Report on 16-Jun-2000 Hall D Meetings at JLab

[Elliott Wolin <wolin@jlab.org>]

	    Report on 16-Jun-2000 Hall D Meetings at JLab
	    ---------------------------------------------

					Elliott Wolin
					20-Jun-2000



Purpose
-------

A large group met to discuss civil and safety related issues for the
new CDR.  A smaller group met afterwards to work out a preliminary
beam safety design.


Present
-------

Lew Keller (consultant from SLAC), Kelly Mahoney (Safety), Lee Harwood
(head of 12 Gev upgrade), Pavel D. (Radcon), Jay Benesch
(Accelerator), John Domingo (official Kibbutzer and jack of all
trades), Richard Jones, Elton Smith, and Elliott Wolin.


Summary
-------

The first (two hour) meeting was very productive, as we came to
agreement on a number of important safety and civil issues.  Pavel
will perform more refined radiation dose calculations over the next
two weeks to clarify a number of items.

Lew, Elton, and I met afterwards and worked out a preliminary beam
safety design that we will submit to the JLab Safety and Accelerator
groups for comment.  Lew produced a document describing our proposed
strategy.

Below I summarize the highlights of the two meetings. Referenced below
is Lew's report on beam safety design.  Pavel is looking into many of
the questions listed below.  Also referenced below is Lew's report on
muon rate calculations.


Highlights
----------

What should we use for the maximum beam power during an accident?  All
work to date has used 60 kW for 1 sec. The accelerator can deliver 1 MW
to Hall D by mistake.  (Note that the maximum short-term dose rate is
15 Rad/hr for 1 sec, and that typical safety systems can turn the beam
off at the source in 0.1 sec).  Many existing areas at JLab do not
meet the 1 MW requirement.

The strategy we'll follow is to account for single failures, but not
for multiple failures (e.g. too much beam sent to the hall AND failure
of tagger magnet interlocks).  Thus the electron dump should be sized
for a 1 MW incident, 60 kW continuous, everything else can be sized
for 60 kW.

All agreed that using permanent magnets in the beamline safety system
makes sense (I'm in the process of getting 3 magnets from Fermilab
right now...EJW).

1 m x 1 m x 10 m electron dump shielding minimum is required for 60
kW.  Not sure what's needed for 1 MW for 1 sec.  Detailed calculations
have been done for the 120 kW BSY dump [ref 1], which has 1 m thick
concrete walls.

The lab has a lot of small green shielding blocks (solid Fe).  We need
more of the larger ones (I'm working on this...EJW).

The collimator generates 1.2e-9 muons/electron for 1.e-4 radiator and
5 m x 1.5 m Fe (concrete?) in collimator.  We should get 1.4 kHz in 4
m diameter at the end of the hall for 3 microamps, and many will miss
the photon dump (4.e-4 mRad/hr at wall).  Most muons are a few gev
[some of the above still needs to be checked].

5 m Fe plus dirt cover should be adequate for the photon dump.  There
should be a 1' x 1' x 3' tunnel at the front of the dump so that the
hall is shielded from radiation coming back from the dump itself.

So far hall dose rates assume no shielding around the target.  Now
that all the gaps in the magnet will filled with iron, can we assume
the target will always be shielded?  Without shielding we need 10 cm
thick concrete walls and ceiling.  We may not need any concrete if the
target is shielded.  Note: typical radiation levels in Hall A during
routine operation (dumping 10 W in the target) is 1 mrem/hr.

The maximum boundary dose must account for all sources in the hall.

We probably don't need additional service buildings beyond the two
Accelerator has already specified [need to check with Omar Garza?].

A local radioactive water cooling system is needed in the electron
dump.  This can fit on a 2 m x 3 m skid.  Does this need to be next
to the dump, or can it be above ground in the entrance?

The lab may locate a new satellite refrigerator building (IBM 4k
HELIOS system) near Hall D.  If it doesn't appear, the cryo line will
run along the beam line.

We need an estimate for the dose rate in the counting house (Pavel).

No one knows why we need access to the beam pipe between the tagger
and the collimator, so we'll probably use a buried 4" or 6" beam
pipe.  There should be beam monitors at each end.

Have to account for H2 creation in high-power water-cooled dumps.

We (Pavel) need to study the flux coming back to the tagger from the
electron dump.  Lew estimated 10e9 photons/sec for 5 cm pipe, 20 m
away, and 5.e7 neutrons/sec.  We later increased the distance to 40
m.  If there's a problem we can increase the distance again and/or add
a bend in the pipe.


Proposed beamline safety system
-------------------------------

See note number 32 in http://www.phys.cmu.edu/halld/notes_main.html

Some of the devices in the note are commonly used at SLAC, but not at
JLab. JLab can either develop/borrow this technology, or propose
substitutes.


Lew's muon rate calculations
----------------------------

See note number 33 in http://www.phys.cmu.edu/halld/notes_main.html



Ref 1
----- 
Memo: Pavel to May, Stapleton (May 1997), and CEBAF-TN-93-003 Tech
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