Alessandro Variola

RESOLUTION POWER OF OPTICAL TRANSITION RADIATION : THEORETICAL CONSIDERATIONS

Abstract The spatial resolution power of Optical Transition Radiation (OTR), applied to beam profile measurements at high Lorentz factor γ, is studied taking into account diffraction and self-diffraction effects. Microscopic and macroscopic points of view about the different geometrical natures of the forward and backward OTR sources are presented. Properties of the impact parameter profile I(b) of the OTR emitted by one electron are described. Curves for the modulation transfer function and for the OTR profile of a laminar beam are given. Two methods of improving the resolution are investigated : (a) putting a mask to eliminate small-angle photons, (b) using a polarizer.

On the nonparaxial modes of two-dimensional nearly concentric resonators.

A nonparaxial scalar diffraction integral is used to determine numerically the resonance modes of a two-dimensional nearly concentric Fabry-Perot resonator. Numerical examples are provided, and results are compared to those published by Laabs and Friberg [IEEE J. Quantum Electron. 35, 198 (1999)]. Discrepancies are reported and further discussed on the basis of the difference between the solution space supported by the numerical method used here and the one used by Laabs and Friberg.

Development of an intense positron source using a crystal-amorphous hybrid target for linear colliders

In a conventional positron source driven by a few GeV electron beam, a high amount of heat is loaded into a positron converter target to generate intense positrons required by linear colliders, and which would eventually damage the converter target. A hybrid target, composed of a single crystal target as a radiator of intense gamma–rays, and an amorphous converter target placed downstream of the crystal, was proposed as a scheme which could overcome the problem. This paper describes the development of an intense positron source with the hybrid target. A series of experiments on positron generation with the hybrid target has been carried out with a 8–GeV electron beam at the KEKB linac. We observed that positron yield from the hybrid target increased when the incident electron beam was aligned to the crystal axis and exceeded the one from the conventional target with the converter target of the same thickness, when its thickness is less than about 2 radiation length. The measurements in the temperature rise of the amorphous converter target was successfully carried out by use of thermocouples. These results lead to establishment to the evaluation of the hybrid target as an intense positron source.

The CLIC electron and positron polarized sources

The CLIC polarized electron source is based on a DC gun where the photocathode is illuminated by a laser beam. Each micro-bunch has a charge of 6x10 9 e

OPTICAL FIBER BEAM LOSS MONITOR FOR THE PHIL AND THOMX FACILITIES

Fiber monitors are an attractive beam loss diagnostics tool. They are based on the detection of the electromagnetic shower produced by the beam losses. Cherenkov radiation is produced by the electromagnetic shower charged particles within the multimode fibers attached to the vacuum chamber. This radiation is consequently converted to an electrical signal containing the information about the position and intensity of the beam losses. Therefore, a system based on fibers installed alongside the whole accelerator together with a signal detection system forms a continuous, real-time Fiber Beam Loss Monitor (FBLM). In this context, the FBLM is a very useful tool for the commissioning and beam alignment. In this article we report on the development of the real-time display system for the FBLM at PHIL (PHotoInjector at LAL, Orsay, France) as a prototype of the beam loss monitor for the ThomX project, the compact Compton based X-ray source under construction in Orsay

Carrier envelope phase drift of picosecond frequency combs from an ultrahigh finesse fabry-perot cavity

The carrier envelope phase shift of a stacked picosecond pulse train for Compton scattering experiments have been measured to an accuracy of 80 mrad by spectrally resolved interference pattern of a stabilized multiple beam interferometer.