Current status of Lebedev Physical Institute far infrared free electron laser
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Назва видання: | Вопросы атомной науки и техники |
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| Цитувати: | Current status of Lebedev Physical Institute far infrared free electron laser / A.V. Agafonov, A.I. Bukin, A.V. Koltsov, V.G. Kurakin, A.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 3-5. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-815102015-05-18T03:02:32Z Current status of Lebedev Physical Institute far infrared free electron laser Agafonov, A.V. Bukin, A.I. Koltsov, A.V. Kurakin, V.G. Lebedev, A.N. 1999 Article Current status of Lebedev Physical Institute far infrared free electron laser / A.V. Agafonov, A.I. Bukin, A.V. Koltsov, V.G. Kurakin, A.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 3-5. — Бібліогр.: 4 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81510 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| format |
Article |
| author |
Agafonov, A.V. Bukin, A.I. Koltsov, A.V. Kurakin, V.G. Lebedev, A.N. |
| spellingShingle |
Agafonov, A.V. Bukin, A.I. Koltsov, A.V. Kurakin, V.G. Lebedev, A.N. Current status of Lebedev Physical Institute far infrared free electron laser Вопросы атомной науки и техники |
| author_facet |
Agafonov, A.V. Bukin, A.I. Koltsov, A.V. Kurakin, V.G. Lebedev, A.N. |
| author_sort |
Agafonov, A.V. |
| title |
Current status of Lebedev Physical Institute far infrared free electron laser |
| title_short |
Current status of Lebedev Physical Institute far infrared free electron laser |
| title_full |
Current status of Lebedev Physical Institute far infrared free electron laser |
| title_fullStr |
Current status of Lebedev Physical Institute far infrared free electron laser |
| title_full_unstemmed |
Current status of Lebedev Physical Institute far infrared free electron laser |
| title_sort |
current status of lebedev physical institute far infrared free electron laser |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
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http://dspace.nbuv.gov.ua/handle/123456789/81510 |
| citation_txt |
Current status of Lebedev Physical Institute far infrared free electron laser / A.V. Agafonov, A.I. Bukin, A.V. Koltsov, V.G. Kurakin, A.N. Lebedev // Вопросы атомной науки и техники. — 1999. — № 4. — С. 3-5. — Бібліогр.: 4 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T06:29:55Z |
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| fulltext |
CURRENT STATUS OF LEBEDEV PHYSICAL INSTITUTE FAR
INFRARED FREE ELECTRON LASER*
A.V.Agafonov, A.I.Bukin, A.V.Koltsov, V.G.Kurakin, A.N.Lebedev
Lebedev Physical Institute of RAS, Moscow, Russia
INTRODUCTION
Far infrared free electron laser (FEL-100), under
commissioning now, is the first stage of Lebedev
Physical Institute Radiation Complex [1]. It was nice
idea to cover infrared bandwidth in the range 10 - 100
microns with three or more FEL being excited by
electron beams with energies 7 -25 MeV from different
orbits of high current race track microtron under
operation since mid of 80-th [2, 3]. The range
mentioned is attractive from many viewpoints and for
numerous applications as well, including for example so
different fields of human activity as fundamental
research and medicine practice. We are close to put
FEL-100 into operation thus making the crucial step in
starting light application program in the range 80 - 160
microns of coherent radiation. Following is the current
status of far infrared laser project including hard ware
description and adjustment as well as beam and light
dynamics study.
ELECTRON BEAM SOURCE, BEAM LINE AND
INJECTION
Electron beam from existing racetrack facility
with average energy 7 MeV is used to drive FEL-100.
Low voltage electron gun with chicane magnet,
bunching cavity and disk loaded waveguide of racetrack
form almost linac configuration. This configuration
along with compensated beam channel in the vacuum
chamber of first microtron bending magnet is used to
produce high current bunches for FEL, focusing and
diagnostic elements of race track being included in such
a linac. There is a vacuum valve at the entrance of FEL-
100 beam line, that along with some other elements of
beam extraction system makes it possible to operate
independently with either racetrack or FEL-100 facility.
FEL-100 beam line itself formed by quadrupole doublet,
correction coils, beam diagnostic system, ending by
laser injection system. The latter consists of three
bending magnets providing achromatic 120 grad
electron rotation in horizontal plane to direct beam from
linac to laser axis. As calculations have been shown
such beam line configuration allows linac beam
injection and matching as well. The latter means that
one can provide with quadrupoles strength changing
flexible transverse beam dynamics tuning, including the
possibility of stationary phase space ellipse forming at
undulator part of electron trajectories. Beam diagnostic
system includes non intercepting current monitors and
luminescent screens providing together with Faradays
cups at the beam line terminals and movable
luminescent screen inside helical undulator electron
beam tuning.
FAR INFRARED FEL
Far infrared FEL (FEL-100) will provide
coherent radiation in the wavelength range 80 - 160
microns. The are several features of this laser that differ
it from other similar devises. We use pulse helical
undulator with passive field correction [4] and short
open resonator. The former imposes serious limitations
on laser repetition rate as well as results in some
specific beam and light diagnostic procedures. The latter
leads to smaller diffraction losses and together with
relatively high laser gain per path allows to reach FEL
steady state (laser saturation) during short accelerator
pulse. Resonator of nearly confocal type is formed by
two spherical copper mirrors, each one being adjusted
under vacuum condition with electromechanical
equipment. The undulator's double-start winding has a
period of 32 mm and consists of 32 turn of copper wire
with diameter of 2.5 mm, the average winding diameter
being equal to 35 mm. The coil is placed in slots to
provide mechanical stiffness. A capacitor bank,
discharged through a water cooled ignitron, provides
undulator excitation. Undulator and power supply
parameters allows to maintain a flatness of 0.1% during
the accelerator pulse. The magnetic field of
approximately 0.35 T on the undulator axis is achieved
at a current of 40 kA through undulator winding.
Maximum lasing repetition rate depends on guiding
undulator magnetic field, cooling condition and power
supply available. We expect this value to be reached
around 0.1 -0.2 Hz for application experiments. The
layout of the Lebedev Physical Institute Radiation
Complex is presented on Fig. 1, while the main far
infrared FEL parameters are collected in Table 1.
Fig.1 Layout of Lebedev Physical Institute Radiation
Complex. Far Infrared FEL is at the upper left corner.
Table 1 Far infrared FEL parameters.
Wavelength range (µm) 80 - 160
FEL radiation power 60 kW
Pulse duration (µs) 5 - 6
Micro pulse duration 30 ps
Electron beam energy (MeV) 6 - 8
Energy spread at FEL entrance (%) 1.5
Gain per path (at peak current 10 A) 20
Optical cavity length 165 cm
Mirror diameter 2.8 cm
Waste of laser mode 5mm
Accelerator wavelength 16.5 cm
Accelerator repetition rate (Hz) 0.1 - 5
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 3-5.
3
Vertical beam emittance 3⋅π⋅mm⋅mrad
Horizontal beam emittance 7⋅π⋅mm⋅mrad
Undulator period 3.2 cm
Number of turns 35
Beam pipe aperture 2.7 cm
Maximum current through winding 45 kA
Repetition rate at maximum current 0.05 Hz
Undulator parameter 0 – 1.4
ELECTRON BEAM DYNAMICS
The last two years we were adjusting various
elements of FEL facility and studying beam dynamics.
It had been found while commissioning racetrack
microtron that beam energy spectrum at the linac exit
was very sensitive to injection system tuning. This
remarkable feature allows to form intense electron beam
with narrows energy spectrum width down to 1 - 1.5 %
with simultaneously short phase bunch length down to
18-20 degrees, thus allowing to use racetrack
accelerating system as effective driver for far infrared
FEL. At the same time this imposes very strong
requirements on many accelerator parameters stability
to provide necessary beam quality. The easiest way to
maintain good beam quality at linac exit is appropriate
phase adjustment of injected beam at accelerating
structure entrance according beam spectrum that is
achieved along with phase shifter in buncher power
supply waveguide. We use the first racetrack bending
magnet to control electron beam energy spectrum, the
latter being measured with secondary emission beam
profile monitor installed at focal plane location after 180
degrees beam rotation. Pulse signals from monitor wires
are amplified and transmitted through cable to control
room where these are processed by analogue-to-digit
converter under computer control. Together with other
facility parameters energy spectrum is displayed on
computer monitor, thus allowing effective beam control.
Optical resonator and undulator are the most critical
FEL's parts from many viewpoints. We had developed
original computer governed equipment to control beam
profile and position along undulator. According
program being chosen step motor positions luminescent
screen at any desired point inside undulator, while TV
camera transfers electron beam image to monitor at
control room. Special mirror system extract luminescent
light from resonator during beam dynamics studying.
Beam profile and position measurement system is
placed in special "home" position at light generation
phase. The software allows to automate completely
beam dynamics exploration, if special video card is used
to enter beam co-ordinates directly to computer. Up to
now we enter his values manually. Although manual
input does not increase experiment time measured
values are less objective because of man factor
influence. The main reasons of detailed beam dynamics
studying in undulator is the correction of guiding field
as well as undulator input and output. Although we had
made such a correction at undulator stand test, it is
difficult to guaranty field quality after a lot of steps of
undulator and its accessories assembling, vacuum
sealing and so on. As preliminary study has shown,
electron beam offset does not exceed 2-3 mm along
undulator length and two quadruple doublets together
with correction coils are tools that effective enough to
form desired beam sizes inside undulator.
Beam monitoring system had been used to
align helical undulator on FEL bench. Alignment
procedure is quite necessary for our undulator because
its stiffness is not sufficient and undulator sagging may
result in large dynamics perturbation. The light from
He-Ne laser was injected into undulator through the
small aperture in its end flange and detected at the
opposite undulator end, while moving luminescent
screen with small aperture in its centre along undulator
beam pipe. Undulator supports were adjusted and fixed
when maximum intensity was detected in transmitted
light.
WHERE WE GO AND WHERE WE ARE
Fig.2 Typical interface for accelerator and FEL
parameters measurements.
Our aim is a multi purpose radiation centre. Such
a complex might activate research in many fields. We
plan to start light application program from the
experiment on searching energy gap in high Tc
superconductors by radiating superconducting film
samples by submillimeter FEL radiation with light
frequency scanning. We have prepared some necessary
equipment to start such a program. Our next step in FEL
commissioning will be searching for stimulated
radiation from our far infrared laser. We are almost
ready for this step having been adjusting laser mirrors
and diagnostic system and finishing mirror position
monitor.
Computer with CAMAC interface is used to
measure the main accelerator and FEL parameters in
one accelerator pulse, that not overcomes some system
inconveniences connected with low laser repetition rate
only but makes it possible also on line and off line
signals processing. Fig. 1 and. Fig. 2 are examples of
such a measurement and control. New measurement
system for any parameters monitoring in different
modes is under development. The main future of this
system is the possibility for operator to create any
desired graphical interface before experiment run in any
display mode: time dependent spectrum for multi
channel measurement or oscilloscope mode for any
single signal.We expect to fix stimulated radiation from
our far infrared FEL to the end of 1999.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 3-5.
4
Fig.3. Computer interface for beam dynamics
exploration in helical undulator.
ACKNOWLEDGEMENTS
The authors are very grateful to former coworker
E.B.Gaskevich for large contribution in designing and
assembling of many FEL elements. We also want to
thank A.I.Karev and V.A.Kuznetsov for some
computation of beam line, V.P.Busigin and
V.P.Alexeev for designing and manufacturing of
analog-to-digit converter and fruitful discussions.
The work is partly done in the frame of support
of Russian Research Program “Physics of microwaves”.
REFERENCES
1. K.A.Belovintsev, A.I.Bukin, E.B.Gaskevich,
A.V.Koltsov, V.A.Kuznetsov, V.G.Kurakin and
S.V.Sidorov. The Radiation Complex for Fundamental
Research, in Proceedings of the 4th European Particle
Accelerator Conference, London, 27 June to 1 July
1994, pp. 861-863.
2. K.A.Belovintsev, A.I.Karev and V.G.Kurakin, "The
Lebedev Physical Institute Race-Track Microtron",
Nuclear Instruments and Methods, A261, pp. 36-38,
1987.
3. A.V.Agafonov, V.G.Kurakin, A.N.Lebedev,
V.A.Papadichev. "Infrared free electron laser for
spectroscopy", Microwave Physics, Nigniy Novgorod,
pp. 63 - 70, 1999, (in Russian).
4. A.I.Bukin, E.B.Gaskevich, V.G.Kurakin and
O.V.Savushkin, "The experimental study of helical
undulator", Trudi FIAN, vol. 214, pp. 155-163, 1993,
(in Russian).
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. № 4.
Серия: Ядерно-физические исследования (35), с. 5-7.
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