Real-Time Schottky Measurements in the LHC

The accelerator complex at the European Organization for Nuclear Research (CERN) is a diverse collection of machines, tailored for different energy ranges, and concatenated in order to accelerate/decelerate particle beams. Leading up to CERN’s flagship accelerator, the Large Hadron Collider (LHC), every accelerator in the chain boosts the particles to higher energies before they are injected into the next machine in the sequence. The LHC is a circular synchrotron accelerator consisting of two 27-kilometer vacuum tubes equipped with superconducting magnets and accelerating RF cavities in order to increase the energy of the particles along the way. Inside the vacuum tubes, two counter-rotating high-energy particle beams travel at velocities close to the speed of light before they are made to collide inside particle detectors at a centre-of-mass energy of 13 TeV. As the particles are accelerated, they experience various external and internal forces. RF cavities are used to boost the speed of the particles and keep them in discrete bunches, dipole magnets are used to bend the particles into a circular orbit while some higher order magnets act as lenses that focus the beam. For ensuring the quality of the beam and controlling its stability, a set of important machine parameters need to be measured/estimated. The LHC Schottky beam diagnostics system was designed with the intent of measuring important beam parameters such as tune, chromaticity, synchrotron frequency, momentum spread, etc. Compared to the presently available invasive methods that can cause significant particle losses, the LHC Schottky system is able to measure in a passive way. It does so by detecting internal statistical fluctuations of the beam particles, the so-called Schottky noise, and extracting the information that is encoded in the obtained frequency spectrum. In this report we present the real-time implementation of the analysis of Schottky signals in the LHC. In particular, focusing on the measurement of the betatron tune, chromaticity and synchrotron frequency. Chapter 1 provides insight into the history and evolution of a few significant accelerators while introducing the LHC accelerator chain. chapter 2 introduces the physics of synchrotron accelerators and the importance of tune and chromaticity for beam diagnostics. chapter 3 presents the theoretical background of the signals measured by Schottky systems. Chapter 4 introduces both the analog signal treatment chain and the implemented digital signal processes for the LHC Schottky system. chapter 5 presents the real-time software that executes the digital signal processing steps introduced in the preceding chapter. In chapter 6 the results of the implemented measurement methods and future work is discussed.