Free Electron Laser Commissioning/Diagnostic Meeting
Tuesday, April 30, 1996
Recorder: G. Krafft
Next Meeting
- Date: May 7, 1996
- Time: 3:00 - 4:00
- Place: Test Lab Conference Room
Attendees
K. Jordan, J. Denard, C. Bohn, D. Douglas, L. Merminga, G. Neil,
S. Benson, D. Kehne, and G. Krafft
Items of Discussion
There were no changes to the minutes. Douglas began the discussion by
outlining some updates to the optics of the main machine that will have
to be made because fringe fields were not done correctly in the 180 deg
bends. There was some sort of double counting of the effects of dipole
fringe fields. The bottom line is that the optics in the reverse bends
will
have to be changed somewhat. He is working to get these issues
resolved.
Action Items
- A-01 Two updates to the machine were proposed and discussed. The first
addition was to make the the dipole that merges the injector beam onto the linac
have
reversible polarity. This would allow the injector tuneup dump to be
located in a more convenient location, and perhaps increase the emittance or
energy spread measurment precision. It was generally agreed that this was a
good idea. Benson is to coordinate this request with Bialas, with the
commissioning group's
blessing. It was noted however, that this region is not entirely
designed from an optics point of view, and will probably be changed a bit when that
final design is done.
- The second proposed change was to beef up the dipole on
the downstream end of the cryomodule that directs the beam into the 10 MeV dump
in recirculation mode. The idea is to be able to crest the 42 MeV beam
in that dump. There is a clear advantage to crest early after the cryomodule,
but given the chicane is nearby, it was not so clear that this proposal buys us
much. It seems that the original plan with a quad just downstream of the chicane
in the bypass is a better solution (I verified that this was Legg's opinion
too!), because of the potentially higher dispersion. I believe that the general
feeling from the meeting was that if the addition was easy, go ahead and get
it, but if not, we are covered with what we got. Krafft will contact Harwood on
this one.
From three weeks ago, the magnet choice for the ITS was made. Thanks to
Kehne and Harwood for getting this done.
- A-03 No documentation confirmation as of 4/9/96.
- A-17 A large portion of the meeting was spent discussing, and adding to J.
Denard's requirements table for the BPMs. The additions have to do with the
performance requirements for the SEE BPMs that will be added in the wiggler region,
mainly to help define the beam orbit giving the maximum gain, and allowing us
to rereprodicibly achieve that orbit. These BPMs will be the primary data
source for a slow lock that will hold the beam in a constant orbit (to order 20
micrometers) in the wiggler. Several related but not decidable issues were brought
up as a result of this discussion.
- The first issue was what the update rate for
the BPMs should be. It was asserted that an update rate of at least 3 Hz is
needed to facilite commissioning, and in response, it was asserted that the 3 Hz update
rate was not really an issue of the BPMs but and issue of permissible
beam loss in tuneup mode. No resolution of the issue was forthcoming, and it was
agreed that tentatively 1 Hz will stay in the requirements, but an off-line
discussion involving Douglas, Jordan, Krafft, Bohn, and Neil will try to find a mutually
acceptable tuneup mode pulse structure.
- Once that's done, and Lia is happy about
the beam loading, we will update the BPM requirements as needed. However, all
other requirements as stated on the document were approved by those present.
Denard will distribute his almost final version this week. A question arose
whether the having more SEEs near the wiggler, perhaps for example to more
precisely measure the incident angle of the beam in the wiggler, might facilitate laser
commissioning. There was no clear resolution of this question, and it is added to the
pending list. The decission to buy at least 3 SEEs ((2) for wiggler and 1 spare) was
generally agreed to.
- The final issue regarding the BPMs discussed had to do with
the beamline hardware. Denard expressed reservations about heating of the
electrodes by beam loss, and proposed to recess the electrodes in order to reduce
potential loss. He wished to hear that the impedance change would be OK, and he was
assured that given our budget, that would probably be fine. However, he was
criticized for his general conception that beam loss could be shielded by recessing the
electrodes. In view of a reviewer suggestion that one could more or less expect that at some time
the beam would hit the BPM electrodes, after much discussion it was
agreed that the BPMs should be designed robustly enough that the full beam power in
tuneup mode should not cause problems. (This is of order 200 W beam power) At
least one of the meeting participant were dubious about shadowing the electrodes
from the beam. Denard was not sure at this point that this could be done, but
will report back later.
- Some new items were added to the pending list as a result of the
review. The only one that ellicited serious comment was the beam scraping plan.
Albertine had apparently mentioned this problem again to Bohn in a conversation.
Lia mentioned that she had worked on scraping at SLAC. After other
discussions on some of the other items (see below) it was agreed that sometime in
the next two weeks Lia would present a plan outlining her contributions to
these issues over the summer. Krafft and Bohn volunteered to start thinking
about What If studies. G. Neil volunteered to handle the suggested FEL
commissioning review. He requested an example of an ``acceptable'' plan, and Krafft
voluteered to try to find an old commissioning plan for the main machine.
Finally, Douglas expressed reservations about the magnet specification
process, especially given the relative newness of some of his designs. He was
worried that good information would not be used to specify magnets, only
engineering judgement. After much discussion, it was agreed that Douglas, Bohn,
Harwood, Bialas, Jordan, and Krafft would meet on Monday to try to find some
mutually
acceptable solution.
First Cut List of Commissioning Tasks
C-1 RF gradients verified
C-2 Operational RF phases determined
C-3 Drifts (of phases if like main machine) quantified
C-4 Gun current verified/operational procedure complete
C-5 Beam jitters determined
C-6 Cryounit Focussing/Convergence determined
C-7 High power CW beam is delivered for ``awhile''
C-8 Cathode lifetime studied
C-9 Engwall/Kehne studies on gun transverse/longitudinal emittance complete
C-10 PARMELA ``verified''
After the move to the FEL building the following tasks must be completed
to prepare the beam for injection into the linac.
C-11 Transverse phase space at injection verified
C-12 E-beam matched at injection point
C-13 Longitudinal phase space verified
C-14 Longitudinal tilt checked at injection
C-15 Above determined at high power
At this point C. Bohn emphasized again that some kind of scheduling with the
SRF group will be necessary in order to run efficiently during the test stand
commissioning, as cryo-commissioning and beam running are best done not in
parallel. This item has been added to the pending list.
Action Items (assigned)
A-01 Update Drawing Bohn 4/16/96
A-03 Stray fields in test stand Legg complete
A-04 Unit gradient precision Bohn, Liu 4/16/96
A-05 Injector energy precision Douglas 4/09/96
A-06 10 MeV dump optics Douglas 5/14/96
A-07 Bypass optics Douglas 4/30/96
A-08 M56/RF phasing and beam load issues Neil, Douglas, Liu
A-09 Dump Instrumentation Legg 5/23/96
A-10 Back leg diagnostic placement Douglas 5/30/96
A-11 Multifrequency CSR Measurements Krafft 4/30/96
A-12 How should the path length be checked? Krafft, Jordan 4/30/96
A-13 Impedance Layout for Wiggler Yunn, Neil complete
A-14 Reduce M56 to under 30 cm Douglas complete
A-15 Commissioning Procedure Legg, Krafft 5/16/96
A-16 Average Current Measurement Legg
A-17 4-Channel BPM on the IRFEL Bohn, Denard 4/30/96
A-18 Trombones Douglas, Krafft 4/09/96
A-19 Experiment Plans, 10 MeV line, etc. Kehne 4/09/96
A-20 Flip viewer Kehne 5/07/96
Action Items (pending)
P-01 Determine Beam Pulse structure for setup
P-02 Laser phase modulator
P-03 Slit emittance measurement
P-04 Is an energy compression scheme needed?
P-05 Devise fine-tuning procedure for buncher gradient
P-06 Web Documentation
P-07 Diagnostics "Freeze"
P-08 How do we change energy? What is the energy range?
P-09 Do we need bunching after the module
P-10 Will the SLM monitor work to center the large beam
P-11 Calculate from Hall C data how much scatter the BPMs can take
P-12 FEL/OTR interaction question
P-13 Do we have sufficient diagnostics for emittance degradation measurements
P-14 How is the gun/laser operated?
P-15 Discussion on robustness of controls??????
P-16 Injector diagnostics in the main machine
P-17 Gang of power supply for backleg quads
(must include emittance meas. capability)
P-18 Technote by Yunn summarizing machine impedance
P-19 Consistent linac/bunching phase sets
P-20 Lock plans (who in particular)
P-21 Save/restore plans
P-22 FSD plans
P-23 Transverse Effects in CSR
P-24 FEL Commissioning review
P-25 RF control sensitivities/Microphonics Diff for FEL/Pathlength effect
P-26 What if studies
P-27 Plan to measure beam loss
P-28 Scrapers: Where and How?
P-29 FEL/linac interaction
P-30 Tracking including realistic wiggler fields
P-31 What drives the vacuum spec.
P-32 Are two sextupole families enough to tune M56
P-33 Is path length feedback needed?
P-34 More than two SEEs in wiggler
P-35 Coordinated ITS beam running/SRF commissioning plan
P-36 Beam power robust BPMs
Agenda for Next Meeting
Item Person Responsible Time
---- ------------------ ----
* Review agenda/corrections to minutes Krafft 5 min.
* New drawing Bohn 5 min.
* New issues
Wiggler instrumentation and planning Neil
Dipole gang power scheme Krafft
Requirements and reviews for diagnostics Jordan
Flip viewer
Shielded viewers as bolt-in upgrades of regular viewers
Overpower dipole after cryomodule; a microdump?
Asses need for faraday cup
Special OTR viewers in optical chicane
Powering of back-leg magnets
* BPM requirements Denard 10 min.
* Task List Discussions All 30 min.
* Unit Gradient Precision Bohn, Liu 10 min.
* Agenda for next meeting All 5 min.