Transcript MEIC IR Summary

IR summary
M. Sullivan
Nov. 3, 2011
JLAB MEIC IR workshop
Basic Design
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Overall the basic design looks good
It has held up for nearly a year
The detector people seem reasonably satisfied
There are still a lot of machine studies that need
to be done to make sure this can still work
– Dynamic aperture studies
• Incorporating the detector field
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Beam-stay-clear adequate for electron injection
Polarization
Ring vacuum
Impedence
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IR magnets
• The IR magnets are reasonably placed for
the machine needs
– Can they be built?
– We had a meeting to initiate preliminary
designs
• Apertures were specified by physics needs
• Envelopes were specified by physics needs
• Strengths specified by machine needs
– Initial impression is encouraging
• The physicist engineers did not run screaming
from the room
IR Magnets (2)
• The most difficult magnets look to be the
electron final focus doublets
– Very close to the ion beam
– Must be either super-quad or permanent magnet
(inside the detector field)
– Super-quads may put too much fringe field on the ion
beam
– Fixed initial permanent magnets may be a reasonable
alternative but these would make the design a bit less
flexible and somewhat less robust
• Suggest keeping the PM option as a backup plan if superquads become too difficult
• This means that this alternative plan should also be studied
Run scenarios
• A great help here would be some information
from the detector people on possible run
scenarios
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What collision energies are envisioned?
How often do the beam energies change?
How continuous are the energy changes?
Is there a machine setting that will be the dominate
setting?
• Some possible beam energy settings together
with detector field settings
• The machine can get to the entire energy range
for each beam but we all know that the machine
performance gets better and better the longer it
runs at a particular setting
Vacuum Pressure
• This is something that needs to be
estimated
• Detector background sensitivity needs to
be checked
• First order estimate of required vacuum
and pumps needed to achieve desired
vacuum
– Program VACCALC can help here (see next
talk)
SR background
• It never hurts to review a particular background
but I ran out of time to double check the SR
background calculations I made last time I was
here
• Presently the conclusion is still the same: SR
backgrounds do not seem to be an issue
• A conservative beam tail distribution was chosen
and the central beam pipe is large
• As changes occur in the design and as
engineering constraints become known this
background needs to be rechecked to make
sure all is still well
Luminosity backgrounds
• Radiative bhabha events from the collision
will be a background for the physics in the
electron forward direction
• This is also an excellent way of measuring
the instantaneous luminosity
– This reaction was measured in PEP-II and
was used to keep the beams in maximal
collision through a position feedback at the IP
– PEP-II measured the zero degree gamma
rate
HOM Issues
• After a beam pipe design has been initially laid
out for the IR, I suggest you get an estimate of
the local impedence as well a calculation of the
overall electron ring impedence
• The present central chamber is a very nice
looking RF cavity and will no doubt capture
some of the wake field power of the electron
beam
• This is also in conjunction with estimating how
much RF will be needed to drive the electron
ring
Conclusions
• I think the IR design is converging to a
good, robust interaction region
• The design has been stable for some time
• There is always more to do
• The design looks to be flexible enough to
bend under new demands (as engineers
tell us what can and can not be done)
without breaking