Laserwire

Introduction

The aim of the Laser Based Beam Diagnostics (LBBD) Collaboration was to study the feasibility of laser based diagnostics tools for a future linear electron-positron collider and proton accelerators. The objectives of the laserwire project are to develop laser based techniques for determining the dimensions of electron (or positron) bunches and optimising their application using simulations. The laserwire projects at Royal Holloway are:

• ATF extraction line laser wire
• ATF2 laser wire project
• PETRA3 LaserWire

The performance of a linear collider depends strongly on the control of the transverse particle beam size along the complete machine. For example, to verify particle beam optics and to measure the transverse beam emittance. Some of the expected beam sizes are in the range between 500 nm and 10 µm, where conventional wire scanners are at the limit of their resolution, are destroyed by high energy beam and are invasive themselves. To provide a non-invasive measurement we suggest to use a laser beam to probe the electron beam. The central idea is to use Compton-scattering between electrons in the bunch and photons in the laser beam, which produces high energy scattered photons. Scanning across the particle beam with the laser modulates the intensity of Compton-scattered photons and this scan can be used to measure the particle beam size.

Installed laser wire projects

After a first round of ATF extraction line laserwire operation, we upgraded the laser wire to operate within the ATF2, ATF2 laser wire project. Similarly after a test installation at PETRA2, we have commissioned a turn key laser wire system for PETRA3 where fast laser scanners were also developed. The PETRA3 laserwire is capable of high repetition rate measurements (hundreds of kiloHertz) and the ATF2 laserwire was able achieve sub-micrometre resolution.

Papers, conference proceedings, theses

• Lawrence Deacon : A Micron-Scale Laser-Based Beam Profile Monitor for the International Linear Collider, April 2009.
• Michael Price : Laser-Wire Studies for PETRA and the International Linear Collider, November 2007.
• Stephen Malton : Laser Interactions with High Brightness Electron Beams, February 2007
• John Carter : Particle Physics and Beam-Line Studies for the Electron-Positron International Linear Collider, October 2006
• Freddy Poirier : Beam Diagnostic Laser-wire and Fast Luminosity Spectrum Measurement at the International Linear Collider, July 2005

Publications

• Laserwire at the Accelerator Test Facility 2 with submicrometer resolution Phys. Rev. Special Topcis - Accel. Beams, 17, 072802 (2014)
• Micron-scale laser-wire scanner for the KEK Accelerator Test Facility extraction line Phys. Rev. Special Topics - Accel. Beams, 13, 122801 (2010)
• Beam emittance measurement with laser wire scanners in the International Linear Collider beam delivery system Phys. Rev. Special Topics - Accel. Beams, 10, 112801 (2007), Issue 11
• A two-dimensional laser-wire scanner for electron accelerators, A. Bosco et al, Nucl. Instrum. Meth. A 592, 2008, issue 3, 162-170
• A large aperture electro-optic deflector, Appl. Phys. Lett. 94, 211104 (2009)

Public resources

• Accelerator tracking code in python
• Optical simulation codes

References

• Parameters of Compton x-ray beams: Total yield and pulse duration. Phys. Rev. Special Topics - Accelerators and Beams 8, 030703 (2005) Article
• Measurement of an electron beam size with a laser wire beam profile monitor. Phys. Rev. Special Topics - Accelerators and Beams 4, 022801 (2001) Article