Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons
System of homogeneous extraction of gamma-beam from the 1.2 GeV electron synchrotron "Pakhra" is discussed. Accelerated electrons are slowly brought to the tungsten target, which is placed inside the synchrotron vacuum chamber. During extraction high frequency voltage on accelerator’s cavi...
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| Zitieren: | Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons / Yu.A. Bashmakov, V.A. Karpov // Вопросы атомной науки и техники. — 2012. — № 3. — С. 142-144. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-1087342016-11-16T03:02:17Z Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons Bashmakov, Yu.A. Karpov, V.A. Динамика пучков System of homogeneous extraction of gamma-beam from the 1.2 GeV electron synchrotron "Pakhra" is discussed. Accelerated electrons are slowly brought to the tungsten target, which is placed inside the synchrotron vacuum chamber. During extraction high frequency voltage on accelerator’s cavity is hold constant. Limited electron betatron oscillations are exiting by means of the gradient and the octupole pole face windings. Time uniformity of gamma quanta flow is provided by a special choice of the time dependence of the index of the synchrotron guide magnetic field. Control of the extraction process by a computer with usage of a feedback circuit will be performed. Обсуждается система однородного во времени вывода гамма-пучка из электронного синхротрона "Пахра" на энергию 1,2 ГэВ. Ускоренные электроны медленно направляются на вольфрамовую мишень, которая размещена внутри вакуумной камеры синхротрона. Во время вывода высокочастотное напряжение на ускоряющем резонаторе поддерживается постоянным. Ограниченные бетатронные колебания электронов возбуждаются посредством градиентной и октупольной полюсных обмоток. Однородность потока гамма-квантов во времени обеспечивается специальным выбором зависимости от времени показателя спада ведущего магнитного поля синхротрона. Для эффективного управления процессом вывода может быть использована цепь обратной связи. Обговорюється система однорідного у часі виведення гамма-пучка з електронного синхротрона "Пахра" на енергію 1,2 ГеВ. Прискорені електрони повільно спрямовуються на вольфрамову мішень, яка розміщена всередині вакуумної камери синхротрона. Під час виведення високочастотна напруга на прискорюючем резонаторі підтримується постійною. Обмежені бетатронні коливання електронів збуджуються за допомогою градієнтної і октупольної полюсних обмоток. Однорідність потоку гамма-квантів в часі забезпечується спеціальним вибором залежно від часу показника спаду провідного магнітного поля синхротрона. Для ефективного управління процесом виведення може бути використаний ланцюг зворотного зв'язку. 2012 Article Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons / Yu.A. Bashmakov, V.A. Karpov // Вопросы атомной науки и техники. — 2012. — № 3. — С. 142-144. — Бібліогр.: 3 назв. — англ. 1562-6016 PACS: 29.27.Bd http://dspace.nbuv.gov.ua/handle/123456789/108734 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Динамика пучков Динамика пучков |
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Динамика пучков Динамика пучков Bashmakov, Yu.A. Karpov, V.A. Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons Вопросы атомной науки и техники |
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System of homogeneous extraction of gamma-beam from the 1.2 GeV electron synchrotron "Pakhra" is discussed. Accelerated electrons are slowly brought to the tungsten target, which is placed inside the synchrotron vacuum chamber. During extraction high frequency voltage on accelerator’s cavity is hold constant. Limited electron betatron oscillations are exiting by means of the gradient and the octupole pole face windings. Time uniformity of gamma quanta flow is provided by a special choice of the time dependence of the index of the synchrotron guide magnetic field. Control of the extraction process by a computer with usage of a feedback circuit will be performed. |
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Article |
| author |
Bashmakov, Yu.A. Karpov, V.A. |
| author_facet |
Bashmakov, Yu.A. Karpov, V.A. |
| author_sort |
Bashmakov, Yu.A. |
| title |
Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons |
| title_short |
Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons |
| title_full |
Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons |
| title_fullStr |
Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons |
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Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons |
| title_sort |
gamma-beam generation at the synchrotron "pakhra" by resonance excitation of accelerated electrons |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2012 |
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Динамика пучков |
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http://dspace.nbuv.gov.ua/handle/123456789/108734 |
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Gamma-beam generation at the synchrotron "Pakhra" by resonance excitation of accelerated electrons / Yu.A. Bashmakov, V.A. Karpov // Вопросы атомной науки и техники. — 2012. — № 3. — С. 142-144. — Бібліогр.: 3 назв. — англ. |
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Вопросы атомной науки и техники |
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ISSN 1562-6016. ВАНТ. 2012. №3(79) 142
GAMMA-BEAM GENERATION AT THE SYNCHROTRON "PAKHRA"
BY RESONANCE EXCITATION OF ACCELERATED ELECTRONS
Yu.A. Bashmakov, V.A. Karpov
P.N. Lebedev Physical Institute of the Russian Academy of Science, Moscow, Russia
System of homogeneous extraction of gamma-beam from the 1.2 GeV electron synchrotron "Pakhra" is dis-
cussed. Accelerated electrons are slowly brought to the tungsten target, which is placed inside the synchrotron vac-
uum chamber. During extraction high frequency voltage on accelerator’s cavity is hold constant. Limited electron
betatron oscillations are exiting by means of the gradient and the octupole pole face windings. Time uniformity of
gamma quanta flow is provided by a special choice of the time dependence of the index of the synchrotron guide
magnetic field. Control of the extraction process by a computer with usage of a feedback circuit will be performed.
PACS: 29.27.Bd
1. INTRODUCTION
Generally at electron synchrotrons stretched beams
of bremsstrahlung are obtained by means of modulation
of accelerating high-frequency voltage. In the present
paper a possibility to use the nonlinear resonance excita-
tion of accelerated electrons for high energy gamma-
beam generation at the synchrotron is discussed. The
nonlinear fourth order resonance of the radial betatron
oscillations have been successfully used for a slow ex-
traction of the electron beam on the 1.2 GeV synchro-
tron "Pakhra" [1]. The main synchrotron parameters are
given in [2].
2. BASIC OUTLINE
Required resonant conditions are fulfilled by two pole
face windings, and there are separate pairs of quadrants
for either winding. The gradient winding placed at the
first and third quadrants brings the index of magnetic
field from working value 0.51 (νx=0.802, νz=0.819) to
resonant one 0.63. The necessary third azimuthal har-
monic of cubic nonlinearity of magnetic field exiting
resonance growth of electron oscillations is forming by
octupole winding. The winding occupies second and
fourth quadrants.
At resonance the amplitude of the radial betatron os-
cillation a will increase if the following condition will
meet
4/3122
3 −> xvaA , (1)
where ( ) ( )03
33
03 !3// HxHRA z ∂∂= is the amplitude of
third azimuthal harmonic of cubic nonlinearity of mag-
netic field, R0 is the equilibrium orbit radius in guiding
magnetic field H0. In this case the amplitude increment
at two successive passage (within four revolutions) near
the target, whose distance from the central orbit is xs, is
equal to
3
38 3
2
sxAa π
=Δ π . (2)
The extraction efficiency is determined just by this
expression. Having defined A3 from (2) the boundary
frequency detuning 4/30 −=δ xv can be find accord-
ing to known distribution of the betatron oscillation am-
plitudes (see (1)).
3. EXTRACTION SYSTEM EQUIPMENT
POLE FACE WINDINGS
Gradient winding: The gradient winding contains 38
straight conductors lying on the magnet pole which are
connected with reverse conductors such that 19 are in-
ternal and 18 are external relative to the magnetic gap.
One ampere current in this winding excites in the center
of the working space the gradient equal to
=∂∂ xH z / 0.524 Oe/cm.
Octupole winding: The octupole (cubic) magnetic
field is formed by 17 straight conductors. The current in
three centrally located conductors flows in reverse di-
rection from current in remaining fourteen conductors.
Six internal and five external reverse conductors are
used. The radial dependence of the field and gradient of
the winding are shown in Fig.1. One ampere current
excites in the center of the working space the octupole
field =∂∂ 33 / xH z 0.0445 Oe/cm3.
Fig.1. Magnetic field (1) and gradient (2) distributions
introduced by the octupole winding
Besides required nonlinearity there are others ac-
companying nonlinearities. Thus it is rather essential the
presence of the constant (dipole) component of the field
=zH -0.160 Oe. At the large distances from the equilib-
rium orbit it is appreciable fifth order nonlinearity
=∂∂ 55 / xH z -0.194 Oe/cm5.
ISSN 1562-6016. ВАНТ. 2012. №3(79) 143
It can has an influence on the particle motion at xs as
a result, the amplitude increment πΔ 8a can be reduced
in comparison with value given by (2). Indeed for the
real "octupole" field distribution shown in Fig.1 dra-
matic changing is observed. The electron motion on
phase plane at azimuth of the target for following pa-
rameters =ΔnI 4.956 A, =3xI 10.5 A, is shown in Fig.3.
The rate of the betatron oscillation growth is reducing in
comparison with equation (2).
The third azimuthal harmonic of the perturbation is
produced by reversing the current direction in the octu-
pole winding in going from second quadrant to fourth
one. Its amplitude is ( ) ( )33
3
33 /58.0/ xHxH zz ∂∂=∂∂ ,
where 33 / xH z ∂∂ is constant within the quadrants. Un-
der such connection circuit the dipole component of
octupole winding introduces first harmonic of the azi-
muthal distortion of the equilibrium orbit.
4. PULSER
The pole face windings are feeded by two current
pulsers. The pulses shapes are designed to work on the
flat top part of the pulse of the guiding magnetic field of
the synchrotron. The leading edge of these pulses is
1 ms and their flat peaks range from 2 to 3 ms. Repeti-
tion rate is 50 Hz. The accuracy of current stabilization
at the flat peak is 0.3 %. The possibility of deformation
of the top of the gradient winding current pulse is fore-
seen. The range of this change is few per cent of the
height. All current pulses are turn on simultaneously.
The triggering moment measured from the injection can
be varied over a wide range.
5. EXTRACTION PROCESS
The extraction was accomplished after the electrons
have reached 670 MeV energy. The amplitude of accel-
erating voltage on the synchrotron cavity was almost
constant. Due to the sharp radial dependence of the gra-
dient introduced by the octupole winding (see Fig.1) it
is essential to accurate select the frequency of accelerat-
ing voltage which determines position of the equilib-
rium orbit. The starting detuning of the radial betatron
oscillation frequency at which extraction is beginning is
determined not only by the amplitude of this oscillation
but also by synchrotron one. The dynamic of the elec-
tron beam in the "Pakhra" synchrotron was investigated
in Ref. [3]. Two-dimensional distribution of electrons in
the transverse cross-section of the beam is shown at
Fig.2. Both betatron and radial-phase oscillations make
a contribution into radial beam dimension and the later
is twice as much former (Fig.3). In the circumstances
the range of the resonance action is being widened in
comparison with (1).
Time dependence of the circulating current at slow
extraction mode is show at Fig.4.
The gradient and octupole currents are accordingly
=ΔnI 4.4 A and =3xI 20 A. This picture is very sensitive
to the nI Δ current, whose value is choosing to obtain
during extraction the very smooth fall down of the cir-
culating current. The typical extraction duration is be-
tween 2 and 3 msec, which at 50 Hz repetition rate of
magnetic cycle corresponds to a duty factor of 15 per
cent. Fig.4 displaies more than 80 % of accelerated par-
ticles leaving the synchrotron chamber. Note that the
nature of the steps on Fig.4 very likely is caused by the
manifestation of synchro-betatron resonances.
Fig.2. Two-dimensional distribution of electrons
in the transverse cross-section of the beam
Fig.3. Computed phase plot of the electron resonance
betatron oscillation
Fig.4. Time dependence of the electron current circulat-
ing in the synchrotron (signal from pick-up electrodes)
during slow extraction process, 2 ms/square
CONCLUSIONS
Time uniformity of gamma quanta flow is provided
by a special choice of the time dependence of the index
of the synchrotron guide magnetic field. To hold the
gamma-beam intensity in the given range it is suggested
to use special circuit which will process signal from
gamma-beam intensity monitor and then introduce
proper correction into the gradient winding current.
ISSN 1562-6016. ВАНТ. 2012. №3(79) 144
REFERENCES
1. Yu.A. Bashmakov, K.A. Belovintsev, V.A. Karpov.
An extraction of electrons from a synchrotron on
fourth-order resonance // Proc. of Epac’90, Nice,
June 12-16, 1990, Proc. 2nd European Particle
Accelerator Conf., Editions Frontieres, v.2, р.1601-
1603.
2. P. Kurakin, V. Alekseev, V. Busygin, et al.
Automation of the Lebedev institute synchrotron to
the energy 1.3 GeV as the first stage of the
accelerator upgrade // Proc. of IEEE Particle
Accelerator Conference (PAC-2001), Chicago,
Illinois, June. 2001, р.2778-2780.
3. Yu.A. Bashmakov, V.A. Karpov, A.S. Yarov.
Optical diagnosis of electron beam in the "Pakhra"
synchrotron // Instrum. Exp. Tech. 1984, v.27,
р.1329-1333.
Статья поступила в редакцию 23.09.2011 г.
ГЕНЕРАЦИЯ ГАММА-ПУЧКА НА СИНХРОТРОНЕ "ПАХРА" ПУТЕМ РЕЗОНАНСНОГО
ВОЗБУЖДЕНИЯ ПОПЕРЕЧНОГО ДВИЖЕНИЯ УСКОРЕННЫХ ЭЛЕКТРОНОВ
Ю.А. Башмаков, В.A. Карпов
Обсуждается система однородного во времени вывода гамма-пучка из электронного синхротрона "Пах-
ра" на энергию 1,2 ГэВ. Ускоренные электроны медленно направляются на вольфрамовую мишень, которая
размещена внутри вакуумной камеры синхротрона. Во время вывода высокочастотное напряжение на уско-
ряющем резонаторе поддерживается постоянным. Ограниченные бетатронные колебания электронов возбу-
ждаются посредством градиентной и октупольной полюсных обмоток. Однородность потока гамма-квантов
во времени обеспечивается специальным выбором зависимости от времени показателя спада ведущего маг-
нитного поля синхротрона. Для эффективного управления процессом вывода может быть использована цепь
обратной связи.
ГЕНЕРАЦІЯ ГАММА-ПУЧКА НА СИНХРОТРОНІ "ПАХРА" ШЛЯХОМ РЕЗОНАНСНОГО
ЗБУДЖЕННЯ ПОПЕРЕЧНОГО РУХУ ПРИСКОРЕНИХ ЕЛЕКТРОНІВ
Ю.А. Башмаков, В.О. Карпов
Обговорюється система однорідного у часі виведення гамма-пучка з електронного синхротрона "Пахра"
на енергію 1,2 ГеВ. Прискорені електрони повільно спрямовуються на вольфрамову мішень, яка розміщена
всередині вакуумної камери синхротрона. Під час виведення високочастотна напруга на прискорюючем ре-
зонаторі підтримується постійною. Обмежені бетатронні коливання електронів збуджуються за допомогою
градієнтної і октупольної полюсних обмоток. Однорідність потоку гамма-квантів в часі забезпечується спе-
ціальним вибором залежно від часу показника спаду провідного магнітного поля синхротрона. Для ефектив-
ного управління процесом виведення може бути використаний ланцюг зворотного зв'язку.
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