Design of the CFC composite brazed HFS first wall on the NBI shine-through area of the EAST device

Abstract

The high field side (HFS) first wall is the inner wall nearest to the vertical center axis in tokamak. To avoid high Z impurity sputtering due to plasma interaction and neutral beam injector (NBI) radiation, graphite is adopted as the plasma facing material (PFM) of the HFS first wall on the NBI shine-through area (NBISTA). In the experimental advanced superconducting tokamak (EAST), graphite tiles are bolted to the CuCrZr heat sinks by screw on the NBISTA, but cracks, fractures and ablations were observed on the graphite tiles after experimental campaigns because of insufficient heat removal capability. Thus, a new design of the HFS first wall on the NBISTA was proposed by adopting the carbon fiber composite (CFC) and brazing technology. In the new design, CFC tiles were brazed to the CuCrZr heat sink, and the oxygen-free copper (OFC) sheet was adopted between CFC tiles and CuCrZr heat sinks as stress-buffer layer. To avoid potential brazing failures or CFC tiles detachments, a modular pattern active cooling panels was proposed for the HFS first wall on the NBISTA. Steady heat transfer analysis of those panels was carried out and results show that the heat removal capacity satisfied the design requirements. Meanwhile, feasibility of the CFC brazing process was verified by nondestructive testing (NDT), mechanical property testing and high heat flux (HHF) testing, and testing results indicate that the CFC/OFC/CuCrZr bonding processed by one-step brazing had good mechanical property and heat removal capability.