Physics of high-intensity nanosecond electron source

Alberto Herrera-Gomez; William E. Spicer

doi:10.1117/12.158588

15 October 1993 Physics of high-intensity nanosecond electron source

Alberto Herrera-Gomez, William E. Spicer

Proceedings Volume 2022, Photodetectors and Power Meters; (1993) https://doi.org/10.1117/12.158588
Event: SPIE's 1993 International Symposium on Optics, Imaging, and Instrumentation, 1993, San Diego, CA, United States

Abstract

A new high intensity, short time electron source is now being used at the Stanford Lineal Accelerator Center (SLAC). By using a GaAs negative affinity semiconductor in the construction of the cathode, it was possible to fulfill the operation requirements, such as peak currents of tens of amperes, peak widths of the order of nanoseconds, hundreds of hours of operation stability, and electron spin polarization. The cathode is illuminated with high intensity laser pulses, and photoemitted electrons constitute the yield. Because of the high currents, some non-linear effects are present. Very noticeable is the so called Charge Limit (CL) effect, which consist of a limit on the total charge in each pulse, that is, the total bunch charge stops increasing as the light pulse total energy increases. In this paper we will explain the mechanism of the CL and how it is caused by the photovoltaic effect. The treatment is based on the Three Step model of photoemission. We will relate the CL to the characteristics of the surface and bulk of the semiconductor, such as doping, band bending, surface vacuum level, and density of surface states. We also discuss possible ways to prevent the CL to take place.

Citation Download Citation

Alberto Herrera-Gomez and William E. Spicer "Physics of high-intensity nanosecond electron source", Proc. SPIE 2022, Photodetectors and Power Meters, (15 October 1993); https://doi.org/10.1117/12.158588

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