MEMORANDUM

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief --May 10-14, 2004

**Date:** May 14, 2004

**Highlights:**

This week we completed the second week of our 3-week shut down prior to
starting up with the newly installed third cryomodule in the FEL Upgrade
linac and a new photocathode. By tonight we will have completed all of
the items we had planned for this week and are on track for starting up
operations on or about Monday May 24^th^. Significant accomplishments
this week include:

1.  Improvement of the vacuum and diagnostic hardware in the beamline
    between

> the photogun and the injector cryounit (this included replacing an ion
> pump and getter pump; installing a new beam tube with an internally
> evaporated getter coating, and replacing a beam position monitor).
> This hardware along with the photogun will all be baked at 250C
> starting later today.

2.  A new photocathode was prepared with an anodized ring around the
    outer circumference in order to minimize halo production. The
    cathode was installed

> in the gun vacuum chamber. The bakeout of the gun chamber starts
> today. This is typically a week long process.

3)  We modified an important connection on the Machine Protection System
    (MPS), that shortens the time constant between the detection of an
    arc in the injector rf window assembly to the drive laser EO
    modulators from 500 microseconds to 32 microseconds. This should
    significantly lower the potential for arcs in the injector to
    initiate arcs and possible cathode damage in the photogun. (Thanks
    to Todd Smith for this suggestion).

4)  The injector cryounit was cycled to 20k and desorbed gases from the
    both the beamline and waveguide vacuum systems were monitored. We
    observed only minor amounts of He and H~2~ which confirms that we do
    not have any significant He leaks in this system. A similar 20k
    cycling of the first linac cryomodule is planned for today.

5)  We have completed the modifications (including adding extra coils)
    to the sextupoles in the first recirculation to allow operation at
    150 MeV (the new energy limit with the 3^rd^ cryomodule).
    Modifications on the sextupoles in the second arc started yesterday
    and will be completed by early next week.

6)  New high power shunts were installed in the arc magnet power
    supplies to allow operation at 150 MeV.

7)  Dave Douglas and George Biallas designed a skew quad system that can
    be installed in the existing back-leg with no interference as a new
    hardware system for dealing with potential "beam-break-up" (BBU)
    instabilities if low current thresholds are observed with the third
    cryomodule. This system was designed using existing spare
    quadrupoles that will eventually be used in the UV chicane.

8)  Couplers and RF diodes were installed on the HOM load terminations
    on the third cryomodule to allow us to observe HOM power for planned
    studies of BBU thresholds and amelioration methods.

9)  The final alignment was completed on the quadrupole assemblies
    upstream and downstream of the third cryomodule. This module is now
    ready for hot check-out procedures scheduled for next week.

10) The first 3 micron outcoupling (OC) optic was installed in the OC
    assembly along with completion of some housekeeping items. On Monday
    new high reflector (HR) optics at both 6 and 3 microns will be
    installed in the HR assembly

11) The largest vacuum pipe in the THz beamline from the optical chicane
    to User Lab 3 was successfully installed this week.

> Finally, we spent considerable effort this week preparing a detailed
> plan for re-start of operations with the hardware described above and
> the 3^rd^ cryomodule. This plan along with two reports which further
> describe our FEL modeling results and emittance measurements were
> forwarded today to our Navy program managers and FEL steering
> committee for their review and comments.
>
> I would like to thank all the troops who contributed to a very
> successful week of completed shut-down activities and spirited
> discussions on our start-up plans. I apologize for my omission last
> week of the Mechanical Engineering Group for their efforts which
> insured that last week's installation of the 3^rd^ module went
> smoothly and for this week's machine modification tasks.

If next week goes as smoothly with the gun bake-out, completion of the
optics installation in the HR assembly and the numerous "hot check-out"
procedures on all the FEL systems, we will be re-starting our campaign
for 10 kW on May 24^th^.

**Management:**

We compiled several reports responding to action items from the May
6^th^ Navy review (noted above) and distributed this to our Navy program
managers and FEL steering committee.

We sent the bimonthly FEL Upgrade financial report to the DOE and ONR
Program Offices. The project monthly report for April for the Army
funded THz project was sent to the DOE and Army Program Offices. With
the initiation of the Phase 4 (FY04) UV FEL project last month, a new
monthly report series is being prepared.

On Weds. May 12^th^ we had visitors from Dahlgren and NAVSEA to discuss
the NAVSEA/JTO funded laser-materials lethality experiments planned for
initial user operations of the FEL Upgrade. The progress in the design
of the interim optical transport system was discussed.

**WBS 3 (Beam Physics):**

Evaluation of recommended BBU suppression methods has led to
implementation schemes for two likely candidates. The first,
point-to-point imaging, uses a phase trombone in the backleg (3F) region
to independently vary horizontal and vertical phase advances without
significantly altering the betatron match. This allows steering of a
\"BBU-driven kick\" so as to null the resulting displacement at the
second pass through the offending cavity. It requires only a software
script to alter operating excitations of existing quads. The method has
been documented in a JLAB-TN available at
<http://www.jlab.org/~douglas/FELupgrade/technote/JLABTN04017.pdf>

The second, H/V phase space rotation, was determined as noninvasively
tractable using a 5 quad rotator built out of available components. This
can be turned on and off at will, and can thus be rolled back to the
nominal operating configuration without difficulty. It is documented in
a JLAB-TN at
[www.jlab.org/\~douglas/FELupgrade/technote/JLABTN04016.pdf](http://www.jlab.org/~douglas/FELupgrade/technote/JLABTN04016.pdf)
.

**WBS 4 (Injector):**

As noted in the highlights section above, a new cathode was prepared
including an anodized ring to suppress halo formation. After hydrogen
cleaning and a pre-bake the cathode assembly was installed in the gun
chamber today and the chamber is currently being prepared for a week
long vacuum bake at 250C. We also made the planned modifications to the
vacuum pumping and instrumentation in the beamline between the gun and
the cryounit. This area will be baked at the same time as the gun
chamber.

Gun HVPS - The current measuring amplifiers were modified to reduce
noise and adjusted to minimize their errors between -200 kV to -500 kV
to 0.01 ma. The maximum current readback error is -0.1 ma at 0 kV. This
will allow better current monitoring during high voltage processing of
the Gun. The HVPS Tank was opened and the stacks inspected and wiped.
There were no visible particles on the stacks. Very minor amounts of
dust were wiped off the bottom of the tank. The Conditioning Resistor
and Mechanism were inspected, several screws tightened, and the
Mechanism was reinstalled.

**WBS 6 (RF):**

Zone 1 - The Quarter was cryo-cycled to remove any trapped helium and
hydrogen gases. Little of either gas was found. The power supply for the
cavity waveguide ion pump was found defective and replaced.

Zone 2 - The cryomodule for this zone is being cryo-cycled today.

Zone 3 - This zone is ready for its final operational testing.

Zone 4 - This zone is operational.

**WBS 8 (Instrumentation):**

Well another screamer of a week has passed by. The I&C team is grateful
that proper bakeouts of the gun region takes more than a couple days;
the time has been put to very good use. All optics and parts were
ordered for the streak camera installation at ISM2F06. The camera will
be taken down next week and setup prior to resuming operations. Spare
channels from the cryo diode were rerouted to the quarter and to the
module in zone 2 for monitoring the warmup and pump out.

   New BPM electronics are being installed for the BPM in the injector
line. The BPM is a short stripline, the electronics will be the Switched
Electrode Electronics(SEE) type. We will also run a single heliax cable
directly above to Zone 1 as an experiment to look at the longitudinal
distribution on our sampling scope (7 picosecond rise time). An initial
plan has been devised to look at both beams in the linac BPMs. We
purchased fast RF switches (10 nsec), initially these will be used to
run at the beam frequency and turn on and off for each individual
micropulse of the (accelerating beam) and off for the all of the other
micropulses (decelerating beam or vice versa). Step two will then use
two sets of BPM electronics and the switch will route every other pulse
to same electronics giving a live display of both the accelerated and
the energy recovered beam simultaneously. The frequency response of the
dump BPM (IPM1G03) was measured in preparation for the HOM studies. All
four of the electrodes will be wired to the gallery for monitoring on
the spectrum analyzer as the current is cranked up.

   The Framegrabber\'s system for calibration of the beam viewers is
progressing well. The user interface dynamically adjusts itself
depending on what type of viewer needs to be calibrated. Testing on the
different features has been completed as they are finished. Once the
interface is finalized the instructions for use will be written; then a
walk-through will be performed testing the whole system.

   Re-installation of the magnet, BPM, Viewer and vacuum power/signal
leads was completed for the 1F03, 1F04 region. The other 2 modified high
voltage shunt modules and load resistors for the GY dipoles were
received from EES and installed. Check out of the box supplies will
begin early next week. Wiring was completed for the add-on coils for the
1st Arc sextupoles and the 2nd Arc sextupoles wiring is in progress.

   Modifications to the Beam viewer Chassis began in order to upgrade
the EPICS interface with CAN-BUS.  The chassis have had mechanical
modifications to accommodate the RJ-45 CAN connections and the
associated wiring inside the chassis.  All of the modifications to the
chassis can be reversed to the previous EPICS interface with relative
ease.

   SF6 pump plans were reviewed and final preparations are being
conducted for pre installation. We continued support of the THz beam
line installation. Additional read backs were installed for the 1/4
cryomodule temperature diodes. Repairs and/or assembly of 8 viewer
cameras were completed. Population of 2 Temperature diode back planes
has begun.  A spare stepper motor chassis was completed and tested.

   The new backplane for the Si Diode Temperature Control Crate was
populated as were the Shield cards for the crate.  All parts are on
order to complete the backplanes as well as those required to complete
the upgrade of the video system.   Safety issues concerning conduct of
the THz experiment were discussed and responsible parties designated in
the areas of instrumentation, fire prevention, electrical power
installation.

**WBS 9 (Beam Transport):**

***Sextupole Lite Re-coiling to obtain higher field***

• In Magnet Test, the one sextupole lite with 50% greater coils tested
well. A small amount of saturation was evident at the maximum current of
20 A. We also needed fans to keep the coils cool at the 20 A setting.

• We are treating the first arc differently because it will run at about
14 A at 150 MeV/c while the second arc runs at half that current. Thus,
only in the first arc, we are setting a software and power supply limit
at 20 and installing a set of four fans to be running all the time.

• In the second arc, we will set the power supply and software current
limit to 15 A without fans.

• The sextupole task is going slower than we originally scheduled, but
it matches the pace of the down. Kevin Sullivan has shouldered the
entire tedious task because Mike Beck and Don Bullard (gun work) can't
help. The sextupoles in the first arc were split from doubles in two
positions to singles in four positions, one was tested, and all were
recoiled and wired up and aligned. One of the four sextupoles in the
second arc was recoiled and wired up without moving it. The magnets at
this end will need no alignment work.

***Skew Quadrupole Eigenvalue Exchange Module (SQEEM)***

• We laid out the positions for the seven quadrupoles of this beam
rotator to intersperse between the 12 quadrupoles of the return leg
before the optical chicane per David Douglas' DIMAD. We are lucky that
there is no interference with existing hardware such as beam tube
bellows or girders.

• We are also fortunate to have all seven quadrupoles and their power
supply, trim card circuits available (borrowed from the UV line) plus
two of the seven stands. The remaining stands and the 7 simple girder
plates will be here by June 1. Five of the quadrupoles will need
additional work to make them skew quads. They need taps in their cores
to mount them at the 45 degrees to their normal orientation and they may
require some refiducialization by the alignment group.

***Wiggler***

######### Electromagnetic Wiggler for 2.8µ 

• We hoped to start assembly on Wednesday. A last minute glitch of the
water jet cutter not being accurate at the .036 inch over 8 feet level
halted production of the Kapton insulation strips. All other parts are
in tolerance. The water jet vendor recalibrated the encoders on the
machine and made the insulation strip correctly. This was proven with
some trial fits of the first parts from the new calibration. Assembly
will start on Monday.

***Sextupole (SF)***

• Procurement on hold, pending 10 kW efforts

**WBS 10 (Wiggler):**

The wiggler poles have all been mounted on the magbases and one magbase
has been pinned to its strongback.  The measured height of the poles is
uniform to ±0.001\".  This should produce acceptable field variations.
 The special end correction magnets arrive today.  The magnet test
facility is ready to accept the wiggler.  STI Optronics hopes to start
permanent magnet block installation by next Tuesday.  So far they are
holding the original schedule.

**WBS 11 (Optics):**

**Plan A is to obtain low loss 6 um optics.  **

Plan A is to obtain low loss 6 um optics.  

 

The flaws in the coating\'s of both HRs was more carefully documented
with our noncontact profilometer and photomicrographs.  We will send the
optic with the worst flaw back for rework. The other is being
installed. 

 

**Our three Plan B\'s had the following progress:**

***Cryomirror (with G. Biallas input):***

-   The inner perimeter of the cryogenic mirror mount was successfully
    indium plated.  The indium annulus still needs to be prepared,
    we\'ve been delayed due to competing work required for the
    accelerator.

-   We tested a new cooling setup where the output cryogen is
    subcooling before it is brought to vapor.  We were able to double
    the flow rate (to \~ 2 grams/sec) before vibration became too severe
    to take interferometer data.  We will carry these tests forward once
    we get the mounted cryomirror.

-   Based on this positive result, we re did the drawings for the
    exhaust line being vacuum insulated and restarted the task in the
    shop. The shop received the lengths of flex hose for this
    modification.

***2.8 micron mirrors: ***

3\" dia OC mirrors are in fabrication.  Metrology for the mirrors in
hand continues.

***Scraper outcoupler:***

A requisition was placed for new substrates.  We\'ll have them coated
with low loss coatings.

***Other activities:***

Work on the HR assembly this week mirrored (pun intended) what occurred
in the OC last week.  RTDs were added to better understand the amount of
power being absorbed by the mirror mounts.  The ion pump was removed and
baked.  Installation of the HR mirrors has been delayed into next week,
as we had problems getting them bonded with low aberrations. 
We received a new OCMMS (HR side) viewport assembly, which will be
installed next week.  On Tuesday we had a representative from Veeco
Metrology here to optimize the noncontact profilometer and give us more
training.  On Wednesday we met with representatives from NAVSEA.

**Terahertz:**

We took advantage of the FEL vault being open all week.  The beamline
support structures were installed after the sprinkler system had been
moved.  The large 13 foot pipe that will carry the beam from the vault
to lab 3 was installed. Mirror boxes M2 and M3 were hung from the
ceiling support and connected to the long pipe.  M1 arrived on site this
week, and will be sent to Brookhaven for metrology.  A second meeting
was held to discuss safety and operational issues.  The THz beam will be
treated as a class 4 laser.  A follow-up meeting was held with radiation
control and installation of the requisite shielding modifications was
started. These will replace those that had to be removed for the
installation of the beamline.  Beamline viewers and shutters were also
discussed and work commenced on their design.  These are based on
modifications to existing FEL viewers which are in-house.