Structural Optimization of Discrete Dynode Electron Multiplier for Mass Spectrometers

A device structure of 19-stage discrete-dynode electron multiplier (DDEM) for mass spectrometers was designed, and its structure model was constructed. The effects of the key configurational parameters of the dynode and collector as well as the last-stage voltage-division resistance on the DDEM gain were numerically investigated, and their mechanisms were explored by analyzing the internal electric field distribution and electron motion trajectory of the DDEM. Based on these analyses, the configurations of the dynode and collector as well as the last-stage voltage-division resistance were optimized. The simulation results show that when the length of the left sidewall of the 3rd dynode and the top length of the collector are 2.35 mm and 1.9 mm, respectively, and the last-stage voltage-division resistance is 0.7 MΩ, the electron collection efficiencies of the 3rd dynode and the collector can be improved so as that the DDEM gains at the operating voltages of 1800 V and 2500 V attain 3.70×10⁴ and 5.09×10⁷, respectively. Moreover, the single-electron pulse rise time and pulse width of the optimized device reach 2.38 ns and 3.21 ns at 1800 V, respectively. The structurally optimized electron multiplier meets the design requirements in terms of gain and time characteristics.