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Control of the Dipole Cold Mass Geometry at CERN to Optimize LHC Performance
CERN.
CERN.
CERN.
CERN.
2006 (English)In: IEEE transactions on applied superconductivity (Print), ISSN 1051-8223, Vol. 16, no 2, 212-215 p.Article in journal (Refereed) Published
Abstract [en]

The detailed shape of the 15 m long superconducting LHC dipole cold mass is of high importance as it determines three key parameters: the beam aperture, nominally of the order of 10 beam standard deviations; the connectivity of the beam- and technical lines between magnets; the transverse position of nonlinear correctors mounted on the dipole ends. An offset of the latter produces unwanted beam dynamics perturbations. The tolerances are in the order of mm over the length of the magnet. The natural flexibility of the dipole and its mechanical structure allow deformations during handling and transportation which exceed the tolerances. This paper presents the observed deformations of the geometry during handling and various operations at CERN, deformations which are interpreted thanks to a simple mechanical model. These observations have led to a strategy of dipole geometry control at CERN, based on adjustment of the position of its central support (the dipole is supported at three positions, horizontally and vertically) to recover individually or statistically their original shape as manufactured. The implementation of this strategy is discussed, with the goal of finding a compromise between conflicting requirements: quality of the dipole geometry, available resources for corrective actions and magnet installation strategy whereby the geometry tolerances depend on the final magnet position in the machine.

Place, publisher, year, edition, pages
2006. Vol. 16, no 2, 212-215 p.
Keyword [en]
dipole geometry, feed down, mechanic aperture
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:kth:diva-8401DOI: 10.1109/TASC.2006.870507ISI: 000244804100036OAI: oai:DiVA.org:kth-8401DiVA: diva2:13711
Note
QC 20100921. Uppdaterad från manuskript till tidskrift (20100921).Available from: 2008-05-09 Created: 2008-05-09 Last updated: 2010-11-24Bibliographically approved
In thesis
1. Accelerators for Physics Experiments: From Diagnostics and Control to Design
Open this publication in new window or tab >>Accelerators for Physics Experiments: From Diagnostics and Control to Design
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis develops techniques of control-methods, optimization, and diagnostics of accelerator equipment and the produced particle beams with emphasis on the Large Hadron Collider (LHC) project at CERN. From a solid knowledge of the characteristics of the manufactured accelerator equipment gained from in-depth measurements and analysis of measured data, a link to an enhanced equipment design can be made. These techniques will be demonstrated in applications related to the LHC magnet production and to the LHC upgrade studies.

The LHC is a 27 km long superconducting accelerator, which CERN, the European high-energy particle physics research organisation, is presently being commissioned in a tunnel 80 m under ground level in the Geneva region. This machine forms the last link in an interconnected chain of several particle accelerators at CERN. The overall system performance, i.e. the quality of particle beams being accelerated in this accelerator chain is directly related to the control of the quality of the superconducting magnets used in the last link, in the LHC. Different upgrade scenarios to reach the ultimate design luminosity and beyond that, implying major machine changes are presently being studied. These scenarios all pose very challenging design requirements for magnets situated in the beam collision regions where extremely radioactive environments have to be dealt with. The LHC is expected to produce very highly energetic and intense particle beams for a number of physics experiments during the next decades, making the subjects of the thesis both timely and important.

The work described has been performed at CERN, which has become the largest high-energy physics laboratory in the world. Here, a number of particle accelerators are connected in series to permit the acceleration of particles to unprecedented high energies to explore the nature of our universe. The accelerators at CERN are assembled of a large number of parts requiring a high level of technological know-how. Control systems and optimization procedures play a natural and necessary role to fulfil the requirements. Diagnostics and control system technology have been used to increase the efficiency of accelerator operation. An extensive analysis of the measured magnetic field have been used to optimize the delicate process of controlling the assembly of superconducting accelerator magnets for the LHC. This paper also describes the control procedures developed, to permit the adjustment of the geometric shape of the 15 m long dipole to optimize the field quality and beam aperture.

From a detailed statistical analysis of the collected geometry data from the 1232 LHC main dipole magnets unresolved issues concerning the measurements were explained and corrected, providing more accurate information for the alignment of the main dipoles and quadrupoles.

The LHC will start operation in 2008, after a most careful installation of all magnets and a huge volume of other equipment in the accelerator tunnel. In particular, the very specialized welding techniques and the brazing of tubes, bellows and conductors, have posed great challenges. Tenths of thousands of welds that have to withstand temperature changes of 300 K and operation with super-fluid helium at 1.9 K have been made. The magnet systems that create the conditions for particle collisions in the two main experiments, the insertion triplets, will have to be exchanged when upgrading the performance of the machine. The upgrade of the machine’s luminosity is expected after 4 years of LHC operation at nominal luminosity. Unless the new magnets are very carefully designed and well shielded the particle debris from the increased collision rates will perturb their operation. Using a new superconductor technology, limiting the probability of magnet quenches, combined with a new layout of the insertion region can minimize the effect of the impinging debris. The necessary shielding layout to protect the magnet coils will be discussed.

The future of accelerators for particle physics is important: the development of accelerator technology to produce neutrino beams from beta decaying ions is one possibility for new physics. This subject will be treated from the aspect of energy deposition from decay products in superconducting magnet coils.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. 101 p.
Series
Trita-FYS, ISSN 0280-316X ; 2008:14
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-4739 (URN)978-91-7178-931-0 (ISBN)
Public defence
2008-05-14, Sal FB55, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100921Available from: 2008-05-09 Created: 2008-05-09 Last updated: 2010-09-21Bibliographically approved
2. Controlling accelerator beams for physics experiments
Open this publication in new window or tab >>Controlling accelerator beams for physics experiments
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 49 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:9
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-3915 (URN)
Presentation
2006-04-19, Sal FA31, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101124Available from: 2006-04-10 Created: 2006-04-10 Last updated: 2010-11-24Bibliographically approved

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