The installation of the tomography beamline started in August with the SESAME machine shutdown. Now that the beamline is taking shape physically, with many of the major components in place, we focus on exploring one of the major sections of the beamline, the Front-End. What is the Front-End exactly? What is its role and how is it configured?
The Front-End, situated inside the storage ring downstream from the source, is the final configuration through which the photon beam travels before arriving on the beamline. It plays a major role in personnel and equipment safety during experiments, as well as ensuring the integrity of the storage ring vacuum.
Here is a description of the main components and their function:
| Component | Function |
| Crotch absorber
Section view of the crotch absorber with concentric water outlet |
This is the first element to be hit by the white beam from the BEATS X-ray source and adjacent dipoles. This water-cooled glidcop structure can take a thermal load of 4kW. It rejects all the unwanted radiation. |
| Assembly
|
1: fixed mask; 2: photon absorber; 3: vacuum fast shutter; 4: primary slits; 5: first window |
| Fixed mask
|
A fixed frame with a rectangular opening made of water-cooled OFHC copper, it defines the maximum aperture of the beamline. |
| Photon shutter, bremsstrahlung stopper
|
Switches on and off the radiation delivery to the beamline. It is designed to completely intercept the photon beam and to isolate downstream components from the source.
When closed, it ensures safe access to the beamline hutches. |
| Vacuum fast shutter
|
A fast closing valve that quickly isolates the beamline from the storage ring. It protects the level of vacuum inside the storage ring in the case of a vacuum incident on the beamline. |
| Primary slits
|
Horizontal and vertical water-cooled blades made of tungsten and copper allowing to manipulate the size of the beam (within the limits set by the fixed mask).
|
| Window
|
During normal operation, the window separates the vacuum in the beamline from the vacuum in the storage ring.
Chemical vapour deposited diamond window 11mm (h), 5.5 mm (v), several 100 microns thick, low surface roughness (< 5nm Ra.).
|
| Beam position monitor
|
A moveable system of blades to determine the position of the beam. |
| Attenuator
|
A mechanical assembly enabling to insert foils of different materials and thicknesses into the beam. |
The Front-End shapes both the spectrum of the pink beam (via the attenuator)and the geometrical parameters (size) of the beam( via fixed mask and the slit system). It has a key role, as it:
- – absorbs undesired radiation (and corresponding thermal load) emitted in the direction of the beamline during injection and operation, ensuring personnel and equipment safety during experiments
- – provides the beam collimation,
- – prevents the white X-ray beam from impinging on unprotected and uncooled surfaces,
- – allows to extract the useful part of the X-ray radiation,
- – shapes the beam and allows to fully stop it in full safety, in case access to the beamline components downstream is required,
- – assures the integrity of the storage ring vacuum.
The BEATS Front-End was installed during the September and October 2022 machine shutdowns at SESAME. In October, the BEATS team connected all Front-End components and baked-out the whole assembly. Vacuum levels are within expectations. The next step will be the final commissioning of the X-ray source, a phase during which the Front-End will see beam for the first time.