Speaker
Stefan Lagotzky
(University of Wuppertal)
Description
Enhanced field emission (EFE), resulting in dark currents and electric breakdowns, is one of the main gradient limitations for the CLIC accelerating structures (actual design Eacc = 100 MV/m, Epeak = 240 MV/m) [1]. Measurements on diamond-turned, flat (Ra = 158 nm) Cu samples showed first EFE at surface fields Es = 130 MV/m [2]. In order to reduce EFE, we have installed a commercial dry ice cleaning (DIC) system in our clean room (class iso 5). As expected, the number density of emitters (N) was significantly decreased from N = 52 cm-2 to N = 12 cm-2 at Es = 190 MV/m after DIC. Furthermore we have tested two diamond-turned and chemically etched (SLAC treatment, Ra = 150 nm) Cu samples after DIC resulting in first EFE at 230 MV/m. Locally measured I(V) characteristics of the strongest emitters revealed field enhancement factors β = 10 – 90 on the diamond-turned sample and β = 10 – 85 on the chemically etched samples. SEM and EDX investigations of the located emission sites will be presented at the workshop.
