1Department of Physics, Korea University, Seoul 02841, Korea
2Busan Center, Korea Basic Science Institute, Busan 46241, Korea
Correspondence to: J. K. Ahn
High-energy bremsstrahlung photon emission beyond a critical energy from ECR heating has long attracted much attention, and its nature has yet been unsolved. We have measured bremsstrahlung photons from the 28-GHz ECR ion source at Busan Center of Korean Basic Science Institute. We measured photon energy spectra at nine azimuthal angles at the RF power of 1 kW using four NaI(Tl) detectors with FADC readout circuits. We found that the azimuthal angular distributions of bremsstrahlung photons were consistent with the structure of the ECR ion source and the shape of ECR plasma.