Secondary electron yield of a thin film coating on the APS rf cavity tuners

Abstract

A thin film coating of titanium nitride was applied to the surface of rf cavity tuners to reduce secondary electron generated when the existing copper base material is in place. The tuners are used in high-field gradients, where electron heating of the tuner is a problem. By reducing the generation of electrons the temperature of the tuners will be reduced, for better reliability. This paper compares characteristics useful for rf cavity tuners, such as surface composition and secondary electron yield, for copper, titanium-coated copper, and titanium-nitridecoated copper. The process and the setup of equipment used to apply the coatings are summarized.

The influence of the secondary electrons induced by energetic electrons impacting the Cassini Langmuir probe at Saturn

“…This yield is known to peak (with a yield above one) at incident electron energies near 200–1000 eV for metal layers [ Hastings and Garrett , ]. The peak energy for the Cassini LP was determined by G12 close to 350 eV, in agreement with laboratory measurements of TiN surfaces by Walters and Ma [] or Lorkiewicz et al []. The exact form and the maximum yield value are, however, essentially unknown and will be discussed further in sections 5.2.1 and 5.3.…”

“…No laboratory measurements were indeed performed for the Cassini LP surface. However, laboratory measurements may be found in the literature for similar surfaces [ Baglin et al , ; He et al , ; Walters and Ma , ; Lorkiewicz et al , ]. These authors propose a broad range of possible maximum yield values, between 1.1 and 2.4.…”

The detection of energetic electrons with the Cassini Langmuir probe at Saturn

“…[32] Moreover, the energy range of the source particles, compared with the secondary electron emission yield peak (with a yield above one) usually located near 200-1000 eV for metal layers [Hastings and Garrett, 1996;Walters and Ma, 2001;Lorkiewicz et al, 2007], supports the conclusion that the energetic current I ener is driven by the secondary electrons contribution. An example of such yield curve for a TiN surface [Walters and Ma, 2001] is plotted in yellow in Figure 3, revealing a similar peak energy near 300 eV. Our correlation analysis does however not provide the yield curve directly, which does not allow to compare both curves beyond the peak energy.…”

“…Pearson's correlation coefficient between the temporal evolutions of the current induced by energetic particles ( I ener = I sec * + I *) and the particles fluxes—electrons (e‐) and ions—as a function of the particles energy; “all periods” refers to both the SOI and the high inclination orbit periods. The secondary electron emission yield curve by Walters and Ma [2001] is plotted in yellow and normalized so that the maximum yield is placed at the same ordinate value as the maximum value of the green curve.…”

“…[31] The correlation analysis during the SOI period alone with using the anode 5 CAPS ELS data revealed a peak near 400-600 eV. Considering the two periods together (SOI and high inclination orbit) determines the energy range of the Walters and Ma [2001] is plotted in yellow and normalized so that the maximum yield is placed at the same ordinate value as the maximum value of the green curve.…”