Hi Liz! Thanks for your answer.
Yes, I remember, I could see your seminar. I got impressed with
what you were planning to the beamlines! Huge infra-structure!
Regarding stability, as far as we are able to realize the drifts
we observe do not repeat at each user shift but each 2 shifts (1 day).
It seems the features are more related to the room temperature
variations than with any other thing (they reach 3°C maximum). That’s
exactly what we are starting to do next days. We have installed
temperature sensors along the beamline to keep track of the room
temperature and of the optical elements. In this way we’ll be able to
see if the they are responsible for introduce the profile we see both in
energy and vertical position.
By now, we control the DCM 1st crystal surface temperature
through a dedicated thermal bath, but the 2nd crystal is not cooled and
we don’t have temperature data for it so far. Regarding a feedback loop
for the 2nd crystal, we used LabView to implement a Lock-in. It worked
but we still have to improve the reading electronics in order to get the
required resolution to keep the beam within a few microns at the sample
position.
Find attached 3 graphs demonstrating the drift profile we see:
• BBPM2 – Blade BPM installed just after the collimating mirror. It can
show vertical position changes coming form SR and coupled by thermal
deformations of the mirror (which also have a dedicated thermal bath)
• QBPM - Quadrant (Photodiodes) BPM located just before the sample.
• ENERGY - Measured using the absorption edge of Se normalizing the
reading of 2 ion chambers.
Any suggestions that can help us build an effect approach to
this problem are super-wellcome.
I hope things are going well at Diamond.
Regards,
Lucas.
Lucas.
-----Mensagem original-----
De: Duke, EM (Liz) [mailto:[log in to unmask]]
Enviada em: sexta-feira, 25 de julho de 2008 11:32
Para: [log in to unmask]
Assunto: RE: [ccp4bb] Beamline Stability Issues
Hi Lucas,
I am a Principal beamline scientist at Diamond Light Source, the UK
synchrotron and have built many beamlines both here at Diamond and also
at the SRS.
I think that your energy drifts are likely to be thermally related.
Having a second mono crystal not thermally linked to the first crystal
is likely to be a significant problem. Have you looked at the pattern of
your instabilities. Are they worse at higher currents/certain times of
the day? If you send me data I would be happy to take a look.
I have visited LNLS twice and was very impressed with your facility.
Good luck.
Liz
From: CCP4 bulletin board on behalf of Lucas Sanfelici
Sent: Fri 25/07/2008 15:19
To: [log in to unmask]
Subject: [ccp4bb] Beamline Stability Issues
Hello all!
Does someone have experience in minimize energy instabilities in
beamlines?
MX2, our new beamline devoted to MX experiments, are facing problems
with energy drifts. As far as we could notice, theses drifts are results
of the contribution from several sources - possibly electron beam
movements, heating of optical elements, etc...
LNLS is a 2nd generation machine with 4 straight sections available for
insertion devices. MX2 is a 2T wiggler-based beamline and produces a
peak flux of 10^11 photons/s.
What I'd like to know, before start performing calculations, how far
should I expect the heating of a non-cooled 2nd crystal affects energy?
Does someone know cases of a few eVs drifts?
Thanks in advance and regards,
Lucas Sanfelici
Physicist
Brazilian Synchrotron Ligth Source- LNLS (www.lnls.br)
Diagnostics Group
PO Box 6192 Postal Code 13083-970
Campinas-SP Brazil
Phone: +55-19-3512-1153/1152 Fax: +55-19-3512-1006
E-mail: [log in to unmask]
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