Info collection for the BAM

Last modified by sndueste on 2025/02/06 10:58

Some general stuff:

  • There are several BAMs in FLASH. Essentially one in the accelerator section  (FL0.DBC2, Previously: 4DBC3) and one close to the respective undulator section (FL1.SFELC and FL2.SEED5).
  • The BAM measures the arrival time for each single electron bun in the bunch train (for working principle see MSK SDiag Projects or literature listed below)    
  • The data format of the BAM has been completely altered in the 2022 shutdown
  • before 2022 BAMs were always saving the arrival time information for each 1µs bucked regardless if there were electrons in the accelerator or not. In addition the arrival times for  FL1 and FL2 were saved in the same parameter ...
  • THIS is now different. There are new parameters saving only the arrival times for pulses that go to FL1 and to FL2 (in detail: first time slot of the accelerator and second)
  • (typically) 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

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