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1 -== Some general stuff: ==
1 +=== Some basic stuff: ===
2 2  
3 -* (% style="color:#000000" %)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).
4 -* (% style="color:#000000" %)The BAM measures the arrival time for each single electron bun in the bunch train (for working principle see [[MSK SDiag Projects>>url:https://confluence.desy.de/display/SDiagPublic/MSK+SDiag+Projects||shape="rect" style="color: rgb(0,0,0);"]] or literature listed below)   
5 -* The data format of the BAM has been completely altered in the 2022 shutdown
6 -* (% style="color:#003366" %)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 ...
7 -* (% style="color:#003366" %)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)
8 -* (% style="color:#003366" %)(typically) Bigger numbers indicate later arrival time of the electrons
9 -* (% style="color:#003366" %)The arrival time should be within -20 ps and +20 ps - otherwise there might be a problem ...
10 -* (((
11 -(% style="color:#003366" %)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.
12 -)))
13 -* (((
14 -(% style="color:#003366" %)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.
15 -)))
16 -* (((
17 -(% style="color:#003366" %)Those deviations and drifts happen usually only in the order of 50fs to 200fs; depending on the machine setup.
18 -)))
19 -* (((
20 -(% style="color:#003366" %)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.
21 -)))
22 -* (((
23 -(% style="color:#003366" %)The actual measurement resolution of a BAM can be - currently - as good as 3fs, for each bunch in the full train.
24 -)))
3 +* The relevant data is the arrival time FLASH.SDIAG/BAM/4DBC3/LOW_CHARGE_ARRIVAL_TIME
4 +* 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 {{code language="none"}}/FL2/Timing/start time flash2{{/code}}))
5 +* There are LOW and HIGH charge channels. For now the LOW_CHARGE Channel is the relevant one.
6 +* Bigger numbers indicate later arrival time of the electrons
7 +* The arrival time should be within -20 ps and +20 ps - otherwise there might be a problem ...
25 25  
26 -== Data structure ==
9 +=== Data structure ===
27 27  
28 -* (% style="color:#000000" %)The details about the functionality and the data structure can be found on the page:  (%%)**[[ BAM Data Structure>>https://xwiki.desy.de/xwiki/bin/view/SDiag/How-to%20articles/BAM%20Data%20Structure/||shape="rect"]]**
29 -* also see  [[doc:FLASHUSER.Data Acquisition and controls.DAQ and controls overview.Offline data analysis (DAQ).The FLASH HDF5 structure.WebHome]]
30 -* an example for the correction of pump-probe delay [[can be found here>>doc:FLASHUSER.Data Acquisition and controls.DAQ and controls overview.Offline data analysis (DAQ).Collection of HDF5 sample data from different beamlines.WebHome]]
11 +(% style="color: rgb(0,0,0);" %)The details about the functionality and the data structure can be found on the page: (%%)**[[ BAM Data Structure>>url:https://confluence.desy.de/display/SDiagPublic/BAM+Data+Structure||shape="rect"]]**
31 31  
32 -= Publications related to BAM =
13 +\\
33 33  
34 -=== BAM principle ===
15 += General information for the data analysis of pump-probe experiments =
35 35  
36 -1. (% style="color:#172b4d" %)A. Angelovski, et al.(%%)
37 -(% style="text-align:left" %)//Evaluation of the cone-shaped pickup performance for low charge sub-10 fs arrival-time measurements at free electron laser facilities//(%%)
38 -(% style="color:#172b4d" %)Phys. Rev. ST Accel. Beams (% style="text-align:left" %)**18**(% style="color:#172b4d" %), 012801 (2015)(%%)
39 -[[https:~~/~~/doi.org/10.1103/PhysRevSTAB.18.012801>>url:https://doi.org/10.1103/PhysRevSTAB.18.012801||rel="nofollow" shape="rect" style="text-align: left;"]]
17 +\\
40 40  
41 -=== Two publications showing how to use the BAM data to improve the time resolution: ===
19 +please have a close look to the publication:
42 42  
43 -1. Evgeny Savelyev, et al, 
44 -//Jitter-Correction for IR/UV-XUV Pump-Probe Experiments at the FLASH Free-Electron Laser//,
21 +Evgeny Savelyev, et al,  //Jitter-Correction for IR/UV-XUV Pump-Probe Experiments at the FLASH Free-Electron Laser//,
45 45  New J. Phys. **19**, 043009 (2017), [[https:~~/~~/doi.org/10.1088/1367-2630/aa652d>>url:https://doi.org/10.1088/1367-2630/aa652d||shape="rect"]]
46 -1. (((
47 -Dennis Mayer, Fabiano Lever and Markus Gühr,
48 -//Data analysis procedures for time-resolved x-ray photoelectron spectroscopy at a SASE free-electron-laser//,
49 -J. Phys. B: At. Mol. Opt. Phys. **55**, 054002 (2022); [[https:~~/~~/doi.org/10.1088/1361-6455/ac3c91>>url:https://doi.org/10.1088/1361-6455/ac3c91||shape="rect" style="text-decoration: none;"]]
50 -)))
51 51  
52 -=== Publications showing the correlation between the values measured by the BAM and the XUV pulse arrival time ===
24 +describing in detail the usage of BAM, streak camera and delay line data in order to get the actual time axis as reliable as possible.
53 53  
54 -1. (% style="color:#000000" %)//** Description of the FLASH synchronization system**//(%%)
55 -(% style="color:#000000" %)S. Schulz, et al.(%%)
56 -(% style="text-align:left" %)//Femtosecond all-optical synchronization of an X-ray free-electron laser//(% style="color:#000000" %),(%%)
57 -(% style="color:#000000" %)Nature Communications (% style="text-align:left" %)**6**(% style="color:#000000" %), 5938 (2015); (%%)[[http:~~/~~/dx.doi.org/10.1038/ncomms6938>>url:http://dx.doi.org/10.1038/ncomms6938||shape="rect" style="text-decoration: none;text-align: left;"]]
58 -
59 -1. //**Showing a correlation of 11 fs rms between BAM and XUV arrival time**//
60 -R. Ivanov, et al to be published 2022  
61 -
62 -1. (((
63 -//**Showing a correlation of 20 fs rms between BAM and XUV arrival time**//
64 -R. Ivanov, J. Liu, G. Brenner, M. Brachmanski and S. Düsterer,
65 -//FLASH free-electron laser single-shot temporal diagnostic: terahertz-field-driven streaking//,
66 -Special Issue (PhotonDiag2017),
67 -J. Synchrotron Rad.** 25**, 26-31 (2018);[[ https:~~/~~/doi.org/10.1107/S160057751701253X>>url:https://doi.org/10.1107/S160057751701253X||shape="rect" style="text-decoration: none;"]]
68 -)))
69 -1. (((
70 -//**Study of arrival time fluctuations**//
71 -Ivette J. Bermúdez Macias, Stefan Düsterer, Rosen Ivanov, Jia Liu, Günter Brenner, Juliane Rönsch-Schulenburg, Marie K. Czwalinna, and Mikhail V. Yurkov,
72 -//Study of temporal, spectral, arrival time and energy fluctuations of SASE FEL pulses//,
73 -Optics Express 29, 10491-10508 (2021); [[https:~~/~~/doi.org/10.1364/OE.419977>>url:https://doi.org/10.1364/OE.419977||shape="rect" style="text-decoration: none;"]]
74 -)))
26 +\\
75 75  
76 -
28 +Here is a summary of the ideas:
29 +
30 +== Streak camera info ==
31 +
32 +* the streak camera measures the delay between optical (amplified) laser and FEL (dipole radiation). - not in respect to the master clock !
33 +* streak camera ONLY delivers data which is averaged over several 10 seconds. There is NO shot to shot info.
34 +* a larger value of the streak camera delay (typically) indicates that the optical laser comes later than the FEL (or FEL earlier than the laser ...)
35 +
36 +\\
37 +
38 +\\
39 +
40 +{{info title="Correction of pump-probe delay"}}
41 +* BAM measurement: difference between electrons and timing system
42 +** usually the BAM signal has to be added to the delay ...
43 +** it is the best to test addition/subtraction and check the results on a step function (more/less sharp) - if there is no change of the data with + and - there is anyway something wrong. please contact your local contact for more information / help
44 +* Streak camera: difference between electrons and optical laser
45 +** it is a slow signal and should only be used as a rolling average over multiple minutes
46 +** if you see a drift in the streak camera which you do not see in the BAM it is resulting from the optical laser
47 +** if this (BAM - streak camera signal) is significant e.g. 200 fs over 1 h, it means the drift compensation was probably off and it should be compensated
48 +** addition/subtraction is dependent on the setup and have to be checked
49 +{{/info}}
BAM-basics and outlook-2018_DESY-template_16-9Format.pdf
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FLASH-seminar-2011_BAM_study_results.pdf
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