• A.M. Porcellato, L. Boscagli, F. Chiurlotto, M. De Lazzari, D. Giora, S. Stark, F. Stivanello
  INFN/LNL, Legnaro

The av­er­age ac­cel­er­at­ing field of the ALPI 160 MHz sput­tered QWRs has been im­prov­ing with time up to reach, after the last con­di­tion­ing cycle, the av­er­age ac­cel­er­at­ing field of 4.8 MV/m @ 7 W. Such value can be ef­fec­tive­ly sus­tained in op­er­a­tion due to the in­trin­sic me­chan­i­cal sta­bil­i­ty of the sput­tered cav­i­ty whose fre­quen­cy is prac­ti­cal­ly not in­flu­enced by fluc­tu­a­tions in the bath He pres­sure. The pre­sent av­er­age cav­i­ty per­for­mance ap­proach­es the max­i­mum av­er­age ac­cel­er­at­ing field ob­tain­able in the present­ly in­stalled cav­i­ties, most of which were pro­duced by re­place­ment of Pb with Nb in the pre­vi­ous­ly in­stalled sub­strates. A high­er av­er­age value can be ob­tained in ALPI re­plac­ing the less per­form­ing units; it is in­stead nec­es­sary to sput­ter on ap­pro­pri­ate­ly built sub­strates to pro­duce QWRs which can re­li­ably ex­ceed 6 MV/m @7W. The cav­i­ty Q-curves, which were re­cent­ly mea­sured in ALPI, show a wide range of Q₀ and Q-drop, main­ly as­so­ci­at­ed with the sub­strate char­ac­ter­is­tics, but in some cases also in­flu­enced, as dis­cussed in the paper, by cryo­stat as­sem­bling pro­ce­dures and by cav­i­ty pro­duc­tion and con­di­tion­ing.

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