Operating the beamline

General

The user-controlled electropneumatic valves of the beamline (labelled by numbers 1-10 in the screenshot adapted from the Beamline Control System (BCS) webpage above). Before using the beam for data acquisition the beamline must be open for at least 30 minutes in order to reach thermal stability of its optical elements (warm-up), mainly of the prefocusing mirror, which is being hit by the most intense light (40 W incident, of which 90% absorbed). The valves can be operated using

• the Beamline software, or
• the BCS webpage (single click on the valve) on the MSB-MASTER or MSB-STATION computers, or
• the BCS section of the Kleopatra software (double click on the valve) from the MSB-MASTER computer (or its VNC copy on the MSB-STATION computer).

The simplest one is the first option where you can use just 3 buttons Close (to close all valves), Standby (to keep open valves 1-9 to keep the beamline warming up) and Acquire (to let the beam enter the analysis chamber for data acquisition). The correct order is automatically respected.

The other two options open a webpage where the desired command (1) open or (0) close can be selected and Submitted. It will open another webpage with the result of the operation. The status of each valve is indicated by color (green - closed, red - open). The displayed status is refreshed only every 10-40 s so the change might not be immediately visible..

Opening the beamline using the Beamline software When the Beam status is OK open valves 1-9 using the Standby button. When done you should see Mesh current > 0. Leave the beamline warm up for at least 30 minutes. Proceed with setting the beam position if needed. For data acquisition open valve 10 using the Acquire button. Proceed with sample alignment (full or fast check as needed). Start your measurements.

Closing the beamline Immediately after data acquisition and before any operations in the analysis chamber that may cause pressure increase close valve 10 using the Standby button so the beamline stays warming up.. At the end of the day close all valves using the Close button.

 

Opening the beamline using the web-based method Check that the beam is available for users (beam energy ≥2 GeV, accumulated current ≥100 mA, machine status User Dedicated, "luce utenti" announced). Check that the pressures along the beamline are in the 10-9 mbar order or below (except for the shutter chamber being 10-7 mbar due to incorrect measurement). Open the electropneumatic valves 9 to 1 (in this order). After this you should observe some mesh current in the Mesh Monitor software. Wait at least 30 min (until the mesh current stabilizes). Proceed with setting the beam position if needed. Open the electropneumatic valve 10. Proceed with sample alignment (full or fast check as needed). Start your measurements.

Closing the beamline Close the electropneumatic valve 10 (if not done before). Close the electropneumatic valves 1 to 9 (in this order).

Notes

Valves a, b and c cannot be controlled by the user.

• Valves a and b are closed by the machine operators before the injection (e.g. in the case of a beam dump) and open after it. If the operators forget to open these valves after the injection call the Control Room (telephone number is on the machine status webpage) and ask kindly to open the machine shutter of the beamline 6.1 Materials Science.
• Valve c is a security fast valve closed automatically if vacuum is broken.

Valves 1 and 3 (shutter and stopper) are also closed by the machine operators before the injection in the case of a beam dump, locked during the injection (symbol  in Kleopatra) but not open automatically after. So when the beam is again available, open them using the Standby button in Beamline software or manually in the correct order. (valve 3 and then valve 1). If they keep being locked although the injection is finished (machine status User Dedicated, "luce utenti" announced), call the Control Room (telephone number is on the machine status webpage) and ask the operator to unlock the beamline shutters and stoppers.

Valve 1 also automatically closes when there is not enough flow of the cooling water of the beamline prefocusing mirror, entrance slit and/or monochromator. Check Water status being OK in the Beamline software or on the web and increase it if needed.

The correct opening/closing order of valves 1-7 is important. The scope is to avoid hitting any of the valves 2-7 by the photon beam when they are closed. Therefore the valve 1 should be open as the last one and closed as the first one, as it is the only one that can support the heat load of the beam (it is water-cooled). Although there are some interlocks that should avoid user errors please respect the correct order.

Open the valve 10 to the analysis chamber only for the period of photoemission measurements and close it immediately after. Double-check that it is closed especially when performing operations leading to pressure increase in the analysis chamber, typically sample transfer, ion sputtering or gas exposure, or during photoemission with X-ray source (to avoid mixing two different excitations). Moreover, some sensitive samples might be damaged by long exposures to the photon beam so there is no reason to illuminate them when not needed.

If the BCS webpage does not open at all and the BCS section of Kleopatra is of grey color and does not react on double-clicks on valves wait for several minutes. If the problem persists follow Troubleshooting - BCS communication problem.

Setting the beam position

Along the beamline there are 3 axes affecting the position of the photon beam:

axis	actuation	photon beam position	scope
prefocusing mirror roll (J1)	motorized (by Prefocus or Kleopatra) 1	vertical on the entrance slit	maximum intensity passing through the entrance slit
prefocusing mirror pitch (J2)	motorized (by Prefocus or Kleopatra) 1	horizontal all along the beamline	photon beam horizontally in the center of the exit slit and in electron analyzer focus 2
refocusing mirror pitch	manual (by micrometer) 3	vertical on the sample	photon beam vertically in electron analyzer focus

1 Due to mechanical reasons, both axes can be operated directly only in the increasing direction but always with reasonable backlash in the opposite direction. Reasonable means that a change in mesh current can be observed. Examples: To increase the value of J1 from 0.42 to 0.43 use move j1 0.43. To decrease the value of J1 from 0.43 to 0.42 use move j1 0.32 and then move j1 0.42. To increase the value of J2 from 1.62 to 1.63 use move j2 1.63. To decrease the value of J2 from 1.63 to 1.62 use move j2 1.4 and then move j2 1.62.

2 Primarily to the center of the exit slit. The correct focus of the analyzer is then adjusted by x,y sample position during alignment. 3 Micrometer location:

By moving these 3 axes we can compensate for the position variations of the electron beam in the storage ring that can be slightly different after each injection and/or modified by the machine operators on request of other beamlines (mostly SYRMEP with which we share the same photon source).

All other optical elements are aligned the way that the beam position on the sample does not significantly change upon photon energy and resolution setting.

Procedure

1. Open the beamline (electropneumatic valves 9-1) and let it warm up for at least 30 minutes (preferably 2-4 hours).
2. Set the photon energy to any value between 100 and 150 eV using Kleopatra software.
3. Set the mesh current (monitored by Mesh Monitor) to maximum, either by
   • performing an automatic full J1 scan procedure by clicking on AutoRoll button in the Prefocus section of Kleopatra (that will move J1 to 0.29, scan J1 up to 0.45 while observing the mesh current, determine J1_max by fitting the 5 experimental points nearest to the maximum, move J1 to J1_max-0.1 (backlash) and finally move J1 to J1_max; or
   • moving J1 (in 0.002 steps) to reach the maximum mesh current, by using directly the Prefocus software or PrefocusConsole or Kleopatra console in Kleopatra. This procedure is faster for smaller corrections than the full AutoRoll scan if you are not too far from the maximum.
   This procedure ensures you that you are using the highest possible photon beam intensity and the least possible is being cut off by the entrance slit.
4. Check the horizontal beam position through the mirror in the downstream viewport near the exit slit which is covered by a luminofor. (There is a 45° mirror near the beam line which permits you to look at the exit slit in the downstream direction.)
   
5. You should see a vertical line in the middle of the slit. If it is too much on the left side, increase the value of J2 in the Prefocus software or PrefocusConsole or Kleopatra console in Kleopatra. If it is too much on the right side, decrease the value of J2 (use backlash to 1.4). This procedure ensures you that the beam will pass through the focal point of the electron analyzer in horizontal direction.
6. Proceed with sample alignment with respect to the analyzer and photon beam.
7. With the intensity timescan in the SpecsLab2 software still running sligtly change the refocusing mirror pitch and check that the intensity is at the maximum or not far. Usually no adjustment is necessary. This procedure ensures you that the beam will pass through the focal point of the electron analyzer in vertical direction.

Setting the photon energy

The photon energy can be set using the following software:

• MSB-MONO Client (manually in Energy window) that commands MSB-MONO Server via TCP/IP;
• Kleopatra (manually using the SetEnergy button or Kleopatra console command) that commands MSB-MONO Server via TCP/IP;
• Beamline (manually using the Set button) that commands Kleopatra via TCP/IP,
• SpecsLab2 (automatically according to Eexc value in the Region Edit window) that commands Kleopatra via RS232;
• KolXPD (manually using the Monochromator control panel) that commands Kleopatra via TCP/IP;
• KolXPD (automatically according to excitation energy value in the region view or the actual position in the running CIS/CFS/NEXAFS/RESPES scan) that commands Kleopatra via TCP/IP.

Photon energies in the range between 40 and 1000 eV can be set freely, without any constraints. Bear in mind that tuning from lower towards higher photon energies is faster than in the opposite direction because of automatic procedure compensating for backlash in this case (the monocromator tunes first to a lower energy than requested in order to arrive always from lower to higher values).

Such backlash compensation may lead to a collision of the optical elements inside the monochromator when tuning to photon energies between 22 and 40 eV! Therefore, when setting energies in this range coming from higher-energy position, always perform this operation in a step-wise manner. E.g. if you require 22 eV photons, tune first to 40 eV, then 35, 30, 25, 24, 23, and then 22 eV. In the increasing direction no caution is needed, as the backlash compensation is not applied.

If you fail and the collision appears, ask the beamline scientist for permission to follow the troubleshooting procedure of unblocking and reference mark searching.

Photon energy error

Due to mechanical design of our monochromator, the error in photon energy setting and reproducibility appears to be similar to multiplicative. Therefore, in the photon energy range up to 50 eV the tuning will be almost perfect with the error below 0.1 eV, at 100 eV below 0.2 eV, at 500 eV and higher not more than several eVs. If your sample is metallic it is a good idea to measure some well defined sharp core levels or Fermi edge in order to have a reasonable energy reference for your data processing. Alternatively, a piece of clean Au foil can be mounted on the sample holder for reference measurements.

If the monochromator is heavily miscalibrated it may have lost its reference marks. They can be found using the procedure described in troubleshooting (ask the beamline scientist for permission first). If it does not help a more complicated monochromator calibration must to be performed.

Setting the photon energy resolution

Photon energy resolution can be set by opening and closing the beamline entrance and exit slits. Typical setting is 100 μm entrance and 200 μm exit slit apertures. (We use the exit slit aperture to be 2 × entrance slit aperture.)

The slit apertures are set by corresponding micrometers using the following tables. The equation to estimate the experimental photon energy resolution is listed for each slit combination. The default setting is bold.

entrance slit aperture entrance slit micrometer 35 μm 16.65 mm 50 μm 16.8 mm 100 μm 17.3 mm 150 μm 17.8 mm 200 μm 18.3 mm 250 μm 18.8 mm 300 μm 19.3 mm

exit slit aperture exit slit micrometer 70 μm 14.1 mm 100 μm 14.4 mm 200 μm 15.4 mm 300 μm 16.4 mm 400 μm 17.4 mm 500 μm 18.4 mm 600 μm 19.4 mm

photon energy resolution 0.000010 × (hν)1.5 0.000015 × (hν)1.5 0.000030 × (hν)1.5 0.000045 × (hν)1.5 0.000060 × (hν)1.5 0.000075 × (hν)1.5 0.000090 × (hν)1.5

Of course the resolution setting is also influencing the photon flux. However, the usual setting 100 μm entrance and 200 μm exit slit seems to be a good compromise, as at low photon energies the flux is usually sufficient and at high photon energies opening the slits would cause too bad resolution.

If for your measurements you decide to change the slit setting do not forget to write it down into the labbook, inform you colleagues about this change and reset everything back afterwards.