 s −1 and erosion rates of 5.6–8.1 ng cm −2 s −1 were observed in the inner divertor of JET -ILW with the inner strike point positions close to the bottom edge of vertical tile 3 and at the horizontal tile 4 respectively. The erosion with averaged rates of ≈2.1 ng cm −2 s −1 and ≈120 ng cm −2 s −1 were observed in the outer divertor for the outer strike point positions at tile 5 and tile 6 respectively.