Hall D civil / update

[Elton Smith <elton@jlab.org>]

We met yesterday to review the status of civil construction since the
recent Hall D review. 

Present:
Elton Smith, Elliott Wolin, Jay Benesch, Suresh Chandra, Bob May, Pavel
Degtiarenko, Scott Schwahn,  Helmut Walter.

The Hall D Review is available on the web from http://www.jlab.org/Hall-D/
under "Report from Hall D Review Committee."

Issue raised by the review is the sufficiency of shielding against muons,
especially from the electron beam dump. 

Bob May and his group agreed to 
1. Respond to the review committee's direct concerns by decoupling the
issue of muon shielding from the elevation of the facility.
2. Check shielding against muons both inline with the beam and transverse
to it. (The transverse shielding from muons has not been addressed in any
detail to date). This will include a study of the option of putting a lot
of the muon shielding in the photon line upstream of Hall D with only a
"plug" behind the hall. This option has the advantage that the detector
itself will be shielded from muons and perhaps minimize the amount of
transverse shielding needed by stacking it closer to the source (i.e.
radiator).

Other Radiation Issues: 
1. Verify that 5 cm of concrete is adequate shielding for the Hall D
enclosure.
2. Check to see if there is adequate separation (and shielding) between
the electron beam dump and the photon beamline / Hall D.
3. What advantages are gained by bending the electron beam into the ground
(for the above-ground option) using an additional (vertical bend) magnet
after the tagger.

Note: Hall Crannell from CUA is willing to help design the beam dump,
which he has experience based on the tagger dump for Hall B.


Civil: Items to be included specifically in our plans
1. Pilings required for above-ground facility
2. Service buildings. Jay estimated that a service building 13x36 would be
required to house power supplies for dipoles and 5 racks of diagnostic
racks. Most likely the equipment would be divided into buildings. Jay will
give Suresh number, sizes and locations to pencil in on the drawings.

We should come up with approximate "equivalent" thicknessess of dirt,
iron, and perhaps lead, so that costs can be optimized for either
shielding material. These equivalences might be different depending on
which form of radiation (e.g. neutrons or photons) is dictating the amount
of thickness required.

Steel: It was noted that there is significant amount of steel in the north
accelerator stub which will have to be moved to make room for the
transport line. This steel will be available for shielding other areas.

Beamline: Jay mentioned the option for bringing the electron beam down the
photon line for diagnostic purposes. (This had been mentioned previously
in exchanges with Richard Jones.) However, presently we plan to have
permanent magnets installed in the photon line to prevent any electrons
from reaching the hall in case of failure of the tagger magnet. Therefore,
we assume that there will be NO PRIMARY ELECTRON BEAM IN HALL D (See
Design report p. 115). The accelerator must use the photon beam for
diagnostics about beam position near Hall D.




Elton Smith
Jefferson Lab
elton@jlab.org
(757) 269-7625