The LHC Collimation system is a system designed to provide beam cleaning and limited passive protection to the LHC. The precise control of the jaw positions versus time and beam position has important relevance for machine protection of the LHC. The system is protected by various interlocks against wrong positioning. These interlocks are subject to thourough testing as part of MP procedures.

The results of machine protection (MP) tests for the LHC collimation system are documented in EDMS reports and in the MTF database system (also used for production and quality control of collimators). Here we provide easy links to the relevant documents for all installed collimators, which are treated through the LHC collimation project.

Quick jump to:

General testing history:

A document describing the specific machine protection tests can be found in:
https://edms.cern.ch/doc ument/889345/

And the link to the LHC Machine Protection can be found at Machine Protection Web Page

Test Position/Gap Interlocks vs Time, Energy and Beta-star

The collimator position interlocking is based on the comparison between the measured jaw positions and collimator gap values against user-defined limit thresholds that can be expressed as a constant (discrete) value, as time-, energy- and beta-start- dependent functions. If the measured values exceed the interlock thresholds, the collimator survey unit (PRS=Position Readout Survillance) removes the beam permit.

Each LHC collimator has 6 LVDT (Linear Variable Differential Transformer) sensors for direct jaw position and gap measurements. Each of them can trigger a beam interlock if the measured readout exceed INNER or OUTER limit values. In total, there are therefore 12 interlocks per collimator that have to be tested in order to validate the machine protection functionality of the PRS unit. In addition, there are energy-dependent and beta-star-dependent limit functions (one OUTER limit for each of the gap LDVT for the energy limits and one OUTER and one INNER limit for each of the gap LDVT for the beta-star limits, i.e. six additional interlocks per collimator (2 for the energy-dependent and 4 for the beta-star-dependent). An example of the offline analysis test is given in figure bellow.

Summary: Test Position/Gap Interlocks

Test Local Mode Interlock

The test consists on chequing the interlocks caused by taking single collimators to local mode (where collimator could be moved). The local mode was tested individually for each front-end in January 2010 and in a random sub-set of collimators in 2012.

Summary: Test Local Mode Interlock

Test Power Cut and PRS Reboot Interlock

Check correct interlock response to a power cut and a reboot. Verification that the chane of status of the PRS untis causes an interlock whenthe PXI is rebooted. The software implementation is the same for all the units, therefore the tes on one unit is considered sufficient. It's possible to try 2 types of reboot: (1) software and (2) hardware (power cut). The same behaviour is expected for the two cases as far a s the interlock response is concernd. The hardware reboot alsos causes a reboot of the PXI that controls the MDC.

Verification followed:

1. PXI rebooted.
2. Beam permit removed.
3. MDC errors (motors blocked).
4. Connection error (collimator appears in blue in the status).
5. Collimator unconfigured (red in the status) while reboot takes place.
6. Collimator back to operation and interlock clear after reset.

Summary: Test Power Cut and PRS Reboot Interlock

Test temperature interlock

Summary: Test temperature Interlock

Test RBAC interlock

Summary: Test RBAC interlock

Test MCS-Collimator role

Only MCS-collimator can change MCS thresholds: EnergyThreshold, InterlockThreshold, InterlockThresholdFunct for the active beam process. Tested systematically during collimator remote commissioning (non-authorized persons frequently calling persons with MCS-collimator role to move collimators out of interlocked status). See for example LHC e-log page

Summary: Test MCS-Collimator role

Test Crystals Goniometers Interlock

Summary: Test Crystals Interlock

The MP reporting for the LHC collimation system is done in the MPP home tracking web page (linking back to the present page).

May 2017
S. Redaelli, B. Salvachua, G. Valentino