Beam position monitoring at CLIC [Elektronische Ressource] / vorgelegt von Jan Erik Prochnow

Sujets

• Physik

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2003
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 5 Mo

Extrait

Beam Position Monitoring at CLIC
von
Jan Erik ProchnowBeam Position Monitoring at CLIC
Von der Fakultät für Mathematik, Informatik und Naturwissenschaften
der Rheinisch-Westfälischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigte Dissertation
vorgelegt von
Diplom-Physiker Jan Erik Prochnow
aus Düren
Berichter: Universitätsprofessor Dr. A. Böhm
Univ Dr. J. Mnich
Tag der mündlichen Prüfung: 27. November 2003
Diese Dissertation ist auf den Internetseiten der
Hochschulbibliothek online verfügbar.Summary
At the European Organisation for Nuclear Research CERN in Geneva, Switzerland the design of
the Compact LInear Collider (CLIC) for high energy physics is studied. To achieve the envisaged
high luminosity the quadrupole magnets and radio-frequency accelerating structures have to be
actively aligned with micron precision and submicron resolution. This will be done using beam-
based algorithms which rely on beam position information inside of quadrupoles and accelerating
structures.
After a general introduction to the CLIC study and the alignment algorithms, the concept of the
interaction between beams and radio-frequency structures is given.
In the next chapter beam measurements and simulations are described which were done to study
the performance of cavity beam position monitors (BPMs). A BPM design is presented which is
compatible with the multi-bunch operation at CLIC and could be used to align the quadrupoles.
The beam position inside the accelerating structures will be measured by using the structures
themselves as BPMs. This concept was demonstrated on an undamped and a heavily damped
and detuned accelerating structure. The performance of accelerating structures as beam position
monitor was evaluated based on simulations and measurements.
Finally a technique to compute the transverse wake of a periodic accelerating structure based on
calculation of the fields in one cell is presented.Contents
1 General Introduction i
2 The Compact Linear Collider CLIC 1
2.1 Physics with a multi TeV e e Collider . . . . . . . . . . . . . . . . . . . . . . . 1
2.2 The CLIC Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.3 The CLIC Test Facility CTF II . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Controlling Linear Collider Beams 10
3.1 Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1 Alignment Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4 The Interaction between Radio Frequency Fields and Beams 13
4.1 Modes in a Resonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 in an Accelerating Structure . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Damping and Detuning of Disk loaded Waveguides . . . . . . . . . . . . . . . . . 17
4.3.1 Examples of damped and detuned Accelerating Structures . . . . . . . . . 18
4.3.2 Impact of Damping on the dispersive Properties . . . . . . . . . . . . . . . 19
4.4 Beam-Cavity Interaction and Particle Acceleration . . . . . . . . . . . . . . . . . 20
4.4.1 Wake Potential and Impedance of a Radio Frequency Structure . . . . . . . 20
4.4.2 Panofsky-Wenzel Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.4.3 Bunch Train Pattern of the CLIC Main Beam . . . . . . . . . . . . . . . . 25
4.4.4 Beam Loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.5 Concept of a Resonant Cavity Beam Position Monitor . . . . . . . . . . . . . . . . 27
4.6 The Finite Element Program HFSS . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.6.1 Benchmarking the Simulation Code . . . . . . . . . . . . . . . . . . . . . 30
4.7 Taking Advantage of the Periodicity . . . . . . . . . . . . . . . . . . . . . . . . . 30
5 Resonant Cavity Beam Position Monitors for CLIC 32
5.1 Shock Excitation of a resonant Cavity BPM by a Beam . . . . . . . . . . . . . . . 32
5.2 Simulation of Beam excited Signals . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.1 Current Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.2.2 Impedance Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
5.3 The Excitation of a Cavity by a Tilted Beam Trajectory . . . . . . . . . . . . . . . 35
5.4 The excitation of a Cavity by a Tilted Beam . . . . . . . . . . . . . . . . . . . . . 36
5.5 Beam Experiment with 30 GHz Resonant Cavity BPMs . . . . . . . . . . . . . . . 37
5.5.1 Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.5.2 Beam Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
ii Contents
5.5.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.6 Common Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.7 The CLIC Single Bunch Beam Position Monitor . . . . . . . . . . . . . . . . . . . 55
5.8 The CLIC Beam Position Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
6 Beam Position and Angle Measurement with an Undamped Accelerating Structure 60
6.1 Extracting Beam Position and Angle from the Pulse . . . . . . . . . . . . . . . . . 61
6.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.2.1 Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.3 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.4 Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
7 Beam Position Measurement with Heavily Damped and Detuned Structures 69
7.1 The Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
7.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2.1 The Accelerating Structure . . . . . . . . . . . . . . . . . . . . . . . . . . 70
7.2.2 The double ridged Waveguide to Coaxial Cable Transition . . . . . . . . . 74
7.2.3 Electronics with an RF Mixer . . . . . . . . . . . . . . . . . . . . . . . . 79
7.2.4 with a Diode . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.2.5 Measurements with the Spectrum Analyser . . . . . . . . . . . . . . . . . 83
7.2.6 Installation in the CTF II . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.3 The expected Signal Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
7.3.1 HFSS Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
7.3.2 GdfidL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.3.3 Comparison between HFSS and GdfidL . . . . . . . . . . . . . . . . . . . 87
7.4 Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.4.1 The Signal from the Damping Waveguide . . . . . . . . . . . . . . . . . . 90
7.4.2 The from the Coupler Cells . . . . . . . . . . . . . . . . . . . . . . 91
7.4.3 Correction for Beam Position Jitter . . . . . . . . . . . . . . . . . . . . . 91
7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
8 Conclusions 100
A An Intuitive Method to Calculate Long Range Wakefields 102
A.1 The Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
A.2 The Geometry tested at ASSET . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
A.2.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
B The Scattering Matrix 114
C Mixer and Diode Rectifier 115
Bibliography 117i
Chapter 1
General Introduction
The content of this thesis is based on the work that I carried out as a doctoral student between June
2000 and June 2003 in the CLIC studies team of the radio-frequency group at CERN in Geneva,
Switzerland. I was supervised by Prof. Dr. A. Böhm at my home university, the RWTH Aachen,
and Dr. W. Wuensch at CERN.
At CERN a study on the feasibility of the 3 TeV e e Compact LInear Collider CLIC is
being conducted. The motivation for CLIC is to probe the standard model of particle physics
and provide an exploratory power for the physics beyond it. CLIC will give access to particle
production in the TeV range and allow finding new physics up to an energy scale of about 200 TeV.
To provide reasonable event rates at such high centre-of-mass energies CLIC has to provide the
very high luminosity of 10 cm s . Accelerating the leptons to two times 1.5 TeV requires a
machine with an overall length of about 40 km even with the ambitious accelerating gradient of
150 MeV/m. The CLIC machine is characterised by high gradient normal-conducting accelerating
structures and a two-beam power source. The high luminosity requires a low beam emittance to
be preserved from the particle production to the interaction point and especially during particle
acceleration.
Emittance growth comes from misaligned accelerating structures and quadrupoles which create
wakefields and dispersion respectively. Actively aligning these elements with respect to the beam
to the required accuracy relies on beam based alignment algorithms which strongly