We require three viewers in the IR Demo wiggler. The viewers
will be viewed by a CCD or CID camera mounted on the floor.
The viewers have the following technical specifications:
Range of motion of the flag 1 inch
Size of flag as seen by the electron beam 8 mm diameter for end OTRs
2 times 6x6 mm for center OTR
Size of hole in center 0.5 mm diameter.
Position reproducibility 50 µm rms in both x and y
Flag material Poco graphite or beryllium
Resolution of imaging system 30 µm
Speed of imaging optics f/15
Minimum viewable current 10 nA
Each viewer must have a hole in the center so that the alignment laser can go through the viewer.
The flags must withdraw so that the edge of the flag is no less than 2 cm from the beam center. Since the vacuum chamber is only 1 cm in height, their is no need for RF sheilding if the flag withdraws this far.
The viewers must be carefully mounted to the supporting girder such that their position is rigidly determined independently of the wiggler.
The center viewer must be able to see the alignment laser coming from either end of the optical cavity. The other two only need to see the electron beam which comes from upstream of the wiggler.
The viewer flag must have calibrated fiducials so that distances can be calculated from the camera image
The camera must have a filter which can be flipped in front of the camera when the laser is imaged.
The viewer flag position must be adjustable so that the holes in the flags can be aligned along the magnetic center of the wiggler to 50 µm precision in both x and y directions.
The image of the flag must fill the sensitive area of the camera. Thus, if the camera has an 8x12 mm imaging area, the magnification of the imaging optics should be unity. Note that this spreads the available photons over more pixels and may decrease the signal to noise ratio. The current imaged per pixel might be only a few picoamps.
The camera must see the viewer via a mirror and not look directly at the flag. This greatly reduces the radiation damage to the camera.
The camera will probably be approximately 1.2 meters from the viewer. In order to keep both the magnification and the f number large, a relay imaging system will probably be needed. One 15 cm focal length lens 30 cm from the viewer flag images the flag to a point 60 cm from the flag. This may be imaged one to one onto the camera with reasonably sized lenses.
Since these are OTR viewers, the flag surfaces must be oriented at a 45° angle with respect to the electron beam to ±0.5°.
IR Demo Tech Specifications, rev.1(pdf)