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BE: Beschleunigerphysik
BE 13: Beam Dynamics and Fields II
BE 13.5: Vortrag
Donnerstag, 3. April 2014, 10:30–10:45, ZEU 255
Prediction of severe electron loading of high-gradient accelerating structures based on field emission sample measurements — •Stefan Lagotzky and Günter Müller — University of Wuppertal, D-42097 Wuppertal, Germany
Enhanced field emission (EFE) limits the performance of both superconducting and normal conducting high-gradient accelerating structures. Systematic field emission scanning microscopy and correlated SEM/EDX measurements of relevant Nb and Cu samples have revealed particulates and surface irregularities with field enhancement factors β = 10 - 90 as origin of EFE. Based on sufficient emitter statistics, an exponential increase of the emitter number density N with increasing surface field (E) was found. This allows a prediction of the EFE loading of future ILC and CLIC accelerating structures by scaling of N to relevant E and using a weighted integration over the high-field cavity surface. Accordingly, an electropolished (Ra < 300 nm) and dry-ice cleaned (DIC) TESLA-shape 9-cell 1.3 GHz Nb cavity [1] will still suffer from EFE at Eacc = 35 MV/m (N = 0.3 cm−2 at Epeak = 70 MV/m). Moreover, a diamond-turned, chemically etched and DIC 11.2 GHz Cu structure [2] will breakdown at Eacc = 100 MV/m (N = 20 cm−2 at Epeak = 243 MV/m). Possible improvements, i.e. by emitter processing will be discussed.
The work is funded by BMBF project 05H12PX6.
[1] ILC Technical Design Report (2013)
[2] A. Grudiev and W. Wuensch, LINAC2010, pp. 211 - 213
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