BEAM LOSS MONITORING SYSTEM B. Dehning, E. Effinger, G. Ferioli, J.L. Gonzalez, G. Guaglio, M. Hodgson, E.B. Holzer, L. Ponce, V. Prieto, C. Zamantzas CERN AB/BDI External Review of LHC Collimation Project July 1, 2004

Outline BLM System Hardware Dynamic Range Positioning of Monitors Signals from the BLM system Simulations of Cleaning Insertions Momentum Cleaning (Igor A. Kurochkin, IHEP) Betatron Cleaning (M. Brugger, S. Roesler, CERN SC/RP) Summary

THE BLM SYSTEM Purpose: Challenges: Machine protection against damage of equipment and magnet quench Setup of the collimators Localization of beam losses and identification of loss mechanism Machine setup and studies Challenges: Reliable (tolerable failure rate 10-7 per hour per channel) High dynamic range (108, 1013) Fast (1 turn trigger generation for dump signal)

Families of BLM’s Type Area of use Time resolution Number of monitors BLMC Collimation sections 1 turn ~ 100 BLMS BLMS* Critical aperture limits or critical positions 1 turn (89 us) ~ 500 BLMA All along the rings (ARC, …) 2.5 ms ~ 3000 BLMB Primary collimators bunch-by-bunch ~ 10 BLMC & BLMS: In case of a non working monitor this monitor has to be repaired before the next injection

Loss Detectors: Ionization Chamber SPS Chamber Gas: N2, Volume: ~ 1 Liter, 30 Al disks of 0.5 mm, Typical bias voltage: 1500 V. New LHC chamber design Diameter = 8.9 cm, Length 60 cm, 1.5 litre, Filled with Ar or N2

Secondary Emission Monitor Diameter = 8.9 cm Length 15 cm

Dynamic Range (I) Secondary Emission Monitor P < 10-7 bar Ionization Chamber P > 1bar Efficiency SE ~ 0.05 charges/particle Efficiency ioniz. Chamber ~ 50 charges / (particle cm) Efficiency Ionization Chamber / Efficiency SE ~ 3 104

Dynamic Range (II) Beam Loss Current BLMC and BLMS* Pilot bunch: 5e9 p, lower limit of measurement in the collimation region 400 – 4000 protons -> level of 10e-6 !

System Layout Threshold Comparator: Losses integrated in 12 time intervals to approximate quench level curve.

Quench and Damage Levels Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses BLMS* & BLMC Quench level and observation range 450 GeV 7 TeV Damage levels Dynamic Arc: 108 Collimator: 1013 BLMS*: 3.2E13 protonen (nominal SPS injection) lost in about 10E-5 seconds. Special & Collimator1 turn Arc 2.5 ms

Loss Levels and Required Accuracy Relative loss levels 450 GeV 7 TeV Damage to components 320/5 short/long 1000/25 short/long Quench level 1 Beam dump threshold for quench prevention 0.3 0.3/0.4 short/long Warning 0.1 0.1/0.25 Specification: Absolute precision (calibration) < factor 2 initially: < factor 5 Relative precision for quench prevention < 25%

Monitor Positions in Arc Installation of BLMAs on a SSS quadrupole

Monitor Positions in Collimation Collimator interconnect with ion pump and BLM (possible positions)

Signals from the BLM system Dump signal to beam interlock controller (BIC), 2 types: Not mask able: BLMC and BLMS, ~ 600 monitors. Can be masked when “safe beam” flag is set: BLMA, ~ 3000 monitors Post mortem: 2000 turns plus integral of 10 ms. Logging: Once a second Stored in database Used for graphical representation in the control room: Values measured for each detector and time interval are normalized by their corresponding threshold values.

“Artist View” of the Logging Display

Momentum Cleaning Igor A. Kurochkin IR3 (6.2) – length and positions of collimators have changed BLM position TCS 6,5,4 TCS3,2 TCP1 TCS1 Collimator length: 20cm primary and 50 cm secondary, reduced shielding present. Codes: K2 and MARS. Activation will reduce the sensitivity of the monitors in the low signal range. Expected activation: 10-2 to 10-4 of mean loss rate (SPS 10-3) Monitors close to vacuum chamber to reduce cross talk and background. Monitors 30 cm downstream of collimator

Relative contribution to BLM signal from primary inelastic interactions in the collimators Igor A. Kurochkin “Good” signal (from upstream collimator) BLM1 – 100% BLM2 – 4% BLM3 – 57.4% BLM4 – 9% BLM5 – 5% BLM6 – 4% BLM7 – 1% TCP1 - major contributor to background BLM2 – 96% BLM7 – 20% Igor A. Kurochkin 7 TeV TCP 1 TCS 1 BLM signal: Good measure for heat load in the corresponding collimator Does not represent the number of proton inelastic interactions of the corresponding collimator

Transversal Variation of Monitor Location Igor A. Kurochkin TCS1 Igor A. Kurochkin Total energy deposition. The contribution from beam 2 (crosstalk) is small (<1%) due to longitudinal distance. Best signal to background and signal to cross talk at position near to the beam

Betatron Cleaning M. Brugger, S. Roesler Primary interactions Inelastic interaction rate (star), threshold 20MeV Comparison of energy deposition [GeV] to inelastic interaction rate in IP3: They scale for the downstream secondary collimators (2 – 3 GeV per inelastic interaction) Primary collimator: 0.4 GeV First secondary collimator: 3.3 GeV “Primary” refers to 7TeV proton interactions, whereas the “Loss Distribution” includes all secondary particles (threshold of 20MeV), however the latter are dominated (~98%) by high-energy particles close to 7TeV (single- or multiple-scattering). Secondary particles are dominated (~98%) by high-energy particles close to 7TeV

Contribution to the number of inelastic interactions from beam particle losses in upstream collimators M. Brugger, S. Roesler Values similar to momentum cleaning. Higher inter beam crosstalk can be expected due to reduced longitudinal distance between collimators of beam 1 and 2.

Summary BLM system: machine protection First priority (downtime) Detectors next to possible loss locations protect local equipment Monitors in collimation region Measure energy deposition in the collimators Can not measure primary inelastic interactions (response matrix) High activation (reduce sensitivity) Possible noise problems to be investigated (analogue signal cables of BLMs are up to 300 m long and close to numerous stepping motor control cables)