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102nd Impedance Working Group meeting (PSB quad. chamber, TDIS)

→ Europe/Zurich
6/R-012 - conference room (CERN)

6/R-012 - conference room

CERN

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Carlo Zannini (CERN), Christine Vollinger (CERN)
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Present: Chiara Antuono, Tristan Calvet, Paul Demarest, Miguel Díaz Zúmel, Jose Antonio Ferreira Somoza, Dora Gibellieri, Ivan Karpov, Patrick Krkotic, Jintao Li, Elena Macchia, Michela Neroni, Benoît Salvant, Leonardo Sito, Carlo Zannini.

Excused: Sergio Calatroni, Christine Vollinger

Change of quadrupole chamber in PSB – Jose A. Ferreira

The following modification is foreseen for LS3: addition of one intermediate chamber, with

  • 2 flanges  

  • 1 bellow with one convolution  

Discussion 

Carlo points out that this will result in a (small) increase of the impedance. 

Jose Antonio will go ahead with the ECR. 

TDIS simulations and spring heating - Jintao Li

1. Context and Motivation

  • Past issues with TDIS:

    • Melted springs (indicating high local temperatures, ~100 °C).

    • Low-frequency resonances when fingers lose contact.

  • Aim: quantify induced power on probes and springs under different configurations.

2. Simulation Models

  1. Simplified model with temperature probes.

  2. Model with realistic fingers (more detailed geometry).

  3. Simplified model with probes and springs

Jaws assumed closed unless otherwise specified. Losses computed using the BIHC code (open-source).

3. Probe loss calculation

  • Model with simplified fingers (as copper strips):

    • Cases: ideal contact, missing contact in 1 module, missing contact in 2 modules.

    • More missing contact → new low-frequency resonances + higher power loss.

    • Beam-induced power rises from a maximum of 375 W (ideal contact) to a maximum of 728 W (2 modules missing) with 1.0 ns bunch length (HL-LHC nominal filling scheme).

    • Maximum power loss on the probe is 0.55 W with 1 ns bunch length.

  • Model with realistic fingers:

    • Cases: missing 10, 35, or 96 fingers (≈1/3 module).

    • Beam power loss significantly higher than ideal case → maximum beam induced power ranges from ~600 up to ~800 W with missing contact and real fingers.

    • Power loss on the probe reaches 0.74 W with 1 ns bunch length.

    • Explanation: different numbers and positions of missing fingers shift resonance modes, affecting power distribution.

4. Simulation of springs

  • Each module has 10 springs and the springs are in contact with the outer tank.

  • Modeled missing finger contact over 150 mm.

  • Impedance spectra almost identical with/without spring, and also no significant difference between beam loss calculation for the two models.

  • Probe loss and spring loss calculated with 1 ns bunch length:

    • Maximum spring losses up to 1.32 W (with missing contact).

    • Maximum probe losses is 0.26 W in same scenario.

    • Higher loss of springs at ends under ideal contact and higher loss of spring when missing contact.

    • Power on springs depends strongly on finger contact condition.

5. Simulation of stuck jaws

  • Simulated asymmetric cases due to damaged bellows during operation:

    • Middle jaw open and two jaws open case simulated→ significant impact on the impedance (new modes from 0.8 GHz).

    • Beam-induced power increases with respect to the case with closed jaws.

6. Summary

  • Additional resonances appear when contacts are missing.

  • Estimated induced power (normal 2023 run) is ~0.5 W on probes, ~1 W on springs.

  • With HL-LHC nominal beam is ~1 W on probes, ~2 W on springs.

  • Anomalous configurations (e.g., open jaws, missing contacts) increase power deposition significantly → Power on the spring to be evaluated.

Discussion 

Tristan points out that the spring was melting, so probably reaching a temperature in the order of 100 °C. He asks how much the simplification in the simulation model is impacting on the induced power. Carlo says that the uncertainty can be estimated by looking at the power loss with simplified and real fingers in case of ideal contact. Here the power loss is significantly higher when adding fingers details. Jintao mentions that the total power loss is for the full 3 modules assembly. 
Patrick asks why the case with more missing fingers (96) is giving a lower value of power loss on the probe. Carlo and Jintao reply that this depends on where the resonances are building up and so on the specific location of missing fingers.

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