Quartz micro-balance results of pulse-resolved erosion/deposition in the JET-ILW divertor

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.