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Site Details ATF Newsletters 
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2000 ATF NewslettersJan | Feb | March | April | May | June | July | Aug | Nov | DecApril 14 | April 21
Hi everybody, The HGHG experiment
succeeded in implementing an autocorrelator at 5 micros and measuring
the HGHG output pulse width. The STELLA
experiment worked a miracle in designing, simulating, building, measuring
and delivering a wiggler for the STELLA 2nd stage in less than
two weeks. Amazing! The results of the simulations look very promising
for the experiment. Ilan Ben-Zvi.
Two weeks
ago, the decision was finalized to substitute a permanent magnet wiggler
in place of the ICA gas cell
as the second (accelerating) stage for STELLA.
The quick change in direction came after many weeks of struggling
with the optical alignment of the ICA's radial polarization system. The optical alignment & characterization of the first wiggler
(prebuncher) usually takes less than a day, so we expect that this second
nearly-identical wiggler should be just as reasonable.
This reduction in complexity should increase the probability that
positive staging results are achieved in time for AAC 2000. At STI, calculations
were done to assure proper beam and wiggler parameters;
the final design called for a 33mm period (untapered) assuming
400 MW delivered laser power [see 4_14_IFEL_2nd_stage.htm
]. The fabrication
and testing of the wiggler & mounting components was then finished
in only 1 week! During that
time, magnetic measurements and adjustments of the new wiggler were completed
to assure there was no dipole effect [see 4_14_IFEL_final_perf.htm
]. On Friday
(4/14), the wiggler arrived at ATF.
Our plan is to install/align it into beamline #1 and begin pumpout
by as early as Monday evening. Laser
alignment modification is currently underway to bypass the existing ICA
optics and deliver an annular vertically-polarized laser beam to the second
wiggler via GPOP3 mirror. Our
goal is to be ready to run beam studies on Thursday (4/20), and look for
modulation the following week.
Wednesday
we made important progress: Adnan and Marcus’s autocorrelator got a preliminary
measurement for the HGHG pulse length measurement. (See report by Adnan
Doyuran, below). Another progress
is the 1-D array detector begins to work yesterday after the efforts by
Ron Nawrocky, Bob Malone, Timur Shaftan, and Jack Tallent. The SASE profile
of single shots at 5 micron were displayed yesterday. As reported
by Adnan last week, Adnan and Marcus aligned the autocorrelator and were
able to measure the YAG laser pulse length successfully, thus determined
the zero position of the two arms of the autocorrelator. During the last
few months, Adnan rebuild the autocorrelator to separate the two collinear
beams by larger angle, so the collinear beam would be discriminated
from the non-collinear beam much more easily. We also used normalization
to overcome the fluctuation. Our main purpose
was to test the autocorrelator, and due to the limited running time and
the rep rate of every 20 seconds, we started to test the autocorrelator
right after we obtained the HGHG signal, without trying to optimize the
CO2 attenuation. So most of the time we were not working at the designed
working condition. The result is that when the CO2 energy is small, such
as 0.4 mJ, we may obtain large HGHG signal of order of 15 microJ in a
Joule meter which took about 40% of the radiation (thus 15 microJ corresponds
to 37.5 microJ in HGHG total output). And sometime when the CO2 energy
is a few mJ, we get order of 5 microJ. The output of the 2.6 micron signal is divided by the square of the 5.2 micron HGHG signal for each shot at different delay arm length, the result is plotted by Marcus in the attached figure. The blue dots
are for HGHG signal smaller than 15 microJ, the red dots are for those
larger than 15 microJ. The horizontal axis (the delay arm position) is
in unit of mm. As explained before, the fluctuation is partly due to CO2
fluctuation from shot to shot. Because the attenuation was not optimized,
there are not sufficient data points for HGHG signal larger than 15 microJ.
Also, near the peak (delay position 18.7 mm) the detector signal reached
saturation (15 V). So the measurement still does not give sufficient accuracy,
even though the apparent FWHM of these points is between 1mm and 1.5 mm
(corresponds to 4 to 6 ps). HGHG simulation
and the single shot spectrum predicted the pulse length is 3.5 ps. The
electron beam pulse length is about 6 ps. We need to improve our precision
to distinguish between 3.5 and 6 ps. To improve the accuracy of this measurement,
we need to optimize the CO2 attenuation, and improve the alignment and
normalization in the autocorrelator to reduce the fluctuation of the 2.7
micron signal, and improve the statistics. This will be the topic of our
next few runs. Last night
the participants are Adnan Doyuran, Marcus Babzien, Timur Shaftan, Igor
Pogorelsky, and Li Hua Yu. Last week,
after successfully testing the autocorrelator with the Doubled CO2 oscillator
beam, In the link
below you'll see the signal vs. delay data. I measured Peak-to-Peak and
maximum signals to get the most accurate result. They both show a pretty
good agreement.
Previous week: Last Friday’s
run We did radiation vs. charge and it is still linear: Last run caused
us to think we were not seeing a clear OTR signal because only the “core”
of the spot would change. A series of BPM picts with different filtering
is included in the above pdf document. In the pict, much x-ray background
and this caused huge error in the emittance measurements. We will need
to shield the emittance measuring cameras better in the experimental hall
for his measurement. The transport
is currently being installed. Once up we’ll put in the optics and align
and hopefully be able to transport radiation to the FEL room, where the
noise is considerably less. We need to
make sure that we are ready for the shutdown the week of May 8. This includes
the new pop-in installation before Robert comes out, alignment laser stability,
and interferometric laser alignment team travel plans. This week: Thursday and
Friday were run days for VISA. We mainly studied the trajectory through
the undulator. Using a simplified trajectory algorithm, the oscillation
amplitude was reduced from about 3mm in the beginning to <1mm. The
trajectory was improving but with 8 BPMs the process takes much time per
trajectory measurement. Improvements in the data acquisition should speed
up the process and reduce error. Next week we will look into the more
formal algorithm and push to incorporate the orbit correction in to the
controls system. Emittance
measurements made in the matching section were found to be 12 mmmrad.
There could be two problems with the high emittance measured. The beam in
our two run days had abnormal structure in the profile and the optics
for the measurement are resolution limited (used YAG screen in BPM). By
next run the BPM used in the emittance measurement will be changed to
OTR, thus increasing the resolution and accuracy of the measurement. Emittance
measurements were done on the H-line, and an emittance of 9mm-mrad was
observed at 500pC. The ATF engineering report has more to say about these
measurements. Optics have
been ordered (polarizers/filters) and hopefully will be here by the next
run which has been changed to next Friday. It has been found the cameras
pick up much spontaneous emission and filtering optics are needed to remove
undulator radiation. The shutdown
for the week of May 8th is still on the agenda. The new pop-ins will be
ready and installed before the shutdown week. Roberts alignment team will
come out for another interferometric alignment that week. A detailed
description of the VISA alignment laser:
Monday urgent
realignment of the demo oscillator was performed to restore optimum mode
locking, phase stability, and output power.
Late last week all of these parameters had degraded nearly to the
limit of operation. With
the experience gained on the new oscillator, Bob Harrington and I were
able to achieve the same average power with much lower pump, and therefore
lower heat load. This week
the oscillator performed extremely well in both phase and pointing.
No realignment into the amplifiers was required after Monday, and
the system operated for experiments the rest of the week. Today XJ and
I performed some beam studies to try to understand the cause of degraded
e- beam quality. By using
different masks to shape the laser profile on the cathode, we demonstrated
that the e-beam imaged from the cathode through the linac shows structure
in the laser beam. Different regions of higher and lower intensity in the laser
spot map onto the e-beam distribution.
This helps to explain structure observed in the e-beam after the
linac. Previous week: We have finally
come to the end of the road as far as the YAG laser covers are concerned.
All of the units have been fabricated and installed. The remaining pop-in
for VISA was installed and leak tested, everything is A-OK.
The Smith-Purcell
chamber was leak tested and is OK also. New control cables were pulled
for the HGHG Experiment, allowing finer control of diagnostics. NSLS electricians
have assisted with the cable pull and remedied the existing safety violations
found on the last “tier 1” inspection. The “x-wing fighter canopy” cover
for the terawatt laser breadboard
is in need of a structural modification. It is changing the position
of the laser when operated. The unit will have to be braced from the wall,
allowing complete independency from the optic table. Work will begin early
next week. The Klystron cooling enclosure is developing nicely. BNL Sheetmetal people have fabricated and installed the metal
wall and will complete the hatchway and a/c unit early next week. Also
on next Mondays agenda is
the modification of the Linac water circulation system plumbing.
Masons will open the shielding wall and plumbers will modify the
copper lines to accept the new water system Which will be installed in
May. Thursday, we had a failure
in the switching contactor for the FD5 trim.
Appears to be oxidized contacts. Repaired. The SDL had requested
the return of the borrowed high voltage power supply used for the ATF
gun modulator. As the new Maxwell power supply has recently arrived, this
was a good opportunity to install it and field check it’s reliability.
As the borrowed supply was being disconnected, it was found that an ac
lead for the incoming power had become loose. This would have been difficult
to find if it weren’t for the supply change. After the reinstallation,
the stability greatly improved. This might have been the major cause of
the mysterious jitter. Time
will tell. Marc Montemagno has fallen victim
to his legal obligations and is on jury duty. It is expected to
last all of next week. We will feed the accelerator gods handsomely in
order to avoid disaster. This week: The electronic
support for the ATF was interrupted this week due to jury duty. Marc will
be back on Monday. Monday’s Maintenance Day was very productive as it
allowed us to utilize the services of the BNL Masons and Plumbers to remove
the Linac shielding and modify the water lines to accept the new, still
under construction, closed loop water temperature control system. This
new array should be ready for installation in the upcoming shutdown. The
Klystron area hatch enclosure and new air conditioning unit have been
installed and we are awaiting the electrical service installation.
The unit should be operational by Tuesday morning. The defunct
personnel a/c unit for the Control Room is being replaced. Just in time
for the upcoming warmer weather. Aside from the normal operational support,
we spent most of the week cleaning up the facility and tending to the
needs of various support groups.
The Terawatt breadboard optic enclosure has been modified to alleviate
the vibration and is now a stand alone unit. Don Davis has been working
steadily to improve the covers and
mechanics of the system and along with John Skaritka,
will see it to completion. The VISA beam transport covers have
been installed by the NSLS Mechanical Group and should bring that phase
of construction to a close. Previous week: 1.
Next Monday maintenance:
three major jobs planned: A.
Preparation for
linac water system improvement (Cahill and Harrington) B.
YAG laser oscillator
alignment (Marcus) C.
Network connections,
this may interrupt the e-mail. 2.
this week operation: A.
CO2 alignment problem
prevented HGHG experiment from taking data. B.
Fix Magnets power
supply and relay circuit problem. C.
Install new charging
power supply for the gun modulator, return SDL power supply. 3.
YAG work: improvement
of the YAG laser profile on the cathode will be the major focus. We also
discussed how to improve the humility in the YAG room. 4.
TW CO2 laser work:
Igor reported that the final decision on the discharge cell
repair should be made next week. Major work will be fixing the
cover. 5.
Fast detector experiment
will exchange next Friday running time with VISA for May 23 run. 6.
UCLA requested
decrease the magnetic bunch compressor ID to 13.5 mm from 15 mm. This week: 1.
ATF schedule modification:
To help HGHG and other ATF experiments, I have discussed with parties
involved to modify next week ATF schedule by exchange experiment dates:
Monday: ATF maintenance, Tuesday -Wednesday: HGHG, Thursday: Stellar,
Friday: VISA. To compensate the lost date, HGHG will give up two days
in the May. May 2 to Stellar, and May 24 to fast detector experiment. 2.
Next Monday ATF
maintenance jobs: a.
Checking RF gun
field balance due to the temperature variation (XJ and Harrington). b.
YAG laser improvement:
to improve the YAG laser profile and spatial stability (Marcus). c.
Install new IFEL
undulator (Karl and Done). 3.
Next shutdown jobs:
It seems YAG oscillator will not be ready for the shutdown (week of May
8), we hope to install the chiller for the amplifier. ATF will focus on
getting the new linac water system ready for the shutdown, Mark will focus
on the electronics, and Harrington will work on the plumbing. 4.
TW CO discharge
cell still waiting for the decision, optics cover was fixed this week. 5.
ATF operation: A.
QE of cathode dropped
by about a factor of two on Thursday, and we have established a correlation
between the HGHG runs and all last four QE drops. The best guess is that,
CO2 laser or 5 micron HGHG radiation causes the release of some elements
that contaminate the cathode. More detailed studies are needed, but a
more powerful ion pump installed at HGHG will definitely do no harm. B.
Linac and gun water
temperature drift: I have observed both linac and gun drift about 0.5
deg C on Friday. Linac water system improvement is under construction
while gun solenoid water system is on order. C.
Gun and linac RF
system: We have observed both linac and gun RF systems instability between
5 and 7 PM. I will ask Mark
to check connections and install some monitors. D.
Emittance studies:
we have tried to measure the emittance at 71 MeV for VISA. We observed
many structures in the e-beam, using an imaging technique we were able
to trace the major source to the laser profile, and maybe some from non-uniformity
of QE due to QE drop. At such high energy, the emittance measurement is
much more sensitive to the measurement error and resolution of the BPM.
We have measured a large emittance 8 - 10 mm-mrad (normalized rms) for
0.6 nC at 71 MeV, and 6 mm-mrad at 54 MeV for the same gun condition (just
adjusted solenoid magnet). More studies are needed to understand this.
Two possible explanations are: First - measurements are dominated by the
measurement error, another - emittance compensation is better matched
at lower energy due to strong edge focusing from the linac entrance. We
intend to continue this study next week after laser improvements. 7.
Next Monday (April
17) 9:30 AM ATF BLOSA training at the ATF conference room. Starting Tuesday,
April 18, all ATF users are required to have BLOSA form before starting
work at the ATF.
In the Friday
ATF meeting, we discussed the material below: Lessons-learned
- NSLS Requirements for Configuration Control of Radiation Security and
Shielding Systems, Bob Casey, NSLS Associate Chair for ESH/Q. Recently
an active beamline radiation interlock system for X17B2 was disconnected
when components for the beam line were being removed.
The beam line itself had not been used for some time, and it was
understandable why an impression had developed that the security system
was inactive. One of
the lessons-learned from the incident was to ensure that all staff were
advised of the issue and reminded of the NSLS Configuration control practices
for interlock systems. ---------- Everyone who
does work on the experimental floors or in the machine areas is responsible
for knowing and obeying the restrictions on work affecting shielding or
safety interlock systems. Anyone
who initiates work which impacts a radiation security system or removes
shielding must obtain and post a Safety System Work Permit at the work
site and ensure that any required safeguards have been put in place before
starting the work. Anyone
who joins a job in progress which involves moving shielding, modifying
beamlines, or working on safety systems must verify the status of the
permit or other authorization for the work.
If there is any question, usually an Operations Coordinator can
provide an answer or determine whom to ask.
The operations groups at the ATF and SDL will know the status of
permits for safety system work at those facilities. Most of our
shielding is pretty obvious: concrete, lead bricks, and hutch walls. Other structures may provide shielding as well: beam pipes
and other components such as monochromator tanks.
There are parts of the interlock systems which may not be obvious,
for example, the overhead lights in hutches and tunnels are connected
to the interlock as part of the warning system.
Because of the nature of the interlock systems, the interlocks
associated with beamlines and hutches which are not in service are usually
still connected to the rest of the safety system. All of these things are under configuration control, and a
permit must be approved before work is done on them.
If you are ever in doubt regarding this issue, get the necessary
information before beginning the work. Consult
NSLS SEAPPM NS 3.4.1b for detailed procedures for using Safety System
Work Permits.
Last Modified: December 3, 2007 |
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