Development of a quartz crystal microbalance diagnostic for measuring material erosion and deposition on the first wall in EAST

A quartz crystal microbalance (QMB) diagnostic system has been established in Experimental Advanced Superconducting Tokamak (EAST) for real-time and in situ measurements of erosion and deposition rates of plasma-facing materials at the first wall. A ∼70 nm aluminum (Al) film has been coated on the QMB crystal surface to measure the erosion rate by charge exchange neutral particles. Dual sensors of the QMB system have been used with a closed sensor for reference. The stability and light sensitivity of the QMB system have been tested in the lab, demonstrating its feasibility on the application of EAST experiments. The QMB system with cooling water has been successfully applied in the 2018 EAST campaign. The net erosion thickness measured by the QMB has been well validated by thickness measurements using the Rutherford backscattering spectrometry. The developed QMB systems can help us to understand the physics processes of material erosion and deposition at main chamber walls for long pulse operations in EAST.