Dresden 2013 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 25: Beschleunigerphysik VI (Resonatoren, HF)
HK 25.5: Talk
Monday, March 4, 2013, 17:45–18:00, WIL-C207
Surface roughness and field emission measurements on diamond turned Cu samples — •Stefan Lagotzky and Günter Müller — University of Wuppertal, D-42097 Wuppertal, Germany
The enhanced field emission (EFE) from particulate contaminations or surface irregularities is one of the main triggers of electrical breakdowns in normal-conducting accelerating structures for CLIC [1]. Deep and quantitative understanding of the EFE of flat and clean Cu surfaces is important to minimize high-gradient (Eacc=100 MV/m) breakdowns at the required peak surface fields (Epk/Eacc=2.4). Therefore we have systematically measured the surface quality of flat diamond turned Cu samples with an optical profilometer and AFM resulting in a linear roughness of 32-56 nm and geometrical field enhancement factors βgeo of at least 5.8. The EFE of the samples was measured with a field emission scanning microscope (FESM) and showed an exponential increase of the emitter number density with the applied surface field, i.e. up to 72 emitters/cm2 at 190 MV/m. Furthermore the activated emitters showed onset fields down to 92 MV/m and field enhancement factors βFN of up to 90 as determined by local I-V measurements. High resolution SEM images indicated a variety of surface features in the emitting areas. The discrepancy between the values of βgeo and βFN will be discussed. First results on the influence of dry ice cleaning (DIC) on the EFE of the Cu samples will also be presented.
[1] K.L. Jensen et al., Phys. Rev. ST Accel. Beams 11, 081001 (2008)
Funded by BMBF 05H12PX6