ID6 Undulator

Imaging the central cone

Introduction

In these pages you will find some movie sequences presenting the undulator radiation footprint at a 30.5 m distance from the source after monochromatization. The aim of this presentation is a tutorial that could be useful to beamline users to better understand the angular pattern of undulator radiation starting from a real example. In fact the information contained in these sequences of images is enormous. Proper treatment could allow an estimation of the electron beam emittances and energy spread, undulator field errors and perturbation induced by the filters in the front-end part of the beamline.

Beamline

The white undulator radiation propagates through a number of beryllium, graphite and aluminium filters. The images are recorded at a distance of 30.5 m from the middle of the undulator. The radiation is diffracted by a single silicon crystal (3 1 1) in the horizontal plane. The monochromatic beam at 29.5 keV is then converted to visible light by a 1 mm thick CsI(Ti) scintillator and image.

Images

Each movie sequence is made of 100 images recorded every 0.01 mm of gap. Therefore the whole sequence corresponds to a gap range of 1 mm. The movie for each harmonics recorded around the gap corresponding to the selected harmonic emitted on axis of the electron beam for a photon energy of 29.5 keV. The dimensions of the image correspond to 3.24  (1.73) mm in the horizontal (vertical) plane

Harmonic #5  (566 kb)

Harmonic #6  (527 kb)

Harmonic #7  (468 kb)

Harmonic #8  (507 kb)

Harmonic #9  (566 kb)

Comments on the Content of the Images

The images on all harmonics show a central cone size around  1 x 0.5 mm fwhm. The horizontal size of the central cone is dominated by the horizontal emittance of the electron beam. In the vertical plane the contributions of the emittance, energy spread and single electron emission are similar. Starting from the gap corresponding to the highest intensity, one notices that the radiation decay for lower or larger gaps in a very different way. For lower gap values the radiation keeps a single spot and decays rather rapidly (vs gap). For higher gap values, the radiation splits into two spots whose separation increases and intensity decreases with the gap.

How these pages were made

The Images are digitized by a SCION LG-3 Frame-grabber in a Mac IIvx at a rate of 5 images/seconds and processed with NIH Image (image processing) and GifBuilder (Gif Animation).