1. S. Verdú-Andrés, LARP Toohig Fellow Brookhaven National Laboratory
CRYOGENIC TEST OF THE PoP DQWCC AT CERN Experience in preparing and cryo-testing the PoP DQWCC at BNL
S. Verdú-Andrés, LARP Toohig Fellow
Brookhaven National Laboratory

2. Crab cavities for LHC Crab crossing LHC Crab Cavities
Potential benefits from crabs:
Luminosity increase
Luminosity levelling
Alleviate pile-up
2-cavity module
SPS test
4 cavities/IP/side/beam
Between D2 and Q4
LHC Crab Cavities
𝜃 𝐶 2
Crab crossing
reestablish head-on collision for maximal ℒpeak
Need 32 crab cavities

3. Phases of the LHC Crab Cavities project
Today
SPS Test
Final Implementation
LHC crab cavity program phases:
2003  Conceptual design, feasibility study and system development
2009  Proof of Principle Cavities
2014  Cavities and Cryomodules for a validation test in the SPS
2017  HL-LHC system

4. The PoP DQWCC
…and stiffening frame
Electric field
Magnetic field

5. PoP DQWCC history Bulk and light BCP Light BCP 600°C bake for 10 h
BNL - Test II
BNL - Test I
120°C bake
CERN - Test III
Light BCP

6. BNL insert

7. Port assembly

8. Diagnostics for BNL Test II#1
Top
TEMPERATURE MONITORING
Number: 6 thermosensors
Type: CX-1050
Assembly: EPOXY plus kapton tape #5 #4 #2 #1
On top of the upper large port flange (niobium flange) #2
On FPC port pipe #3
On inner ring of cavity dome #4
On PU port pipe #5
On the pipe of the upper small port at the 4-port side (flange with copper disk) #6
On top of the lower large port flange (niobium flange) PU
FPC #3
4-port side
Vacuum #6
Bottom

9. Timeline CAVITY PREPARATION (about 2 days)
Wipe cavity with ethanol in buffer area and move into class 10,000 cleanroom.
The next day, check particle counting. If OK, then wipe cavity with ethanol and move into class 100 cleanroom (ISO 5)
The next day, check particle counting. If OK, then cavity ready for opening ports.
PORT ASSEMBLY (about 1 day)
FPC, PU, particle trap and blank-off flanges in class 100 cleanroom
CAVITY ASSEMBLY INTO INSERT (about 1 day)
Cavity into insert
Connect vacuum line in class 100 cleanroom
SLOW PUMPING WITH NEEDLE VALVE (overnigth), TURBO PUMP (half day), LEAK CHECK + RGA, ION PUMP (overnight)
Class 100 cleanroom
DIAGNOSTICS INSTALLATION (about 1 day)
TOP PLATE RIGGING INTO DEWAR AND ROLLING DEWAR INTO TEST BUNKER (about 1 day)
CONNECT RF CABLING (CALIBRATION, TIME DOMAIN REFLECTOMETRY) AND CRYO LINE (about 1 day)
COOLDOWN TO 4.5K (~)
COOLDOWN TO 2.0K (~)
TEST (about 3 days)

10. Measurements and Results
Q0 at around 3~4.5e9.
In CW mode, temperature of beam pipe flanges increase.
Reached 4.5MV kick in pulsed mode, limited by quench, consistent with conditioning test.
Temperature increase on pickup port blending area.
Quench field at ~110mT, with peak E field at 52.8MV/m
𝑅 𝑟𝑒𝑠 : ~18.3nΩ

11. Measurements and Results
Lorentz detuning (df/dVdefl)  freq = f(V)
-206 Hz/(MV)^2
from CW measurement at 2K
Pressure sensitivity (dp(=dT)/df)  freq = f(Tbath=p)
-336 Hz/Torr
from low power measurement during cooldown from 4.2K to 2K

12. Measurements and Results
Residual surface resistance
𝑅 𝑟𝑒𝑠 : ~18.3nΩ

13. Cavity status
BNL cadeau arrives at CERN
on July 10, 2014
PoP DQWCC and its stiffening frame in bldg 252-R-003 now
Sealed with stainless-steel flanges* after light BCP at Argonne in May 2014.
Cavity is equipped with its own stiffening frame.
* BNL property, to be shipped back to BNL inside transportation box.

14. PoP DQWCC test at CERN - objectives
CERN Test III
PoP DQWCC test at CERN - objectives
Test all the candidate crab cavities on the same baseline.
Prepare CERN test facility for future SPS cavity tests.
Quench in Nb-coated DN100CF flanges?
Freshly Nb-coated flanges may lead to better performances.
Plus evaluate technology for SPS DQWCC
e.g. tuning system

15. Test program for PoP DQWCC at CERN
CERN Test III
Test program for PoP DQWCC at CERN
1st – fixed FPC (vertical test) 2nd – movable FPC (vertical test) 3rd – SPS tuning system (horizontal test)
Fixed FPC (bolts)
CERN FPC actuator based on BNL design
CERN Insert Type I

16. Cavity assembly - ports
CERN Test III
Cavity assembly - ports #
FUNCTION
CONNECTION A
blank-off
solid DN100 – non-standard port B
FPC
FPC actuator system C
solid DN40 D E PU
PU feedthru DN40 F
vacuum
DN10040 and valve G H

17. Clean assembly – BNL class 100 cleanroom
Stiffening frame wrapped in plastic to reduce contamination
Port assembly on wire table

18. CERN Insert – SPL type Bottom plate a’ la SPL  leak test in cleanroom
CERN Insert Type SPL
Bottom plate a’ la SPL  leak test in cleanroom

19. Fixed FPC - bellow length for critical coupling?
Facts:
Critical coupling (b=1) depends on:
Q0, given by cavity performance
Qext, given by FPC settings
Impossible to predict Q0 beforehand
Overcoupled (b>1) structure preferred
as lower power requirement
Strategy:
From 2nd cryo test at BNL, Q0 ~ 4e9.
After light BCP at ANL, better performances expected: Q0 > 4e9.
b=>1  Qext slightly lower than expected Q0.
e.g. set Qext = 4e9 -> d’=21.2mm
bellow length
The FPC is set at 21.2mm away from the cavity inner surface to the FPC tip, with a Qext at 4e9. If you want to change Qext to 1e10, the distance will be 25mm.
Tuesday, Sept 23 (S. Belomestnykh)
As the FPC is not adjustable,
set Qext somewhat lower, 3e9 or 2e9,
to help conditioning the cavity.
 Bellow length ~ 27mm.
Remarks:
FPC coupling depends on coupler shape, penetration and orientation.
 Pay special attention during assembly to the coupler orientation.

20. FPC coupler orientation for fixed FPC

21. Diagnostics – 6 CERNOX CX
old PU CX
Inner radius of cavity dome (highest E-field)?
Or outer radius of cavity dome… (high B-field)
FPC
Inner radius of cavity dome
(highest B-field) CX CX PU CX
Vacuum
heater
Other thermosensors in all these regions plus in old and new pick up ports and, if possible, in all ports (on blended area of cavity and port plus on flange) CX

22. Diagnostics – OSTs Possible quenching regions:
FPC PU
Possible quenching regions:
beam ports
plate
Possible quenching regions:
Cavity dome
FPC PU
plate
Vacuum

23. Diagnostics – 3 unidirectional fluxmeters

24. Measurements to be performed
CERN Test III
Measurements to be performed
Monitor vacuum level, radiation (field emission and multipacting) during operation at different field levels
Q slope (i.e. Q=f(V)) at 4K and 2K
Q = f(T) for low field level to get residual surface resistance estimation
Residual magnetic field level and corresponding residual magnetic field surface resistance
Lorentz force detuning (df/dVdefl)  freq = f(V)
Pressure sensitivity (dp(=dT)/df)  freq = f(Tbath=p)
Determine multipacting regions.
Radiation spectra
Magnetic field

25. Cavity far from ideal… heat loss
CERN Test III
Cavity far from ideal… heat loss
FPC bellow is not coated (difficult to coat welded flanges).
Spacing between flanges will let field see SS from flanges and Cu from gasket.
FPC and PU hooks made of copper (Nb coating was not adherent enough on copper surface).

26. Thanks for your attention
Questions?

27. Cavity assembly – hardware (I)
PORT
FUNCTION
CONNECTION
BOLT
TYPE
#BOLTS
#NUTS
#WASHERS A
blank-off
solid DN100
M8x55
x16
x32 B
FPC system
bellow DN40
M6x35 x4 x8
anti-collapse
???
feedthru DN40 C
solid DN40 x6
x12 D E PU F
Vacuum: DN10040 and valve
DN10040
valve DN40 G H
In addition,
bolts and ¿pins? for stiffening frame in case of magnetic hardware is found
hardware for the piece on top of the cavity for transportation

28. Cavity assembly – hardware (II)
BOLT TYPE
# BOLTS
# NUTS
# WASHERS
M8x55 32 64
M6x35 48 44 88
Anti-collapse? 4 16 8
Total DN40 copper gaskets: 8
Total DN100 copper gaskets: 2
Remarks:
all bolts are Ag-coated A4-100 stainless-steel
apply safety factor of 2--3 when ordering

29. Cavity assembly – FPC system
Two options:
Fixed FPC: 1st test
Movable FPC: 2nd test
Remarks:
FPC coupling depends on coupler shape, penetration and orientation.
 Pay special attention during assembly to the coupler orientation.

30. FPC actuator
T. Renaglia (CERN) based on BNL design

33. Framework – LHC Crab Cavities
If head-on collisions, debris can interact with the machine
Crossing angle
but decreased peak luminosity
𝜃 𝐶 2
𝜃 𝐶 2
Crab crossing
reestablish head-on collision for maximal ℒpeak
Need crab cavities (deflecting cavities in phase 0)
For LHC, need 4 cavities per side per IP per beam…
32 cavities!!!