Re: possible pair spectrometer magnets (fwd)

["Hrachya.Hakobyan" <hakopian@atlas.yerphi.am>]

Hello Jim,

The C-shape magnet mentioned has a BL=2T*m. This ls slightly shorter than 
expected(2.6T*m) for the wide range of momentum analysed  from 3 to 
8GeV/c at maximal field setting as I showd in the draft of PS proposal. 
But decrease of the gap, currently 20cm, down  to f.e. 5cm , will 
slightly increase the mean field and its homogeneity. If there is no 
other choice, this magnet may  be used with reduced acceptance of momentum 
analysis and the measurements of the photon spectrum in the range of 
6-12GeV (within assumption  of reasonable energy resolution)  will be 
realized with  more than one magnetic field setting,so 
not simultaneously. That is acceptable in the presence of the beam 
monitors for the absolute integral flux measurements.
        
Hrachya

On Tue, 3 Jun 2008, Jim Stewart wrote:

> 
> Hello Dan
> 
> How serious a concern do you think this is? If we reduce the gap to 40mm
> or so, there should not be that much bulging of the field. The pole shape
> is however rounded at the ends so the magnet will need mapped.  I think we
> definitely want to use the pair spectrometer to calibrate the tagger
> absolute energy so we need a good energy sum measurement.
> 
> Jim
> 
> 
> On Tue, 3 Jun 2008, Daniel Sober wrote:
> 
> > Dear Jim et al.,
> > The one disadvantage of the C-magnet is that it would require a more
> > detailed field map to precisely identify symmetric pairs for an energy
> > calibration measurement -- in case that is on anyone's agenda.
> > Dan Sober
> >
> > Jim Stewart wrote:
> > > Dear tagger
> > >
> > > While at BNL I went looking for possible magnets for the pair
> > > spectrometer. I found several which look like good candidates.
> > >
> > > The 20x42 looks to be very interesting. It is a C-Magnet with the
> > > following characteristics:
> > >  pole width  508mm
> > >  pole gap    203mm
> > >  pole length 1067mm
> > >  Max field   1.85T
> > >
> > > The gap is too large but it would be easy to add plates to the poles to
> > > reduce this. A C-Magnet has the advantage that on one side of the magnet
> > > we can measure very low momentum particles. Installing the vacuum chamber
> > > can also be done without taking the magnet apart.
> > >
> > >
> > > The 24-8-72 is an H-magnet with a field clamp and relatively wide poles.
> > >  pole width  609mm
> > >  pole gap    203mm
> > >  pole length 1829mm
> > >  Max field   1.85T
> > > To reduce the gap here you would need to add tapered plates. This could
> > > be done but requires a simulation.
> > >
> > > The 18D36 is also an H-magnet. It has a somewhat narrower pole and is more
> > > compact.  (18" wide pole and 36 inches long)
> > >
> > > They may also have power supplies for the magnets above. We would need to
> > > install new controls in any supply we got.
> > >
> > > I feel that the 20x42 is a rather good match to our needs.
> > >
> > > Please let me know what you think!
> > >
> > > Jim
> > >
> > > ------------------------------------------------------------------------
> > >
> > >
> > > ------------------------------------------------------------------------
> > >
> > >
> > > ------------------------------------------------------------------------
> > >
> >
> > --
> > /Daniel Sober
> > Professor and Chair
> > Physics Department
> > The Catholic University of America
> > Washington, DC 20064
> > Phone: (202) 319-5856, -5315
> > E-mail: sober@cua.edu/
> >
>