[Halld-tagger] updated quotation for goniometer
Ken Livingston
Kenneth.Livingston at glasgow.ac.uk
Tue Apr 3 04:52:31 EDT 2012
Hi Hovanes,
The jpeg of the current design is here:
http://nuclear.gla.ac.uk/~kl/GlueX/newport_v3.jpg - it was read only,
which I've now fixed. The only final change I'll ask them to make is to
flip the base round by 180deg to make the thing take up less space
horizontally.
What you say about the motions is pretty much correct. If it was crucial
to come back to withing 0.0001 deg every time there's a movement we'd
need to get an even higher spec. What happens (at least in Hall-B, and
elsewhere) is more like this:
a. We do one of the Stonehenge type scans (or some other method) to get
the zero offsets for a crystal (to about+/-0.1 mrad for yaw and pitch
and +-0.25 deg for roll (azimuth). These offsets are then valid unless
the goniometer or crystal is remounted. Before proceeding we fix the phi
angle (roll) for that crystal to make the PARA and PERP horizontal and
vertical.
b. This allows us to put (for example) the PARA peak approximately where
we want it in photon energy by setting the value on the yaw axis (eg.
~3mrad for ~9GeV out of 12GeV)
c. pitch is set to a relatively large angle (eg >15mrad) to push the
PERP contributions out to a high photon energy where they don't
interfere with the PARA. For this value, we don't need repeatability
better than 0.001deg.
d. We then tweak on the yaw axis to put the PARA peak exactly where we
want it (at ~9GeV out of 12GeV beam we get a precision of ~2.4MeV on the
edge.) We also save the enhancement as a reference / template.
e. We save the pitch and yaw numbers as the PARA setting for that crystal.
f. We repeat the above process, swapping PARA for PERP and pitch for yaw
and save the PERP settings.
g. We check the repeatability by moving between PARA and PERP defined
positions and overlaying the enhancement on the reference. This is a
small movement on each axis (eg. 3 ->15mrad on yaw and 15 -> 3 on pitch
to go from PARA to PERP, and vice versa).
h. If the peak is not in the reference position to within the required
precision, and the beam is stable, then the shift worker needs to tweak
it with the buttons on the control GUI. Generally in Hall-B we've done
runs in the ratio of 2:2:1 PARA:PERP:AMO keeping 2 or 3 runs on the same
setting without changing, so we don't change.
i. For big linear translations (eg moving the whole goni out of the
beam) there also tends to be a little tweaking of the peak position
required when it's put back in place.
... actually it's set up to go in Hall-B. There's just a minor issue of
getting a polarized target for the photons to impinge upon!
Cheers,
Ken
On 04/03/2012 01:32 AM, Hovanes Egiyan wrote:
> Hi Ken,
>
> This one is nice, really close to our specs. I could not see the GIF
> file of the goni, there is
> some kind of access problem. Is this the nice color drawing? But I
> could get the PDF file
> with the four drawings. Although I do not have much experience with
> the goniometers,
> I am trying to see how we would be operating a goniometer with these
> specs based
> from what I remember from Hall B shifts.
>
> The angular resolutions of the rotational stages are on the order of
> 0.0001 deg,
> the absolute accuracies on the order of 0.03 deg, and the repeatability
> 0.001 deg or (17 microradians). This means that we will not be able to
> come
> back blindly to a previous orientation of the crystal better than 17
> microradians,
> but we can tweak it again to optimize the position each time we go
> back to desired
> crystal orientation if 17 microradians is not good enough.
>
> Also I noticed that there is ~50 microradians of angular runout for
> the linear stages.
> In particular, the the yaw for X and Y stages would affect the U and V
> (or V and U)
> angles of the crystal orientation. And I am not sure if this is
> repeatable. I guess
> each time we retract the goniometer, next time we put it back into the
> beam it may not be
> aligned better than 50 microradian, and will probably require tweaking
> to set the peak position.
>
> Is this consistent with your plans on how to operate it?
>
> Cheers,
> Hovanes.
>
>
>
> On 03/30/2012 09:00 AM, Ken Livingston wrote:
>> Hi All,
>> I've reveived an updated quote for the goniometer where the
>> outstanding questions have been addressed (attached). I believe
>> that's a suitable spec. now. There are no encoders on the rotational
>> axes - apparently that's standard with such high precision stepper
>> motors - the position is kept by counting pules. However, I think
>> the specification for the box and controller is good.
>>
>> The latest design drawings (newport_v3) are at
>> http://nuclear.gla.ac.uk/~kl/GlueX/
>>
>>
>> I met with Tim Whitlatch, Chuck Hutton and Krister Bruwhel to talk
>> about the vacuum chamber design. Tim also gave me a template to use
>> for specification to complete if we need to get alternative quotes
>> (as opposed to single sourcing it). I'll get this completed in the
>> next few days and circulate it.
>>
>> Regards,
>> Ken
>>
>>
>>
>>
>>
>> -------- Original Message --------
>> Subject: Quotation 1056722 for JEFFERSON
>> Date: Thu, 29 Mar 2012 22:50:23 +0100
>> From: Dorothy Sablan <dorothy.sablan at newport.com>
>> To: Kenneth Livingston <Kenneth.Livingston at glasgow.ac.uk>
>>
>>
>>
>>
>>
>> Dear Kenneth Livingston
>> ,
>> ;
>> ;
>> Thank you for your interest in Newport Corporation products. Our
>> quotation is attached for your review. Please use the contact
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--
=======================================================
Ken Livingston
Dept. of Physics& Astronomy, Tel: +44 141 330 6428
University of Glasgow, Fax: +44 141 330 5889
Glasgow G12 8QQ.
Scotland. UK.
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