Since the REB system was opened after May 2001 and serviced after a major failure of the high voltage switch, the need for measurement and calibration of the beam energy was required.  A magnetic evergy analyzer was used for this purpose, with targets measuring both the phosphorescence as well as deposited current using appropriate targets.

For a relativistic electron beam traversing thru a perpendicular magnetic field, the relation between the Larnour radius and the energy can be emperically described as



The calculations of the energy analyzer

Photograph of the evergy analyzer mounted with current collectors

For optical measurements, the  image on the phosphor film placed in line with the slt is recorded at a frame speed of about 27 fps over a period of 5 sec using a digital camera operating in the video capture mode. The camera shutter is manually triggered just before the REB is fired. The video is then analyzed to detemine the distance of the phosphorescence band and then energy is calculated. The curved nature of the image is due to non uniformity of the magnetic field in the analyzer region. For calculations, only the average field along the centre of the analyzer is taken into account. Results of both the methods showed similar results. Experiments are being done now to calibrate the energy meter with some REB parameter that can be monitored in-situ during the FEL experiment in order to account for pulse-to-pulse variations in beam energy.

Results of the optical and current measurement  experiments with the energy analyzer

Prior to the malfunctioning and subsequent shut down of the system for repairs, initial beam propagation studies through the 50-period wiggler were carried out. Initial results were encouraging and it was seen that more than 90% of the injected current was transported across  the 50 cm length of the wiggler. The experimental setup for the beam transport measurements are shown here.

It was also observed that the percentage of transported current decreases with increase in the wiggler field above 1 kG. The reason for this behavior  will be investigated in detail once the wiggler experiments resume.

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