Improving the precision of linear optics measurements based on turn-by-turn beam position monitor data after a pulsed excitation in lepton storage rings

Beam optics control is of critical importance for machine performance and protection. Nowadays, turn-by-turn (TbT) beam position monitor (BPM) data are increasingly exploited as they allow for fast and simultaneous measurement of various optics quantities. Nevertheless, so far the best documented uncertainty of measured ß -functions is of about 10‰ rms. In this paper we compare the ß -functions of the ESRF storage ring measured from two different TbT techniques—the N-BPM and the Amplitude methods—with the ones inferred from a measurement of the orbit response matrix (ORM). We show how to improve the precision of TbT techniques by refining the Fourier transform of TbT data with properly chosen excitation amplitude. The precision of the N-BPM method is further improved by refining the phase advance measurement. This represents a step forward compared to standard TbT measurements. First experimental results showing the precision of ß -functions pushed down to 4‰ both in TbT and ORM techniques are reported and commented.Postprint (published version

Local optics corrections in the HL-LHC

In order to increase the performance of particle colliders, it is crucial to make the beam sizes at the collision points as small as possible. This causes an increase of the beam size in the region surrounding the collision points thus enhancing the effect of magnetic errors. These errors must therefore be kept under tight control to ensure the performance and safety of the accelerator. The present thesis studies effects of the expected magnetic errors in the regions around the collision points on the beam optics that determine the beam size in the future High-Luminosity upgrade of the Large Hadron Collider (HL-LHC), a 27 km particle accelerator situated on the French-Swiss border near Geneva, Switzerland. It has become clear in recent years that in correcting the magnetic errors in this region a crucial requirement is an accurate measurement of the beam optics at the collision point. This thesis demonstrates that the technique used traditionally in recent years, called “K-modulation”, is not accurate enough to ensure the performance of the HL-LHC and therefore alternative methods of performing this measurement must be studied. To perform these studies a new automatic optics correction tool has been developed and is presented in this thesis. This new tool allows faster and more systematic calculation of corrections of the magnetic errors around the interaction regions and has been successfully tested during commissioning and experiments in the LHC. Two complementary techniques are proposed in order to improve the accuracy of the determination of the beam sizes at the collision points, namely determining the minimum beam size near the collision point using the “phase-advance” of the beam oscillations around the accelerator and locating the position of this minimum, the “beam waist”, by displacing it and maximising the collision rate characterized by the collider luminosity. In the thesis these techniques are studied theoretically, and the first results of their experimental validation performed in the LHC are presented. This push for smaller beam sizes at the collision points not only increases the beam sizes in sections around this point but also, though to lesser degree, in the arcs of the accelerator. These regions also become susceptible to smaller magnetic errors. As some regions of the accelerator do not count with adequate corrector magnets alternative solutions are needed. Here we present the first experimental results of an optics correction performed by traversing sextupoles with off-central beam in the LHC as a solution proposal. Another consequence of the growth of the beam sizes in the regions around the collision points is the eventual necessity for larger beam pipes. This is the case for HL-LHC where the magnetic lenses around the collision points are going to be replaced by new ones with the beam pipe of larger diameter. In order to keep the same magnetic strength though a new superconducting technology is going to be used to build these magnets. A downside of this novelty is that it is susceptible to a type of magnetic instability called “flux-jumps”. In the thesis the effect of the flux-jumps on the beam sizes is studied theoretically and concrete predictions using measurements of this effect on the prototypes of the new magnets of the HL-LHC are given. The study is also extrapolated to the Future hadron-hadron Circular Collider (FCC-hh), a proposed 100 km circular collider, in which superconducting magnets of this type are expected to be installed all around its circumference. Finally, the thesis presents a summary of software developments performed during the previously mentioned studies, including a user interface to facilitate the use of the automatic correction tool, a new harmonic analysis program that replaces legacy code and many refactors and rewrites that have significantly eased the development of the optics measurements and corrections programs.Con el fin de incrementar la eficiencia de los colisionadores de partículas, es crucial reducir el tamaño de los haces en el punto de colisión tanto como sea posible. Esto causa un incremento del tamaño de los haces en las regiones que rodean al punto de colisión, lo cual incrementa el efecto dañino de los errores magnéticos. Los errores en esta región deben, por tanto, mantenerse bajo estricto control para asegurar que el acelerador se comporta de forma eficiente y segura. Esta tesis estudia los efectos de los errores magnéticos alrededor de los puntos de colisión en la óptica del haz, la cual determina su tamaño en estos puntos, en la futura mejora de Alta-Luminosidad del Gran Colisionador de Hadrones (HL-LHC por sus siglas en inglés), un colisionador de partículas de 27 km de circunferencia situado en Ginebra. En los últimos años se ha hecho evidente que, para corregir los errores magnéticos en estas regiones, es crucial una medida precisa de la óptica del haz en el punto de colisión. Esta tesis demuestra que la técnica de medida usada tradicionalmente, llamada “K-modulation”, no es lo suficientemente precisa para asegurar la eficiencia del HL-LHC y que por lo tanto se deben estudiar métodos alternativos. Para llevar a cabo este estudio, se ha desarrollado y se presenta en esta tesis una nueva herramienta automática de corrección de la óptica. Esta nueva herramienta permite calcular correcciones de los errores magnéticos alrededor de los puntos de interacción de forma más rápida y sistemática, y ha sido probada experimentalmente con éxito en el LHC. Se proponen dos técnicas complementarias que mejoran la precisión de la determinación de los tamaños de los haces en los puntos de colisión: la determinación del mínimo tamaño del haz en la región cercana al punto de colisión usando el “avance de fase” de las oscilaciones del haz y la localización de la posición de este mínimo, desplazándolo y buscando maximizar la frecuencia de las colisiones. En la tesis se estudian estas técnicas de forma teórica y se presentan los primeros resultados de su validación experimental en el LHC. Este impulso para reducir el tamaño de los haces en los puntos de colisión no solo incrementa su tamaño alrededor de este punto sino también, en menor medida, en los arcos. Por tanto, estas regiones también se vuelven sensibles a errores magnéticos más pequeños. Dado que algunas de estas regiones no disponen de imanes correctores, en la tesis se presentan los primeros resultados experimentales en el LHC de una corrección de la óptica atravesando sextupolos con un haz desplazado de su centro. Otra consecuencia del crecimiento del tamaño de los haces en las regiones alrededor de los puntos de colisión es la necesidad de tubos del haz de mayor diámetro. Ese es el caso en HL-LHC, donde las lentes magnéticas alrededor de los puntos de colisión van a ser remplazadas para aumentar su diámetro. Para poder mantener el mismo campo magnético, una nueva tecnología de superconductores se va a utilizar para construir estos imanes. Una desventaja de esta nueva tecnología es que es susceptible a un tipo de inestabilidad llamada “salto de flujo”. En esta tesis los efectos de estos saltos en el tamaño del haz se estudian de forma teórica y se dan predicciones concretas para el HL-LHC. Este estudio se extrapola también al Futuro Colisionador Circular de hadrones-hadrones (FCC-hh por sus siglas en ingles), un colisionador circular propuesto de 100 km en el cual se espera utilizar superconductores de este tipo alrededor de toda su circunferencia. Finalmente, la tesis presenta un resumen de diferentes desarrollos de software realizados durante los estudios antes mencionados, incluyendo una interfaz de usuario para facilitar el uso de la herramienta automática de corrección, un nuevo programa de análisis harmónico que remplaza código heredado y diversas mejoras y rescrituras de software que han desarrolladoPostprint (published version

MD3287: Luminosity scans with waist shifts

This note reports on the first measurements of the beam waist displacements in the LHC using luminosity scans. The experiment consisted on applying an optics knob designed to displace the betatron waist and to measure the response of the luminosity, in order to find its maximum. One knob per beam was designed beforehand to displace the vertical betatron waist of Interaction Point 1 (IP1). Two scans were performed for each knob. During the MD it was noticed that the knobs were largely affecting the tunes and therefore the second scan of each knob was performed correcting the tune between steps. After processing, the beam waist position was determined with better precision than that of K-modulation

LHC MD 1988: Automatic coupling correction test

This paper reports on the tests of new software development for automatic coupling correction and automatic model generation for data acquisition extending functionality of the Multiturn application

LHC MD 4505: Forced 3D beam oscillations

This note summarises the detailed programme of an MD testing the new chromaticity and fast optics measurement methods. It demonstrates experimentally forced 3D beam excitation by AC dipoles and RF phase modulation. Optics measurements based on such an excitation are foreseen for LHC Run 3 commissioning. Further work on method development, excitation automation, and beam dynamics simulations is planned

Beam dynamics requirements for HL–LHC electrical circuits

A certain number of LHC magnets and relative electrical circuits will be replaced for the HL-LHC upgrade. The performance of the new circuits will need to be compatible with the current installation, and to provide the necessary improvements to meet the tight requirements of the new operational scenario. This document summarises the present knowledge of the performance and use of the LHC circuits and, based on this and on the new optics requirements, provides the necessary specifications for the new HL-LHC electrical circuits

Update of beam dynamics requirements for HL-LHC electrical circuits

Since the publication of the document providing the specifications of the new circuits of the HL-LHC (see CERN-ACC-2017-0101), using criteria based on beam dynamics considerations, more accurate performance expectations of the power converter technology have been made available. Moreover, cost optimisation and technological considerations on the initially-proposed choices made it necessary a review of the previous document together with some clarifications of some details of the previous analysis. The impact on beam parameters of the newly-proposed solutions and new power converter specifications is carried out in this document, and a summary of the new choices is presented

First beam test of a combined ramp and squeeze at LHC

With increasing maturity of LHC operation it is possible to envisage more complex beam manipulations. At the same time operational efficiency receives increasing attention. So far ramping the beams to their target energy and squeezing the beams to smaller or higher beta are decoupled at the LHC. (De-)squeezing is always performed at the target energy, currently 6.5 TeV. Studies to combine the ramp and squeeze processes have been made for the LHC since 2011, but so far no experimental test with beam had ever performed. This note describes the first machine experiment with beam aiming at validating the combination of ramp and squeeze, the so-called combined ramp and squeeze (CRS)

TFS-Pandas

Python 3 package to handle TFS files

MD Test of a Ballistic Optics

The ballistic optics is designed to improve the understanding of optical errors and BPM systematic effects in the critical triplet region. The particularity of that optics is that the triplet is switched off, effectively transforming the triplets on both sides of IR1 and IR5 into drift spaces. Advantage can be taken from that fact to localize better errors in the Q4-Q5-triplet region. During this MD this new optics was tested for the first time at injection with beam 2