The meeting took place on Friday, October 17^th^, 2025, 10.00h-12.30h, in 513/1-024 and on Zoom.

Participants: H. Bartosik, E. Bravin, R. Bruce, X. Buffat, A. Butterworth, R. Cai, M. Calviani, A. Donadon, N. Duarte, Y. Dutheil, C. Emilio, M. Hostettler, S. Kostoglou, C. Lannoy, D. Lazic, A. Lechner, B. Lindstrom, L. Mether, Daniele Mirarchi, S. Morales, S. Redaelli, C. Roderick, B. Salvachua, M. Solfaroli, G. Sterbini, R. Tomas, G. Trad, N. Triantafyllou, A. Tsounis, J. Uythoven, A. Vella, D. Veres, J. Wenninger, C. Wiesner, D. Wollmann, C. Zamantzas, C. Zannini and M. Zielinska.

The slides of all presentations can be found on Indico.

Current options for 2026 high-intensity test (J. Wenninger)

Summary:

• Context and constraints of high-intensity test

  • Dual approach presented in Chamonix 2025:

    • Push operation toward 1.8 × 10^11^ ppb (now only B2, asymmetric intensities due to WMSIO.A6L2 and TCLD situation on B1)

    • Run a dedicated high‑intensity test at the end of the 2026 run. Proposal of an earlier short HI test at the end of 2025 to reduce risk of being blocked during the HI test itself

  • HI test limitation:

    • e‑cloud heat load: prevents ramping both beams at nominal HL intensity levels (≥2500 bunches) Work-around: single beam operation or lower energy operation (3 TeV).

    • TCDS: limited to 8b4e beams (max ~< 2000b) or other beam variants with specific bunch intensity limitations. Given no asynchronous dumps in Run 3, could consider ignoring this limitation, accepting limited risk during the two‑week HI test.

• HI test scenarios and ramp‑up options:

  • Considered scenarios:

    • Nominal HL-LHC filling at injection

    • 8b4e/hybrid at 6.8 TeV (limited by number of bunches)

    • Nominal HL-LHC filling at 3 TeV (likely N×48b rather than 4×72b)

    • Single‑beam operation at high‑energy (interesting for e-cloud situation, but not sufficient for common beam regions in IR2/8)

  • Possible ramp‑up strategies:

    • Increase bunch number at constant maximum bunch intensity (favored by e‑cloud/cryo)

    • Increase bunch intensity at constant number of bunches (possibly better for vacuum conditioning)

• Feedback from 2024/5 operation/MD

  • Even at constant beam intensity, elements can break (e.g., 6L2). The HI test cannot address this

  • Don't start probing at the last minute in June 2026, plan intermediate milestones.

  • End‑2025 option:

    • Push for ~1 day just after the ion run, likely limited to B2

  • Possible 2026 intermediate milestones:

    • After intensity ramp‑up, fill at injection with intensities above regular operation

    • Include MD1/2 intermediate heating‑power steps above regular operation

Analysis of TCLD vacuum behaviour and beam losses (S. Kostoglou , C. Zannini, N. Triantafyllou)

Summary:

• Observations (2022--2025): vacuum/BLM spikes occurred at TCLD under multiple conditions (low, medium and high intensities, across all cycle phases) with an increased activity (but low amplitude) in 2023 with hybrid beams.

• In 2025 first big spike appeared with 400 BCMS bunches (nominal conditions, reduced number of bunches), and another with 8b4e HL MD at ~2.3e11 ppb.

• No simple correlation to total intensity or bunch length; some possible sensitivity to 8b4e

• Impedance simulations ongoing and temperature probes installed.

• MD4 request conservative: 25 ns, 24b, 2.1e11 ppb, 144 bunches total to avoid impact on ion run.

• MD4 will not probe the same regime as the 8b4e MD and criticality can't be assessed before the 2026 high-intensity tests unless post-ion-run tests are performed.

• Uncertainty remains for all HL-LHC train types, not just 8b4e. This could become a major bottleneck for 2026 HI tests and HL-LHC operation.

Discussion concerning the first two talks:

• Near‑term and 2026 path

  • MD4: play it safe due to proximity of the ion run, avoid exposing TCLD to high‑risk now.

  • Post‑ion HI probe: consider requesting 1--2 days to specifically test TCLD/8b4e, one day likely insufficient due to loss maps/validation.

  • 2026: consider two proton MD blocks to sample higher intensities ahead of the loaded two‑week HI test at the end of the run. Introduce early milestones (e.g., injection and 3 TeV toward ~2.0 × 10^11^ ppb).

• TCLD approach

  • Prefer endoscopy (YETS) as low‑risk diagnostic, replacement only if clear non‑conformity. Beware conditioning reset and activated devices. Symmetric behavior suggests general design problem rather than single non-conformity.

Decision:

The Collimation Working Group and the Machine Protection Panel agreed to keep a conservative approach for MD4 given the proximity to the ion run and the TCLD/6L2 situation.

Both the CollWG and the MPP acknowledged the value of allocating 1--2 post-ion days to explore the TCLD limits.

ACTION (MD coordinators): Explore feasibility and possible configuration for a beam test after the Pb-ion run and agree with MPP on the required revalidation and intensity ramp-up.

API change for the BLM threshold GUI (B. Salvachua)

Summary:

• The BLM system currently manages about 3,600 ionization chambers, most of them are connected to the BIS.

• The applied thresholds are obtained by multiplying a master threshold matrix (32 energy levels × 12 running sums = 384 values), which is shared across each of the 141 BLM families, by an individual scalar monitor factor ranging from 0 to 1.

• Existing threshold GUI is built on JavaFX (unmaintained) and uses an RMI-based library (deprecated since 2020), creating maintenance and security risks.

• Similar problems with the BLM internal parameters GUI.

• Solution: migrate client/server communication from RMI to REST API; development in dev version and human testing (not programmatically) already performed with bug fixes applied to API and GUI.

• Proposal: Deploy the migration to REST during the Technical Stop, during daytime, with actions taken for a safe upgrade (BLM tables copied and rollback possible).

Discussion:

• M. Hostettler suggested pre-testing procedures in LSA Next (clone of production) to reduce risk; easy to reset if needed. B. Salvachua agreed it could be an additional test, but emphasized programmatic verification is required. C. Zamantzas pointed out, that the planned change of the API does not impact the LSA next and therefore this test is not required at this moment to complement to already performed validations. When the whole tool will be updated, this type of test should be performed.

Decision:

The MPP endorses the proposal to change the API during TS2 and the proposed testing plan. No additional tests required beyond those proposed by B. Salvachua.

Operation with asymmetric beam intensities (X. Buffat)

Summary:

• Operate with lower intensity in B1 to avoid further degradation from 6L2 while increasing B2 intensity to limit performance degradation.

• Plan to adiabatically increase B2 intensity from 1.48e11 toward 1.7e11 ppb, keeping risk low for B1 with intensity of 1.4e11 ppb.

• Integrated luminosity target still achievable with this scenario.

Decision:

The MPP endorses proceeding with an adiabatic asymmetry increase toward ~1.7e11 ppb, with no machine-protection show-stoppers identified. Maintain the 1.75e11 ppb cap until the next LMC and require LMC approval for any change beyond 1.75e11 ppb.

Collimation strategy for the 2025 Pb ion run (M. Zielinska)

Summary:

• Same cycle as 2024 but with tighter squeeze in IR8.

• New dispersion-correction bumps substantially reduce beam losses at a few critical locations. IP2 horizontal TCT losses reduced from ~1e-5 to ~1e-7.

• Taking out TCSG.A6R7.B2 has minimal impact on global cleaning. This is expected, as the first crystal collimator, which is acting as primary is sitting downstream of the TCSG.

• Single-particle trajectory studies show that losses occur at desired locations (e.g., BFPP to TCLD or MB, EMD1 to primary collimators).

• Operational suggestion: open the other jaw of the TCLD in IP2 to minimize the losses in sensitive regions. To be tuned during commissioning.

• The proposed loss maps matrix for Pb ions is identical to the one used in 2024 (see Slide 19).

Decision:

The CollWG and the MPP endorse the proposed loss maps matrix for the 2025 Pb ion run.

Proposed intensity ramp-up for Pb ions in 2025 (C. Wiesner)

Summary:

• Lead ion run scheduled after MD4/TS2.

• Overall: No major changes in optics and cycle compared to 2024. Main part of the cycle has been used for p-O (and partly for O-O) during 2025. Same ramp and same collimator settings as in 2024, except TCT8.

• The changes with respect to 2024 are the IP1/5 triplet polarity (following pp optics) and a smaller β* = 1.0 m in IP8 requiring additional dispersion-correction bumps to avoid increased background to IR2.

  • To be verified as early as possible during the commissioning or ramp-up.

• R. Bruce suggested running an early background check in the first two days of lead-ion commissioning. If problematic, skip β* = 1.0 m and revert to β* = 1.5 m for qualification loss maps (~half a day rollback overhead).

• Proposed ramp-up sequence:

  • Cycle setup with low intensity

  • 120b, one fill, >2h in Stable Beams

  • 450b, two fills, >5h in Stable Beams in total

  • Combined checklist before going to the next intensity step

  • 800b, two fills, >5h in Stable Beams in total

  • 1240b (full machine)

• This represents a similar approach as in 2023/24, however, skipping the ~250-bunch step. This is in line with the intensity ramp-up for protons, which has also been streamlined for 2023 in a similar way.

• After ALICE polarity reversal: Cycle with low intensity → 450b, one fill → 1240b (full machine).

Decision:

The MPP endorses the proposed intensity ramp-up.