BLM Thresholds on Collimators History and Open Questions

B. Auchmann, O. Picha, Joint CWG/BLMTWG Meeting August 25 2014

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, http://indico.cern.ch/event/BIQ2014

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-2008-092.

• 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 92.44 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. 2009 EDMS 995569. 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 eMail

“The numbers do not contain any safety factor for Collimator jaws for 7 TeV (some for 450 GeV)” CWG Meeting 081217

“These values … contain already the safety factor 10” EDMS 995569

Formulas for energy- and time-dependence

• Input:• dN>10/dt

• dN1-10/dt

• dN<1/dt

• Linear scaling with energy.• Scaling with time:

• t < 1 s: Nmax = dN<1/dt * 1 s

• 1 s < t < 10 s: Nmax = dN1-10/dt * t

• For t > 10 s: Nmax = dN1-10/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-2009-023

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-2008-092. • EDMS 995569 Ralph Assmann priv. com.

• @ 450 GeV:

• @ 7 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 eMail

“The numbers do not contain any safety factor for Collimator jaws for 7 TeV (some for 450 GeV)” CWG Meeting 081217

“These values … contain already the safety factor 10” EDMS 995569

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-0002.

• Question: How do we ensure radio protection compatibility in case of thresholds changes? Is this ever an issue?

Overview Families: TCP

THRI_3_TCP THRI_7_TCP

• EDMS 995569• 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_F5 THRI_7_TCSGTHRI_3_TCSG

• EDMS 995569• 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: TCLATHRI_TCLA

THRI_07_7_AB_TCLA THRI_06_7_CD_TCLA

THRI_06_7_AB_TCLA

TCLA.B7L7

TCLA.B7R7

• EDMS 995569• 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-

0034 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: TCTTHRI_TCT THRI_TCTVA THRI_TCTVB_OI_RC8

• EDMS 995569• 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, TCLITHRI_TCL

THRI_TCLI

• EDMS 995569• Initially identical settings

• Documentation of changes lost.• No ECRs.

Overview Families: TDI

THRI_TDI_RC8

B2 B1

THRI_TDI_RC180

B1 B2

• Not contained in EDMS 995569• 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?