1. Towards a ground motion orbit feed-forward at ATF2
K. Artoos, A. Jeremie (LAPP), M. Patecki, Jürgen Pfingstner, Y. Renier (many slides taken from him), D. Schulte, R. Tomas
18th of March 2014

2. A. Introduction

4. Overview of the experimental setup
Acquisition of:
BPM readings
Beam on/off
Acquisition of
GM readings
Beam on/off
Beam arrival signal

5. Difficulty of the experiment
Ground motion is smaller then the measured beam jitter by a factor of about 100 in horizontal and 20 in vertical.
To be able to observe the ground motion, jitter has to be removed very efficiently.
Experiment at ATF2 is much more difficult than it would be at CLIC, were ground motion is the dominant jitter source.

6. BPM number

7. Status of Installation
14 ground motion sensors have been installed (K. Artoos, A. Jeremie, Y. Renier, ATF2 team)
Measurements are available: (PSD and correlation)
Data have already been used to estimate the expected beam jitter at IP, due to final focus magnets (A. Jeremie, Okugi-san)
Also BPM and ground motion data have been taken in parallel.
Setup works very well.

8. Problem with sensor 6 (at QF11X)
Horizontal
Vertical

9. B. Data Analysis

10. Use of a different jitter reduction (simulation)
In simulation: py = 0.85
All meas. of downstream BPMs are decorrelated from selected upstream BPMs.
This is done via the multiplication with the inverse of the covariance matrix.
Advantage:
No system knowledge assumed
No structure of noise assumed
Assumed to be more more robust
Method is more sensitive vertically than horizontally. py

11. Application to the real jitter measurements
Jitter subtraction is starting to work (also horizontally).
The p-value is still around 1 at the moment.
But further investigations are ongoing.

12. c. Improvement of BPM resolution

13. Use of improved BPM resolution by the FONT team
BPM electronics of FONT team can improve the BPMs at the beginning of the beam line from about 5μm to about 1.0μm.
Installation and measurements have been performed in February and March.
This helps in two ways:
Potentially jitter sources can be detected an removed
Second experiment (jitter removal) that is performed in parallel.
The jitter removal algorithm is more efficient
High signal to noise ratio in the first BPMs is essential for the subtraction of incoming jitter.

14. Simulation results with FONT electronics
Better resolution improves jitter subtraction
py = 0.73
Plot for resolution of 0.4um (initial assumption).

15. Measurement of beam jitter with FONT electronics (Neven, Douglas)
Resolution was measured (with more restrictive method) to be :
MQ1X: 1.2um
MQ3X: 1.4 um
MQ5X: 1.6 um
Data are about to be analyzed.

16. D. Work on Synchronization issues

17. Different synchronisation aspects
Ground motion and beam synchronisation:
It has to be known which ground motion measurement corresponds to the beam arrival time.
BPM acquisition via EPICS
Pulses should not be missed or recorded twice in EPICS.
Beam on off experiment (noise will increase in BPMs)
Ground motion and EPICS time reference
The time stamps of the ground motion system and the EPICS time stamps have to have the same time reference.
New signal recorded by both systems (beam on off).

18. Ground motion and beam synchronisation

19. Signal used to synchronize GM and beam
Signal is generated by increment of beam trigger signal. This is done in an motion controller (details have to be investigated).
Large noise on signal, therefore low-pass filtering.

20. Time difference of beam arrival
Detected time between beam pulses is not exactly 1/3.12=320ms.
Reason has to be investigated.
Should not be a bug problem, but not ideal.

21. BPM acquisition via EPICS

22. Time difference between BPM time stamps
If data were acquired together with the beam on/off signal, with the initially used tool (not Yves tool) many pulses were lost.
The shown plot is not the worst example.

23. Problem with the current data acquisition tool
There old software was polling all 1/3.12s the BPM PVs with the lcaGet() command.
This should in principle work.
Two problems:
Loop for polling took too long and timing was lost (some pulses were missing).
Even with fast enough polling some data sets were lost.
Improvement:
Polling loop was cleaned up (speed up)
Now we poll more often 1/(4*3.12)s. The loop is fast enough for that now and hardly any data are lost anymore.

24. Time difference between BPM time stamps (new acquisition tool)
With the new tool nearly no pulses are lost (no problem).
BPM time stamp is very exact, but beam on/off timing varies a bit (but should be okay).

25. Ground motion and EPICS time reference

26. Beam on/off experiment
Recoding of the beam on/off signal
Offset varies between 1 and 3 pulses?
Network delay seems to be too large
We have to search for a better signal

27. Conclusions and Outlook
The installation of the experiment works very well.
Still the indented result is not achieved yet.
Therefore, work on two aspects has been performed:
Improvement of the BPM resolution at the beginning of the beam line by the FONT team.
Tests of the synchronization.
Data are about to be evaluated.
Remark:
Project is challenging but it is not yet finished.
There is still some work necessary.

28. Thank you for your attention!