DISCUSSION Flashback Diagram flow Dream world Main points CERN – STFC – US-LARP Crab Cavity Collaboration Meeting | 18 March 2016 DISCUSSION BCP procedure for the SPS DQW CC OUTLINE Flashback Diagram flow Dream world Main points Discussion on different BCP setups HPR, draining and drying Silvia Verdú-Andrés | Brookhaven National Laboratory

Flashback… from our last discussion on the topic done still pendent Also, another discussion about BCP for the SPS DQW CC: https://indico.cern.ch/event/464604/

no feedback received yet Diagram flow schemes for etching and BCP no feedback received yet Silvia Verdú-Andrés | BNL| 19 March 2016 | Slide 3

Dream world BCP in ISO Class 4 clean room U.S. degreasing  BCP  acid drain  U.S. degreasing  HPR  water drain  dry Instrumentation: Thickness gauge (min. 4 for DQW CC) to get thickness removal rate during BCP process Witness sample to get resulting thickness removal at given location Temperature monitoring of cavity surface Monitor resistivity of water after draining acid to identify full acid evacuation Rotating BCP device unless Tom Jones’s simulations tell the contrary During rotation, flow of N2 to avoid niobium oxides forming. Specific orientations for HPR, draining and drying to minimize stagnation. Temperature control during BCP by water curtain.

Silvia Verdú-Andrés | BNL| 19 March 2016 | Slide 5 Common BCP procedure for DQW and RFD crab cavities BCP at ISO Class 4 clean At least the light BCP must be performed in clean room. The heavy BCP is not as critical because a light BCP will always be performed before testing. Thickness measurement probes installed on cavity to monitor thickness removal rate while the BCP is being conducted. 4 probes at different locations depending on the cavity geometry. BCP recipe: Acid mixture of HF (49%) :HNO3 (69.5%) : H3PO4 (85%) at 1:1:1 in volume Sump temperature: 8 oC Extras Witness sample to monitor thickness removal Monitor resistivity of water after draining acid Silvia Verdú-Andrés | BNL| 19 March 2016 | Slide 5

BCP Setups 1 Fixed BCP (e.g. JLab) Horizontal 2 EDMS Cavity orientation Advantages Disadvantages 1 Fixed BCP (e.g. JLab) 1570107 v.2 Horizontal Requires structure to ease flipping the cavity Dumping of acid every time cavity is flipped implies safety concerns. Hose functionality (inlet <-> outlet) switches every time the cavity is flipped over. Different thickness removal for cavity bottom and central region due to time spent for fill up and drain out. 2 Rotating BCP (e.g. ANL) 1570107 v.4 More uniform thickness removal (Tom’s studies?) Constant rotation prevents stagnation of residues produced by acid acting on niobium surface. Requires rotating device structure with special flanges. 3 Fixed BCP (e.g. CERN) Why facility in bldg118 better than SM18? TBD Vertical? House functionality (inlet <-> outlet) is switched every time the cavity is flipped. Difference between thickness removal due to fill up and drain out is at the cavity mid-plane, where critical regions are found and steps are not desired. Stagnation in corners, where high magnetic field region is.

feasible in all facilities? The BCP procedure also includes HPR, draining and drying Recommended orientations for SPS DQW CC High-Pressure Rinsing Draining and drying  goal: avoid stagnation Do not use N2 for drying Requires fixtures for cavity holding and flipping, as well as system that allows relative movement of water sprinkler and cavity. feasible in all facilities?

Thanks for your attention Silvia Verdú-Andrés | Brookhaven National Laboratory