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Summary of meeting concerning Hall D critical devices



Date:    22-may-2000, 15:00-16:00
Topic:   beamline critical devices for Hall D
Where:   Bldg 89 Conf. room A, JLAB
Who:     Jay Benesch, Kelly Mahoney, Pavel D., Elton Smith, Elliott Wolin


We met with members of the Accelerator department involved with beamline design
(J.B.), beamline personal and equipment protection systems (K.M.), and RadCon
(P.D.) concerning conceptual design of beamline safety systems for Hall D.  We
focused on how to keep the e- beam from reaching the hall, and related issues.

As this was our first meeting on beamline critical devices, a lot of time was
spent describing the Hall D beamline, working out possible failure modes, and
learning about JLab protection strategies.  

The following should be considered preliminary, part of a work in progress.  Our
goal is to have a conceptual design for the critical devices by mid-June, to be
included in our revised writeup on civil construction and beamlines.

Failure scenarios identified were:

	1. vertical beam transport fails, shooting e- beam into the sky
	2. too much current down beamline
	3. too thick radiator (e.g. a wrench) giving too many photons into the hall
	4. bad vacuum giving too high photon flux into the hall
	5. tagger magnet not operating, letting e- down the beamline
	6. bad tuning
	7. there are more!

K.Mahoney will extend the list above, taking the viewpoint of a reviewer of
beamline safety for Hall D.  Kelly needs to know how long and how intense an e-
beam in the hall is acceptable during an accident, as this drives the strategy
for choosing critical devices (e.g. how fast they must react). Pavel D. will
provide a preliminary estimate for Kelly.

Issues that came up during the discussion, somewhat random order:

1.  What kind of beam pipe will we have?  A 3 foot pipe will allow access all
along the beamline, but leaves a path for particles to get from the tagger bldg
to the collimator.  Using a buried 8 inch pipe gives no easy access to the
beamline, but provides lots of shielding for stray particles and radiation.  How
about 3 foot part of the way, and 8 inch part of the way?

2.  If we bend the e- beam that gets past the tagger into the ground, how much
bend is needed?  This partly depends on the geometry of the beamline between the
tagger and collimator (e.g. 3 foot vs 8 inch pipe).

Currently Fermilab has some 4m permanent magnets available that can bend a 12
Gev beam 1 degree.  We need to find out whether they are C or H magnets, their
cross section, etc. (E.W. will continue on this).  A new permanent magnet that
can bend a few degrees costs between approx. $75K and $200K.

3.   If the beam pipe is large, will loading it periodically with absorber keep
radiation from getting to the collimator?


Much still needs to be worked out and discussed.  I propose we have another
meeting in approx 2 weeks, to see where we are.


				Sincerely,
					Elliott
 

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