**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- February 14-18, 2005

**Date:** February 18, 2005

**Highlights:**

Effort this week concentrated in two major areas:  installing high power
1 micron and broadband mirrors and recovering operation of the middle
cryomodule by warming it to room temperature.  A leak was found in a rf
window braze on cavity 4.  It is impractical to replace it in situ so we
are taking that cavity off-line for now and will raise the gradient in
the other cavities to compensate. We are cooling the module back down
today and plan on re-establishing rf operation over the holiday weekend.

We have placed with STI the purchase requisition for the gap mechanism
for the PM wiggler.

We also put the PR in the system for 80 kW IOTs to power the AES
cryounit in the injector test stand.  An advance copy of the spec is
already on the street.

**Management:**

ONR has signed and delivered to DoE the 3-year MOA for JLab operations
and maintenance activities.  

We have received the signed MIPR THz contract from the Army NVL and are
in the process of completing the Work for Others subcontract with AES
for their activity.

We released the January monthly JTO reports.

**WBS 3 Beam Physics** (David Douglas):

Absent actual electrons, we contemplated the problem of recovering a
high current beam in a small space for the next version FEL. Several
notions floated up \[deranged ravings qualified by square brackets\]:

1\. It is likely that a high-power driver\'s footprint will be defined
by optical cavity and accelerator, not transport system. This is because
a) you can\'t make the machine shorter than the linac, and b) if the
optical cavity is not much longer than the linac, and you have to get
the electron beam into and out of the optical cavity, it\'ll take a
additional little space to do that as well.

> 2\. As working parameters \[we asked some people that will remain
> nameless but have actually built this kind of stuff, gotten it to work
> to spec, and therefore qualify in our sick little mind as reliable
> sources\], we have adopted a linac length of 11 m and an optical
> cavity length of 16 m. With these numbers, there\'s really not space
> to bring the beam around from the linac to a symmetrically located
> optical cavity without embedding the cavity in a much longer transport
> system (as in the IR Demo or the IR Upgrade, as opposed to embedding
> the transport system within the cavity footprint, as in the UV
> upgrade).
>
> 3\. You need to bend RIGHT after the wiggler. Or, as a novel
> alternative technology, you can splatter THz radiation all over the
> downstream end of the optical cavity if you want, but you\'ll be
> really unhappy in that case. So plan on bending RIGHT after the
> wiggler.
>
> 4\. This suggests the machine might best be \[oh no, I\'ve been
> absorbed by the south! I see kudzu everywhere\...\] asymmetric, with
> the energy recovery transport starting with a right stout deflection
> \[more kudzu\] IMMEDIATELY after the wiggler so as to direct the THz
> away from the downstream mirror from as far away as possible (but,
> after all, you can\'t get farther away than the wiggler, at least not
> without a negative length drift).
>
> 5\. After an extensive study \[consisting of an evening with the
> laptop while watching CSI reruns and killing a bottle of Chateau St.
> Jean chardonnay (hey, it's the south. It was that or Jack Daniels. We
> make do. If you want me to drink better wine, get me a job someplace
> that makes better wine or at least imports better wine\...)\], we have
> concluded that a viable energy recovery solution might be derived
> through use of a THz deflection chicane followed by a simple mirror
> bend. As the mirror bend compaction is completely linear, the RF
> curvature correction is imposed by the chicane T_566; the mirror radii
> are then selected to compensate the M_56. By juggling the various free
> parameters of chicane angle, spacing, and bend radii (chicane and
> mirror), you seem to be able to get to a place in parameter space with
> appropriate longitudinal properties (at least to second order, which
> may be enough at 750 MHz) and transverse properties that are not
> totally untoward.
>
> 6\. We have djinned up a notional design based on this concept. It is
> quite compact (figure 1). The business end of the optical cavity would
> hang past the end of the machine by 4 m or more (for our assumed 16 m
> cavity), and there\'d likely be space back upstream to do all sorts of
> matching, reflecting, rotating, and avoiding of other ends of the
> optical cavity. By playing with the chicane radii, angle, and spacing,
> we controlled the T566 and the focusing properties. By playing with
> the mirror bend radii, we control the M56 in a parametric region with
> rational transverse behavior. By messing with chicane and mirror
> external pole faces (ones at dispersion free points) we fine-tune the
> betatron behavior through the system \[okay, okay, theres a skinny
> little quad between the chicane and the mirror. I thought I had gotten
> it out of there, but turns out I left in a bit of it. I\'m working on
> it. So sue me\]. The final edge of the last dipole and a quad triplet
> are used to match to reinjection envelopes appropriate for energy
> recovery through a 100 MeV/750 MHz accelerator. Figure 2 shows the
> beam envelopes; they\'re not wild. The chromatic behavior is most
> charitably characterized as \"maybe not fatal\" but needs some work,
> though if you believe the hole is big in the linac it might fit\...
>
> 7\. Machines of this ilk are NOT going to be very flexible. So, if
> some real bright FEL weenie decides - \"oh, gee, this other Rayleigh
> range with attendant different betatron match looks waaaayyyyy better
> and by the way I wanna use this other wiggler\" half way through
> construction - TOO BAD. You get what you get, and if you build it
> right, you might even get it. But you\'re not going to be able to
> change it once you start cutting metal, and you need to know pretty
> much what it's going to be before you start doing the transport system
> design. So speak now, or forever hold your peace. And plan on building
> the dipoles with pole faces you can machine after the fact. Because
> you\'ll want to.

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On the topic of general studies of the IR and UV machines: Max and Kevin
have made considerable progress on the Elegant model of the IR system.
Once this is running, we\'ll merge the UV into it and start examining
the modeled performance of both sides of the machine.

**WBS 4 (Injector):**

It has been exactly two months without the need to re-cesiate the
cathode since it was made back in December 17, 2004. This cathode has
delivered over 425 Coulombs at

135 pC/bunch (at least) of CW (typically 5-6 mA) and pulse beam for FEL
ops since then. The previous cathode also lasted two months without a
re-cesiation, but delivered only around 50 Coulombs. I remind our
readers that a new cathode is made without need to break vacuum (a new
cathode is made on the same GaAs wafer each time by heating the wafer in
vacuum, removing the old Cs layer, and depositing a new one).\
A flat electrode coated in the W&M\'s plasma chamber has been coated and
mounted in our high voltage test stand (125 kV) for testing. The high
voltage test stand chamber is being baked. The electrode will be tested
under voltage next week.\
The drawings for the new-concept segmented tube that supports the ball
cathode on the second gun assembly have been signed-off. It was decided
to cut the ball cathode support tube in three sections to eliminate
arcing during the plasma-deposition of the field emission suppression
coating. The original one-piece tube (about 34inches long) suffered
unipolar arcing in the transition region from plasma to vacuum during
the processing. By cutting the tube, each piece will fit entirely inside
the plasma.\
The ball cathode for our second gun assembly is being mounted today in
the W&M\'s plasma chamber. The ball will be coated in two 8 hr-long runs
(bottom first, then top) next week.\
PARMELA modeling of the UV injector (operating at 7 MeV) for 67 pC/bunch
is in progress.

Gun HVPS - is fully operational. The specification for an upgraded Gun
HVPS has been written, reviewed by prospective vendors and is awaiting
funding.

**WBS 5 (SRF):**

-   AES is planning to ship the completed 750 MHz cavities at the end of
    this week. They are expected to arrive at JLab by the middle next
    week. QA will be the first priority.

-   End can fabrication continues.

-   AES/JLab coordination meeting is expected to be held in March.

-   A meeting is scheduled to clarify operational parameters for CASA
    analysis.

-   Plans have started regarding a project status presentation at the
    May FEL Conference/Workshop.

**WBS 6 (RF):**

RF - A small leak was found around the window of FL03 cavity 4. This
cavity\'s window was sealed with a gasket and a blanked off flange. The
cryomodule\'s capability is thus reduced by 10.5 MeV. The plan is to
cool FL03 this afternoon and pump it down to 2 K this evening. It will
be tuned this weekend and ready for start-up operations on Monday.

The RFP to purchase two 80 kW IOT\'s and their HVPS for a new Injector
Test Stand was released and is \"on the street.\" Advanced copies of the
technical specifications were made available and are in the hands of
many prospective vendors. The RFP has a

6 month option to purchase the required 3rd IOT & HVPS when additional
funds are available.

**WBS 8 (Instrumentation):**

The I&C group again took advantage of the down period to perform some
minor maintenance activities. Realignment, replacement of lenses and
lamp rings took place in the 3F and 5F region along with adjustment of
the image quality on ITV1G01 in order to make it useful for the beam
operations crew. Control Room Operator patch panel FL07B2 was replaced
with a panel located under the workstation as part of the control room
upgrades. Cables have been rerouted and new cable hangers installed to
reduce the clutter on the floor.  This is the first station to be
modified.  The other stations will be modified when the new monitors are
installed.  A new patch panel was added in FL07B09 for the AMS upgrade
cables. There was a small leak at the 1G dump, we coated the ceramic
with Vacseal and the pressure recovered an order of magnitude in couple
hours, this is the second time. We plan to replace the ceramic during
the next down (\~April). Since the steel shielding was removed we
re-terminated and recalibrated the Dump Current monitor. We raised the
external termination resistor from 33 ohms to

100 ohms to see if that changes the discrepancy between the dump current
and the high voltage power supply at the higher currents.\
With being down we are addressing UV installation and operational issues
as well as being involved in a number of maintenance and repair items.
The major source of tune time for this machine has been the
irreproducibility of the magnetic fields in the quadrupoles. Operation
of the UV leg will make this problem even worse. Each of the quads are
mapped in the magnet test area and these field maps are entered into the
magnet control software, the problem is that the trim power supplies
that we use are not capable of making the hysteresis loop (not enough
volts), multiple proposals have been floated including to JTO but all
have been denied. We have decided on a plan to quantify the
discrepancies and to look for systematic affects that might be
compensated for. This work will go on for the next few weeks in magnet
test, thanks to Tommy, Ken and the gang for trying to fit this extra
work into their tight schedule!\
The software focus this week was put into the epics-to-devlore project.
The system is being tested and will perform a test run over the
weekend.  The software will be submitting several EPICS records from the
control system to the web server to be recorded.  The trigger for
submitting data is time-based (e.g. once a minute) and/or event-based
(e.g. button press).  We continue to support Carlos on the calibration
of viewers ITV0F06 and SLM2F08.  The calibration is based on the change
in position with respect to the change in the energy spread. Visit:
<http://laser.jlab.org/status> to see in real-time what the status of
the machine is. We have slapped together a quick page to \'show-off\'
the incoming data stream from EPICS. The presentation of the page is
undeniably crude at the moment, but it does provide the latest
operational numbers for our voyeuristic fanbase.  :-)   We have included
the Gun voltage to be used to \'qualify\' most of the other values. When
the gun is off, the other numbers are not meaningful. These are the
EPICS values we are currently archiving:\
       Injector gun voltage (kV),\
       eBeam current at the 1G Dump(mA),\
       eBeam Micropulse Frequency (MHz),\
       eBeam Energy (MeV),\
       eBeam Charge/Bunch (pC/),\
       FEL Duty Factor (%),\
       FEL Power (W),\
       FEL wavelength (microns)\
The next values that we will be archiving will be all RF phases and
gradients, quad, sextupole & octupole fields. The page will improve as
time permits, but the important thing now is that we are archiving the
data.
[\<http://laser.jlab.org/devlore/devlore.asp?List=UV\>](http://laser.jlab.org/devlore/devlore.asp?List=UV)\
The MPS was updated to include the logic for Laser Alignment Mode.
Somehow this had been forgotten, when we did the lab certification last
week, it was just not there\... Extra care was taken to ensure the
fail-safe implementation of the system. We are now testing the inputs to
be sure they respond correctly, but the MPS logic is tested and ready.
The MPS Summation Chassis located in the Control Room was modified to
increase the channel capacity from 12 to 24 channels.  The sketches of
the modifications were submitted to EECAD for proper documentation
records.  The drawings are currently being reviewed for accuracy.  Four
more signals were connected to the MPS Summation Chassis to provide
status and protection for the Lab Optical Transport System.  We now have
MPS status for \"Laser Permit\", \"Alignment Mode Key\", \"Lab Lockout
Key\", and \"Lab 1 Harmonic Filter\".  All of the cables for the current
signals have been installed, labeled, and terminated.\
Installation effort continued on the new DC power rack (to support full
sex IR & UV) in FL07.  The 480 volt, 300 Amp breaker box and 20 Amp
plugs and receptacles have been received.  The electricians will begin
installation as soon as work winds down on the main machine. The
extruded aluminum parts were delivered from the machine shop for the Lab
3 THz hutch and fabrication continues. Check prints of the OC Fail-safe
Solenoid Interlock were received from EECAD, revised and re-submitted
along with the FEL High Power Dump Multiplexer Box.\
   The RF-DC Linear Converter PCBs are making progress.  The
documentation has been completed, the order for the PCB manufacturing
has been sent out, and completed PCBs should be received middle of next
week.  The check prints of the modifications to the Charge Totalizer PCB
are under review as part of the Charge/Dump Current Monitor Chassis
upgrade.  The CAN BUS test cable used on the Charge/Dump Current Monitor
Chassis was replaced with the proper final installation cable.\
   All of the elements shown on the latest mechanical drawing of the UV
line have been added to the database. The Devlore interface to the
controls database is sufficiently power enough to generate component
lists of any level of complexity for one who is savvy in using it, but
for the convenience of all, we are preparing a set of custom element
listings that can access by a simple link that can be bookmarked. Our
first custom list link is for the UV line. Use the following link to
directly list the beamline elements of the 6F, 7F, 8F and 2V regions:
<http://laser.jlab.org/devlore/devlore.asp?List=UV>

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

•   Fabrication is continuing at New England Techni-Coil. Conductor is
being sent for insulation coating. Steel has arrived at NETC and is
being prepared for machining into the blocks that reform into the cores.

***Replacement Chicane Dipoles GW)***

•     Fabrication is continuing at New England Techni-Coil.
Unfortunately, a snowstorm cancelled the weekend's only (because of long
cool down) heat treatment. The steel for two of the four magnets will be
heat-treated this weekend in anticipation of finish machining start next
week. The first coil layer was complete. They are working on clamp bars
that hold down the windings during the remainder of the windings.

***UV Line***

•   The latest changes were verified and the layout was broken into the
sub regions and distributed to two other designers for detailed layout
to expand the effort to three designers.

• Design of the three-inch differential Pump Station was complete and is
ready for signature.

• We are holding a review of the goals and proposed solutions of the UV
vacuum next Tuesday.

• Contrary to our account last week, the Vacuum Ion Pumps were not
ordered; the requisition was stuck in a paper pile in Procurement -- a
rare event.

• With regard to our plan to regain our schedule slip, the ME Group is
working its plan to concentrate a number of designers on getting the
beam line designed.

• We are reviewing a number of resumes with respect to our initiative to
have a NASA design engineer spend a sabbatical at Jlab.

• DULY Research has magnetically modeled the original sextupole to
benchmark their code before they convert the model of the SC sextupole
to the SS sextupole. They achieved the same field strength as was
measured on the SC Sextupoles.

• The faster PC workstations are late by 2 weeks because the requisition
got stuck between signature and Procurement.

• Tim Whitlatch's vacuum analysis is taking a back seat to dealing with
CEBAF problems during the 3 week CEBAF down period.

• The procurement to send the dipole chicane stands and vacuum chamber
to an outside firm for design is out for bid.

•   Design of the upstream and downstream corner chambers (now being
done as a pair) is almost complete. We solved restraint and downstream
beam line space issues.

•   DD requires QX Quads in the UV Line to meet specification of "part
in 10\^4" repeatability and "part in 10\^3" setting accuracy. The
original **Trim Card I's** don't meet this specification using Bang-
Bang ramp because it can't supply the required voltage and control
uncertainty leads to variable overshoot and ring. The new **Trim Card
II's** (which will be used in the new UV, 32 card Trim Rack) can have
internal programmed hysteresis loop. We can cycle the quads with a
precise ramp. We will measure one quad under differing ramp conditions
to find out if we can reach David's specifications. (All quads may need
re-testing with programmed ramp rather than "Bang- Bang ramp").

***Injector Multi-slit upgrade***

• The fine slot paddle parts were checked for slot width and spacing and
sent for UHV cleaning.

***UV Wiggler Progress***

•   The stay-out zone drawing was almost complete and awaits a final
decision on the vacuum chamber and gap configuration before signature.
We received the drawings of the Argonne wiggler chamber styles and will
conference call to them this afternoon to firm up how to match our needs
to their available designs and extrusions.

**WBS 10 (Wiggler):**

The order for the IR Upgrade permanent magnet wiggler gap mechanism was
placed this week with STI Optronics.  We are working to schedule the
kickoff review and shipment of the permanent magnet wiggler jaws to
them.\
We continue to refine the vacuum chamber concept for the UV wiggler
vacuum chamber in consultation with an engineer from Argonne National
Lab.  We would like to use as much of their design as reasonable in our
chamber design.  We are looking at the possibility of using a slightly
larger chamber to make production easier.  This would limit operation at
higher energies than we can now achieve but we may have a new wiggler by
the time we get higher energy so this may be a moot point.

**WBS 11 (Optics):**

***2.8 and 1.06 micron mirrors: ***

Given our current emphasis on 1.06 microns and lower power tunable
operation elsewhere, we removed the 2.8 micron HRs and replaced them
with a spare broadband and 2 inch dia 1.06 micron HRs.  We also removed
the broadband outcoupler and remelted its braze to try to correct the
astigmatism.  The result was that the axis of the astigmatism rotated
about 60 degrees, but remained about the same in magnitude.  A spare
mirror was installed with silver-doped vacuum grease used for
thermal conduction.  With these changes we\'ll be able to better explore
the relationship between astigmatism and lasing efficiency that was
briefly discussed in last week\'s report.  Later we will replace the
pasted versions with regular DMAs.

***Other activities:\
***Late Friday we completed the low level certification of User Lab 1. 
We did not have the opportunity to actually run beam into the lab, but
hope to this coming week.  We\'ve set up beam diagnostics hardware on
the optical table in anticipation of characterizing the FEL.  We spent
this week performing a series of tasks: installing cavity mirrors,
upgraded OCMMS, upgrades to the hot nitrogen purge system, and a more
permanent mount for the power meter that intercepts light directed to
the diagnostics hutch located in the vault.  (Thanks to the Vacuum and
Survey and Alignment Groups for their help.)  We repaired the exterior
cable that connects the HR LVDTs to the Control Room.  We also fixed one
of our windowed gate valves downstream of the OC assembly, and did some
troubleshooting on the other one.  We also installed more ion pumps on
the OTS, two in the vault and one upstairs.  We plan to install another
in the OCR early next week, or when time frees up.  This will free up
our pump carts for their primary purpose.  We fabricated holders that
will accept GaAs wafers (for harmonic filters needed during alignment
mode operation) and tested one of the IR Demo insertable mirror
assemblies to check its leak rate.  We found that it doesn\'t leak, but
bursts gas when actuated.  We\'ll see if that can be tolerated by the
ion pumps in the OTS.  New optical transport systems were designed for
transport of light from the 180 deg dipoles to the streak camera, and
planning for installation has started.  We tried boosting the SHG power
of the drive laser by installing a longer LBO crystal, but found the
conversion was much less.  We have contacted the vendor to discuss this
with them.

## UV FEL

The cryomirror modeling group met and finalized the baseline model, with
follow on work to extend power handling capabilities.  We began
researching options for in situ plasma discharge cleaning of the
mirrors.  We held some meetings to resolve the very cramped area between
the dipole magnet and the OC assembly.

**Terahertz:**

Planning work was done for the phase 2 part of the project.  Discussions
continued with vendors concerning laboratory equipment, particularly
spectrometers and detectors.