Post mortem analysis of a JET quartz microbalance system

In the year 2001, a quartz microbalance system (QMB) was installed in the remote area of the inner JET divertor to investigate in situ material erosion and redeposition processes. When removed in 2004, the system was found to be coated all over with carbon deposits. The deposit on the quartz oscillator and the outer and inner housing was analysed by various methods, as SIMS (secondary ion mass spectroscopy), stylus depth profilometry, EPMA (electron probe microanalysis), TIPT (Tritium imaging plate technique) and colorimetry and compared to the frequency change of the quartz. The layer thickness was determined to 1.85 ± 0.1 μm in average on an area of 0.95 cm2 which has to be related to the equivalent of 1.77 × 10−4 g measured from the frequency change of 23 640 Hz. This corresponds to a carbon areal density of 9.3 × 1018 C atoms/cm2. Significant deposition was found also on the surfaces inside the QMB housing which can only be understood if reflection and low sticking is assumed for a high fraction of particles.