Beam-Based Error Identification and Correction Methods for Particle Accelerators
Doktorsavhandling, 2014

Modern particle accelerators have tight tolerances on the acceptable deviation from their desired machine parameters. The control of the parameters is of crucial importance for safe machine operation and performance. This thesis focuses on beam-based methods and algorithms to identify and correct errors in particle accelerators. The optics measurements and corrections of the Large Hadron Collider (LHC), which resulted in an unprecedented low β-beat for a hadron collider is described. The transverse coupling is another parameter which is of importance to control. Improvement in the reconstruction of the coupling from turn-by-turn data has resulted in a significant decrease of the measurement uncertainty. An automatic coupling correction method, which is based on the injected beam oscillations, has been successfully used in normal operation of the LHC. Furthermore, a new method to measure and correct chromatic coupling that was applied to the LHC, is described. It resulted in a decrease of the chromatic coupling by a factor ∼2 for both beams. The good control of the optics is a significant part of the success of the LHC and hence contributed to the discovery of the Higgs particle. Following the discovery of the Higgs particle there is a demand for precise measurements of its properties in a lepton collider. Compact Linear Collider (CLIC), an electron-positron collider aiming at collision energies up to 3 TeV, is one of the leading candidates. The acceleration in CLIC relies on a two-beam acceleration scheme where one of the beams, referred to as the Drive Beam, is decelerated while transferring its energy to the Main Beam. This scheme puts tight constraints on the parameters of the Drive Beam in terms of beam current, phase and bunch length. In CLIC Test Facility 3 (CTF3) the mechanisms behind the observed drifts of these parameters have been studied in detail. The findings have shown that these drifts are mainly linked to variations in the amplitude of the Radio Frequency (RF). A feedback to mitigate the RF-amplitude fluctuations has been implemented and is described in detail. In conjunction with a dedicated energy feedback it reduces the energy variation by a factor ∼3. Together with precise machine tuning this has resulted in a beam current stability very close to the CLIC requirement. The beam phase stability is improved through a feedback operating on the two first klystrons in the CTF3 injector. Two-beam acceleration at the nominal CLIC gradient of 100 MV/m and above has been demonstrated in CTF3. These results, and other recent achievements in CTF3, are presented in this thesis.


Accelerator Optics


Pulse Compressor


Two-beam acceleration



Radio Frequency


PJ-salen Fysikhuset, Chalmers University of Technology
Opponent: Prof. Philip Burrows, University of Oxford


Tobias Persson

Chalmers, Fundamental fysik

Improved control of the betatron coupling in the Large Hadron Collider

Physical Review Special Topics - Accelerators and Beams,; Vol. 17(2014)

Artikel i vetenskaplig tidskrift

Commissioning and Operation at beta = 1000 m in the LHC

IPAC'13,; (2013)p. 1983-1984

Övrigt konferensbidrag

Record low β beating in the LHC

Physical Review Special Topics - Accelerators and Beams,; Vol. 15(2012)

Artikel i vetenskaplig tidskrift

Beam Stability at CTF3

IPAC 2012 - International Particle Accelerator Conference 2012,; (2012)p. 1888-1890

Paper i proceeding

Drive beam stability studies and stabilization algorithms in CLIC Test Facility 3

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,; Vol. 735(2014)p. 152-156

Artikel i vetenskaplig tidskrift

Two Beam Test Stand Experiments in the CTF3 Facility

IPAC'11,; (2011)

Övrigt konferensbidrag

Chromatic coupling correction in the Large Hadron Collider

Physical Review Special Topics - Accelerators and Beams,; Vol. 16(2013)

Artikel i vetenskaplig tidskrift

Experimental Verification of the CLIC Two-Beam Acceleration Technology in CTF3

IPAC 2013: Proceedings of the 4th International Particle Accelerator Conference,; (2013)p. 1436-1438

Paper i proceeding


Acceleratorfysik och instrumentering



Grundläggande vetenskaper



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

PJ-salen Fysikhuset, Chalmers University of Technology

Opponent: Prof. Philip Burrows, University of Oxford

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