# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- October 25-29, 2004

**Date:** October 29, 2004

**Highlights:**

We have made great progress this week bringing the FEL Upgrade back on
the air after the recent installation period:

\- an initial injector set-up is in place

\- the linac has been phased

> \- e-beam has been transported from the gun through the linac, first
> arc, the new wiggler, THz
>
> chicane and second arc to the beam stop in front of the re-injection
> point

\- the above machine set-up activities have been used to train three new
operators

> \- the optical transport system from the outcoupler in the FEL vault
> to the Optical Control
>
> Room is under vacuum

**Management:**

As we check-out the machine and train new operators we are using this
opportunity to review and improve all of machine operational procedures
and related documentation.

We have confirmed Dec. 16^th^ as the date for status review of the UV
FEL project with our AFRL program office. In the past few weeks, we have
made good progress in design of the UV chicane which is now modified to
deal with THz mirror heating.

On Thursday, we hosted a visit from four members of the council that
governs the American Society of Photobiology. This group is surveying
various light sources around the country for application to frontier
problems in the field.

**Commissioning (Steve Benson):**

We made good progress this week in getting beam most of the way around
the machine and roughly phasing the RF systems.  The injector is steered
up and ready for the final phasing algorithm.  We discovered this week
that we can accelerate the beam through the cryounit at two points in
injection phase.  One of them is the one we want.  The other has large
losses in the cryounit and quite ratty beam after the unit.  Of course
we first found the wrong one.  This provided good enough beam to thread
the beam to the straight ahead dump and do transient phasing on those
cavities.  Once we found the correct phase for cryounit injection, we
roughly phased the injector and carefully phased the linac.  During
linac phasing we worked to check out the diagnostics and steering in the
backleg.  We found a group of punch list items that are being fixed
today.  We should be ready to finish the MPS checkout on Monday.  At
this point most systems are functional but not signed off.  Next week
will involve system checks so that systems can be signed off.

**WBS 3 (Beam Physics):**

Work continued on UV transport layout and tuning. A draft design for the
linac-to-wiggler transport is more or less complete. Progress has been
made on the UV energy recovery transport. Moving the chicane to this
region influenced aberration control in an untoward manner, and some
effort has been required in learning to balance the various effects. In
a preliminary study, it appears that making the chicane in the vertical
plane will allow an acceptable balance of chromatic and geometric
aberrations. Dynamic chromatic acceptance appears to be 6% or better
(we\'ve simulated the recovery of an 8% wide beam), softly limited by
phase space distortion during energy recovery, in a chamber with a
physical acceptance of well over 10%. The most recent spec from the
felman (Friday AM) is  6% \"but I\'d rather have 7\". With this
chromatic configuration, noticeable geometric aberrations are induced by
the sextupoles, becoming apparent at large, but not enormous,
amplitudes. Orbit dependences to the optics will therefore become
visible as the beam is steered toward the nether regions of the chamber,
but do not appear too severe under normal operating conditions.
Investigation of these effects is ongoing.\
\
Machine operations provided training opportunities for a number of
folks, got beam through the recirculator for checkout, and once again
astounded the audience by presenting yet another longitudinal beam
dynamical marvel. During injector setup, it was observed that the beam
accelerated at multiple cryounit phases - the \"normal\" operating phase
(where the beam quality was \"good\") and phases around 180 degrees
either way  (where the beam quality was \"ratty\"). After some acrimony
(particularly by DD, who ultimately insisted on putting his fingers
\"into the wounds\", and thus now has bloody fingers), all agreed that
the off-phase acceleration was due to a conspiracy of phase slippage in
the first SRF cavity. This is readily simulated (\"the wounds\", so to
speak) by solving the equation of longitudinal motion through a 5 cell
pi-mode cavity. The nominal acceleration profile through such a cavity
is shown below in Figure 1 for an injection kinetic energy of 350 MeV
(energy in MeV vs. time in RF periods in blue, longitudinal position in
RF wavelengths vs. time in RF periods in pink; note that the energy
starts at around 861 MeV because it is *full*, not *kinetic*, energy).
Both energy and position increase monotonically to around 5 MeV/0.5 m.

Figure 1:\
![](media/image1.png){width="5.477083333333334in"
height="3.321527777777778in"}\
\
A dephased profile, with the injection time offset by \~2/3 RF period,
is shown in Figure 2. The energy (blue) initially sags to nearly the
rest energy; the beam slows down (the pink curve of z(t) showing a sag)
until the beam is well into the cavity, at which point the energy again
rises to 4 or 5 MeV. The beam arrival time at the second cavity is
delayed by an additional half RF period - so (with the initial phase
offset) it is displaced by a full RF period from the nominal timing -
*and can be accelerated by the second cavity as well!* However, because
the beam spends a prolonged time at low energy, space charge (and who
knows what other nonlinear electrodynamic effects in the SRF cavity)
severely degrades the beam quality.

Figure 2:\
\
![](media/image2.png){width="4.740277777777778in" height="2.875in"}\
\
Amongst all the other entertainment, we also (inadvertently) found it
possible to process a field emitter site off an SRF cavity. For some
months, the first injector cavity (of multiphase fame, above) has
provided a well-defined back-streaming low current electron beam when at
nominal gradient. This could be observed on the viewer upstream of the
cryounit.  As of this week, it was also observed to provide
fore-streaming field emission as well; the fore-streaming becoming
apparent only after installation of the new DESY-style viewer after the
cryounit. Using this very sensitive viewer we noted that the emission
turned on at around 6.75 MV/m. It was in fact apparent enough to the
hardware that it correlated with trips of the arc detectors; pushing the
cavity gradient up and down through this point a few times led to some
arcing and sparking which, after a few (well, okay, several) iterations
provided suppression of the emission site altogether.

**WBS 4 (Injector):**

The gun continued to deliver pulse beam for machine setup operations
during this week.

Support to the THz beamline installation continued during the week.

The Ground ring for the high voltage test stand has been polished and
ready for cleaning. Modifications (jack screws) have been made to the
top flange of the high voltage test stand for easy insertion/retraction
of the coated test tube. A second test tube is being polished to be
coated later in the W&M\'s plasma-source ion-implant chamber. Started
polishing work on the ball electrode for the second gun assembly.

The cathode coulomb counter archiver is operational. This will be a
valuable tool for cathode lifetime studies. Below is an image of the
coulomb archiver for beam run during this week. It shows all the
conditions and the totals for charge and time.

Gun HVPS - The HVPS is operational.

WBS 4 -- Fig 1

![](media/image3.jpeg){width="6.049305555555556in"
height="4.303472222222222in"}

**WBS 6 (RF):**

RF - All RF systems are operational.  

 

CHL had a planned outage this week and cryomodule FL03 was run dry of
liquid helium.  Since the cavity temperatures never exceeded 40°K, there
was no Q disease degradation.

 

The Buncher experienced low LCW flow through a filter and a sticky
control valve this week.  The filter and valve were changed and tested
today.

 

The CHL outage and recovery provided a good opportunity for training new
operators on how to recover and tune RF cavities.

 

After recovering the Quarter from arc trips, that were originally caused
by wandering beam, an emitter site was burned off.  This reduced the
radiation level from the cavity and should help preserve the
photo-cathode from back-ion bombardment.

**WBS 8 (Instrumentation):**

The week progressed with getting the machine into Operations mode. Check
off lists were compiled and completion continues of these lists for
various diagnostic, instrumentation and magnetic transport systems. The
wrong DESY type flag was installed on ITV0F04, this was changed out
today and realigned. It was good the vacuum group had time to support
this since the shield on the viewer was catching and causing this viewer
to hang up. All is good now. Additional viewer electronics (cameras,
interface boxes, etc.) were fabricated for the 0G dump, OCR shutter
solenoid, THz M1 mirror and new SLM at 4F09. The calibrations for the
beamviewers are being done. With the new calibration setup all the
different types of viewers around the machine can be properly scaled for
the beam profile data gathered with the Framegrabber. Pico motor, video
power and video were installed for the OPTS Lite mirror cans. Wiring for
the THz M2 mirror was completed and tested.\
    The first article for the User Lab Laser Safety System has arrived.
There are going to be a few things we will change for the balance of the
7 units. This one will be mounted to a heavy duty cart and be set up
with switches, motors, keys, and shutters to completely simulate a user
lab. This will be very helpful when new versions of the PLC code are
released and need to be tested without impacting operations. We also
received configuration cards for the iClass LPSS card readers (Mifare
cards). The cards worked perfectly and the reader is now in the proper
mode for LPSS use.  Working on setting up a new laptop with the
simulation tools needed to characterize the FEL (for Carlos).\
    The Machine Protection System Certification Procedure is undergoing
revisions to make it more user-friendly.  The final draft will be
checked operationally next week and then a final revision out before the
end of November.\
    The final \"tweaks\" are being done to the Analog Monitoring System
(AMS), timing, and Video distribution systems. We installed the SVGA to
NTSC video converter boxes for the two new scopes (now located remotely
in the gallery) and routed them into the video system. These are the
scopes named: FELscope01 and FELscope02. Scope01 is being dedicated for
the Happek and M55/M56 diagnostics. To this end, we have re-installed
all of the necessary cabling for these systems to operate properly,
namely: the connections through the 4Ch. Pre-Amp Chassis and into the
digitizer in iocfel8. Also, the AMS was used for the first time in
operations this week and we noted the considerable improvement in the
over-all system performance from the old system. In using the system we
also decided that the o-scope interface that is built-in to the new
scopes (felscope01 & 02) is a bit awkward. Since the ops crew has not
embraced the web interface (yet) we decided to go ahead and add a GPIB
controller to the scopes from iocfel8. This activity is in progress. Six
of the seven additional 32x32 AMS/Video Crosspoint Switcher Modules that
were being fabricated by FSI Systems have been completed and are on
their way back to the lab for testing. An additional AMS chassis has
been fabricated and checked out as ok, and is on its way to ECAAD for
documentation.\
    The Multipass BPM system is progressing. The 4 channel programmable
timing module in iocfel3 has been fully tested and is ready for initial
testing late next week under real-beam conditions. This timing module
will is synchronized to the master oscillator (/40) at 37.425MHz and
then further divides that signal down to 1.17MHz. When we run beam at a
matching micropulse frequency of 1.17MHz, the system will be able to
separate the Accelerating and Decelerating beam pulses to make
independent measurements of beam position for each.\
    We have been working to update the configuration control database
accessibility from the internet to restrict access to certain
information based on user-authentication. We will change the site to
require a valid JLAB user-login before ANY information is made
available. This change should be posted by COB today. The more time
consuming approach of having some areas public will be done as time
permits.

**WBS 10 (Wiggler):**

The wiggler viewer cameras were set up and properly focused and steered
so that optical alignment could continue.  The wiggler power supply
control code was tested with the power supplies active this week and
worked flawlessly.  The plexiglass cover is being installed today and
the Earth\'s field compensation coil will be set.  We will then be ready
for commissioning with beam next week.

**WBS 11 (Optics):**

***2.8 and 1.06 micron mirrors:\
***The 2.8 micron HR and OC mirrors are installed and their figure
checked in-situ.  After a hot nitrogen purge, we will start the ion
pumps and be ready for lasing.  No change in status for the 1.06 micron
coatings; the vendor is awaiting receipt of the specially backed
aluminum target.

 

***Other activities:\
***We continued to make great progress.  At this writing, we had
repaired wiring for position readbacks for mirrors we will use in the
near future.  We\'re installing absorber plates that will capture the
light that would otherwise be absorbed and scattered off the mirror
mounts.  (We measured the reflectivity at 10.6 microns to be 0.3%.)  We
aligned the optical transport (OTS Lite version) to the vacuum valve in
User Lab 1.  We also pumped the OTS down, and are chasing down a few
leaky connections.  Work continues on a new, fast scanning (\~ 10 Hz)
autocorrelator progresses, as does the design for the optical beam
positioning system.  We discovered the gratings for the spectrometer
that will be used for the FROG (pulseshape measurement) setup were out
of calibration, and we realigned them.

 

**Terahertz Project:**

The M2 mount was tested, and the M2 and M3 mirrors were successfully
installed. Discussions continued to define the instrumentation
requirements of the laboratory.