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Opportunities
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For application at future linear colliders, laser based diagnostics tools are foreseen for the measurement of the transverse charge distribution of the electron beam. Beam sizes in the order of a few ten micrometer and bunch charges in the nC range are expected for the beam delivery system. To measure this small beam sizes it is planned to scan a finely focused laser beam under 90 degree angle through the electron beam and collect the Compton back- scattered photons as a function of the relative laser beam position. The Research and Development effort is carried out by the Laser Based Electron Beam Diagnostics Collaboration, in which the RHUL group is responsible for the laser system.
The laser final focus system is of major importance for the successful
operation of the laserwire beam size monitor. In order to use the laserbeam
as a non-invasive scanning techniques, the transverse beam size of the
laserbeam at the interaction point must be in the order of a few micrometer.
To achieve this, an aberration-corrected optics design must be developed
to focus the intense laser beam inside the electron beam chamber.
In this project a student can achieve skills in laser optics for intense laser
beams as well as accelerator physics. The study includes the design
of an optical system and realization on a testbench in lab at RHUL.
The outcome of the work will find an application at the laserwire experiments
at the PETRA/TTF2 accelerators at DESY or at the ATF at KEK.
In order to maintain the electron-laser-interaction it is
necessary to control the position and the size of the laser
beam and the position of the electron beam during the measurement.
While for the electron beam standard beam position monitors
are foreseen, the laser beam imaging section has to be developed.
The task of the imaging section is to take over the laser beam
from the final focus section and process the beam by magnification
and imaging techniques for display in the control system of
the laser. In this project a student can achieve skills in
laser optics and imaging techniques as well as control systems.
The study includes the design and test of an imaging system as
well as the implementation at an experiment at an accelerator
test facility.
To provide a non-invasive measurement of the electron beam size using a laserwire it is necessary to scan the laser beam through the electron beam. For this it is possible to use piezo scanning mirrors or acousto-optic deflectors or other novel techniques. The aim of this study is to find out which techniques is the most appropriate for the laserwire monitor regarding resolution, stability, and repeatability. In this project a student can achieve skills in acousto-optic devices, piezo scanners, and accelerator physics. The study includes theoretical studies of the various techniques and the setup of one technique on a testbench in lab at RHUL. As with the other projects, the outcome of this study will find an application at one of the laserwire experiments.
The operation of a laserwire monitor requires a stable and perfectly aligned laser beam starting from the laser until the interaction region. This study aims at possible sources for perturbation of the alignment such as ground motion, temperature drifts, or air flow and their impact on the performance of the complete system. Furthermore it is necessary to develop techniques canceling these effects to achieve maximum performance of the monitor system. With this study a student can obtain skills on environmental impacts of physics experiments and possible cures. The work includes theoretical studies of ground motion and air flow models and their application on the laserwire monitor. Furthermore it should be envisaged to perform measurements of these effects in lab.
Once possible impacts on the performance of the laserwire monitor are identified feedback system can be implemented to reduce these effects. Such a system may be an automatic alignment of the optical transport system with piezo mirrors and movable delay lines. Suggestions for laser beam diagnostics elements and a way to incorporate the re-imaged laser spot are expected as the outcome of this study. With this project a student can achieve skills in feedback and control systems.
Compton photons are generated in the interaction between the higher power laser beam and the electron bunches. These photons will be detected in a dedicated calorimeter made of lead tungstate crystals. It is planned to setup one detector channel including scintillator, photo multiplier, readout electronics, and ADC at RHUL for studies of time and energy performance. The photons for this purpose will be supplied by a radioactive source. The work includes the upgrade of an existing setup, data taking and analysis. With this project a student can achieve skills in particle physics detectors and analysis.
Back to RHUL particle physics group h omepage.
Content: Grahame Blair
15 Nov 2000