Commissioning of BLM system L. Ponce With the contribution of C. Zamantzas, B. Dehning, E.B. Holzer, M. Sapiensky

Outlines Overview of the system signal available in the CCC Strategies for the thresholds settings 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 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 system damage protection, no redundancy Quench protection system (damage protection)

Detector about 3800 ionisation chambers + 320 Secondary emission detectors measure the secondary shower outside the cryostats created by the losses

BLMS Signal Chain Multi-plexing and doubling Optical TX Channel 8 Detector Digitalization VME Backplane Optical RX Superconducting magnet Secondary particle shower generated by a lost Demulti-plexing Signal selec-tion Thres-holds comp-arison Channel selection and beam permits gener-ation. Status monitor FEE 2 Beam Energy TUNNEL SURFACE FEE 1 Unmaskable beam permits Maskable beam permits Front End Electronics (FEE) Back End Electronics (BEE)

Thresholds and interlocks 12 running sums for 32 energy levels for each channel, 16 channels per card, 345 surface cards. → table of 2 millions values! Any of this signal over the thresholds generate a beam dump request via the BIC

1. Principle of the simulation Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize) 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 impacting angle is 0.25 mrad longitudinal scan performed to optimize the BLM location

Definition of the thresholds Loss pattern given by R. Assmann team (C. Bracco, S. Redaelli, G. Robert-Demolaize) 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 impacting angle is 0.25 mrad longitudinal scan performed to optimize the BLM location

Geometry description 3 transverse positions of impact outermost, innermost and top

Typical result 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)

Particle Shower in the Cryostat 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

2. Position in the ARCS Example of topology of Loss (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) More simulation are needed to get better evidence (higher populated tertiary halo)

Particle shower in the detector Addition of all the weighted signals from the previous locations Positions chosen for the arcs also optimum for the DS.

BLMs for the arcs beam 1 beam 2 Mainly BLMQI at the Quads (3 monitors per beam) + cold dipoles in LSS Beam dump threshold set to 30 % of the quench level (to be discussed with the uncertainty on quench level knowledge) Thresholds derived from loss maps (coll. team), secondaries shower simulations (BLM team), quench level simulations and measurements (D. Bocian)

BLMs for warm elements beam 2 beam 1 top view 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

Mobile BLM use the spare chambers use the spare channels per card : 2 in the arcs at each quad, a bit more complicated in the LSS. electronics is commissioned as for connected channel a separate Fixed display for non-active channels is planned : to be discussed detection thresholds: ???

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. For every location a threshold for 7 TeV will be calculated. Table will be filled using parametrized dependence on Energy and Integration time. MASTER table, MAPPING table (BLM location vs electronic channel) will be stored in safe database.

Calibration and Verification of Models Calibration needed for: verification: Detector model (Geant) = (CERN /H6) Detector (particle - energy spectrum dependence) Magnet model (Geant) = HERA beam dump (tails of shower measurements) Shower code (prediction error large for tails) Threshold table Magnet quench (2 dim, energy, duration, large variety of magnet types) Magnet model (SQPL) (heat flow, temp. margin, …) = fast loss: sector test slow loss: SM18

Reasons to change the thresholds? How often? to check Machine Protection functionalities of BLMs (interlocks): decrease the thresholds in order to provoke a dump with low intensity frequency: during the commissioning, after each shut-down (?), for a set of detectors study/check of quench levels (“quench and learn” strategy?): implies dedicated MD time, post-mortem data analysis, could be related to check the correct setting of the thresholds Frequency : ? Probably during shut-down For HERA, only one change since the start-up

some flexibility would help operation but is not an absolute need commissioning of individual systems (MSI, LBDS, collimators) : to get a loss picture of a region, to give “warning” levels adjust thresholds after studies of the systems to optimize the operational efficiency vs. the irradiation level frequency : 1 or 2 iterations after determination of the thresholds and localized in space (injection region, IR7…) To match quench level during commissioning (operational efficiency): Probably few iterations some flexibility would help operation but is not an absolute need

Systematic Uncertainties at Quench Levels about 1 % Radiation & analog elec. Electronic calibration < 10 % Electronics sim., measurements with beam (sector test, DESY PhD) < 10 - 30 % fluence per proton Simulations measurements with beam (sector test), Lab meas., sim. fellow) Source, sim., measurements Correction means ? Topology of losses (sim.) < 200 % Quench levels (sim.) < 10 – 20 % Detector relative accuracies Gianluca: radiation SEE B. Dehning, LHC Radiation Day, 29/11/2005

3. Proposed implementation Threshold GUI Reads the “master” table Applies a factor (<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. SIS receives all tables Compares tables Notifies BIS (if needed) Note: possible upgrade by adding a comparison with master table on the board BUT feasibility has to be checked

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 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?).

System ready for LHC and fulfill the Specifications? Hardware expected to be ready for LHC start-up Threshold tables (calibration of BLM) based on simulations. Analysis effort of BLM logging and post-mortem data (LHC beam data, “parasitic” and dedicated tests) to be started in 2006! Calibration of threshold tables Interpretation of BLM signal pattern  Extensive software tools for data analysis essential to fulfill the specifications! Start now to specify and implement

BLMS Testing Procedures PhD 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 (under discussion) Threshold table beam inhibit test (under discussion) 10 pA test (implemented) Double optical line comparison (implemented) Thresholds and channel assignment SW checks (implemented) Inspection frequency: Reception Installation and yearly maintenance Before (each) fill Parallel with beam

Commissioning Procedures - Steps Calibration Functional test Environmental test Beam energy detector LBDS BIC surface elec. tunnel elec. magnet Particle shower Environmental test: temperature dose & single event Steps: Elec. tunnel, 20 year of operation & “no” single event effects Elec. tunnel, 15 – 50 degree Functional test: before installation during installation during operation All equipment, LAB, current and radioactive source Connectivity, current and radioactive source Connectivity, thresholds tables Calibration: before startup after startup Establishing model (detector, shower, quench behavior) a: no beam abort , no quench, no action b: use loss measurements and models for improvements

Hardware commissioning complete detailed procedure documented in MTF functionalities linked with Machine protection will be reviewed in the Machine Protection System Commissioning working Group validation of the connectivity topology: registration in database of the link position in the tunnel-channel identification-thresholds

Commissioning with beam see presentation of A. Koshick in CHAMONIX Motivation of the test: Establish thresholds = establish the correlation between quench level and BLM signal = Calibration! Verify or establish „real-life“ quench levels Verify simulated BLM signal (and loss patterns) In particular: What BLM signal refers to the quench level of a certain magnet type? => Accurately known quench levels will increase operational efficiency!

How to do the quench test: Implementation if circulating beam, possibility to check steady state losses quench limit. If sector test, fast losses quench limit Simple idea: Steer beam into aperture and cause magnet quench Initial conditions & requirements: Pilot beam 5x109 Clean conditions, orbit corrected (to better +/- 3 mm?). BPM data/logging available  Trajectory BLM data/logging available 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

How to do the test: What we want to learn Beam Parameters Emittance Intensity Momentum spread Optics Parameters -function Dispersion Trajectory/Orbit Impact Length Impact Position Proton density that caused quench in SC magnet Determination of quench level Calibration BLM signal

Conclusions Controlled, defined test to establish Absolute quench limits BLM threshold values Model and understanding of correlation of loss pattern, quench level, BLM signal This test is essential for an early calibration of the BLM system, even if beam time consuming It has to be done before increasing intensity