Monte Carlo optimization of a Compton suppression system for gamma-ray diagnosis of combustion plasma

The use of Gamma-ray spectrometers provides very important diagnostic tools in large-scale tokamak experiments. In this study, the Geant4 toolkit was used to simulate a Compton suppression system based upon a High-Purity Germanium (HPGe) primary detector in order to gain the optimal sizes for the construction of the system for 0.1 MeV-10 MeV γ-rays which are emitted from the HL-2A tokamak. BGO crystal is selected for the anti-coincidence secondary detector. Simulation results show that when the closer the HPGe primary detector is set to the beam entrance and the smaller the entrance size is, the higher the Compton Suppression Factors (CSFs) are. Moreover, adding a BGO crystal to the back of the HPGe detector can also improve the CSFs, and the CSFs increase more significantly with the higher γ-ray energies. And a BGO crystal with the thickness of 25 mm in front of the HPGe detector can reach a good suppression effect. For the BGO hollow cylinder, the CSFs do not increase obviously after its thickness reaches 60-70 mm. Finally, optimal parameters for the Compton suppression system are suggested. Moreover, for the optimal Compton suppression system, γ-rays produced by neutrons which are also one of fusion products, can be well suppressed.