[Fwd: Re: Pre-collimator]

[Elliott Wolin <wolin@jlab.org>]

-------- Original Message --------
Subject: Re: Pre-collimator
Date: Wed, 31 May 2000 12:08:29 -0400
From: "Richard T. Jones" <Richard.T.Jones@uconn.edu>
Reply-To: jonesrt@uconnvm.uconn.edu
Organization: The University of Connecticut
To: Elliott Wolin <wolin@jlab.org>
CC: Elton Smith <elton@jlab.org>,Alex Dzierba
<dzierba@anthrax.physics.indiana.edu>,Curtis Meyer <cmeyer@ernest.phys.cmu.edu>

Hi Elliott,

In any case we want to collimate in stages.  In the following discussion
I distinguish three different functions that parts of the collimation system
must perform:

1) provide position feedback (active collimator)
2) define the apperture of the collimated beam (defining collimator)
3) sweep away charged particles after the defining collimator (sweeping magnet)
4) block swept charges, shield detector from defining collimator radiation
(shielding collimator)

The SLAC beam line combined (1) and (2) and called it the primary collimator.
They followed it by a sequence of two (3)-(4) sweeping magnet/collimator
arrangements with successively larger diameters.  Some things to consider in
thinking about precollimation:

a) The active collimator needs to be first because it has to sense the center of
the beam. If it is downstream of a precollimator that extracts an appreciable
amount of energy from the beam then what it will sense is not the position of
the beam but the shadow of the precoll.

b) We are going to need a substantial amount of shielding around the cave where
the 
collimators are housed, and we don't want to make it any longer than necessary
to
save on the RadCon shielding for lateral radiation (sky shine, boundary limits,
that
sort of thing).

Here the minimum legnth is set by the combination of sweeping stages we want and
the length of shielding needed to cut down the muon flux to what the detector
people
would accept.  How much room have the civil designers left us for shielding
between
the defining collimator (80m from the radiator in our design) and the start of
the
experimental hall?

Richard Jones

Elliott Wolin wrote:
> 
> Hi Richard,
> 
> RadCon thinks it's a good idea to try to pre-collimate the beam, i.e. try to
> extract as much energy from the beam as far upstream as possible.  This limits
> the radiation and background in the hall.
> 
> They suggest a pre-collimator around 10m upstream of the final collimator.
> 
> Any and all thoughts will be welcome...
> 
>                                 Sincerely,
>                                         Elliott
> 
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> 
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