High power experiment and heat load evaluation of transmission line for the ECH/CD system in JT-60SA

•High-power test of the waveguide transmission line for the ECH/CD system in JT-60SA.•A transmission line with a pre-load enabled simulation of tokamak experiment without reflection from the dummy load.•The waveguide temperature rise of 120 K for 1 MW/100 s operation at 110 GHz in the worst case.•The head load evaluated as 23 kW/m^2 for 1 MW long-pulse operation in the worst case.