[Halld-pid] B-field in region of TOF PMTs

[Matthew Shepherd]

Hi all,

Just to add my 2 cents...  I would be weary about any field calculation in that region that does not include the steel frame of the FCAL.  There will be a lot of steel in the box tubing that makes up the core support structure of the FCAL.  The PMTs will be sitting very close to this steel, which will likely concentrate the magnetic field lines in the region of the PMTs.  

Bottom line is I think that ToF design will need a multi-layer steel/mu-metal shield (like the FCAL) to cope with potentially high fields.  I'm not sure how all of this drives the field spec -- seems like a more detailed field calculation coupled with any mechanical constraints of the ToF (e.g., maximum shield diameter) is really needed to set a spec.

-Matt

On Aug 26, 2010, at 10:14 AM, David Lawrence wrote:

> 
> Hi All,
> 
>     This is mainly directed at the folks at FSU, but since others may have an interest and wish to comment, I'm sending this to the halld-pid mailing list.
> 
>     I'm currently looking at the field specifications for the solenoidal magnet. One aspect of this is the fringe field at the region of the TOF phototubes. A specification based on the field of the LASS magnet was given in GlueX-doc-1542. Elton noticed that this differed by nearly a factor of 2 from a map referenced in an earlier document, GlueX-doc-912. I made some plots from several of our existing field maps in order to compare them. I have placed them on a wiki page here:
> 
> http://www.jlab.org/Hall-D/software/wiki/index.php/Magnetic_Field_in_region_of_TOF
> 
> The main issue is simply whether a specification of <50 Gauss in the TOF PMT region is sufficient. I'm guessing it is since I believe that has been our expectation for some time. However, I would like to make sure FSU (and eveyone else) is on board with that before making it an official specification for a new magnet design. I suppose the other other side of the coin is: can it be higher and if so, how high?
> 
> Regards,
> -David
> 
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