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Multipacting and electron cloud formation remain major limitations for the performance of modern particle accelerators. In superconducting radio-frequency (SRF) cavities, multipacting can prevent stable cavity operation and restrict achievable accelerating gradients. In positively charged particle machines such as the LHC, the build-up of electron clouds results in beam instabilities, vacuum degradation, and additional heat loads on the cryogenic systems. Reducing the secondary electron yield (SEY) of vacuum-facing surfaces is therefore a key strategy to mitigate these effects. To mitigate these effects, several strategies have been proposed, in particular the deposition of thin films designed to reduce the secondary electron yield (SEY) of the relevant surfaces.
We investigated the SEY behaviour of ultrathin TiN/NbN multilayers, with particular attention to the influence of both the number of layers and the TiN/NbN stacking sequence. Multilayers composed of individual 3 nm films were deposited by PVD to probe interfacial effects and possible electronic confinement phenomena. SEY measurements performed before and after electron conditioning reveal a dependence on the multilayer architecture. One particular multilayer configuration achieves a significantly reduced SEY, reaching 0.98 after conditioning.
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