Some basic stuff:

• The relevant data is the arrival time FLASH.SDIAG/BAM/4DBC3/LOW_CHARGE_ARRIVAL_TIME
• Besides the arrival time from FLASH1 there is also the FLASH2/3 electron arrival time saved. The BAM data is saved for the complete RF pulse. First bunches are from FLASH1 then there is a gap for switching and then there is a second part for FLASH2 (starting at the FLASH2 start time (recorded in DAQ as /FL2/Timing/start time flash2))
• There are LOW and HIGH charge channels. For now the LOW_CHARGE Channel is the relevant one.
• Bigger numbers indicate later arrival time of the electrons
• The arrival time should be within -20 ps and +20 ps - otherwise there might be a problem ...

• The actual time t0 = 0ps is an arbitrary offset which is only changed after setting up the system after, e.g., a maintenance time, and has no relevance.

  What one usually does, after defining/finding time zero in the experiment, is either observe the relative changes for a single bunch during the course of the measurement run compared to the starting point,

  or (in addition) observe the relative deviation across all bunches within the same bunch train.

  Those deviations and drifts happen usually only in the order of 50fs to 200fs; depending on the machine setup.

  The short-term timing jitter (over several 100 trains) for each individual bunch, i.e. the standard deviation from their mean value, is usually ~ 20fs.

  The actual measurement resolution of a BAM can be - currently - as good as 3fs, for each bunch in the full train.

Data structure

The details about the functionality and the data structure can be found on the page:   BAM Data Structure

Publications related to BAM

BAM principle

1. A. Angelovski, et al.
   Evaluation of the cone-shaped pickup performance for low charge sub-10 fs arrival-time measurements at free electron laser facilities
   Phys. Rev. ST Accel. Beams 18, 012801 (2015)
   https://doi.org/10.1103/PhysRevSTAB.18.012801

Two publications showing how to use the BAM data to improve the time resolution:

1. Evgeny Savelyev, et al, 
   Jitter-Correction for IR/UV-XUV Pump-Probe Experiments at the FLASH Free-Electron Laser,
   New J. Phys. 19, 043009 (2017), https://doi.org/10.1088/1367-2630/aa652d
   

2. Dennis Mayer, Fabiano Lever and Markus Gühr,
   Data analysis procedures for time-resolved x-ray photoelectron spectroscopy at a SASE free-electron-laser,
   J. Phys. B: At. Mol. Opt. Phys. 55, 054002 (2022); https://doi.org/10.1088/1361-6455/ac3c91

Publications showing the correlation between the values measured by the BAM and the XUV pulse arrival time

1.  Description of the FLASH synchronization system
   S. Schulz, et al.
   Femtosecond all-optical synchronization of an X-ray free-electron laser,
   Nature Communications 6, 5938 (2015); http://dx.doi.org/10.1038/ncomms6938
   
   
2. Showing a correlation of 11 fs rms between BAM and XUV arrival time
   R. Ivanov, et al to be published 2022  
   
   

3. Showing a correlation of 20 fs rms between BAM and XUV arrival time
   R. Ivanov, J. Liu, G. Brenner, M. Brachmanski and S. Düsterer,
   FLASH free-electron laser single-shot temporal diagnostic: terahertz-field-driven streaking,
   Special Issue (PhotonDiag2017),
   J. Synchrotron Rad. 25, 26-31 (2018); https://doi.org/10.1107/S160057751701253X
   

4. Study of arrival time fluctuations
   Ivette J. Bermúdez Macias, Stefan Düsterer, Rosen Ivanov, Jia Liu, Günter Brenner, Juliane Rönsch-Schulenburg, Marie K. Czwalinna, and Mikhail V. Yurkov,
   Study of temporal, spectral, arrival time and energy fluctuations of SASE FEL pulses,
   Optics Express 29, 10491-10508 (2021); https://doi.org/10.1364/OE.419977