B. Auchmann, O. Picha, Joint CWG/BLMTWG Meeting August

Objective Post-LS1 thresholds strategy for BLMs on collimators, i.e., only those BLMs connected to BIS, with thresholds unequal to MAX. To be finalized until BLM thresholds review at BIQ Workshop 2014 September 15-16, Kjell Johnson Auditorium,

BLM Thresholds Formula for Collimators The Master Threshold is computed from three terms (neglecting signal offset correction): The Applied Threshold on a given monitor is scaled by the constant Monitor Factor:

History of the BLM Response Function 2008/9 initial setting based on "Beam Loss Patterns at LHC collimators. Measurements and Simulations". Till Bohlen, Masters Thesis, CERN-THESIS Constant value of 0.54 aC/p used corresponding to 1E-12 Gy/p (with conversion factor 5.4E-5 C/Gy). Energy scaling by factor 3.5 neglected. Reduction by a factor of 100 for a tilted collimator not considered.

History of the BLM Response Function 2008/9: 0.54 aC/p from Till Bohlen thesis. “Injection test data (2009/11/17) give aC/p on an untilted collimator.” Analysis by Aurelien Marsili. “Conservative result of test on tilted TCLA (2009/12/1) yields 33.6 aC/p signal in the BLM is 33.6 aC/p.” Analysis by Annika Nordt End of Run 1: 33.6 aC/p “flat rate” for all collimators, irrespective of collimator type or energy level. Changes not documented in ECRs? Questions: Have the 2009 results been modeled with FLUKA? Do we have improved FLUKA models per collimator type? Is it permissible to use one model for different types of collimators? (Check data shown in BLMT application specification Fig. 2.1!)

Maximum Number of Protons Lost on Collimator Initial input: Ralph Assmann private communication, documented in Aug EDMS In a mail from August 14 he elaborates: 1) The assumption used is that the collimations system should work in regular conditions with the maximum specified loss rates (200 kW at primary collimators). 2) Assuming a correct hierarchy the loss rates at all subsequent collimators are calculated. 3) The resulting thresholds are much tighter than required for survival criteria, but we ensure proper functioning of the whole system, including hierarchy (highest losses at primary collimators). This also ensures correct radio-protection impact, another very important issue. TCP values ensure functioning within design spec. Other values ensure proper collimation hierarchy and radio- protection impact.

Maximum Number of Protons Lost on Collimator “thresholds are much tighter than required for survival” RA “The numbers do not contain any safety factor for Collimator jaws for 7 TeV (some for 450 GeV)” CWG Meeting “These values … contain already the safety factor 10” EDMS

Formulas for energy- and time-dependence Input: dN >10 /dt dN 1-10 /dt dN <1 /dt Linear scaling with energy. Scaling with time: t < 1 s:N max = dN <1 /dt * 1 s 1 s < t < 10 s: N max = dN 1-10 /dt * t For t > 10 s: N max = dN 1-10 /dt * 10 s +dN >10 /dt * (t – 10 s) Corrections of first 3 running sums for fast current change (e.g. quench) in a superconducting D1 magnet. Redundant protection with fast current- change monitor FCCM. Andres Gomez Alonso, “Redundancy of the LHC Machine Protection Systems in Case of Magnet Failures”, CERN-THESIS

Damage Protection – for discussion only Question: How do we ensure damage protection in case of threshold changes? Assumption: Direct impact on collimator (collim. hierarchy not respected). Some input data: LHC Design Report Chapter 18 “Beam Cleaning and Collimation System” single-module dump case study. Till Bohlen, Masters Thesis, CERN-THESIS EDMS Ralph Assmann priv TeV: Melting temperature of graphite is 3823 K. Safety factor < 2? Question: Has this kind of studies been done systematically for all collimator types? “thresholds are much tighter than required for survival” RA “The numbers do not contain any safety factor for Collimator jaws for 7 TeV (some for 450 GeV)” CWG Meeting “These values … contain already the safety factor 10” EDMS

Damage and Radio Protection Question: If the BLM on the device cannot protect against damage – can we judge whether a downstream BLM will protect via cross-talk? This argument was used in one instance of threshold changes in LHC-BLM-ECR Question: How do we ensure radio protection compatibility in case of thresholds changes? Is this ever an issue?

Overview Families: TCP THRI_3_TCPTHRI_7_TCP EDMS Initially identical settings RS01-03 multiplied by 0.06 for fast D1 errors. LHC-BLM-ECR-0033 for IP7, LHC-BLM-ECR-0034 for IP3 Different 200 kW corrections on RS 9, RS12 now allows for 80 kW, MF = 0.4.

Overview Families: TCSG THRI_7_TCSG_F5THRI_7_TCSGTHRI_3_TCSG EDMS Initially identical settings RS01-03 multiplied by 0.05 for fast D1 errors but not implemented. LHC-BLM-ECR_0023 Factor 5 for THRI_7_TCSG_F5. LHC-BLM-ECR-0033 for IP7, LHC-BLM-ECR-0034 for IP3 Different 200 kW corrections on RS 9, RS12 now allows for 80 kW, MF = 0.4.

Overview Families: TCLA THRI_TCLA THRI_07_7_AB_TCLATHRI_06_7_CD_TCLA THRI_06_7_AB_TCLA TCLA.B7L7 TCLA.B7R7 EDMS Initially identical settings LHC-BLM-ECR-002 THRI_06_7_AB_TCLA Factor 2500 THRI_06_7_CD_TCLA and THRI_07_7_AB_TCLA Factor 2 THRI_TCLA Factor 50 “not generally protected against damage” based on RA table. LHC-BLM-ECR-0010 THRI_06_7_CD_TCLA and THRI_07_7_AB_TCLA Factor 10 MF from 1 to 0.1 LHC-BLM-ECR-0032 THRI_06_7_CD_TCLA MF from 0.1 to 0.2 LHC-BLM-ECR-0033 for IP7, LHC-BLM-ECR for IP3 Different 200 kW corrections on RS 9, RS12 now allows for 80 kW, MF = 0.4. What about TCLA.B7L7 and TCLA.B7R7?

Overview Families: TCT THRI_TCTTHRI_TCTVATHRI_TCTVB_OI_RC8 EDMS Initially identical settings LHC-BLM-ECR-0010 All Factor 10 Several asymmetries in families not documented? LHC-BLM-ECR-0012 Creation of THRI_TCTVB_OI_RC8 initially including TCTPV.4L2 Exp. Function created to adjust thresholds. LHC-BLM-ECR-0019 (document not on EDMS) Time constant change for THRI_TCTVB_OI_RC8 from 120 µs to 2(3?) ms. LHC-BLM-ECR-0024 Factors (~2) on THRI_TCTVB_OI_RC8. (Not seen in card files but implemented.)

Overview Families: TCL, TCLI THRI_TCL THRI_TCLI EDMS Initially identical settings Documentation of changes lost. No ECRs.

Overview Families: TDI THRI_TDI_RC8 B2B1 THRI_TDI_RC180 B1B2 Not contained in EDMS Current settings as TCSG. Documentation of changes lost (initial settings?). LHC-BLM-ECR-0005 THRI_TDI_RC180 Hardware changes LHC-BLM-ECR-0007 on in THRI_TDI_RC180 Same settings as TCSGs. MF set to 1 in THRI_TDI_RC180.

How to Set Thresholds Post LS1? Do the families remain the same (despite some changes to collimators)? Updated table for MaxProtonsLost. What kind of update to the BLMResponse? Is there a validated FLUKA model for each collimator type we should use? Proposal how to deal with past ECRs: Neglect changes due to LHC-BLM-ECR-0033 and 0034 (Belen & Daniel analysis) and wait for first Run 2 loss maps to repeat exercise. Maintain factors and “filtering” on TCSGs, TCTs, and TCLAs. Systematically review and validate them with Run 2 data. Check thresholds vs. noise levels for 6.5 TeV. Look into projections for ion operation. Other open questions: How to validate damage protection (and radio protection issues)? Check if MonitorFactors are 1 in all families but those in LHC-BLM-ECR-0033 and 0034? Could a series of tests bring experimental clarity on BLMResponse(E) and cross-talk (for damage-protection) for all collimator types?

2002 work on cross-talk in BLMs

LHC-BLM-ECR-0033 Error AT versus MT in Table 2?