# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- November 10-14, 2003

**Date:** November 14, 2003

**Highlights:**

This week we successfully tested a high voltage electrode to fields of
30 MV/m showing only minimal field emission (\<170 pA). The test
electrode used a re-vamped procedure for depositing the sili-oxynitride
coating that we have previously developed for field emission
suppression. Tighter control of electrode pre-deposition procedures and
a 2-3 times thicker coating was applied compared to our previous
attempts of applying this coating to large area electrodes. As detailed
in the WBS 4 section below, successful use of this coating on existing
and planned upgrades of the dc photogun will improve performance and
decrease conditioning time.

In the main commissioning activity we had an unfortunate setback, a
vacuum leak in an rf warm window of the first linac cryomodule which has
delayed the beam operation a week

**Commissioning:**

On Monday we analyzed the warm window heating problem on cavities 3-8 of
the first linac cryomodule that was described in last week's report.
This heating problem was preventing these cavities to be driven to their
nominal full power ("drive-high") operating conditions. Even though all
other systems including the RF performance of the injector and 2^nd^
linac cryomodule were fully recovered from the hurricane hiatus and
ready to go, we did not want to start up operations with the linac
operating below 80 MeV. Using the IR imaging system developed by Joe
Gubeli, one of the suspect windows was imaged as we ramped up the power.
As noted in one of the IR images copied below we saw excessive window
heating on the ceramic at modest input powers. Temperatures exceeded
160C with forward powers of the order of a kilowatt. Because the windows
are sealed with an In alloy that melts at 230C, the observed
temperatures were deemed excessive. From the IR images the heating
problem appears to emanate from the ceramic braze and not be symptomatic
of the bulk ceramic or anti-multipactor coating applied to the ceramic.
This information is being forwarded to the SRF Department so that IR
imaging can be incorporated in the window QA process and the possible
causes and fixes more fully analyzed.

Late Monday we decided to remove the six suspect 6 windows (windows on
cavities 1 and 2 are qualified to full drive high values). The cryomdule
was warmed up on Tuesday to a nominal 30k where the windows could be
replaced under a helium flushed clean hood environment. Using this
procedure the windows could have been replaced by Thursday, the module
re-cooled on Friday night and RF qualifications re-started by today. On
Wednesday we found that one of the window assemblies had a modest
airleak (\~10e-6 torr) into the waveguide vacuum system. This is
apparently one last remnant of the thermal cycle experienced from the
Hurricane Isabel power outage. After consultation with the SRF team and
to ensure the maximum performance of the cryomodule, we decided to
warm-up the module to room temperature to ensure complete degassing of
the air components from the waveguide vacuum system. This was started on
Wednesday and should be complete by tomorrow morning. The SRF team is
scheduled to replace and leak check the windows over the weekend. This
should allow the module to be cooled down to 4k on Monday, followed by
cooldown to 2k on Tuesday. We plan to complete the RF re-qualification
of the first module on Wednesday if all goes well, and return to the
injector set-up for beam and lasing operations.

![](media/image1.jpeg){width="5.176388888888889in"
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**Management:**

On Monday, we received a fully executed MOA from the ONR for the \$4M
scope of activities for 10 kW FEL operations and testing. We thank the
ONR program office and the DOE Site Office for pushing this important
document through the system. ONR expected to transfer the funds to DOE
by the week's end.

A viewgraph package and summary sheet for the JLab FEL program was
forwarded to Dr. Bhakta Rath, Head of the Materials Directorate at NRL
for his incorporation into a document that describes the Navy's national
research facilities.

Preparations continued for a one day review of the last six months of
progress on the UV FEL program that will be held on Nov. 25^th^ for our
AF program manager, John Eric from AFRL.

On Friday, Gwyn Williams gave the weekly Jefferson Lab accelerator
physics seminar on THz radiation generation and applications.

**WBS 4 (Injector):**

We end this week with a very gratifying result on the field emission
suppression coating tests: we have reduced the field emission current
from a coated electrode about 6000 times with respect to a previous
electrode by going with a thicker coating. A flat stainless steel
electrode, 6-in diameter was first hand-polished to 9-micron surface
finish. Then, on June 21st, it was ion-implanted and simultaneously SiO2
coated in the College of W&M\'s ion-implant plasma source, resulting in
an implant layer that suppresses field emission. On Wednesday and
Thursday of this week we tested the electrode under high voltage in the
field emission testing chamber, achieving 30 MV/m with a field emitted
current of only 170 pA average. For comparison, the highest field on the
electron gun electrode is about 12.4 MV/m. The fact that the coated
electrode was sitting on the shelf for about 5 months and performed that
good indicates a robust coating, although the coating will be analyzed
further. We estimate that the coating thickness is between 0.5 and 0.7
microns. Thickness measurements on silicon under very similar
ion-implant conditions show a deposition rate around 800 Angstroms/hour,
the electrode was processed for about 9 hours. This is twice the
processing time of a previous electrode that produced around 1 microamp
of field emission current at 30 MV/m (Dec. 2001).

Almost all of the parts for our spare dc gun electrode assembly (using
refurbished parts from the 1 kW IR Demo gun) have been fabricated. We
are in the process of dry-fitting all the parts before cleaning them
with solvents. After we complete several more tests of the field
emission suppression coating, including a test on a cylindrical
electrode to mock up the geometry of the cathode support tube, we plan
to coat the complete spare electrode assembly and test for stand-off
ability at 500 kV. We remind our readers that the achieved 350 kV
operation of the dc photogun is sufficient to meet both the current 10
kW IR and planned 100 kW demonstrations.

Operation at 500 kV is desirable to improve both high power IR and short
wavelength UV FEL performance.

**WBS 5 (SRF):**

FEL03 module assembly continues to progress well. The thermal shield
work is complete. The pressure taps on the instrumentation for the
waveguide temperature monitoring had to be extended but this is also
complete. The outer multi-layer insulation on the cold mass is about
half-way done and is expected to be completed this week or early next
week. The next step will be installation of the space frame.

**WBS 6 (RF):**

Zone 2 - A TOSP was written to allow an IR camera to view and measure
the warm window of this cryomodule while receiving RF power. Cavity 8
was tested and it was determined the warm window temperature was getting
above 160°C while still not achieving the otherwise gradient capability
of the cavity.

The warm windows for cavities 3 - 8 of zone 2 are being changed this
weekend to the previous window material. The helium is being removed
from the cryomodule and it is being warmed to room temperature. The plan
is to be back in operation by the middle of next week.

The balance of the RF is up and operational.

**WBS 8 (Instrumentation):**

    The prototype AMS/Video Upgrade crosspoint board (F0253) is fully
functional. The 32 channel inline line driver boards (F0269) are back
from the board house and are with EES being populated. Parts have been
received for the 32 channel in-line VDA board for the new video system
and fabrication is beginning on these boards. Construction of the line
driver chassis is underway and the finished system will be delivered
into operations next week.\
    Calibration of the Dump Current Monitors is complete.  Final
comparisons can be made once beam is available. The Beam Current
Cavities will be calibrated against the dump current with beam beginning
next week.\
    Fabrication of the calorimeter chassis has been completed. The
cleaned and reassembled unit was baked and is vacuum qualified to share
space with the optical cavity. It should be installed today. The final
terminations of the cables will be done Monday.\
    Commissioning of a fifth (spare) 8 channel stepper motor chassis was
completed and put into inventory. The CEBAF machine has borrowed 2 of
our OMS stepper motor VME boards. It turns out the older boards are not
compatible with the new Power PC (PPC) Input/Output Computers (IOCs)
that are replacing the older less reliable IOCs.\
    Final alignment and focusing of SLM5F02 periscope has been completed
and ready for Ops. Both the Horizontal and Vertical raster power
supplies and controller chassis\' were characterized, tested and put
back in service. Final current settings, rastering frequencies and
threshold levels will have to be set during Ops.  Fabrication of the
fourth GC power supply chassis (MGC2F09)  has been completed.\
    A bit of effort was, again, expended getting the cooldown diodes for
the SRF zone 2 recovery. Each of the FEL SRF cryomodules is unique,
hence the instrumentation, cable and connector wiring is non-standard.
In light of this and the new \'upgrade module\' coming in a month or two
the readout to EPICS for the Lake Shore cryo diodes will be redesigned.
There are 54 diodes on the next module! Many of these will be used to
address HOM damping and need reliable instrumentation. A 64 channel
minicrate with 4 channel diode driver cards in being designed to address
this need. Two crates will be needed; one for the injector and zone 2,
the other for the new 7 cell module.\
   The Optics Flipper Motor Controller circuit board deign and layout is
complete. The printed circuit boards were sent out on a 5 day turn,
they\'ll be back next mid-week. The components for them and for the
chassis are on order and expected also next week.\
  Our computer scientist attended the uClinux Seminar last week. The
focus was on such development as advanced kernel building, modules, and
drivers. He met with Phil Wilshire, of System Design and Consulting
services over the weekend to discuss the latest capabilities of uClinux
in the realm of CANS. He is the training specialist in embedded Linux
systems.\
    Progress continues on video acquisition and processing; the bad UDP
messages being received may be linked with bugs in the 3.13 version of
EPICS running as the channel access client. The bad messages were
received on multiple IOCs and occur in varying amounts of time. In a
meeting with Al Grippo today, options about changing to the 3.14 EPICS
will be discussed.\
  Electronic Documentation - an upgrade to the configuration database is
underway. The new changes will solve many of the user-interface issues
that exist with the current version as well as add a much needed file
structure and an online file folders for WBS system documentation and
files, namely the long over-due embedded code library for programmable
devices used here in our FEL. Drawings were completed for the User Lab
Micro-video camera enclosures, the 32 Channel In-Line VDA Board, the
32:32 AMS/Video Crosspoint Switcher Module Board and the Optics Flipper
Motor Controller Board. 

**WBS 9 (Beam Transport):**

***SF Sextupoles***

• Mel Gonzales of the electrical CAD group found some anomalies in the
original design that forced a re layout. We will have to revisit all the
drawings changed to date. He is now making rapid progress.

**WBS 11 (Optics):**

This week\'s work on optical and optics-related subsystems saw the
completion of a number of tasks mentioned in the last few weekly
reports.  Early in the week we vented the outcoupler (OC) vacuum vessel
and opened it to further study the vibration in the yaw plane.  While we
are within spec, we would like to passively reduce vibration wherever we
can, and the OC optics exhibit more jitter than the HR.  An extensive
set of measurements were made, and are undergoing analysis. After
conducting the vibration study, mounting fixtures that better support
the cooling tubes were added.  The pinhole leaks on the inner
circumference of the new outcoupler mirror holder were successfully
repaired, and survived a machining operation to remove the fillet that
had resulted.  It will be cleaned and nickel plated.  The first
water-cooled insertable mirror that routes FEL output to the diagnostics
suite was realigned, and we took the opportunity to install the second
insertable mirror assembly (which routes output to the diagnostic beam
dump).  The calorimeter (and both pump carts) were baked and are now
clean.  The calorimeter needed about 2 days of hot nitrogen purging
while baking to rid it of oil, but it is now clean enough and will be
installed today.  We will then pump the entire region down, and should
be able to open valves on Monday.  The ultrafast laser system that
we\'ll use to analyze the THz radiation emitted by the electron bunches
from the injector was installed and realigned.  We have verified we have
remote control of it and the synchronization electronics.

 

A report of progress and research for the UV-FEL was prepared and
transmitted to management. Drive laser lamps were replaced in
preparation for renewed operations.  A PO was issued to purchase
certified low loss (\</+ 5e-4/cm) ZnSe substrates for spare
outcouplers. 

New cooling ring for the 4\" diameter outcoupler mirror

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height="4.166666666666667in"}

Detail of the cooling line support stand

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height="2.0555555555555554in"}

**Terahertz Project:**

This week we have been working on the mirror details and have been
communicating with vendors who indicate that they can diamond turn our
ellipses in 60:61 aluminum within our original cost and time frame
estimates.  At the same time iterations have taken place with the
mechanical designs at AES.