106th Impedance Working Group meeting (summary SY-BI, SPS TECA)

Tuesday 7 Oct 2025, 11:00 → 12:25 Europe/Zurich

6/R-012 - conference room (CERN)

Christine Vollinger (CERN), Carlo Zannini (CERN)

Present: Chiara Antuono, Miguel Díaz Zúmel, Patrick Krkotic, Michela Neroni, Chiara Pasquino, Hermann Pommerenke, Leonardo Sito, Christine Völlinger, Carlo Zannini.                                                                                                                                                                                           

 

HL-LHC impedance limitations for non-invasive transverse profile measuring devices

Outcome from HL-LHC Transverse Beam Profile Monitoring Review meeting.

SPS BGI (Carlo)

·         He’s working with old model from Benoit, and computed Ploss per mode (slide 9)

·         Issue: induced wake-fields through the grid, that perturb measurements (only with Awake beams)

o   Carlo simulated field leakage through the grid, as a function of the grid spacing

o   Also analytically calculated attenuation as function of size of grid hole (based on cutoff frequency)

 

HL-LHC BGI (Michela)

·         Two design alternatives still on the table: steel cathode, or macor cathode

·         Lower Ploss with steel cathode, therefore seems preferred

·         Further studies needed

BGC (Carlo)

·         It was proposed to introduce a copper liner, that significantly lowers the impedance

·         With copper liner, impedance is not worrying

BSRT (Carlo)

·         Manfred did a good job (simulations agree well with measurements)

·         20W heating of present device don’t seem worrying at the moment

·         The HL-LHC design is promising

 

Discussion

·         In the review meeting, it was suggested to add an absorber in the SPS BGI

HL-LHC BGI

·         For the HL-LHC BGI, the steel seems preferred, but there is no experience with it yet

·         Miguel asks whether the E fields on the cathode edges can lead to electric discharges

SPS BGI

·         Hermann asks why the grid is 45degrees diagonal with respect to the beam direction, and not aligned.

·         Miguel asks whether modelling it aligned, in CST, instead of diagonally as it is now, could be more accurate, since the mesh would better correspond to the grid.

 

Impedance studies of new optimized crystals in the SPS TECA (Hermann)

·         It was proposed to update the layout of the crystals in the TECA: in the new layout, the downstream crystal holder will have 4 crystals instead of 1, as present.

·         A large opening of the RF shield would be needed for the holder of 4 crystals

Simulation results:

·         Hermann observed a worsening of the impedance

·         Increased power loss, although uncertain, due to exact position of the peaks.

Carlo points out that, even in the unlucky scenario, the power loss is low, specially in the crystal (where it’s the most critical)

11:00 → 11:15 HL-LHC impedance limitations for non-invasive transverse profile measuring devices

Speaker: Carlo Zannini (CERN)

Impedance_limitations_HL.pdf

Impedance_limitations_HL.pptx

11:30 → 11:40 AoBs