| Paper | Title | Page |
|---|---|---|
| WEPIK100 | The Applicability of NEG Coated Undulator Vessels for the CLARA FEL Test Facility | 3181 |
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| CLARA is a FEL test facility at Daresbury Laboratory (DL), UK. The undulator vacuum chamber is 20 m long with inner diameter 6 mm and its vacuum performance can benefit from a NEG coating. The thickness of the coating layer must be carefully optimised. A layer ~ 1 um would help the vacuum but a thinner layer would be partially transparent for the EM field reducing the resistive wall wakefields due to the NEG. A very thin layer, however, may not yield the necessary vacuum performance. Two types of NEG coatings produced at DL - dense and columnar - were considered. Their bulk conductivities were measured in a separate study. The resistive wall wakefield impedance was calculated following the standard approach for multilayer vessels. A 250 fs rms electron bunch was generated in ASTRA and its wakefield was obtained from the vessel impedance. The FEL performance was then studied through GENESIS simulations and the result compared to the case with no wakefields. It was found that NEG layers thicker than 100 nm give an unacceptable reduction of the FEL power and the vacuum performance of such thin coatings is unknown. Possible solutions to this problem are discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPIK100 | |
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