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Site Details ATF Newsletters 
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2000 ATF NewslettersJan | Feb | March | April | May | June | July | Aug | Nov | DecAugust 25
Hello friends, I have a strange feeling writing this: Bill Cahill, a most valued staff member of the ATF will retire. I see the ATF as a young and vigorous facility. This year was arguably the most productive time for the ATF and we all fill young and vigorous with great plans for the future, but one of our own will retire... Bill is wearing so many hats, carries so many responsibilities, that it will be too time consuming to list them all. He is the warrior who holds the fort, knows everything and attends to everything, from the needs of users to the upkeep and upgrade of the facility. Having served at BNL for over 35 years (the first digit of his life number is 0!) he knows everybody and has always worked out small miracles using his connections. Above all, Bill is the idea person, and many of the nicer features of the ATF started as a glint in his eyes. He knows how to be firm and gentle, demanding and courteous. Bill, we will miss you! Having entered this retrospective mood, I would like to share with you a brief history of the ATF, which will be the last item in this newsletter. The first item of business is the HGHG experiment. The results of this ATF experiment got published in Science: L.-H. Yu, M. Babzien, I. Ben-Zvi, L.F. DiMauro, A. Doyuran, W. Graves, E. Johnson, S. Krinsky, R. Malone, I. Pogorelsky, J. Skaritka, G. Rakowsky, L. Solomon, X.J. Wang, M. Woodle, V. Yakimenko, S.G. Biedron, J.N. Galayda, E. Gluskin, J. Jagger, V. Sajaev, I. Vasserman, "High-Gain Harmonic-Generation Free-Electron Laser", Science, 289 (2000) 932. In addition, the experiment had a very successful run in early August (good timing for the International FEL Conference!) and the results are in this newsletter. The FEL Conference was a very successful event by
the account of all the persons I talked to. It was held in Duke University,
and marked the first time in which the shortest wavelength record for
FELs was broken by a linac-driven FEL. The TTF-FEL reached 80 nm, by far
shorter than any storage ring. The ATF had a very good showing at the
conference, with an Invited Talk on Tomographic Methods for the Determination
of Electron Beam Phase Space Distributions by Vitaly Yakimenko and
two oral presentations by ATF experiments: The Smith-Purcell Experiment;
Radiation induced by relativistic beams passing over a diffraction
grating. Ilan Ben-Zvi.
During the last three weeks, our HGHG study achieved
major success in 4 different subjects: 1. Adnan and Marcus’s autocorrelator
pulse length measurement has obtained a stable and clear result. The following
is one of the result for 8ps e-beam pulse case, the 9.9ps autocorrelation
FWHM should be divided by 1.5 to obtain the pulse length of 6.6ps FWHM.
For a 6ps e-beam the result radiation by this method is 5.7 ps. 2. We steered the e-beam to monitor
the output by a pyroviewer. The radiation pattern is moved by 2.5mm in
the horizontal steering without blurring the pattern. This may be useful
in future cascading of HGHG stages, when the output of one stage can be
steered for alignment as the input of the next stage. 3. The 2nd, and 3rd
harmonics at 2.6 and 1.7 micron of the HGHG output at 5.3 micron have been measured, showing agreement with simulation and analytical
theory within the error bar of the measurement. The 2.6 micron power is found
to be 1.5*10^(-4) of the fundamental
at 5.3 micron, as compared with 6*10^(-4) based on simulation provided
by Sandra, and also as compared with Juhao Wu’s analytical calculation
result of 3*10^(-4). The 1.7 micron power is found
to be 7*10^(-3) of the fundamental at
5.3 micron, as compared with 10^(-2) based on simulation provided by Sandra
. The measurement of the harmonics
vs. e-beam energy modulation generated by HGHG showed linear dependence
for the fundamental at 5.3 micron confirming energy conservation. while
the 2nd and 3rd harmonics showed exponential increase
for larger modulation, indicating highly non-linearity and saturation. 4. Timur’s Michelson interferometer
measurement generated very clear interference pattern. For 6ps e-beam,
the pulse coherence length based on this method is found to be 5.5 ps,
agrees with the autocorrelator measurement. This showed that the pulse
is fully coherent, a very important result. The interference fringes is in The fringe visibility as a function
of delay is in
A
lot of activity is going on at the ATF this week. With the arrival of
Igor Pavlichin, the Terawatt laser re-assembly is in full swing. Repairs
have been made to the Kilowatt amplifier to improve the amplitude and
output reliability. We have experienced multiple failures with the charging
resistors feeding the Linac PFN. It was found that the resistor power
rating was too low. A new resistor array was installed in both modulators
and the problem should be solved. The long awaited key pad has been installed
at the Experiment hall door. The access number can be obtained from the
operations group. In conjunction with the key pad, we have also completed
the Radiation Interlock Certification. NSLS electricians are installing
the Control Room Service Rack Extensions purchased to house the new frame
grabber and computer chassis. This should expand the capability of new
and existing equipment at the ATF. The last of the remaining bottled gas
cylinders have been moved to the rear of the facility and are now equipped
with weather shields to protect against the elements. As my retirement draws near, I
will be leaving the Laboratory on August 31th. This will be my last report
on the activities of the ATF. As I refer to past writings, it amazes me
on the amount of progress we have made over the years. The ATF is the
6th accelerator I have been a part of and can proudly say that
is has been the most exciting and challenging so far. I will miss the
dedication and hard work of the entire staff knowing they will continue
to be the “best little accelerator in town”. Good luck to all of you and
thanks for letting me be a part of it. Bill Cahill Please note the following: 1) Planned upgrades of ATFSERVER1 are now completed,
as follows:
The CD-RW drive will allow for file & data archiving onto CD-R and CD-RW disks (about 600-650MB per disk). The HP CD-Writer Plus software helps the user to format and copy either type of disk. The second CD drive also enables you to make copies of disks. We have a limited supply of disks available for any user - please ask us (Karl Kusche or Marcus Babzien) if you need them. In addition, the following new software has been installed - MS Office 2000, AutoCAD LT 98, Netscape 4.73, Explorer 5, Corel 8, SigmaPlot 4. 2) In the near future, we expect to purchase at least one new printer for the ATF Control Room and shuffle a "newer" laserjet to ATFSERVER1. More on that later...... The Accelerator Test Facility (ATF)
at Brookhaven National Laboratory (BNL) has been in operation since 1992.
The ATF is the nation's only experimental facility operated for accelerator
scientists as a proposal-driven, program-committee reviewed users facility.
This document is a brief history of this unique facility and also provides
some information about its capabilities, achievements and budget. The ATF
got started as a high-brightness linac R&D by BNL's Claudio Pellegrini
and Robert Palmer in about 1986. The facility got its initial funding
from the system of Exploratory Research Program (now known as Laboratory
Directed Research and Development) under BNL Director Nick Samios.. In
1986 to 1988 the program's goal was to prototype an electron gun and do
modeling of a 50-100 MeV linac, capable of producing a high brightness
electron beam, to be used in the future for the production of coherent
radiation in the IR to soft X-ray region and laser acceleration of electrons.
In 1989 to 1990 the work concentrated on the ATF facility prototypes:
linac, rf systems, low energy beam transport, FEL resonator and wiggler
R&D, control system and gun testing. Ilan
Ben-Zvi arrived at the ATF in 1988 and was appointed the director of the
facility in 1989, following the departure of Claudio Pellegrini to UCLA.
Later in 1989 the first User and Program Committee meeting was held for
the first time and six experiments were approved for operation in the
facility, which was still under construction. The ATF Program Committee
is also serving as a Steering Committee for the BNL Center for Accelerator
Physics, (CAP) headed by Bob Palmer. The membership
of the ATF Program Committee comprises of blue-ribbon accelerator scientists
from universities and national laboratories. It was first chaired by Andrew
Sessler (Lawrence Berkeley National Laboratory), then by Maury Tigner
(Cornell University), followed by Robert Siemann (Stanford Linear Accelerator
Center) and currently by Chan Joshi (University of California at Los Angeles).
The committee members are appointed by the head of CAP, Bob Palmer. Thus
the direction for the ATF comes from both CAP and the National Synchrotron
Light Source (NSLS) department. The ATF staff-members are affiliated with
the NSLS, which also provides administrative, ES&H and a considerable
amount of engineering and technical support for the ATF. Since
any LDRD funding is limited to two or three years at most, the future
of the budding facility depended on stable, larger scale support from
the DOE. A proposal to "complete and operate the ATF as a User facility
dedicated for the Physics of Beams" was submitted to the DOE in March
1990. The emphasis was on the special capability of the ATF to provide
a high-brightness electron beam and high-power lasers, synchronized with
high precision to the electron beam. That makes it possible to 'wed' lasers
to accelerators, opening for the first time systematic research on the
interaction of high power electromagnetic radiation with high-phase-space-density
electron beams, a subject reach in applications. Some of the intriguing
applications are laser acceleration of electrons, Free-Electron Lasers,
generation of ultra-short electron bunches (microbunches) and much more. The
proposal was accepted, and since then the ATF has been funded by the DOE,
as can be seen from Table 1.
Table 1. DOE funding of the
BNL Accelerator Test Facility, (unit $1000). Prior
to 1990 there has been some limited DOE support, but the support took
over from the LDRD only in FY'91. In addition, the ATF continued to enjoy
BNL Directorate support for general plant projects and LDRD dedicated
for special experiments. Examples of support in general plant projects
are the construction of the ATF Experiment Hall, (shown in figure 1),
the ATF power-supply and RF control mezzanine and the construction of
the photocathode laser clean room complex. LDRD support has been provided,
beyond the bootstrapping initial support, to experiments such as the Visible
FEL and High-Gain Harmonic-Generation experiments and for the development
of higher brightness electron beams.
In addition, the ATF benefited greatly from its membership in the
NSLS department and received considerable engineering and technical support.
A great deal of the know-how that went into the construction of the ATF
came from individuals such as Kenneth Batchelor, Joseph Sheehan and Martin
Woodle, to name a few. The association with CAP brought other talents
into play, in particular one may name Harold Kirk, Richard Fernow and
Juan Gallardo of the Physics Department, and Triveni Srinivasan-Rao and
(the late) Joachim Fischer from the Instrumentation Division. Figure
1. The ATF Experiment Hall. The first
experiment to operate at the ATF in 1992 was the Smith-Purcell radiation
experiment, using the 4.5 MeV electron beam from the ATF photoinjector,
by a team from Dartmouth, MIT and BNL headed by John Walsh. The study
of photocathodes, developed by Triveni Srinivasan-Rao and Joe Fischer
was also proceeding with the gun. Later in the same year, the 45 MeV electron
beam was propagated to the newly constructed Experiment Hall and the ATF
became operational. In the
first few years of the ATF, the number of experiments grew rapidly. Later
on the number reached a steady
state, with experiments retiring at about the same rate as experiments
were being approved. This can be seen in Figure 2. Figure2.
The number of ATF experiments as a function of time. At the same time the complexity, sophistication and cost of the experiments continues to grow. The cost of some of the experiments runs in the millions of dollars, provided at times by multi-institutional collaborations. The growth of the scientific activity let to a lot of published results and invited papers in meetings. The number of publications vs. year can be seen in Figure 3. Figure
3. The number of ATF publications as a function of year of publication,
from 1990 to 1999. We at the ATF take pride also in the contribution we provide to the education of graduate students and post docs in accelerator physics. ATF students come from all across the nation, from Ivy League schools to large State Universities and small colleges. The number of students graduating per year and the cumulative number of graduations is shown in Figure 4. The distribution of 17 students (alumni and current students) is shown in Figure 5. Figure
4. Graduate students by year of graduation (yellow) and cumulative total
(red). Figure
5. The distribution of 17 ATF graduate students by school. As a by-product of the R&D to improve the beam brightness, the ATF became a world-leader in the development of laser photocathode RF guns (photoinjectors). The ATF initial gun made its way to France, CERN, Rocketdyne Inc. and UCLA. The second gun, developed as a CRADA with Grumman powered a compact FEL at Princeton and a laser - beam chemical research facility at BNL. The third generation gun made its way to SLAC, UCLA and BNL, and the fourth one is in ANL, BNL and Japan. At the same time the science of metal photocathode was pushed to new heights at BNL with copper, magnesium and niobium cathodes providing high quantum efficiency and long lifetimes. Figure 6 shows a picture of the ATF Gun IV, the latest in the series. Figure
6. ATF gun IV (left) and a rendition of a complete gun assembly (right). Another way to look at the history
of the ATF is to follow a few landmark experimental results. The first
achievement was in the area of laser acceleration of electrons, the demonstration
of a 3.5 MeV acceleration of electrons using the Inverse Cerenkov effect.
The results of the experiment, led by Wayne Kimura of STI Optronics Inc.
of Bellevue, Washington, were published in 1995 [W.D. Kimura, G.H. Kim,
R.D. Romea, L.C. Steinhauer, I.V. Pogorelsky, K.P. Kusche, R.C. Fernow,
X.J. Wang and Y. Liu, "Laser Acceleration of Relativistic Electrons
Using the Inverse Cerenkov Effect", Phys. Rev. Let. 74, 546 (1995)].
At about the same time, an experiment probing the Smith-Purcell mechanism
of radiation generation from relativistic electrons got interesting results
showing forward directed radiation from a grating [K.J. Woods, J.E. Walsh,
R.E. Stoner, H.G. Kirk and R.C. Fernow, "Forward Directed Smith-Purcell
Radiation from Relativistic Electrons", Phys. Rev. Let. 74, 3808
(1995)]. The development of sophisticated
electron beam diagnostics turned out to be a very prolific area of research
at the ATF. The first major result has been the measurement of emittance
of individual picosecond-long slices of an electron bunch, demonstrating
the mechanism of emittance correction at work. [X. Qiu, K. Batchelor,
I. Ben-Zvi and X.J. Wang, "Demonstration of Emittance Compensation
through the Measurement of the Slice Emittance of a 10-ps Electron Bunch,
Phys. Rev. Let. 76, 3723 (1996)]. Another landmark result in laser
acceleration was the Inverse Free-Electron Laser experiment, led by Arie
van Steenbergen of BNL, achieving about 1 MeV acceleration [A. van Steenbergen,
J. Gallardo, J. Sandweiss, J.-M. Fang, M. Babzien, X. Qiu, J. Skaritka
and X.J. Wang, "Observation of Energy Gain at the BNL Inverse Free-electron-Laser
Accelerator", Phys. Rev. Let. 77, 2690 (1996)]. The same experimental setup also
was used by another team led by Xijie Wang to measure the production of
the world's shortest electron bunches, about 1 micrometer long. [Y. Liu,
X.J. Wang, D.B. Cline, M. Babzien, J.M. Fang, J. Gallardo, K. Kusche,
I. Pogorelsky, J. Skaritka and A. van Steenbergen, "Experimental
Observation of Femtosecond Electron Beam Micro-bunching by Inverse Free-Electron-Laser
Acceleration, Phys. Rev. Lett. 80, 4418 (1998)]. Extremely short bunches are important
for a variety of applications, from the generation of coherent radiation
to injection into laser accelerators. Bunching by ballistic compression
in the electron gun an experiment led by Xijie Wang, provided another
record result [X.J. Wang, X. Qiu and I. Ben-Zvi, "Experimental Observation
of High-Brightness Micro-Bunching in a Photocathode RF Gun", Phys.
Rev. E54 No. 4, R3121, (1996)]. A number of important results were
obtained in the area of Free-Electron Lasers (FEL). The first was the
achievement of gain in Self Amplified Spontaneous Emission (SASE) in the
visible and near IR. This result, led by Ilan Ben-Zvi, was shorter in
wavelength by an order of magnitude from any previous result, demonstrating
the very high brightness of the ATF beam. [M. Babzien, I. Ben-Zvi, P.
Catravas, J-M. fang, T.C. Marshall, X.J. Wang, J.S. Wurtele, V. Yakimenko,
L.H. Yu, "Observation of Self-Amplified Spontaneous Emission in the
Near-Infrared and Visible Wavelength", Phys. Rev. E 57 6093 (1998)]. Another FEL
'first' is the demonstration of High-Gain Harmonic-Generation FEL.
This experiment is a proof-of-principle for a new generation of FELs that
can provide highly coherent radiation in short wavelengths where mirrors
cannot be used. The spokesperson of this experiment is Li Hua Yu. [L.-H.
Yu, M. Babzien, I. Ben-Zvi, L.F. DiMauro, A. Doyuran, W. Graves, E. Johnson,
S. Krinsky, R. Malone, I. Pogorelsky, J. Skaritka, G. Rakowsky, L. Solomon,
X.J. Wang, M. Woodle, V. Yakimenko, S.G. Biedron, J.N. Galayda, E. Gluskin,
J. Jagger, V. Sajaev, I. Vasserman, High-Gain Harmonic-Generation Free-Electron
Laser, Science, 289 (2000) 932] We return to the area of diagnostics
by mentioning another 'first' in diagnostics obtained at the ATF. This
one, led by the (then) graduate Palmyra Catravas, is the use of undulator
radiation as a non-invasive diagnostic of beam bunch length and emittance,
[P. Catravas, W.P. Leemans, J.S. Wurtele, M.S. Zolotorev, M. Babzien,
I. Ben-Zvi, Z. Segalov, X.J. Wang, V. Yakimenko, Measurement of Electron-Beam
Bunch Length and Emittance Using Shot-Noise-Driven Fluctuations in Incoherent
Radiation, Phys. Rev. Lett. 82 no. 26, 5261, (1999)]. The list of novel diagnostics does not end there. The precision tomographic measurement of the beam density in phase-space, the work of Vitaly Yakimenko, has been done in a number of ways at the ATF, including the demonstration of the effect of variations in the electron density [V. Yakimenko, M. Babzien, I. Be-Zvi, R. Malone, X.-J. Wang, Emittance Control of a Beam by Shaping the Transverse Charge Distribution, Using a Tomography diagnostic. Proceedings of EPAC'98, June 22-27, Stockholm, Sweden, page 1641], tomographic measurement of a single longitudinal slice and others. An international experiment on beam instrumentation is the experimental test of a high precision, inexpensive beam position monitor for linear colliders, led by Vladimir Balakin of Protvino, Russia. The cavity-based beam-position monitor achieved so far a resolution of 150 nm in a single shot of less than 0.5 nC beam charge, and sub 100 nm resolution is anticipated. The initial result from the experiment was the subject of an invited talk at PAC'99, [V. Balakin, A. Bazhan, P. Lunev, N. Solyak, V. Vogel, P. Zhogolev, A. Lisitsyn, V. Yakimenko, Experimental Results From a Microwave Cavity Beam Position Monitor, Proc. of the 1999 Particle Accelerator Conference, A. Luccio, W. MacKay, Editors, 461, (1999)]. Another international experiment, this time Japanese-American collaboration, is the Thomson Scattering of a laser of the electron beam. The purpose of this experiment is to develop a technique to produce polarized positrons for linear colliders. As a by-product, this experiment is a unique source of picosecond x-rays in an unprecedented number of photons per pulse. This partial list will be concluded by describing the STELLA (Staged Electron Laser Accelerator) results. This experiment is the first of the second-generation laser acceleration experiments. STELLA was designed to demonstrate that one can stage in series two laser accelerators, phase and match them as well as to demonstrate that the beam quality of laser accelerators can be good. These are essential steps on the way to practical future laser accelerators. The experiment succeeded in doing so. [W. D. Kimura, M. Babzien, I. Ben-Zvi, L. P. Campbell, D. B. Cline, J. C. Gallardo, S. C. Gottschalk, P. He, K. P. Kusche, Y. Liu, R. H. Pantell, I. V. Pogorelsky, D. C. Quimby, J. Skaritka, A. van Steenbergen, L.C. Steinhauer, and V. Yakimenko, “Demonstration of a Laser-Driven Prebuncher Staged With a Laser Accelerator - The STELLA Program,” to be published in the proceedings of the 9th Workshop on Advanced Accelerator Concepts, June 10-16, 2000, Santa Fe, NM.] The layout of the experiment is shown in Figure 7, together with three electron beam energy spectra: The spectrum with laser off, with first stage on and with both stages on. The first stage modulates the energy of the beam. Following bunching of the beam (to microbunches about 3 to 4 femtosecond long) the second stage accelerates the bunches with a good energy spread, about 1% to 2 %. The stability is the system is remarkable, although long-term drifts were observed in the phasing of the two laser accelerator sections.
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