Luminosity and luminous region calculations for the LHC

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By measuring and adjusting the β-functions at the interaction point (IP) the luminosity is being optimized. In LEP (Large Electron Positron Collider) this was done with the two closest doublet magnets. This approach is not applicable for the LHC (Large Hadron Collider) and RHIC (Relativistic Heavy Ion Collider) due to the asymmetric lattice. In addition in the LHC both beams share a common beam pipe through the inner triplet magnets (in these region changes of the magnetic field act on both beams). To control and adjust the β-functions without perturbation of other optics functions, quadrupole groups situated on both sides further away from the IP have to be used where the two beams are already separated. The quadrupoles are excited in specific linear combinations, forming the so-called "tuning knobs" for the IP β functions. For a specific correction this knob is scaled by a common multiplier. The different methods which were used to compute such knobs are discussed: (1) matching in MAD, (2) inversion and conditioning of the response matrix by singular value decomposition, and (3) conditioning the response matrix by multidimensional minimization using an adapted Moore Penrose method. For each accelerator, LHC and RHIC, a set of knobs was calculated and the performance compared. In addition the knobs for RHIC were successfully applied to accelerator. Simultaneously this approach allows us theoretically to measure the beam sizes of both colliding beams at the IP, based on the tuneability provided by the knobs. This possibility was investigated. The standard method for LEP to measure the IP β-functions was adapted and advanced to the asymmetric LHC lattice. First of all I would like to thank my wife Eva and two sons, Maxi and Martin, for their love, support and understating during these years of my thesis. The confidence and patience they spent me to face the sometimes difficult time. I would like to thank my university supervisor Univ. Prof. Dr. Bernhard Schnizer of the Institute fuer Theoretische Physik, TU-Graz, who encouraged me, despite of all circumstances, to start and carry out this thesis, for his help and faith. My CERN supervisor Dr. Frank Zimmermann, of the AB Department, Accelerator and Beam Physics group, for his guidance of this thesis, and the confidence in me and my ideas. With their assistance, patience and many fruitful discussions they made this time a great experience. I would also like to thank other members, especially Andre Verdier and Daniel Schulte, who always had time to discuss sometimes crazy ideas. This work would not have been possible without the help of the many members of this group. CERN CERN, from the French "Conseil Europèen pour la Recherche Nuclaire" is one of the world's largest scientific research facilities. It is located at the border between France and Switzerland close to the city of Geneva. In English referred to as the European Organization for Nuclear Research, it was founded in 1953. The motivation for establishing this laboratory was to drive the nuclear research to smaller dimensions to win a deeper insight into matter. Starting with the Proton Synchrotron (PS) Complex, demands to increase the energy of the accelerated particle led to expansion of the facility. Figure 1.1 shows a sketch of the now existing or currently being constructed accelerators. The machine built after the PS is the SPS (Super Proton Synchrotron). It provided the energy to discover the weak force particles W + , W − , Z 0 earning Carlo Rubbia and Simon Van de Meer the Nobel prize 1984 for their discovery. To push the frontier of energy higher and to obtain more precise data the particle accelerator LEP (Large Electron Positron collider) was built. LHC To step one step higher on the energy ladder, currently the LHC (Large Hadron Collider) is constructed. Using two proton beams, it will provide a top center of mass energy of 2 × 7 TeV (Tera electron Volts = 10 12 eV) to the high energy physics community. It is currently being installed in the tunnel that earlier hosted the LEP collider. This tunnel and the adaptations are depicted in Fig.1.2. Contrary to LEP the LHC is based on superconducting magnets which are needed to provide the field strengths for guiding and focusing a beam at this energy level. The LHC will collide the two beams in four interaction points (IPs) which host four different experiments with their detectors (ATLAS, CMS, ALICE, LHC-B), and a fifth experiment (TOTEM) installed close to LHC-B. Figure 1.3: Acceleration chain of the installation located at Brookhaven National Laboratory. The Relativistic Heavy Ion Collider is the final stage of this chain. In RHIC gold ions and spin polarized protons are brought into collision.

2002

We discuss a possible staged upgrade of the LHC and of its injectors, with a view to increasing the luminosity from the nominal 1034 cm 2 s 1 to 1035 cm 2 s 1 in each of the two high-luminosity experiments. We also consider possible scenarios for an upgrade to a proton beam energy of about 14TeV. Starting from beam dynamics considerations and fundamental limitations of the hardware subsystems, we derive realistic requirements for the major components, such as superconducting magnets, cryogenic and RF systems, beam dump and vacuum. We also discuss a novel approach to the optimization of the collider performance, compatible with the beam-beam limit for high intensity proton bunches or long `super-bunches', and sketch a new design of the interaction regions, including an alternative beam crossing scheme. Finally we identify further studies required for an LHC performance upgrade and propose an R&D programme. CERN{EST Division yCERN{LHC Division zCERN{PS Division x CERN{SL Division ...

Journal of Instrumentation

The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will undergo a major upgrade in the 2020s. This will increase its rate of collisions by a factor of five beyond the original design value and the integrated luminosity by a factor ten. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11 -12 T superconducting magnets, including Nb 3 Sn-based magnets never used in accelerators before, compact superconducting cavities for longitudinal beam rotation, new technology and physical processes for beam collimation. The dynamics of the HL-LHC beams will be also particularly challenging and this aspect is the main focus of this paper.

Journal of Instrumentation

Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy √ s. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for √ s = 2.76, 7 and 8 TeV (proton-proton collisions) and for √ s NN = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at √ s = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider.

2017

Long-range beam-beam interactions dictate the choice of operational parameters for the LHC, such as the crossing angle and β^{*} and therefore the luminosity reach for the collider. These effects can lead to particle losses, closed orbit effects and emittance growth. Defining how these effects depend on the beam-beam separation will determine the minimum crossing angle and the β^{*} the LHC can operate. In this article, analysis from a dedicated machine study is presented in which the crossing angle was reduced in steps and the impact on beam intensity and luminosity lifetimes were observed. Based on the observations during the machine study, the intensity decays are compared to expectations from models. Estimates of the luminosity reach in the LHC are also computed.