AUTHOR/CARETAKER: Geoffrey Krafft (krafft@jlab.org) Phone: 757-269-7557
DATE: 11/11/96
REV: 1
Ninety Degree BPM Meeting
Monday, October 28, 1996
Recorder: G. Krafft
Attendees
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P. Piot, R. Ursic, D. Kehne, G. Neil, D. Douglas,
K. Jordan, C. Bohn, J. Denard, and G. Krafft
Items of Discussion
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* The meeting was held in order to come up with an agreed upon plan
for dealing with the operational/beam physics requirement of having
some method for obtaining beam position information at the ninety
degree point in the bends. The goal of the meeting was largely
achieved.
* First, we discussed the additional cost of the button BPMs.
It was agreed that the mechanicals for the BPMs come in around 3 k.
Two complete systems are in the 10-15 k range, depending on what is
``included'' in the price.
* Denard discussed new development work that will have to be completed in
order to make the BPMs work. He showed that there would be significant
non-linearity in the readings at the +-15 mm level, a range that does not
even cover the full path length adjustment range. Significant effort (> 2
man months) will be required to calibrate, check, and develop new software
to account for the non-linearities that the BPMs will produce.
* It was reasserted again, that such BPMs would provide redundant information,
if the SLMs could be made to work. The problem was that we still do not
have a clear statement and agreement that the SLMs will work for pulsed
tuneup beam, a camera choice that works, even on paper, and what additional
stuff (e.g. attenuators for CW beam) will be needed.
* In any case, special devoted cameras, at of order 5 k a pop, will be
needed to provide the information with synchrotron light. Such cameras
will be useful for profile information and will be purchased for that
purpose independent of the position monitoring application. It is un-
known at this time whether the such cameras will have useful longevity,
given the radiation environment expected.
* Given the uncertainty in the SLMs both as to utility for the intended
application and as to operational longevity, it seems at least prudent
to have a back-up plan.
* Beam scraping, and protecting against BPM damage, if installed, was
also discussed in a very cursory way.
* It was mentioned that the BPM mechanicals should account for the fact
that the FEL will take beam energy out, meaning that tails should be
generated towards the inside of the orbit.
General Plan
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We shall take, as our primary method the SLM based system. This choice
stimulates two immediate actions (1) verify they work, and (2) plan to
check for radiation hardness.
George has the action to check camera specs against expected flux and
to try to define an appropriate camera. (Subsequently to this meeting
he suggested it might be easy to verify camera performance at low
flux levels with a HeNe and attenuators).
We will try to verify radiation hardness of the cameras in the ITS. If
they have ``good enough'' properties, (this will probably reduce to see-
ing that the camera doesn't fail during the ITS), we will use them on the
full FEL.
For the future, the minimum work that must be done now in order to have the
button BPM as a viable backup is to install the two button BPMs themselves.
This was agreed to. No additional work will be done on these systems until
it is determined that the SLMs don't work. J. Denard will ensure the
BPMs are protected against beam burn-through incidents, and that the BPM
mechanicals are adjusted appropriately to account for the low energy tail.
Yunn should bless the impedance; Denard or Bohn will make sure this happens.
I have the action to update that diagnostics control list to reflect
this plan. No future meetings on this issue are anticipated.