Introduction¶
jjAttenuator is the karabo device which controls the Solid Attenuator Assembly (SAA) designed by JJ X-Ray [1] to precisely attenuate the XFEL beam intensity in several different circumstances [2]; In cases where the full intensity would be harmful, or would create thermal distortions on downstream x-ray optical devices, and to adjust the beam intensity delivered to the sample for fluence or intensity-dependent experiments.
The attenuator allows the insertion of a combination of absorbers with different thickness and of different materials. Four arms (or rods) holding six different absorbers each can be inserted into the beam, giving a total of 24 different absorbers, Fig. 1.
Fig. 1 Fig. 1: The four rods of the device hold 20 x 20 \(mm^2\) absorbers.
Any absorber on one rod can be inserted into the beam with any combination of the absorbers on the three other rods giving the total number of combinations of \(6^4 = 1296\). In reality, an additional position should be considered per each arm; the upper part of the arm in fact has no clamped absorber on it, and allows the beam to go through unaffected, Fig. 2. This results in a larger total number of combinations, \(7^4 = 2401\).
Fig. 2 Fig. 2: Up to six absorbers can be located in the moving arm. The empty slot at the end side of the arm is used in case no attenuation of the beam is required from that arm.
The distribution of the absorbers is orientatively the following (from the technical report [2]):
| Position | Material | Thickness [mm] | |||
| Arm 1 | Arm 2 | Arm 3 | Arm 4 | ||
| 1 | Diamond | 0.1 | 0.2 | 0.4 | 0.8 |
| 2 | Diamond | 0.4 | 0.8 | 1.6 | 3.2 |
| 3 | B4C | 0.2 | 0.4 | 0.8 | 1.6 |
| 4 | B4C | 0.8 | 1.6 | 3.2 | 6.4 |
| 5 | Silicon | 0.5 | 1.0 | 2.0 | 4.0 |
| 6 | Silicon | 2.0 | 4.0 | 8.0 | 16.0 |
It can change according to the needs of each experimental line.
Solid Attenuator Array devices are being integrated into different UHV beam lines; at the moment it is being used by SPB, FE as well as MID, and it is planned to be used it also for HED.
| [1] | JJ X-Ray, https://www.jjxray.dk/ |
| [2] | (1, 2) JJ X-Ray, Solid Attenuator Array, https://docs.xfel.eu/share/page/site/CIE/document-details?nodeRef=workspace://SpacesStore/be799d9d-0486-4182-be19-448554d009f1 |