Commissioning of BLM system L. Ponce With the contribution of B. Dehning, E.B. Holzer, M. Sapinski, C. Zamantzas and all BLM team

Outlines Overview of the BLM system Principle of the simulations Strategy for BLM positioning and the thresholds settings Signal available hardware commissioning commissioning with beam conclusions

BLM for machine protection The only system to protect LHC from fast losses (between 0.4 and 10 ms) The only system to prevent quench Arc Dipole Magnet dynamic range : 102 -1010 MIPs/(cm2s) Detection of shower particles outside the cryostat or near the collimators to determine the coil temperature increase due to particle losses LHC quench values are lowest BLM BLM + QPS damage BLM Quench

BLM system : Detector about 3600 ionisation chambers + 310 Secondary EMission detectors measure the secondary shower outside the cryostats created by the losses dynamic range : 108 (or 1013 with SEM) corresponding to few pA to 25 A Ionisation chamber: Diameter = 8.9 cm, Length 60 cm, 1.5 litre, Filled with N2 SEM Diameter = 8.9 cm Length 15 cm

BLM system : signal chain 8 channels per tunnel card, 2 tunnel cards per surface card and 335 surface cards 12 integration periods and 32 energy level per channel (= per monitor) signal over the thresholds generate a beam dump request via the BIC Some channels can be maskable with the Safe_Beam flag

Simulation : loss locations Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize) : Example (MQ27.R7) Peak before MQ at the shrinking vacuum pipe location (aperture limit effect) End of loss at the centre of the MQ (beam size effect)

Simulation : geometry description GEANT 3 simulation of the secondaries shower created by a lost proton impacting the beam pipe simulation of the detector response to the spectra registered in the left and right detector (M. Stockner with G4) 500 protons same z position and same energy Typical impacting angle is 0.25 mrad longitudinal scan performed for primary impact to optimize the BLM location Top view

Simulation : typical result Longitudinal distribution of the secondaries outside the cryostat in DS for different loss location (z) Maximum of the shower ~ 1m after impacting point in material increase of the signal in magnet free locations factor 2 between MQ and MB z (cm)

Simulation: Particle Shower in the Cryostat example of MQ27R7: signal for each location given by the loss map (red) and “sum” signal (black) Position of the detectors optimized to: catch the losses: MB-MQ transition Middle of MQ MQ-MB transition minimize uncertainty of ratio of deposited energy in the coil and in the detector B1-B2 descrimination

Strategy :BLM for quench prevention beam 1 beam 2 At each Quads, 3 monitors per beam : 2 aperture limitation + middle positions as much standardized as possible (integration problems) : same procedure for quads in LSS to define families of monitors (about 250) Beam dump threshold set to 30 % of the quench level (to be discussed with the uncertainty on quench level knowledge)

Strategy: BLM for warm elements beam 2 top view collimator TDI beam 1 BLM in LSS : at collimators, warm magnets, MSI, MSD, MKD,MKB, all the masks… Beam dump threshold set to 10 % of equipment damage level (need equipments experts to set the correct values) Simulation from FLUKA team for IR7 and IR6, from MARS for IR3

Generation of threshold table Quench and damage level threshold tables will be created for each family of BLM locations. They will be assembled together into MASTER table (damage or quench threshold vs beam energy and integration time) For every location a threshold for 7 TeV beam will be calculated (seed for parameterization). Table will be filled from the seed using parameterized dependence of quench level on Energy and Integration time. MASTER table, MAPPING table (BLM location vs electronic channel) will be stored in LSA database.

Calibration and Verification of Models Simulation is needed for : secondaries shower simulation magnet quench (dependance with beam energy, duration, magnet types, 2 dim...) detector response Verification : measurements of the tails of the secondary shower with BLM on HERA dump : comparison with G4 simulation (still to validate, M. Stockner) quench tests campaign in SM18 for quench magnet model verification (steady state losses) (D. Bocian, A. Siemko) detector model checked with the CERN/H6 experiment (M. Stockner PhD thesis)

Proposed implementation LSA Threshold GUI Reads the “master” table Applies a factor to a family (<1) Saves new table to DB Sends new table to CPU CPU flashes table if allowed (on- board switch) Thresholds are loaded from the memory on the FPGA at boot. Combiner initiated test allows CPU to read ‘current’ table. Concentrator receives all tables Compares tables Notifies BIS (if needed) -> Details of implementation under discussion

Consequences on the reliability of the system? Flexibility given by changing remotely the thresholds has to be balanced with the loss of reliability of the system Possibility to scale the thresholds by families (to be discussed which families and who can define it) The proposed implementation allows both possibilities But the remote access will have to be validated by machine protection experts when more detailed implementation of MCS and comparator are available (by the beginning of summer?).

BLM system : signals available 12 running sums (40 μs to 84 s) to cover the loss duration and 32 energy levels used for filling different buffers: logging: at 1 Hz, max loss rate in each running sums over the last second + corresponding quench levels + error and status from tests Post-Mortem + study data : the last 1.7 s with a 40 μs sample rate (43690 values) + the last 2 min of the logging data + thresholds and masking tables + system status info XPOC : possible to get up to 32000 values per channel for the chosen running sum (need to be specified by LBDS) Collimation: on request, 32 consecutive sums of 2,54 ms

Fixed Display in the CCC Used thresholds values (change with energy) Loss signals: Max values of integration intervals between 40 us and 84s updated every 1 s Values normalised to the used thresholds or in Gy? BLM concentrated by quad? If decided, possibility to scale the thresholds table by a factor F<1, by families

Other uses of BLM Mobile BLM BLM for ions: Same Ionisation Chambers use the spare channels per card : 2 in the arcs at each quad, a bit more complicated in the LSS because of more elements. electronics is commissioned as for connected channel a separate Fixed display for non-active channels is planned : to be discussed No dump thresholds BLM for ions: same hardware, same electronics, same thresholds as for protons (simulation from R. Bruce) some more specific loss locations : on dipoles in DS and arcs of IR7 and 3 (G. Bellodi, H. Braun), cells 11 & 13 in IR1 and IR5, cells 10 & 12 in IR 2 (BFPP, J. Jowett and S. Gilardoni)

Status of the system Hardware: IC on time for LHC start-up, SEM delivery in summer Installation: sector 7-8 done (cables missing in 7 left), sector 4-5 half done (delayed due to LHC schedule), 8-1 started Acquisition system continuously running at HERA, post-mortem + collimation data check at collimator MD Threshold comparator software and combiner card (first version done) to be implemented Fixed display in CCC to be completed by CO Threshold tables generation : start to specify and implement post-mortem database and analysis still to be defined Extensive software tools for data analysis (essential to fulfill the specification). Start now to specify and implement

Hardware commissioning complete detailed procedure documented in MTF functionalities linked with Machine protection will be reviewed in the Machine Protection System Commissioning Sub-Working Group validation of the connectivity topology: registration in database of the link between position in the tunnel- channel identification-thresholds Radiation source check (moving in the tunnel)

BLM Testing Procedures Ph D thesis G.Guaglio Detector Tunnel electronics Surface electronics Combiner Functional tests Barcode check Current source test (last installation step) Radioactive source test (before start-up) HV modulation test (implemented) Beam inhibit lines tests Threshold table beam inhibit test (under discussion) 10 pA test Double optical line comparison (implemented) Thresholds table and channel assignment SW checks Inspection frequency: Reception Installation and yearly maintenance Before (each) fill Parallel with beam

Commissioning with beam see presentation of A. Koschik in CHAMONIX 06 Motivation of the test: Verification of the correlation between energy deposition in the coil (= quench level) and BLM signal (= thresholds) Verify or establish „real-life“ quench levels Verify simulated BLM signal and loss patterns => Accurately known quench levels will increase operational efficiency! simple idea: steer beam into aperture and cause magnet quench possibility to check steady state losses quench limit with circulating beam (part of the MPS commissioning) possibility to check fast losses quench behavior if sector test

Conditions for a quench test Requirements : Pilot beam 5x109 Clean conditions, orbit corrected (to better +/- 3 mm?): need to know impact position and length for determination of the lost proton density BPM data/logging available -> Trajectory BLM data/logging available Up to 6 additional “mobile” BLMs at the chosen locations Vary intensity 5x109 – max. 1x1011 +logging all relevant data (BPM, BLM,BCT,emittance …) Set optics (3-bump) Magnet quench

Summary BLM system designed to be reliable and cover the specification of machine protection and quench prevention Unique hardware and software for all spec to easy maintenance Controlled, defined test with beam is essential for an early verification of the BLM system, even if beam time consuming Absolute quench limits and BLM threshold values Model and understanding of correlation of loss pattern, quench level, BLM signal Remote access to the thresholds table has still to be approved by machine protection experts Specification of families to scale has to be defined (OP)