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C-Band LINAC for a race track microtron

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252 pages
UNIVERSIDAD COMPLUTENSE DE MADRID FACULTAD DE CIENCIAS FÍSICAS Departamento de Física Atómica, Molecular y Nuclear C-BAND LINAC FOR A RACE TRACK MICROTRON. MEMORIA PARA OPTAR AL GRADO DE DOCTOR PRESENTADA POR David Carrillo Barrera Bajo la dirección del doctor Vasily Ivanovicht Shvedunov Madrid, 2010 ISBN: 978-84-693-8239-4 © David Carrillo Barrera, 2010 CIEMAT Unidad de Aceleradores UNIVERSIDAD COMPLUTENSE DE MADRID Departamento de Física Atómica, Molecular y Nuclear TESIS DOCTORAL LINAC EN BANDA C PARA UN MICROTRON DE PISTA C-BAND LINAC FOR A RACE TRACK MICROTRON MICROTRON Memoria realizada por David Carrillo Barrera para optar al grado de Doctor Director de Tesis: Dr. Vasiliy Ivanovich Shvedunov Madrid - 2010 CONTENTS CONTENTS 1 Introduction .....
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UNIVERSIDAD COMPLUTENSE DE MADRID

FACULTAD DE CIENCIAS FÍSICAS
Departamento de Física Atómica, Molecular y Nuclear





C-BAND LINAC FOR A RACE TRACK
MICROTRON.


MEMORIA PARA OPTAR AL GRADO DE DOCTOR
PRESENTADA POR

David Carrillo Barrera


Bajo la dirección del doctor

Vasily Ivanovicht Shvedunov


Madrid, 2010



ISBN: 978-84-693-8239-4 © David Carrillo Barrera, 2010



CIEMAT
Unidad de Aceleradores

UNIVERSIDAD COMPLUTENSE DE MADRID
Departamento de Física Atómica, Molecular y Nuclear



TESIS DOCTORAL
LINAC EN BANDA C PARA UN MICROTRON
DE PISTA
C-BAND LINAC FOR A RACE TRACK
MICROTRON MICROTRON

Memoria realizada por
David Carrillo Barrera
para optar al grado de Doctor

Director de Tesis: Dr. Vasiliy Ivanovich Shvedunov

Madrid - 2010 CONTENTS CONTENTS

1 Introduction .............................................................................................................................. - 1 -
1.1 State of the art ........................ - 2 -
1.2 Objectives and thesis structure ............................................................................................... - 5 -
1.3 Introduction to Particle Accelerators ...................... - 7 -
1.3.1 The purpose of particle accelerators ........................................................................... - 7 -
1.3.2 History of accelerators ............................................................... - 10 -
1.3.3 Typical components in a particle accelerator ............................................................ - 20 -
1.3.3.1 Particle sources ........................................................................ - 20 -
1.3.3.2 RF cavities ................................................ - 20 -
1.3.3.3 Beam guiding and focusing devices ......... - 21 -
1.3.3.4 Injection and extraction devices .............................................. - 22 -
1.3.3.5 Diagnostics ............................................................................... - 23 -
1.4 Circular and race-track microtrons ....................................................... - 24 -
1.4.1 Circular Microtron ...................................................................................................... - 24 -
1.4.2 Race-Track Microtron (RTM)...................................................... - 26 -
1.4.2.1 Brief history of RTM ................................. - 26 -
1.4.2.2 Principles of operation ............................................................................................. - 26 -
1.4.2.3 Summary of RTM characteristics ............................................................................. - 29 -
1.4.3 RTM applications ...................................................................... - 30 -
1.4.3.1 Low energy nuclear physics ..................................................................................... - 31 -
1.4.3.2 Injectors ................................................... - 31 -
1.4.3.3 Radiotherapy ........................................................................... - 32 -
1.4.3.4 Elemental analysis ................................... - 32 -
1.4.3.5 Medical Isotopes Production ................................................................................... - 33 -
1.4.3.6 Cargo inspection ...... - 34 -
1.5 RTM parameters dependence on operating wavelength ...................................................... - 36 -
1.6 12 MeV RTM specification .................................................................................................... - 39 -
2 Accelerating Structures: Theoretical Background .... - 43 -
2.1 Basic microwave concepts .................................................................................................... - 43 -
2.1.1 Introduction ............................................................................... - 43 -
2.1.2 Waveguides and transmission lines ........... - 45 -
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2.1.3 RF Cavities in accelerators ......................................................................................... - 47 -
2.2 Travelling and standing wave accelerating structures for electron linacs ............................ - 50 -
2.2.1 Travelling wave structures ......................................................................................... - 50 -
2.2.2 Standing wave structures .......................... - 52 -
2.3 Types of normal and superconducting standing wave accelerating structures .................... - 53 -
2.3.1 Normal Conducting Cavities ....................................................................................... - 53 -
2.3.2 Superconducting cavities ........................... - 53 -
2.4 Main parameters of the standing wave accelerating structure ............................................ - 55 -
2.4.1 Quality factor and external coupling with RF cavities ............... - 55 -
2.4.2 Electric field, energy gain, transit time factor, shunt impedance and synchronous
particle - 58 -
2.4.3 Coupling between cavities ......................................................................................... - 60 -
2.4.4 Pulsed and continuous mode: Duty factor ................................ - 60 -
2.5 Dependence of the standing wave accelerating structure parameters on wavelength........ - 61 -
2.6 Standing wave accelerating structure description in lumped circuit theory ......................... - 65 -
2.7 Modes of accelerating structure. Dispersion characteristic .................................................. - 68 -
2.8 Numerical methods and codes for accelerating structure optimization ............................... - 72 -
2.8.1 RTM Trace .................................................................................................................. - 72 -
2.8.2 Superfish .................... - 72 -
2.8.3 Ansys .......................................................................................................................... - 73 -
2.8.4 Ansoft HFSS ................................................ - 73 -
2.8.5 CST Studio ................. - 74 -
2.9 Main steps of standing wave accelerating structure optimization ....................................... - 75 -
3 C-band RTM linac optimization ................................................................ - 77 -
3.1 Peculiarities of RTM linac ...................................... - 77 -
3.2 RTM linac parameters specification ...................................................................................... - 79 -
3.3 Electrodynamics characteristics optimization ....................................................................... - 81 -
3.3.1 2D linac optimization with RF and beam dynamics codes ......................................... - 82 -
2.5.2.1 Regular =1 cell optimization ................................................................................. - 82 -
3.3.1.1 End =1 cell calculations .......................... - 86 -
3.3.1.2 First <1 cell calculation and linac optimization ...................... - 87 -
3.3.1.3 Summary of 2D linac optimization ........................................................................... - 91 -
3.3.2 3D linac cells calculation, coupling factor and field distribution optimization .......... - 92 -
3.3.2.1 Initial considerations ................................................................................................ - 92 -
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3.3.2.2 Order of 3D calculations: Methodology ................................................................... - 94 -
3.3.2.3 Step (a). Calculation of regular cell (2a=2b=3a=3b=4a) without coupling slots. ..... - 95 -
3.3.2.4 Step (b). Calculation of short end cell (1a+1b) without coupling slots. ................... - 97 -
3.3.2.5 Step (c). Tuning 2b+3a assembly with coupling slots .............................................. - 98 -
3.3.2.6 Steps (d), (e). Tuning 2a+1b+1a assembly with coupling slots. ............................ - 102 -
3.3.2.7 Step (f). Tuning 4b+4a+3b assembly with coupling slots ....... - 105 -
3.3.2.8 Step (g). Calculation of the full assembly: 1a+1b+2a+2b+3a+3b +4a+4b .............. - 107 -
3.3.2.9 Step (h) Optimization of accelerating structure coupling with waveguide ........... - 111 -
3.3.2.10 Summary of 3D linac optimization ......................................................................... - 118 -
3.3.3 Calculations of the tolerances for basic cell dimensions ......... - 119 -
3.3.4 Analysis of multipole fields caused by the coupling slots and waveguide ............... - 125 -
3.3.4.1 Effect of coupling slots ........................................................................................... - 126 -
3.3.4.2 Effect of coupling iris ............................. - 130 -
3.3.4.3 Effect of asymmetry in segment 1a+1b ................................. - 132 -
3.3.4.4 Effect of asymmetry in segment 4b+4a ................................. - 133 -
3.3.4.5 Summary and conclusions for multipole fields calculations .. - 134 -
3.3.5 Parasitic modes calculations and beam blow-up current estimation for RTM ........ - 136 -
3.4 Study of thermo mechanical behaviour of accelerating structure ...................................... - 146 -
3.4.1 RF power losses distribution along the cavity surface ............. - 146 -
3.4.2 3D calculations of the cell thermo mechanical behaviour ....................................... - 148 -
4 Methods and stand for cold measurements of accelerating structure .................................. - 155 -
4.1 Methods of the accelerating structure electrodynamics characteristics measurements .... - 155 -
4.1.1 Introduction ............................................................................................................. - 155 -
4.1.2 RF instrumentation and measuring probes ............................................................. - 156 -
4.1.3 EM modes measurements ....................................................... - 159 -
4.1.4 Axial field measurements ........................ - 164 -
4.1.5 Possible causes for resonant frequency changes .................................................... - 171 -
4.1.5.1 Accuracy of simulations ......................................................... - 171 -
4.1.5.2 Machining error ..................................................................... - 171 -
4.1.5.3 Instrumentation errors .......................... - 172 -
4.1.5.4 Brazing ................................................................................................................... - 172 -
4.1.5.5 Environmental Conditions ..................... - 173 -
4.2 Stand for accelerating structure cold measurements ......................................................... - 174 -
5 Linac engineering design, manufacturing and measurements ............... - 179 -
5.1 Test cavities ......................................................................................................................... - 179 -
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5.1.1 Test cavity I .............................................................................................................. - 180 -
5.1.1.1 The goals and the parameters of the test cavity I ................................................. - 180 -
5.1.1.2 Mechanical design, machining technology and results ......... - 181 -
5.1.1.3 Technology and results of brazing ......................................................................... - 182 -
5.1.1.4 Results of RF measurements.................. - 185 -
5.1.2 Test cavity II ............................................................................................................. - 192 -
5.1.2.1 The goals and the parameters of the test cavity ................................................... - 192 -
5.1.2.2 Mechanical design, machining technology and results ......... - 194 -
5.1.2.3 Technology and results of brazing ......................................................................... - 195 -
5.1.2.4 Results of RF measurements.................. - 200 -
5.1.3 Aluminium cavity ..................................................................... - 202 -
5.1.3.1 The goals and the parameters of the test cavity ................................................... - 202 -
5.1.3.2 Mechanical design, machining technology and results ......... - 203 -
5.1.3.3 Results of RF measurements.................................................. - 206 -
5.2 Linac .................................................................................................................................... - 213 -
5.2.1 Mechanical design and machining ........................................................................... - 213 -
5.2.2 Mechanical and RF measurements before brazing ................................................. - 215 -
6 Conclusions ........................................................................................................................... - 225 -
7 .................................................................................................................... - 235 -
8 Bibliography .......................................................................................................................... - 235 -


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ACKNOWLEDGMENTS

It is a pleasure to thank those who have contributed to the successful completion of this
project. My foremost thank goes to my thesis advisor Vasiliy I. Shvedunov (SINP Moscow)
without his help, guidance and wisdom it would have been next to impossible to write this
thesis.
I had the pleasure of working with all members of Accelerators Unit at CIEMAT. I am heartily
thankful to my supervisor Fernando Toral for his constant support and helpful suggestions
through my research. Special thanks goes to Iker Rodríguez for his motivation, encouragement
and fruitful discussions helped me very much. I must acknowledge the effort of Enrique
Rodríguez for his brilliant technical drawings and his helpful contributions during RTM
mechanical design. I appreciate all the help provided by Álvaro Lara with the thermo-
mechanical calculations. I must also thank Laura Sanchez for her splendid collaboration in the
study of brazing of the RTM linac. Finally, I am thankful for the collaboration of Pablo Oriol,
Eduardo Molina and Luís Miguel Martínez for their help with the programming and electronics
needed in the bead pull test bench.
I would like to express my gratitude to Igor Syratchev (CERN) and A.S.Alimov (SINP Moscow),
for whom I have learned a lot about the design and testing of RF cavities.
I also thank Yuri Koubychine (UPC) and Luís García-Tabarés (CIEMAT) for their support and for
keeping the project alive finding financial support. Also, I am aware of this research would not
have been possible without the financial assistance of CIEMAT.



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ACRONYMS AND ABBREVIATIONS

AGS (Alternating Gradient Synchrotron)
BBU (Beam Blow-Up)
BW (Bandwidth)
CERN (European Organization for Nuclear Research)
CIEMAT (Centro de Investigaciones Energéticas Medioambientales y Tecnológicas)
CNC (Computer Numerical Control)
CW (Continuous Wave)
DUT (Device under test)
EBW (Electron-Beam Welding)
FEL (Free- Electron Laser )
Frequency bands:
 S - Band (2 - 4 GHz)
 C - Band (4 - 8 GHz)
 X - Band (8 - 12 GHz)

GSI (Helmholtz Centre for Heavy Ion Research)
HOM (Higher Order Modes)
IORT (Intra Operative Radiation Therapy)
LEP (Large Electron-Positron collider)
LHC (Large Hadron Collider)
LINAC (Linear Accelerator)
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