X-Ray Pinhole Cameras (Emittance-Monitors)

General description :

Two independent X-ray pinhole systems are operated at the dipoles of respectively Cell 9 (down-stream with 0.4T soft-end field) and Cell 25 (up-stream with nominal 0.85T field).

They consist of :

- a 3mm thick cooled Aluminium window to separate the ultra-high vacuum of the Storage Ring from the other components in this system that are in atmosphere.

- an air ventilation system to disperse the particle creation of the intense X-rays with the air particles directly after the Aluminum window.

- a copper wedge that, by vertical positioning, acts as an adjustable attenuator to the X-ray beam.

- a tungsten pinhole assembly, consisting of a set of tungsten bars separated by shims of precise thicknesses in the 25 to 100um range. The assembly constitutes an array of pinholes (all 3mm thick) of different horizontal & vertical dimensions. This assembly is mounted on a motorization stage allowing for X and Z translation and rotation around both X and Z axes. The pinhole is ~4 meters from the dipole source-point.

- a CdW04 scintillator screen with optical system for light collection & imaging onto a CCD camera. This system is at respectively ~16 meters (Cell 9) and 12 meters (Cell 25) from the pinhole, and can also be translated in X and Z directions.

- The video images are transmitted to centralised framegrabbers at more than 200meters via 75ohm video cables for acquisition, treatment and calculation of the beamsizes and emittances in both planes. The images are displayed permanently in the Control Room.

Note : upgrades and improvements are currently underway to use faster cameras (of the IEEE-1394 standard) in conjuction with a pinhole aligned on a small horizontal fan of non-attenuated flux. This allows to attain a measurement rate at ~400Hz thereby allowing the measurement of vertical beam motions in a spectrum up to 200Hz with high resolution.

References & links of relevant papers and presentations :