Free Electron Laser Commissioning/Diagnostic Meeting
Tuesday, September 9, 1997
Recorder: R. Legg
Next Meeting
- Date: September 16, 1997
- Time: 3:00 - 4:00
- Place: Bldg 89, Large Conference Room
Attendees
R. Legg, G. Neil, C.L.Bohn, Q.S.Shu, G. Biallas, D.Kehne, S. Benson,
G.A.Krafft, L. Merminga, P.Piot, K. Jordan, B. Yunn, R. Li, and U. Happek
Addenda/Errata to Previous Minutes
Items of Discussion
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- Uwe Happek (distinguished visitor), discussed the methodology
of the Happek bunchlength monitor. The standard Michelson interferometer
uses a beam splitter and one fixed and one adjustable mirror on
the arms of the interferometer to measure either the frequency spectrum
or the autocorrelation function of the incoming beam. The problem arises
that if one does a frequency spectrum measurement, it rolls off at
low frequencies and that the autocorrelation function is limited
by the reflection and transmission of the splitter and mirrors.
To avoid those problems we use a polarizing michelson interferometer with
twenty micron W wire screens acting as polarizing media. The technique is
also helped by the coherent nature of the light which reduces alignment
sensitivity of the device. To make the device more compact, a further
innovation where a split mirror with one half free to move reflects the light
onto a parabloid reflector which focuses it onto a detector. The amplitude
out of the detector versus the mirror position gives the bunchlength.
The device has a wide range limmited by the throw on the mirror and
a 0.2 wave # resolution, all in a very compact box. We will receive two of
the devices this month with the third to arrive later. There will also be a
programmer to help interface the device arriving in about two weeks.
- Lia talked about rf phase spec's for the injector. She explained
that she had tried to use Geoff's analysis for budgeting phase error,
but run into difficulties due to the non-relativistic nature of the
beam. Her approach at that point was to determine the transfer matrices
numerically for the rf elements and do multi-particle statistical
simulations of the system to determine the overall system sensitivity
to rf phase. The one problem is how to determine the transfer matrices
numerically, but PARMELA is the most likely method.
New Issues
- Lia and Geoff calculated as a by-product of this effort that they
thought the energy spread would be 3E-3 rather than 1e-3 due to the
phasing in the cryomodule and wanted to know if this was consistent
with Byung's model. Byung and Steve will close the loop on this issue
to assure that the accel model we are using is consistent with the FEL.
Action Items
Action Priority Items (assigned)
A-15 1 Commissioning Procedure Legg 7/16/97
A-19 0 Web Documentation weekly
A-34 2 Consistent Linac phasing plan Yunn
A-44 1,2 Start Rui, Jinhu? on emittance code Douglas 8/13/97
Action Items (pending)
P-05 1 Devise fine-tuning procedure for buncher gradient Legg
P-08 1,2 How do we change energy? What is the energy range? Benson
P-20 1 Lock plans (who in particular) Johannes?
P-21 1 Save/restore plans Benesch
P-25 1,2 RF control sensitivities/ Merminga
Microphonics Diff for FEL/
Pathlength effect
P-29 2 FEL/linac interaction Merminga
Agenda for Next Meeting
Item Person Responsible Time
---- ------------------ -----
* Review agenda/corrections to minutes Legg 5 min
* Accel/FEL consistency check Yunn 10 min
* ITS wrap-up Kehne 20 min
* New issues all 10 min
* Agenda for next meeting All 5 min