To: J. Cook, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IR Demo Project Weekly Report, April 26 - May 1, 1998
Date: May 1, 1998
FEL Management
This week was again devoted to commissioning activities except
for one shift of scheduled maintenance on Tuesday and a shift
on Friday with controlled access to the accelerator vault to allow
adjustments of the Beam Positioning Monitors (BPMs). The basic
highlight of the week was establishing a baseline machine setup
for which the electron beam is centered through all of the beam-transport
magnets. This setup constitutes the starting point from which
the electron beam will be fine-tuned for lasing. A summary of
the process currently envisioned is given in the Commissioning
section below.
On Tuesday, April 22, a contingent of accelerator physicists,
materials scientists and RF engineers from the Advanced Photon
Source (ANL) visited the Laboratory to tour the FEL Facility and
the Test Lab and to discuss the application of SRF linear accelerators
to FELs. Final preparations were made this week for the May 4th
Dedication of the Applied Research Center (ARC) building on the
Jefferson Lab campus. The Director's Office and the FEL management
organized a large poster session which will be displayed on the
ARC building during the month of May to highlight research and
development activities to be performed in the building by Jefferson
Lab technical staff and the faculty and students from the ARC
University Consortium. Much of the equipment which will be installed
in the ARC building over the next year will benefit FEL users.
May 1 is the deadline for submission of abstracts to the FEL 1998
Symposium which will be hosted by the Lab during August. Nine
abstracts have been submitted by members of the FEL team.
Installation Activities
The DG and DF µ-metal corrector magnets are measured, signed
off, and ready for installation next week.
The last DY 180° bend magnet was measured and signed off.
It is ready for final assembly with its vacuum chamber. Installation
will be later as the operating schedule allows.
The DC µ metal corrector magnets were measured and found
to be out of specifications. They will be modeled to resolve
the problems.
A good 3-D model of the SC sextupole magnet with a special pole
tip has been verified by measurements. Work continues to lower
harmonics.
Due to space limitations, the remaining 3 SQ skew quads will be
individually fabricated.
In mirror can 6, the mirror was replaced and 1 picomotor was installed.
A Convectron was hooked to the FEL transport line and the line
was pumped down.
The insertable mirror and all FEL diagnostic beam lines in optics
control were installed. In the optical cavity, the mirror gimbals
were locked.
The installation of a CARM for the wiggler area was completed
and the unit is being calibrated.
Commissioning
This week was devoted principally to fine-tuning the electron
beam as part of preparing for lasing, and to miscellaneous measurements
of beam quality, with cw runs interspersed to exercise the machine
and gather more data on cathode lifetime. At week's end, we had
a machine setup for which the electron beam is centered through
all of the beam-transport magnets. There is considerable horizontal-vertical
coupling out of the cryomodule, and so we need to install skew
quadrupoles at both ends of the cryomodule to cancel out the coupling.
A consequence of the coupling is that the beam rotates through
the wiggler region so that there is scraping on the narrow wiggler
vacuum chamber of a magnitude that prohibits cw runs with this
setup. Once the skew quads are in, this should no longer be a
problem. They are already in fabrication and are slated to be
installed Tuesday, 5 May, which is the next maintenance day.
On the positive side, results of difference-orbit measurements
taken this week are entirely consistent with model predictions.
Thus far the machine settings generally remain stable as long
as its hardware is not modified. To do the cw runs we used the
machine settings from late last week. They permit high average
current but are not well suited to be used as baseline settings
for lasing.
Multislit #2, located at the input to the cryomodule, was found
to be rotationally misaligned. Its alignment was corrected, and
one can now see a small number of slits in both the horizontal
and vertical directions. An earnest attempt to take data with
Multislit #2 has not yet been made due to a bug in the user-interface
code that is in process of being corrected. The beam at Multislit
#1, located at the exit of the cryounit, tends to be too small
to submit to accurate measurements of emittance. Indications
now are that the machine setup we are fine-tuning provides emittances
at Multislit #1 in the range 4-6 mm-mrad, versus the PARMELA prediction
of 3.5 mm-mrad. We need to devise a procedure that involves an
off-nominal setting of the quadrupole magnet immediately preceding
the diagnostic.
The zero-phasing technique to measure bunch length was further
refined this week, and at week's end was limited by scraping at
the low-energy edge of the bunch during transport of the beam
through the machine to the energy-recovery dump that is used as
part of the measurement, a circumstance that needs to be rectified.
The quad/viewer measurement of emittance at the wiggler location
was also further refined but still needs more work. Presently
multimonitor data suggest, at the wiggler, an emittance of 7.0±3.5
mm-mrad in the horizontal direction, with the vertical direction
still uncertain. We are trying for <8.7 mm-mrad for first
light. This initial data is rough and in need of refinement before
it can be taken seriously, but it is nonetheless encouraging.
The much-awaited visit of Prof. Uwe Happek and crew from the University
of Georgia to install and commission their interferometric bunch-length
monitors is now scheduled for 7-13 May 98.
Next week the basic program is to do orbit optimization during day shifts and beam diagnostics/beam quality measurements during swing and owl shifts. The following week is devoted to continued beam optimization during day shifts, with cw running during swing shifts and beam-quality measurements during owl shifts. The goal is to be able to insert the wiggler in mid-to-late May and try to lase. It is an optimistic goal, but one that seems to be within reach.