ID11L - HESEB

Photon Source

HESEB Beamline is using an UE56 Apple II type Undulator. The length of the undulator is 1.7 m with 30 period of 56 mm length each. Minimum gap of the undulator magnets are 12.8 mm. so the undulator can produce photons with ~70 eV energy. The undulator has also capability to produce circularly polarized soft X Ray photons for Circular Dichroism studies. 

Beamline Optics

You can see the layout of the HESEB beamline in Figure 2. The total available length from the center of the straight section to the focal spot at the experiment was set at 27.5 m for branch line A and 28.5 m for the second branch line B. Branch A is going to be equipped with an experimental chamber for absorption (electron/fluorescence yield) spectroscopy. The second branch (B) is foreseen for a photoemission (XPS) experimental station planned by a consortium of scientists from Turkey. This is still in production stage. The name of the beamline is TXPES (Turkish soft X-ray PhotoElectron Spectroscopy).

The first cylindrical mirror (M1) is located inside the shield wall deflecting the beam horizontally, collimating it vertically and forming a horizontal focus as indicated. The monochromator has a plane mirror (M2) and two interchangeable plane gratings with 400 l/mm and 1200 l/mm groove density. The ultimate energy resolution is about 10,000 for the 400 l/mm grating and 20,000 for the 1200 l/mm grating. The dispersed beam is offset by 15 mm vertically from the original beam. 

The toroid M3 focuses the beam onto the exit slit. Finally, a refocusing toroidal mirror (M4) images the exit slit onto the sample position, creating a focal spot of 180 x 25 μm². This spot size is largely determined by the source size of the beam in the undulator. In order to accommodate the power load of the undispersed beam, M1, M2 and the gratings are water cooled by side cooling. In regular operation, e.g. M1 absorbs 170 W of 200 W incident power.

Experimental Station (End Station)

Absorption coefficient of Soft X-ray photons is so high that the soft X ray measurements have to be done under vacuum. The HESEB End station is and Ultra high Vacuum chamber. With the help of load-lock system, the sample changes can be done in 45 minutes. The picture of the HESEB end station and components are shown in the figure 3. 

The end station has motorized manipulator arm so that 2D mapping can be done. There are 3 different slot on the receptacle part of the manipulator; 1) low temperature slot 2) e-beam heating slot, 3) High temperature slot in addition to these slot there is a photo diode for diagnostic purposes. Because of the sample transfer system a special holder is used. The maximum sample can be 15x15 mm². In figure 4 you can see the drawing and picture of the receptacle part.  

Technical information about the HESEB Analyze Chamber:

• three slots on the receptacle part 
• calculated spot size on the sample 180x25(hxv)µm²
• the size of the sample holder 15x15 mm²
• samples can be cooled with LN₂ down to -180 °C
• samples can be heated up with a button heater up to 900 °C
• motorized manipulator, 1µm repeatable spatial resolution
• analyze capabilities under He at the low vacuum medium
• Keithley 8485 picoammeter for electron yield measurement
• Bruker XFlash 630S detector for fluorescence yield measurement

• Sample Type: Crystal, Amorphous, Powder, Thin Film.