A very rough calculation shows that a 1 mm thick mu metal (80% nickel)
2 inches in diameter will saturate at approx. 160 gauss (transverse DC
field). The Attenuation will be about 280. I believe it will depend on
the required attenuation to determine if the mu metal will work (what
is the threshold sensitivity of the PMT's to the magnetic field?).
Tim
Elton Smith wrote:
Hall D PID Mail List:
HI all,
I realized we should probably post these comments to halld-pid in case
there is other input.
Cheers, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
---------- Forwarded message ----------
Date: Mon, 16 Apr 2007 04:34:01 -0400 (EDT)
From: Elton Smith <elton@jlab.org>
To: Elke-Caroline Aschenauer <elke@jlab.org>
Cc: Matthew Shepherd <mashephe@indiana.edu>, Tim Whitlatch <whitey@jlab.org>,
Chuck Hutton <huttonc@jlab.org>, Elton Smith <elton@jlab.org>,
Alex Dzierba <dzierba@indiana.edu>
Subject: Re: TOF/FCAL Supporting Documents
Hi Elke and Matt,
We use mu-metal shields in CLAS to shield 30 G with no trouble. I can dig
up the clas notes on the subject. Going beyond that, you need multiple
layers and/or soft iron/mu-metal combinations.
Cheers, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
On Fri, 13 Apr 2007, Elke-Caroline Aschenauer wrote:
On Fri, 13 Apr 2007, Matthew Shepherd wrote:
Hi hi,
okay very quick becaue I'm on the run to the airport. I will look to the
nim paper to see some of it.
But I'm very sure that with normal mu metal you can shield max some gauss.
of course you can put really several layers around it than from layer to
layer it gets less saturated, but in generell and we have done this more
than ones for our tubes in hermes you use a soft steal shielding with a
mu-metal layer inside.
There is some more modern metal to shield tubes, which I have to find the
name again, which is advertised for medium fields.
Cheers and have a nice weekend
elke
Date: Fri, 13 Apr 2007 17:16:45 -0400
From: Matthew Shepherd <mashephe@indiana.edu>
To: Elke-Caroline Aschenauer <elke@jlab.org>
Cc: Elton Smith <elton@jlab.org>, Tim Whitlatch <whitey@jlab.org>,
Chuck Hutton <huttonc@jlab.org>, Alex Dzierba <dzierba@indiana.edu>
Subject: Re: TOF/FCAL Supporting Documents
Hi Elke,
You can find a NIM article on shielding studies done at IU several
years ago for the TOF and FCAL. (NIM A 533, 467) I didn't realize
that mu metal saturated at *that* low of a field. As far as I know
preliminary field studies show of order 100 gauss down around the
lead glass. If what you say is correct soft iron will be a
necessity. You can also find info in this paper about field strength
inside the tube as a function of distance from the tube. We would
plan this into the design -- it is also exactly what motivates the
use of light guides in the FCAL.
-Matt
On Apr 13, 2007, at 8:22 AM, Elke-Caroline Aschenauer wrote:
On Fri, 13 Apr 2007, Matthew Shepherd wrote:
Do we know what the field is because if it is bigger than 2-4 gauss
mu-metal will not do the trick. Please if shields are desiged
account for the fact that to have them really nicely working you
need to
have the shieled extentding by the tube diameter from the tube
surface.
bye elke
Date: Fri, 13 Apr 2007 08:18:23 -0400
From: Matthew Shepherd <mashephe@indiana.edu>
To: Elton Smith <elton@jlab.org>
Cc: Elke Aschenauer <elke@jlab.org>, Tim Whitlatch <whitey@jlab.org>,
Chuck Hutton <huttonc@jlab.org>, Alex Dzierba
<dzierba@indiana.edu>
Subject: Re: TOF/FCAL Supporting Documents
Hi Elton,
I don't know off the top of my head whether or not mu-metal will be
enough for the ToF. Maybe Alex can comment more since he is more
familiar with the ToF design. As far as I know magnetic field tests
were done here at IU using mu metal and soft iron together -- none
were done with mu metal alone. I would assume this means there was
an expectation to use soft iron.
To help with interference between tubes, the tubes could be placed at
an angle alternating back and forth every other bar. The soft iron
and mu metal would not have to go down to the scintillator -- it
would just need to protect the PMT area.
Again, I understand your need and urgency for an actual mechanical
drawing to vet this design and explore potential interferences. For
the last 6 months we have had no one at IU capable of doing any
drawing or mechanical design. We are currently advertising and hope
to hire someone soon.
-Matt
On Apr 13, 2007, at 7:33 AM, Elton Smith wrote:
HI Matt,
Thanks for the documentation. We are trying to get top-level
drawings for
all the subsystems and in particular we want to have a more
realistic
sketch of the light guide/pmt assembly for the tof. Are the any
space
conflicts with stacking the pmt with mu-metal shields? We were
concerned
because we thought that soft iron shields might be necessary.
Thanks, Elton.
Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
On Fri, 13 Apr 2007, Matthew Shepherd wrote:
Hi Elke and Elton,
Attached please find some supporting documents for TOF and FCAL
budget items.
FCAL:
- quote for fabrication of the PCB's for the CW bases
- quote for assembly of *electrical* portion of CW base
- quote for sheets of Sylgard for optical coupling of light
guides to
PMT
On the last item: this quote is mainly proof of principle that
we can
get costs down to ~$1 per cookie. (In small quantities we paid $20
each so there was great concern as to whether or not using a
commercially manufactured cookie was even possible.) It gets
lumped
in with light guide costs in the budget. Sergey has estimated $20K
total to produce aluminized light pipes.
TOF:
- quote for XP2020 tubes, bases and mu metal shields
- quote for scintillator
- quote for cables
-Matt
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