To: J. Cook, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IR Demo Project Weekly Report, February 17-20, 1998
Date: February 20, 1998
Management
Highlights of the week include: (1) diagnosis
of our gun problem; (2) installation of the first 180 degree
bend magnet; and (3) further progress on the optical cavity final
assembly/alignment.
On Feb. 17-18th, the laboratory hosted a project
status meeting on the FEL for the Navy program office. The meeting
was attended by representatives of the Navy, from the Naval Postgraduate
School (NPS), the DOE-BES program office and the DOE Site Office.
Bill Colson from the NPS reported on modelling work that he has
been doing with his students on the proposed 3-cryomodule, 20
kW upgrade to the baseline IR Demo.
On Friday, Feb. 20 three staff scientists
from the NASA Langley Research Center visited the FEL project
to discuss possible experiments in gas dynamics.
Installation Activities
The first DY, 180° bend, magnet was placed
on its mounts in the 3F region. Its vacuum chamber is being instrumented
and will be ready for installation next week.
A shield block was mounted on each of the
insertable dumps in the 4F region.
The installation of an independent Laser Safety
System (LSS) for User Lab Room 6 was finished this week for use
by the Saclay nuclear physics group to test a class 4 laser.
It uses a smart card to gain access to the room. Since the FEL
laser is not being used, it will not be tied into the FEL system.
The key switch for the gun's high voltage
power supply was functionally tested and added to the PSS. This
is to disable the gun power supply during alignment of the drive
laser to the gun cathode.
Trial mirrors for the optical cavity and the
collimator mirrors were installed. The upstream pellicle was
tested and is fully operational.
The high power optical train is instrumented
and operational.
Additional testing of the RF HOM filters and
the cavity Q's was done this week. Miram curves for all the klystrons
are scheduled for this evening.
FEL Commissioning Activities
Regarding refurbishment of the gun, we are polishing the cathode
ball to remove minor blemishes. We designed a stainless steel
shield for the getter pumps and are having it machined. The shield
will protect the pumps and hopefully reduce impurities in the
high-voltage region. Evidence is that the cathode was tilted
about 2 mrad in our last run. A decision whether to straighten
the tilt involves trading the benefit of easier drive-laser alignment
given the design of the light box against the cost of risking
damage to the braze and/or weld on the stalk in the process of
straightening it. Alignment tolerances have not yet been measured.
Accordingly, a "gun alignment plan" was formulated
with the trades in mind: (1) measure the tolerances, (2) do not
straighten the stalk; instead, install it as it was in the previous
successful run, (3) fabricate a spare stalk and install it during
the next refurbishment, if necessary.
Development of optimized PARMELA settings for 60 pC first-light
beam is nearly complete. The package includes images at the various
viewer locations. It may turn out that the 60 pC settings may
be just as useful, if not more useful, than the 135 pC settings
for experiments on coherent synchrotron radiation (CSR). CSR-induced
emittance growth should scale roughly as (bunch charge)/(bunch
length)^(4/3). Compared to the 135 pC case, the bunch charge
is slightly less than half, but with the optimized settings, the
bunch lengths in the wiggler region are also roughly half. We
will give the matter further consideration before drawing conclusions.
A strawman plan for configuration control was formulated. The underlying assumption is that, based on the early February finding of round beam after the cryounit, we should be able to proceed systematically through machine setup. The basic idea is to input an initial save/restore file with optimal 60 pC machine settings based on PARMELA, check resulting beam properties along the machine, and pursue parametric studies, if necessary, starting in the injector. Configuration control involves guarding the baseline save/restore file as well as the process by which it is updated. One would hope that, since space-charge is important mostly only in the injector, once the injector setup is accomplished, the rest of the machine will follow easily. Time will tell.