Accelerators for Physics Experiments : From Diagnostics and Control to Design

• Main Author: Wildner, Elena
• Format: Doctoral Thesis
• Language: English
• Published: KTH, Fysik 2008
• Subjects: Astroparticle physics; Astropartikelfysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4739; http://nbn-resolving.de/urn:isbn:978-91-7178-931-0

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. === QC 20100921