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
still pendent
done
Also, another discussion about BCP for the SPS DQW CC: https://indico.cern.ch/event/464604/
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.
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)
EDMS
Cavity
orientation
1570107
v.2
Horizontal
Advantages
Disadvantages
•
•
•
•
2 Rotating BCP
(e.g. ANL)
3 Fixed BCP
(e.g. CERN)
1570107
v.4
Horizontal
TBD
Vertical?
•
•
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.
•
•
Requires structure to ease flipping the cavity
Dumping of acid every time cavity is flipped
implies safety concerns.
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 midplane, where critical regions are found and
steps are not desired.
Stagnation in corners, where high magnetic
field region is.
•
Why facility in
bldg118 better
than SM18?
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.
•
•
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