To: J. Cook, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IR Demo Project Weekly Report, January 26-30, 1998
Date: January 30, 1998
Management
Agenda topics for the Feb. 17-18th Navy program meeting were generated
and agreed upon. The meeting will include status report on the
installed FEL hardware; a review of the commissioning results
to date and the commissioning plans for the remainder of the year;
a status report on the upgrade activities and a discussion of
the possible outyear upgrade options.
Discussions continued with BNL on potential collaborative activities
with regard to FEL development and applications. An MOU which
covers these activities was signed by the respective light source
managers.
On Jan. 28th, F. Dylla attended the biannual meeting of the AIP
Corporate Associates Advisory Committee. Contacts were renewed
with research directors at Lucent, IBM Research, Xerox, and Ford
Research. All requested status reports on the research proposals
which are currently being prepared for the IR Demo.
On Jan. 30th, Don Swenson from Linac Systems visited the laboratory
to discuss the company's current effort to develop hardware for
RF energy recovery which is being performed under a SBIR contract
to DOE.
Installation Activities
This week the injector gun was HV processed, heat treated, and
a cathode was made and tested. A leak in the SF6 system was also
found and fixed.
Two 8 kW klystrons for the FEL cryomodule satisfactorily passed
their tests this week. They will be installed Monday. Testing
will continue to find a spare unit.
To make the injector more robust, the RF software was modified
and tested. Additional tests will be done next week when the
RF system is operated.
The CAMAC RF buffer cards were modified to allow better contact
with their mating connectors.
The collimator next to the optical cavity was repositioned this
week. The mounting of the first pellicle was modified and is being
installed today.
The first set of data for the DY, 180° bend magnet was completed
and is in review. The vacuum chambers for both DY magnets are
ready for cleaning and installation later this month.
Installation is in progress for the piping to provide LCW cooling
for the trim magnet resistors.
Equipment for the MPS is in-house and is being assembled for installation
early next week.
Commissioning Activities
The FEL cryounit and cryomodule are being cooled to 4K today.
Cooldown to 2K is anticipated to occur during day shift Monday,
2 Feb. 98. Checkout of SRF and RF in both the cryounit and cryomodule
will follow, and it appears that there is sufficient time to complete
both before 0800, 5 Feb. 98, at which time plans are to resume
FEL commissioning with electron beam. Meantime, we have made
steady progress in refurbishing the gun. High-voltage processing
and heat treatment were completed this week, and cathode preparation
commenced this morning.
The GEN target chamber is scheduled to be installed on 17 Feb. 98, at which time the FEL will be used to irradiate targets for polarization in support of the nuclear physics program. Commissioning goals for the preceding time, 5-17 Feb. 98, are:
- MUST: Develop "save/restore" machine settings for GEN runs; verify them just prior to 17 Feb. 98 shutdown.
- SHOULD: Obtain first-light beam quality in injector (~6 mm-mr @ 60 pC bunch charge).
- LIKE: Commission injector with first-light current (1.1 mA).
The shift schedule for the next three months was completed and
distributed to affected Jefferson Laboratory staff.
Installation and configuration of the Machine Protection System
(MPS) is progressing. We project that enough of the MPS will
be complete, prior to resumption of beam operations, to permit
running 1.1mA current in the injector before shutdown for GEN
target installation, and we want to keep that option open per
the aforementioned goals. Discussions about MPS set points for
the currents in the dump-line magnets have been ongoing, and a
formal meeting was held this week to decide on strategies and
inputs.
Over the past few months, Rui Li has made great progress in simulating
the beam dynamics attending coherent synchrotron radiation (CSR).
She has written a two-dimensional self-consistent code that incorporates
gaussian macroparticles and has been benchmarking it. First,
she successfully benchmarked it against analytic theory for a
rigid-line bunch propagating through a simple 90-degree dipole
magnet. Next, she compared the code's predictions to those of
DESY, which lacks self-consistency but should be accurate when
CSR is only a perturbative effect. To do so, she invoked a model
problem posed by Paul Emma at SLAC which involves a single dipole.
Predictions for CSR-induced energy spread were in agreement for
this problem, which is one where the DESY code can be validly
applied. Rui also modeled the first optical chicane in the FEL,
obtaining 2.4% emittance growth for 120 pC bunches. Interestingly,
this compares with 3% emittance growth predicted analytically
from the rigid-line bunch model accounting for transients (one
obtains roughly 10% growth if the steady-state CSR field is used,
which we had inferred to be an upper bound). The reason for agreement
is that the simulation indicates the line bunch serves as a fair
approximation to the actual bunch configuration throughout the
chicane. This will not be true, however, in the first recirculation
arc of the FEL where the bunch dynamics is quite violent. Rui
will be simulating that arc in the near future.
Presently, the basic difficulty with the macroparticle code is
that it takes a long time to run, several hours of Cray II CPU
time for the aforementioned examples, principally due to the necessary
incorporation of causality. Rui has been optimizing the code
to reduce run time, and she continues to do so.