Utilizing an Elongated Thermal Cathode as an Electron Source for Electron Capture Dissociation in a Linear Ion Trap

To achieve efficient electron-capture dissociation (ECD) in a linear ion trap, an elongated thermal cathode is favorable owing to its superior coverage of the ion cloud. An elongated quasi-indirectly heated cathode (QIHC) has been designed and integrated into a flat beam electron gun. The QIHC employs a tantalum sheet (0.8 mm wide, 0.1 mm thick) as the electron emitter and a pure tungsten filament (0.18 mm diameter) as the main heater. Multiphysics simulations indicate that the cathode can be operated in a thermionic-emission regime suitable for ECD and generates an electron beam profile compatible with the linear ion trap. Comparative ECD experiments using the QIHC and a commercial indirectly heated cathode demonstrate that the QIHC can serve as an electron source for ECD, producing c/z· fragment ions of Substance P.