Re: question on pair spectrometer shielding

[Alexander Somov <somov@jlab.org>]

Richard,

The coils will still present some material around the pole though not
as much as iron. There are two tapered lead collimators inserted in this
region; most scattering will proceed on them anyway (two lead bricks
placed right after the magnet should absorb most bg punched through
the poles).

Cheers,
       Alex



On Mon, 23 Mar 2009, Richard Jones wrote:

> Alex,
>
> Aha, ok.  Those arc-shaped plates shown in the assembly drawing attached to 
> the ends of the yoke are actually the cover plates for the coils.  At the end 
> of the magnet, the coils bend up/down away from the gap and wrap up over the 
> yoke to connect across the front and back of the cores.  The only iron in 
> those is a 1/2" steel plate that serves as a cover and support for the return 
> arcs of the coils.  I will modify the geometry to better represent the inner 
> PS geometry.  Thanks for the explanation.  When I first saw it I thought 
> perhaps you had added additional iron there for shielding purposes.
>
> -Richard Jones
>
>
> Alexander Somov wrote:
>> 
>> Hello Richard,
>> 
>> Sorry, I understand what you have asked now :)
>> 
>> Here is how I simulated the magnet and the vacuum
>> chamber:
>> 
>> According to the magnet specification, a nominal effective
>> length of the magnet is 72'' ( 1.83 m). However, there is
>> an additional 7'' plate attached to the side of the magnet
>> (of course this plate would change the field on the edge).
>> 
>> PS hodoscope counters should be installed 1.5 m from the
>> effective field. Sizes and positions of the counters are choosen
>> according to  1.64 T field, 1.83 nominal effective length of
>> the magnet, and 1.5 m fly distance from the magnet.
>> 
>> -----------
>> 
>> In the simulation I assumed that the magnet consists of two
>> pieces:
>>         - 1.83 m long piece with a magnetic field
>>         - 17.8 cm piece without the field
>>          (used to simulate more realistically scattering on the
>>          magnet's aperture)
>> 
>> Of course the magnetic field map has to be simulated.
>> I just put in a model into geometry.
>> 
>> The magnet is followed by a 150 - 17.8 = 132.2 cm long
>> vacuum chamber, so that the counters are positioned 1.5 m
>> away from the magnet's effective field.
>> 
>> 
>> Cheers,
>>        Alex
>> 
>> 
>
>