Comparison of Experimental and Monte Carlo Simulation of Angular Distributions of Bremsstrahlung Photons from 28-GHZ Electron Cyclotron Resonance (ECR) Ion Source

Angular distributions of deceleration radiation or bremsstrahlung in German, both experimental and simulated from Electron Cyclotron Resonance Ion Source (ECRIS) are not well understood so far. The bremsstrahlung photons of the angular distributions from 28-GHz ECR ion source at Busan Centre of Korea Basic Science Institute (KBSI) were measured in nine azimuthal angles for the first time. Three round type NaI(Tl) detectors were used to measure the angular distributions of the bremsstrahlung photons emitted at the extraction side of the ECRIS at the same time. Another NaI(Tl) detector was placed downstream from the ECR ion source for monitoring photon intensity. The ECR ion source was operated at RF power of 1 kW. Monte Carlo simulation based on Geant4 package was performed to study the angular distributions of the bremsstrahlung photons. The simulation was based on a full geometry of the ECR ion source. Geant4 simulation was executed to take the geometrical acceptance and energy-dependent detection efficiency into account due to large non-uniformity in the material budget. True bremsstrahlung energy spectra from the 28-GHz ECR ion source were obtained using the inverse-matrix deconvolution method. The deconvolution method was based on a full geometry of the Geant4 model of the ECR ion source. It is interesting to observe that the maximum simulated photon yields at angle 150° was correlated with the measured photon yields at angle 150° at the extraction side, which can be explained by the internal structure and shape of the ECR plasma. Keywords: Angular distribution; Bremsstrahlung photons; Deconvolution; ECRIS; Geant4 simulation; NaI(TI) detectors; RF power