fringe field

https://doi.org/10.1351/goldbook.12420
Electric or magnetic field that extends from the edge of an electric sector, magnetic sector, lens, or other ion optics element.
Source:
PAC, 2013, 85, 1515. (Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)) on page 1546 [Terms] [Paper]