1. 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

2. Flashback… from our last discussion on the topic
done
still pendent
Also, another discussion about BCP for the SPS DQW CC:

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

4. 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.

5. 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

6. BCP Setups 1 Fixed BCP (e.g. JLab) Horizontal 2
EDMS
Cavity orientation
Advantages
Disadvantages 1
Fixed BCP (e.g. JLab)
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)
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.

7. 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?

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