Study of secondary electron emission from niobium at cryogenic temperatures.

摘要

The objective of this project is to study the properties of secondary electron emission from niobium samples, cleaned at the Los Alamos National Laboratory, at cryogenic temperatures to enhance existing multipacting codes with data on the samples. The predominant cause of power loss in radio-frequency superconducting accelerators cavities is multipacting. This project studies the secondary electron distribution from niobium metal due to incident primary electrons. The experiments on the niobium sample are performed in an environment close to that present in a superconducting accelerator cavity.; The experiment is performed in a vacuum chamber capable of achieving ultra high vacuum levels of around 9x10-10 Torr. The niobium sample is cooled to 23 K using a cryostat to perform experiments in a cryogenic temperature. An electron gun provides the primary beam of electrons of varying energies impacting the niobium sample. The secondary electrons produced by the sample are then collected by a single particle position detector. Secondary electron spreads are studied for varying angles and energies of primary electron incidence.; The experimental setup was simulated and the secondary electrons tracked under various criteria using a finite element electromagnetic software. Using experimental results and the particle tracking simulation a set of initial secondary electron conditions are deduced. These initial conditions are validated using a modified Monte Carlo code for secondary electrons from niobium.