A simulation study of a windowless gas-stripping room in an E//B neutral particle analyzer

The neutral particle analyzer (NPA) is one of the crucial diagnostic devices in a Tokamak facility. The stripping unit is one of the main parts of the NPA. A windowless gas-stripping room with two differential pipes has been constructed in a parallel electric and magnetic fields (E//B) NPA. The pressure distributions in the stripping chamber are simulated by ANSYS Fluent together with MolFlow+. Based on the pressure distributions obtained from the simulation, the stripping efficiency of the E//B NPA is studied using GEANT4. Hadron reaction physics is modified to track the charge state of each particle in a cross-section-based method in GEANT4. The transmission rates (R) and stripping efficiencies $$f_{+1}$$ are examined for particle energies ranging from 20 to 200 keV with the input pressure ( $$P_0$$ ), ranging from 20 to 400 Pa. According to the combined global efficiency, $$R \times f_{+1}$$ , $$P_0$$ = 240 Pa is obtained as the optimum pressure for the maximum global efficiency in the incident energy range investigated.