Abstract
Collimators with embedded beam position monitor (BPM) button electrodes will be installed in the Large Hadron Collider (LHC) during the current long shutdown period. For the subsequent operation, BPMs will allow the collimator jaws to be kept centered around the beam orbit. In this manner, a better beam cleaning efficiency and machine protection can be provided at unprecedented higher beam energies and intensities. A collimator alignment algorithm is proposed to center the jaws automatically around the beam. The algorithm is based on successive approximation and takes into account a correction of the nonlinear BPM sensitivity to beam displacement and an asymmetry of the electronic channels processing the BPM electrode signals. A software implementation was tested with a prototype collimator in the Super Proton Synchrotron. This paper presents results of the tests along with some considerations for eventual operation in the LHC.
Highlights
The Large Hadron Collider (LHC) is a high-energy circular collider located at CERN
Collimators with embedded BPMs will be installed in the LHC to monitor the beam position at the collimator locations with greater precision
Results from tests with a prototype collimator in the Super Proton Synchrotron (SPS) were presented, where an alignment time of ∼20 s was reached with a precision between opposite electrode signals corresponding to 5 μm, at jaw gaps as large as 58 mm
Summary
The Large Hadron Collider (LHC) is a high-energy circular collider located at CERN. It is designed to accelerate 3.23 × 1014 protons in two counterrotating beams to achieve collisions in the experimental insertions at a center-of-mass energy of 14 TeV [1]. The lack of frequent alignments means that large margins need to be placed on the hierarchy settings to cater for possible beam orbit drifts over weeks or months of operation This contributes to a high βà (the β function in the interaction points), which reduces the luminosity reach of the LHC. The successful results from the beam tests motivated the replacement of all 16 TCTs located in the experimental IRs (eight horizontal and eight vertical) and the two TCSGs in IR6 (both horizontal) with new collimators having embedded BPM buttons for LHC operation in 2015. The stage was to test the full data acquisition chain, correction of BPM nonlinearities, and alignment algorithm to benefit from the operational gains offered by the new hardware and reduce the current alignment time required of 1 hr for all TCTs. The beam tests were performed with the same prototype collimator in the SPS in 2012. V, the alignment algorithm together with beam test results are presented
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