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[log in to unmask]" type="cite"> Hi Stepan,
I don't think it's this complicated. Rather, I think it's a simple bug in the visualization, based on other bugginess in how it works. I've seen the maps, and they are reasonable and complete in both +/-z.
Jeremy, when you are back at work we can sit and talk... much easier than trying to explain in email. However, your image (attached) shows the field ramping up correctly at about Z = -50 cm (in magnet coordinates, near the target at the right) and abruptly turning off above approximately Z = +30cm (near layer 5, 70cm downstream of the target, at the left). Also note that no fringe field is shown at the downstream end (at the left). This is obviously wrong! I think the visualization is cutting off at some z, perhaps because at one extreme in x-y that is the largest z that is in the displayed view.
Perhaps you need to make some more images to clear this up.
Tim
On Mar 10, 2014, at 7:25 PM, Stepan Stepanyan <[log in to unmask]> wrote:
Jeremy,
I think you are showing only field distribution what is in the file,
which is
only half plane (X, Z) for Z<=0. If you let me know which files did you use
I can comment on X points. In the field maps points were generated for X=0
to X=25 cm with steps of 1 cm. In addition, Z=0 for the field map should
have
correspond to the center of the magnet, which is not in the picture, I
think.
In the attachment I am sending a zip file which has field maps for
central field
of 5000G. Just want to make sure we are talking about the same maps.
Hope this will help.
Regards, Stepan
On 3/10/14, 7:14 PM, McCormick, Jeremy I. wrote:
Hi, Tim/Stepan,
What about the field display do you think is wrong vis-a-vis the input field map?
I’m in contact with the Geant4 developers on this, so it would be good to know so I can request a fix. Tim, I wasn’t sure what you meant on this.
As far as the extent of the field map in -Z, I think that this is something that needs to be done in the conversion from the unfolded single plane set of points to the 3D version. Norman must have that code/script, but I haven’t seen it. This would be good to put into the SVN someplace (sandbox even) so it can be improved.
—Jeremy
On Mar 10, 2014, at 7:46 AM, Stepan Stepanyan <[log in to unmask]> wrote:
Hi TIm,
Yes, I suspected that it might be a visualization issue.
The reason I was not sure is that I can see the same as you described
about colors and arrows but simply as 1/2 field with Z=0 not at the
center of the magnet.
Thanks, Stepan
On 3/10/14 10:36 AM, Nelson, Timothy Knight wrote:
Hi Stepan,
I think the problems at this point are all due to the visual representation. Colors and arrow lengths are field strength, red being large and green to blue being relatively smaller. I am not sure why the field is cut off on the downstream side, but still well past z=0, in this image but I'm pretty sure that's a problem with the visualization based on the map data I saw that goes into this.
Tim
Sent from my iPad
On Mar 7, 2014, at 8:48 AM, "Stepan Stepanyan" <[log in to unmask]> wrote:########################################################################
Hello Jeremy,
Thanks for implementing the field. I am not sure how much I should trust
the visual picture, but the field you have is generated from the middle of
the magnet (in Z), so if I am reading the picture correctly, field is
shifted
relative to the magnet. For completeness the same (X,+Z) distribution must
be repeated for (X,-Z) half plane.
One of things we have discussed with Norman some time ago is the need
for a full 3-D field map (B_x, B_y, B_z) for (X, Y, Z) points. Will be
good to
know this early on.
Regards, Stepan
On 3/6/14 7:28 PM, McCormick, Jeremy I. wrote:########################################################################
Hi,
I made a few fixes to SLIC/LCDD for the support of 3D magnetic field maps. The map’s offsets were not being set correctly, and I believe this is now fixed in the HEAD configuration of SLIC in ilcinstall.
I also added the missing field data to the SVN at hps/java/trunk/fieldmap which is referenced by the detector that includes the field map.
I was able to get simple visualization working with the 10.00.p01 release of Geant, and the best picture I have so far is this:
http://www.slac.stanford.edu/~jeremym/hps/field/hps_field7.png
This visualization tool is at an “alpha” stage of development in that project, unfortunately, but it at least gives some idea that the field has been loaded in successfully.
That’s the good news.
The bad news is that the performance is approximately 150x worse when using the 3D field in a Proposal2014 geometry compared to a setup with the simplistic fixed dipole. This compares the HPS-Proposal2014-v5-2pt2 detector with HPS-Proposal2014-v4-fieldmap using the event file egs_tri_2.2gev_0.00125x0_200na_5e5b_30mr_001.stdhep.
So it appears to me this is not really going to be useable in large scale simulation production until the algorithm for retrieving and interpolating the field values has been significantly optimized.
—Jeremy
########################################################################
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