Fast Automatic Beam-Based Alignment of the LHC Collimator Jaws

Europe/Zurich
500/1-001 - Main Auditorium (CERN)

500/1-001 - Main Auditorium

CERN

400
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Description

Due to its potentially destructive high energy particle beams, the Large Hadron Collider (LHC) is equipped with several machine protection systems. The LHC collimation system is tasked with scattering and absorbing beam halo particles before they can quench the superconducting magnets. The 108 collimators also protect the machine from damage in the event of very fast beam losses, and shields sensitive devices in the tunnel from radiation over years of operation. The collimator jaws need be placed symmetrically on either side of the beam trajectory to clean halo particles with maximum efficiency. The beam orbit and beam size need to be determined at each collimator, to be able to position the jaws within a certain number of beam sigmas from the beam centre.

 

Beam-based alignment is used to determine these values at every collimator location. In the alignment procedure, each jaw is moved separately towards the beam trajectory until a spike appears in the signal of a Beam Loss Monitoring (BLM) detector positioned a couple of metres downstream of the collimator. In the 2010 LHC run, almost 30 hours were required for an alignment of all collimators, and 8 beam dumps were caused due to operator mistakes. As part of the Ph.D. work, a phased development and commissioning of various algorithms in the 2011-2012 LHC runs allowed the alignment time to decrease to just over 4 hours, with no more beam dumps. The algorithms range from automatic selection of BLM thresholds during the alignment, to BLM-based feedback loops and pattern recognition of the BLM signal spikes.

 

An alignment simulator was developed in MATLAB based on an empirical model of the BLM detector signal steady-state and crosstalk, as well as a beam diffusion model which allows the prediction of the characteristic BLM detector signal spike and decay. The simulator is targeted at validating possible future alignment algorithms which would otherwise require dedicated beam tests. A new collimator design for future LHC operation envisages Beam Position Monitor (BPM) pick-up buttons embedded inside the jaws. The BPMs will provide an accurate and continuous measurement of the beam centres without requiring BLM-based alignment. One quarter of the LHC collimators will be replaced with the new design. Hence, an algorithm to automatically position the jaws around the beam centre at a large jaw gap was developed and tested with a mock-up collimator installed in the Super Proton Synchrotron (SPS). Alignment times of approximately 20 s were reached.

 

Speaker:  Gianluca Valentino / CERN and University of Malta

 


Coffee / tea will be served after the seminar


ATS Seminars Organisers:
H. Burkhardt (BE) T. Stora (EN), G. De Rijk (TE)
Slides
The agenda of this meeting is empty