Theoretical and experimental work has been carried out to study the longitudinal space-charge effects in a retarding field energy analyzer.A one-dimensional, steady state model for both a monoenergetic beam and a thermal beam has been developed for this purpose.Potential improvements of using two-dimensional and time-dependent solutions are also briefly discussed.The study shows that, if the current density inside the device is higher than a critical value, the longitudinal space-charge effect and the formation of a potential minimum similar to the NATO straps virtual cathode formation in an electron gun will distort ANALGESIC GEL ROLL the measured energy spectrum.
The measured FWHM and the rms energy spread will be affected.The measured mean energy will also be shifted toward the low-energy side.By using a two-dimensional correction, the theoretical model also qualitatively explains the appearance of a visible tail at the high-energy side of the spectrum, as observed in experiments.According to the theory, to avoid this measurement distortion due to the longitudinal space charge, care has to be taken to limit the current density inside the device.