Trap ring aperture

Fig. 11.10. Diagram illustrating the inner surfaces of the primary components of a Paul (3D) quadrupole ion trap. Ions generated by an external source are injected into the trap through an aperture in one of the end caps. Scan functions for isolating ions in the trap, exciting the mass selected ions to induce unimolecular dissociation, and ejecting ions from the trap (for detection) are implemented through the application of DC and RF voltages to the ring electrode.

Fig. 1.23. The electron diffraction apparatus developed by Parks and coworkers includes an rf-ion trap, Faraday cup, and microchaimel plate detector (MCP) and is structured to maintain a cylindrical symmetry around the electron beam axis [147]. The cluster aggregation source emits an ion beam that is injected into the trap through an aperture in the ring electrode. The electron beam passes through a trapped ion cloud producing diffracted electrons indicated by the dashed hues. The primary beam enters the Faraday cup and the diffracted electrons strike the MCP producing a ring pattern on the phosphor screen. This screen is imaged by a CCD camera mounted external to the UHV chamber. The distance from the trapped ion cloud to the MCP is approximately 10.5 cm in this experiment...

The scattered electrons strike the MCP as indicated in Figure 7.2 producing a diffraction pattern on the phosphor screen. This pattern is in the form of Debye-Scherrer rings similar to powder diffraction as a result of the orientational and spatial disorder of the trapped cluster ions. This screen is imaged by a charge-coupled device (CCD) camera mounted externally to the UHV chamber. The distance from the trap center to the MCP surface can be varied from ca 8 to 12 cm. The e -beam cross-section and trap aperture limit the detection of scattered electrons to a maximum... 

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