1. Outcome of recent impedance bench measurements on collimators
N.Biancacci, D.Amorim, F.Caspers, I.L.Garcia, F.Giordano, T.Kaltenbacher, G.Mazzacano, E.Métral, B.Salvant, L.Teofili, C.Vollinger

2. Outline Impedance measurements on TCTWH
Impedance measurements on TCSPM (preliminary)
Conclusions and outlook

3. Outline Impedance measurements on TCTWH
Impedance measurements on TCSPM (preliminary)
Conclusions and outlook

4. TCTWH TCTP with embedded wire for beam-beam compensation [1,2].
Validated with impedance bench measurements on
Main outcome: same as a TCTP on , i.e. presence of 87 and 169 MHz transverse HOM -> Detailed analysis confirmed not an issue for beam stability (see also PhysRevAccelBeams )
Tungsten jaw
Ferrite tiles
Wire
Glidcop
[1] D.Pierini, “Advanced collimation design studies (TCT with wire, hollow e lens)” 4th Joint HiLumi LHC-LARP Annual Meeting
[2] O.Aberle , “TCTW production, assembly procedure and validation” LHC Collimation Working Group #202

5. TCTWH
TCTWH
TCTP
169 MHz
87 MHz

6. Outline Impedance measurements on TCTWH
Impedance measurements on TCSPM (preliminary)
Conclusions and outlook

7. TCSPM Main outcome of the measurements:
In operation (MD) can we distinguish the stripes?
Yes we can (preliminary result).
When not in operation (jaw retracted), any issue?
Normally not, but HOMs detected: 455 MHz, 800 MHz and 1.2GHz.
To be crosschecked with simulations.
HOMs present at all gaps, especially large ones.
Which gaps recommended setting for retraction?
Would suggest 15mm. So that the long fingers are not sticking out.
Simulations ongoing to see where HOMs are located.
TiN Mo
MoGr

8. TCSPM
TCSPM test bench
TiN Mo
TCSPM jaw
MoGr

9. TCSPM X In operation (MD) can we distinguish the stripes?
Measured longitudinal impedance vs X position
Z_Glidcop << Z_stripes:
Z_TiN > Z_Mo :
Z_Mo > Z_MoGr: X ?
Possible explanation: moving the wire we do not only change the material underneath but also:
Slightly the geometrical impedance (first taper is shorter). To be estimated with simulations.
Characteristic impedance of the wire-DUT TEM line: decreases for |x|>0. To be estimated with simulations GC
TiN
MoGr Mo GC

10. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan
~ 1.2 GHz
800 MHz

11. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan

12. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan

13. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan

14. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan

15. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan

16. TCSPM When not in operation (jaw retracted), any issue?
Systematic gap scan
Observations:
Presence of HOMs at all measured gaps (i.e. apparently no dependence on length of the long RF finger)
Shunt impedance modulated by jaw position: max Rsh = 35 Ohm
Not an issue from heating point of view 10W at max for a mode at 500MHz (1W at 800MHz).
To be checked:
Further impedance data available (time to process still needed)
Origin of HOMs with simulations.
Are those transverse HOM?

17. TCSPM
Mode at ~ 1.2 GHz identified with probes in transmission: Q~ 115

18. TCSPM
Mode at ~ 445 MHz identified with probes in transmission: Q~ 120

19. Conclusions and outlook
TCTWH
Measurements in line with those ones done on TCTP
Not an issue for beam stability
No apparent effect of embedded wire
TCSPM
Still some analysis to do, but main messages can be drawn:
Can see different impact of coating on RW impedance. Strange behavior when on MoGr: tbc if geometrical impedance change or change in TEM characteristic impedance could play a role.
Identified HOMs at 455 MHz, ~ 800 MHz and ~ 1.2 GHz: work on going with simulations to understand where these are located.
Not an issue from heating point of view. Tbc if these are transverse modes -> unlikely to be an issue for transverse stability.
Recommended to keep jaws partially closed (closer “parking”). At 15mm the long RF fingers fit in the corresponding hole: can avoid unwanted issues (bent RF fingers towards the beam)
Recommended analogous measurements on collimators with similar design.

20. Many thanks!

21. Backup

22. RW theory

23. RW theory

24. RW theory
Delta ~0.1 Ohm
76 MHz