The SA2 XTD1 XGM is current offline since Saturday morning.

Yesterday, Friday, it already started to present communication problems ( https://ttfinfo.desy.de/elog/FileEdit?file=/XFELelog/data/2023/10/10.03_a/2023-03-10T19:06:29-00.xml&xsl=/elogbook/xsl/elog-fileform.xsl&mode=edit )  and today it became clear a Hard drive is broken and need to be exchanged.

Theo M. and Fini J. are preparing to enter tunnel around 13:00. PRC has informed BKR, RC and HXRSS team. We do not expect to have the problem fixed until the end of the Saturday.

In parallel, beam permission to South Branch was removed due to the lack of communication to the XGM. PRC suggested RCs to disable the corresponding Big Brother rule in order to keep beam permission to proceed with few activities until the ZZ takes place, what was done by machine RPO.

*** Update 14:50:

The ZZ was successful and the colleagues managed to exchange the hard drive and reinstall the software. The XGM shall be working again but it will be monitored in the coming hours.

Special thanks to Theo M., Fini J., Soeren G. and Dey-IT colleagues for the precious volunteer work on Saturday.

MID reports an observation that is particular to the operation at the currently high photon energy of 23 keV

MID inserted the XTD6-MID-preabsorber and assumed that it completely stops the beam.
They acquired AGIPD detector images as dark frames but were surprised to still find some weak background signal (not dark).
The explanation by PRC and XRO is that the purpose of the pre-absorber is to protect the shutters against potential
damage and not to entirely stop the beam like a radiation protection shutter itself.
The pre-absorbers contain diamond and B4C but no tungsten. The calculated transmission of the pre-absorber at 25 keV is 4%.
3rd harmonic of the FEL (here at 69 keV) is on the order of 1%, and MID uses the mirror coating
stripes for high photon energies, thus transmitting well these high photon energies.

As another result, the apparent beam size observed on the downstream imagers can be more complex to understand:
MID actually also reports that the beam size appeared larger in the afternoon than in the morning,
depending on the insertion status of the pre-absorber and the lenses.
The scintillation efficiency of the YAG screens is known to be high also for hard x-rays beyond 30 keV.
Additionally, the CRLs focus the various harmonics differently. When CRL1 is set to focus the beam,
it will likely defocus higher harmonics yielding a larger spot size on a downstream imager.

PRC informed XRO to follow up together.

End of 30 keV study

The machine finished their attemps for 30 keV tuning while using NEPAL injector laser, unfortunately unsuccessful.
They could not obtain lasing, and all the pulse energy shown during the day on the level of about 20 uJ was only background, no lasing (as confirmed with FEL imager).

The machine has now switched to 24 keV, HIREX was extracted, XGMs adapted accordingly. Preabsorber was inserted, and CRL1 lenses all retracted.
SA2 beamline is in a safe state for machine tuning.

SASE1 status:

First shift switchover this week at 23h from FXE (19.5 keV) to SPB/SFX (12.4 keV) with issues. 
No immediate lasing at 12.4 keV with standard procedures / files, then tuneup using FEL imager (CBor) in multibunch. Wrong pointing (far off up in vertical).
Recovered lasing by 23h55 with 1 mJ at 12.4 keV at 10 bunches. Handover to SPB by midnight.

Diagnostics:
XTD2-XGM stayed with HAMPv during the photon energy change, which turned out fine, but the signal would be non-linear in multibunch
operation with many bunches, thus switch to XGMDh (HAMPv power remains turned on).
Procedure practiced with BKR-crew. BKR will switch back to HAMPv when switching back to FXE / 20 keV.

SA1 photon beam line status

- CRL1 lenses are in the beam. 

- The shutter between XTD2 and XTD9 is closed (The reason is not known)

I will retract the CRL1 lenses. Asked the machine to open the XTD2 and XTD9 shutter.

SA1 photon beam line status

- CRL1 lenses are in the beam. 

- The shutter between XTD2 and XTD9 is closed (The reason is not known)

I will retract the CRL1 lenses. Asked the machine to open the XTD2 and XTD9 shutter.

Concerning SASE1:

Please note that for this week the "remote power limit" was set to 5 Watt in order to protect CRL1.
The photon energies this week are 5.5 keV (FXE, day) and up to 7keV (SPB/SFX, night).
Daytime SASE1 operation by FXE will not come close to any damage limits (16 pulses at low rep rate).
However, SPB/SFX will operate at 1.1 MHz and up to 356 pulses/train. If there would be a sequence
procedural error during the shift handover switching of parameters, delivery of 5.5 keV at this rate could damage the CRLs.

If this limit would at any point limit the experiment, please get in contact with the PRC.

Info by R.Kammering (mail 20.9.23 18h25), related to the SA1 intensity drops during large wavelength scans:

"We found some problematic part in the code of our wavelength control server.
After lengthy debugging session we (Lars F, Olaf H. and me) did find a workaround which seems to have fixed the problem.
But we are still not 100 % sure if this will work under all circumstances, but this was the best we could achieve for today.
So finally we have to see how it behaves with a real scan from your side and if needed follow up on this at a later point of time."

Together with the finding of the test by FXE this seems to have resolved the issue.

As agreed beforehand, PRC and SPB/SFX re-assessed the SA1 EPS power limit based on actual performance, required number of pulses and rep rate, at the agreed SPB photon energy of 7 keV.
The actual lasing performance is on average 1.3 mJ / pulse at the current 7 keV.
Before the change, the assumed minimum pulse energy per requested bunch was set to 3.0 mJ in the Big Brother EPS power limit SA1, where we had set the remote power limit to 5 W.
To allow for the required 202 bunches at 0.5 MHz for SPB, I changed to an assumed minimum pulse energy per requested bunch of 2.2 mJ while maintaining the 5 W limit (rather than the inverse).
Maintaining in this way the 5 W limitation ensures that even if by human error during the shift change a high number of pulses would be requested at 5.5 keV, this could by no means damage the CRLs.

Additionally the SPB/SFX and the BKR operators were reminded about the safe procedure for the shift handover:
a) first the number of bunches has to be set to single bunch per train
b) then the wavelength could be changed
c) then the respective instrument would make sure that the beamline is in a safe state (e.g. CRL1 retracted) before a higher number of bunches would be requested (in particular at 5.5 keV).

Actually, it looks like the sync was lost shortly before 23h last night as the jitter went to 0fs and recovered at 1am when a new sync search probably started.

03 Jun 2023, 13:46

We called the BKR to ask what they can do about our pulse energy being 50% (~160uJ and slowly dropping) of what it was since we made our hutch intervention (with 0 bunches). BKR were asked to organise a time slot with PRC and the other instruments to make an intervention to try to increase our pulse energy.

We have one cell (CH4) which is low-Z and would require higher pulse energies for x-ray heating. We are flexible as to when this intervention happens this afternoon as in the meantime we can continue to work with other cells.

06:45

Achievements

1. Acquired tr-RIXS data with 4.0 mJ/cm² laser power for 21 delays between -2 and +10 ps at 853 eV. including static XAS and dark hRIXS runs. Totally collected 210 minutes of data i.e. 10 minutes per delay
2. Acquired tr-RIXS data with 4.0 mJ/cm² laser power for 21 delays between -2 and +10 ps at 853.44 eV. including static XAS and dark hRIXS runs. Totally collected 210 minutes of data i.e. 10 minutes per delay

Problems:

1. hRIXS camera number of readout ports was set to 1, increasing the readout time. Set it to 2.
2. Elastic line drifted about 40 meV over 3 hours (first and last trRIXS run at 853)

Achivements:

-We measured vertical spot size for several VFM settings

Problems:

-We cannot focus the x-ray beam with KB. The best value what we can get is ~300 um. We checked the slits of KB. The ALAS is slightly clipped on parabolic mirror of tim ing chamber. TI is not clear if this is the reason. We cannot proceed with the program for hRIXS.

-Still no signal on APD.

Night shift summary 21.10.2023

Achievements

• Found T0 on SiN, but the response is very slow (~10 ps).
• Azimuth (phi) scan
• Start of theta scan with optimized phi

Problems

• Even after finding T0 on SiN, still could not find T0 on sample with XAS
• Beam down at 5:25

Activities:

• Investigated SAXS scattering instability and found it to come from the pointing variation of the PPL
• Recorded microscope images of the PPL spot of the pBN to quantify the pointing for different spot sizes
• Enlarged the beam and measured pumped SAXS. Results seem better than before.

Problems:

• PPL pointing is not stable enough for consistent pumping effect in the probed area.
• Sample scanner x motor went into error due to interaction with the magnet and had to be coaxed back into operation.
• FEL down with cryo problem.

Achievements:

1. Continued measuring time-resolved and static RIXS on water (run table in elog entry #103)

2. Periodically checked spatial overlap and BAM compensator in-between measurements.

3. Refilled and changed cold traps when necessary.

Problems:

1. Some icing issue, solved by changing the nozzle.

Achievements:

Collected more scans on cyanocobalamin, both delays scans and dynamic XAS

Issues with bad signal in beginning but good signal in the last hours

Overall successful beamtime, demonstrating new transmission/absorption setup with liquid jet and DSSC

Problems:

None

Achievements:

1. Performed knife-edge scan. The beam size is currently at 5 um x 120 um.

2. Aligned the spectrometer at O K edge (2.8 pixel FWHM, 110 meV resolution, 4800 resolving power)

3. Performed energy calibration at O K edge (39.3 meV / pixel)

4. Setup the liquid jet environment for water.

Problems:

1. The elastic signal at CoO sample is very weak, so the alignment was done on the multilayer sample.

2. The motor of the ice crusher has some movement problem.