Agenda

1. Agenda

2. BLM ionization chamber space charge and procedures for changes of system settings during LHC running period Eva Barbara Holzer, CERN BLM Audit Sequel CERN, June 15, 2009

3. Content Procedures for changes of system settings during LHC running period Beam tests for threshold verification Space charge induced saturation effects in the LHC BLM Ionization chambers (limits of operational range) Archiving of documentation

4. Documents – Audit Items (2, 5, 6 and 7) • MPS Commissioning Procedure: The commissioning of the LHC machine protection system - MPS aspects of the Beam Loss Monitor system commissioning; EDMS: LHC-OP-MPS-0009. Close to being released (approval of magnet group). Item: 5 (verification of thresholds during commissioning – beam tests), 6 (test procedures, provoked losses) • Procedures for changes of BLM system settings during LHC running period. Preliminary version available. Item: 5 (changing thresholds during the run), 7 (changes to Master Table and propagation of changes) • Space charge induced saturation effects in the LHC BLM Ionization chambers. Treated in PhD thesis of M. Stockner and D. Kramer Item: 2 (saturation effects, limits of current monitor design) • Covered by Mariuzs’ talk: Item: 5 (threshold verification by 2008 beam loss measurements & improved simulations), 7 (definition of initial values of the Master Table)

5. Procedures • Procedures for changes of BLM system settings during LHC running period. Preliminary version available. Item: 5 (changing thresholds during the run), 7 (changes to Master Table and propagation of changes) • Procedures (plus additional software needed) defined • Additional software • Approval process by all involved parties • Test of the procedures during “dry run”

6. Procedures • BLM representative: • The role of the BLM representative will be filled 24/7 by one person, according to a pre-defined rota, reachable by one “BLM telephone line” (forwarded to the mobile of the BLM representative). • Execution of procedures: • The procedures will be executed by the BLM representative on request of the MPP representative (role to be defined);or on request of the BLM representative after agreement of MPP representative or the machine supervisor (to be defined) • The procedures can only be executed from the CCC by the BLM representative together with the machine supervisor (two persons for cross checking). • Agreement of BLM representative: • A written and documented agreement of the BLM representative is needed for: • Any change in the structure of a database (MTF, Layout, LSA, M&L DB) • Any change in RBAG (concerning BLM) • The changes shall be requested by an EMDS document using EDMS approval procedure.

7. MTF LSA FEC concentrator measurement& logging DB fixed displays Manual input of data Manually triggered procedure Automatic procedure Introduce a new monitor in the BLM system DCUMslot expert name (Pascal) MTF specific data (Sonia) Generation of parameter space and settings (Mariusz or BLM rep.) Update (Sonia) Propagation of changes and online check Update (Mariusz) E-mail Layout request ofsettings Update Slot-equipment link +error detection (Julien or automatic at night) Introducingmissing slots (Julien) Settingsof BLM + electronics equipment (Slava) Thresholds + Settings (Mariusz and Jonathan) request ofsettings E-mail on errors Restart (OP) comparison of variables Creationvariables(Chris R.) Restart (OP)

8. Summary of actions needed to be taken in use cases 2. Update MTF (Sonia) 3. Update LSA (Mariusz) 4. Creation of logging variables (Chris) 5. Restart Concentrator (OP) 6. Restart fixed display (OP) 1. MTF->Layout automatic nightly synchronization 1. DCUM slot expert name (Pascal) 2. MTF specific data (Sonia) 3. Settings of BLM & electronics or disable flag (Slava) 4. Introducing missing slots or changing structure (Julien) 5. Thresholds and/or Settings (Mariusz and/or Jonathan) 1. Generation of parameter space and/or settings, propagation to HW and online check using Trim application (Mariusz or BLM rep.)

9. Beam Tests • MPS Commissioning Procedure: The commissioning of the LHC machine protection system - MPS aspects of the Beam Loss Monitor system commissioning; EDMS: LHC-OP-MPS-0009. Close to being released (approval of magnet group). Item: 5 (verification of thresholds during commissioning – beam tests), 6 (test procedures, provoked losses) • Commissioning Procedures defined • Approved by all involved parties (under approval by magnet group)

10. Beam Tests: Basic BLM system functionality • Verifies the correct functioning of the entire BLM BIS-LBDS systems chain by provoking very small losses • Test 1: MPS functionality of the BLM with beam • Decrease thresholds, create local bump • Measure delay between the time where the loss signal exceeds the threshold and the time of the beam dump • Time estimate: 2h • Test 2: Interface of direct BLMs with the beam dumping system • Reduce the voltage setting of the abort threshold. • Dump the injected beam on the collimator TCDQ and TCSG • From the amount of lost beam and the threshold setting, deduce the nominal threshold setting. • Time estimate: 2h

11. Beam Tests: BLM thresholds and quench level • Verify that thresholds are adequate to protect the superconducting magnets against quenches. Must be performed for fast and slow losses; Ideally repeated for different types of magnets • Performed for one beam only. • Test 3: Provoked quench for transient losses • The beam is steered into the selected magnet. • The losses are recorded and compared to the expected quench level. • The intensity is increased step by step until the magnet quenches. • Time estimate: 1h per magnet • Test 4: Provoked quench for steady state losses with circulating beam. • The beam is slowly ‘bumped’ towards the selected magnet. • The losses are recorded and compared to the expected quench level. • The beam is brought closer to the magnet step by step until the magnet quenches. • Time estimate: 1h per magnet

12. Beam Tests: BLM thresholds and reaction times in collimation sections • Collimators are defining the aperture of the machine - Losses should occur first at the collimators or downstream of the collimation sections. • The BLMs at the collimators or downstream of the collimation sections in IR7 and IR3 are the first devices to detect the losses (for fast losses). • Typical fast failure scenarios must be provoked with low intensity beams to verify that BLM thresholds and reaction times are adequate.

13. Space charge • Space charge induced saturation effects in the LHC BLM Ionization chambers. In preparation. • Based on PhD thesis of M. Stockner and D. Kramer

14. Saturation effect due to space charge build-up Slow ions form a quasi field free region next to the cathode, which reduces the active detector volume. From: R.M. Zwaska, PhD thesis, 2005: Critical ionization rate for space charge: LHC IC current at onset of space charge: 26 mA Electronics max input: 1 mA (23 Gy/s for IC) Space charge correction: μ … ion mobility φ … ionization rate U … applied chamber voltage d … distance between the electrodes q … elementary charge V … active detector volume tc … irradiation time

15. IC to SEM comparison SPS internal beam dump • Max LHC signal range (limit of LHC IC readout electronics: 23 Gy/s) ~ factor 100 below the SPS dump dose • ~8% between SEM signal and space charge corrected IC signal

16. HERA internal beam dump measurements Measured IC signal vs beam current, estimated error due to correction: ~11% before correction space charge corrected beam energy: 920 GeV 39 GeV

17. Archiving of Documentation – Item 46 • BI group wants to adopt a common archiving system • A proposal has been made and needs to be approved by the group: • EDMS plus SharePoint webpage for static documents and • SVN for scripts, software codes etc. • BL plans to move existing documentation to EDMS