Propagation of thermally induced oscillation in the KSTAR cryogenic loop

Thermo-acoustic oscillation is well-known phenomena which can generate quite a heat load to a cryogenic system. Here we report that thermally induced oscillation has been occurred in the KSTAR cryogenic system and furthermore that oscillation propagates the cryogenic circuit, affects strongly the overall supercritical helium flow and generates severe mechanical vibration on the system. Additional vibration sensors were attached on the cryogenic circuit to trace the origin of that abrupt thermal leak and detailed hydraulic data analyses have been carried out. It was found that test heaters of flange type inserted in directly the by-pass lines are the origin of the thermally induced unexpected oscillation and thereby by the dismantle of the heaters the oscillation can be permanently eradicated.