Buncher of electron linac-injector for a synchrotron
The application of RF buncher-accelerators for obtaining the short electron bunches is rather known. Their design varies. Linear accelerators with high-current pulsed beams at energy more than 30 MeV are mainly used as injectors into synchrotrons at modern accelerating complexes. The beam should be...
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| Дата: | 1999 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
1999
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| Цитувати: | Buncher of electron linac-injector for a synchrotron / K.N. Chernov, P.V. Logachev, G.N. Ostreiko, G.V. Serdobintsev, S.V. Shiyankov, G.I. Yasnov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 44-46. — Бібліогр.: 7 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
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irk-123456789-813552015-05-15T03:01:59Z Buncher of electron linac-injector for a synchrotron Chernov, K.N. Logachev, P.V. Ostreiko, G.N. Serdobintsev, G.V. Shiyankov, S.V. Yasnov, G.I. The application of RF buncher-accelerators for obtaining the short electron bunches is rather known. Their design varies. Linear accelerators with high-current pulsed beams at energy more than 30 MeV are mainly used as injectors into synchrotrons at modern accelerating complexes. The beam should be previously prepared as series of bunches for injection to obtain stable and effective accelerating regime. In this case RF electron sources would be appropriate for use at the input of a linear accelerator. Such preparing the beam allows one to achieve an effective beam capture into the accelerating regime of linear accelerator for each of the bunches, as well as synchronized operation of the complex with decreased level of radiation background. 1999 Article Buncher of electron linac-injector for a synchrotron / K.N. Chernov, P.V. Logachev, G.N. Ostreiko, G.V. Serdobintsev, S.V. Shiyankov, G.I. Yasnov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 44-46. — Бібліогр.: 7 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81355 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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The application of RF buncher-accelerators for obtaining the short electron bunches is rather known. Their design varies.
Linear accelerators with high-current pulsed beams at energy more than 30 MeV are mainly used as injectors into synchrotrons at modern accelerating complexes. The beam should be previously prepared as series of bunches for injection to obtain stable and effective accelerating regime. In this case RF electron sources would be appropriate for use at the input of a linear accelerator. Such preparing the beam allows one to achieve an effective beam capture into the accelerating regime of linear accelerator for each of the bunches, as well as synchronized operation of the complex with decreased level of radiation background. |
| format |
Article |
| author |
Chernov, K.N. Logachev, P.V. Ostreiko, G.N. Serdobintsev, G.V. Shiyankov, S.V. Yasnov, G.I. |
| spellingShingle |
Chernov, K.N. Logachev, P.V. Ostreiko, G.N. Serdobintsev, G.V. Shiyankov, S.V. Yasnov, G.I. Buncher of electron linac-injector for a synchrotron Вопросы атомной науки и техники |
| author_facet |
Chernov, K.N. Logachev, P.V. Ostreiko, G.N. Serdobintsev, G.V. Shiyankov, S.V. Yasnov, G.I. |
| author_sort |
Chernov, K.N. |
| title |
Buncher of electron linac-injector for a synchrotron |
| title_short |
Buncher of electron linac-injector for a synchrotron |
| title_full |
Buncher of electron linac-injector for a synchrotron |
| title_fullStr |
Buncher of electron linac-injector for a synchrotron |
| title_full_unstemmed |
Buncher of electron linac-injector for a synchrotron |
| title_sort |
buncher of electron linac-injector for a synchrotron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81355 |
| citation_txt |
Buncher of electron linac-injector for a synchrotron / K.N. Chernov, P.V. Logachev, G.N. Ostreiko, G.V. Serdobintsev, S.V. Shiyankov, G.I. Yasnov // Вопросы атомной науки и техники. — 1999. — № 3. — С. 44-46. — Бібліогр.: 7 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T06:04:48Z |
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| fulltext |
BUNCHER OF ELECTRON LINAC-INJECTOR FOR A SYNCHROTRON
K.N. Chernov, P.V. Logachev, G.N. Ostreiko, G.V. Serdobintsev, S.V. Shiyankov, G.I. Yasnov
Budker Institute of Nuclear Physics, Novosibirsk, Russia
INTRODUCTION
The application of RF buncher-accelerators for
obtaining the short electron bunches is rather known.
Their design varies.
Linear accelerators with high-current pulsed
beams at energy more than 30 MeV are mainly used as
injectors into synchrotrons at modern accelerating
complexes. The beam should be previously prepared as
series of bunches for injection to obtain stable and
effective accelerating regime. In this case RF electron
sources would be appropriate for use at the input of a
linear accelerator. Such preparing the beam allows one
to achieve an effective beam capture into the
accelerating regime of linear accelerator for each of the
bunches, as well as synchronized operation of the
complex with decreased level of radiation background.
RF ELECTRON SOURCE DESIGN
The use of standard diode gun and traditional
subharmonical buncher at energy of 100300 keV for
obtaining picosecond bunches for their further
acceleration in a linac faces the problems at intense
beam and fixed number of accelerated particles of the
order of 1010 per cycle because of great action of
degroping longitudinal Coulomb space charge forces.
Therefore bunching and accelerating cavities at a
frequency of the linac are additionally used, as a rule, in
such structures, their cost as high as cost of all the RF
gun, which design as well as instrumentation set of an
electron source for a linear accelerator are shown in
Fig.1. Such RF source allows one to prepare electron
bunches with interval between corresponding to the
period of synchrotron cavity RF voltage, with dividing
each bunch into microbunches, which follow one after
another with a frequency of preinjector RF voltage.
In this RF gun electrons are immediately injected
from the cathode unit into accelerating gaps of the
structure with electric field strength of 150−250 kV/cm
(the value depends on the operating conditions). The
structure operates at 2856 MHz. This allows one to
obtain the particle energy of 0.7−1.5 MeV, decrease
Coulomb space charge forces action, and cut the length
of a drift gap, where a short bunch is formed.
Fig. 1: Sketch of RF gun buncher/chopper system
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 44-46.
44
RF electron source channel towards the beam
motion consists of the following parts (see Fig.1): RF
source – cathode-grid assembly (tetrode), accelerating
section for energy of 0.7×1.5 MeV, focusing solenoid,
beam center position corrector, focusing solenoid,
quadruple lenses, RF chopper, collimator.
Fig. 2: Accelerating section
Thermocathode with two-grid control (tetrode)
placed at the accelerating section input is used in this
design as an electron source. The previous forming of
electron bunches takes place in the tetrode. The bunch
duration depends on a voltage value at the tetrode first
control grid, as well as on RF field amplitude
(178.5 MHz) in the gap cathode-first grid. The number
of bunches is defined by the turn-on voltage pulse
duration at the second control grid. For example, for
50 ns turn-on pulse we will obtain 9 bunches with
repetition frequency of 178.5 MHz. Current level and
bunch series pulse duration are controlled at low-level
operation mode of the gun cathode-grid unit (tetrode),
with the grounded second control grid being in the same
plane as the face wall of the first accelerating gap.
Cathode diameter is about 11.4 mm.
Accelerating section is a biperiodic structure
with π/2 operating mode, it contains 3 accelerating gaps
and 2 coupling cavities (Fig.2.). Type of oscillation is
TM010. An electron bunch is divided into several
microbunches in the first accelerating gap under the
force of RF accelerating field (2856 MHz). Then the
beam is additionally accelerated up to the needed energy
in the second and third gaps of the accelerating section
and gets an energy spread needed for the further
bunching in the drifting tube. RF chopper operating at a
frequency of 2856 MHz is used in the shown design for
the separation of the beam particles by energy, as well
as the collimator to removing the electrons from the
channel, which are out of the phase area captured into
the linac accelerating regime. Focusing solenoids,
quadruple lenses together with correctors of the beam
center position from the linac axis are used for
containment of the beam within the fixed dimensions.
Beam current and position meters are used for control.
Buncher and RF chopper are fed by RF power extracted
form one of the linac powering klystrons, with power
consumption not more than 1 MW in 4-5 µs pulse.
BEAM DYNAMICS
Beam dynamics at the inherent points of the
buncher RF channel is shown in Fig.36. As it was
mentioned above, the previous forming of the electron
beam takes place in the cathode-grid unit. Current
density distribution along the beam after the second
tetrode grid is presented in Fig.3. The series containing
9 such bunches will be delivered to the input of the
accelerating section, provide that turn-on voltage pulse
with duration of 50 ns fed to the second grid. Bunch
repetition rate for the series comprises 178.5 MHz
(16-th subharmonic of the linac frequency). Only one of
9 bunches is presented in Fig.3. For the described
operating mode of the cathode-grid unit every bunch is
divided into 4 microbunches by the action of 2856 MHz
RF field after the first gap of the accelerating section.
RF field strength in the accelerating cavities of the
section is 170 kV/cm. Fig.3 also presents the
distribution of the microbunch current density after the
first cavity. Only one of 4 bunches is considered for the
further describing of the beam dynamics, because they
are all similar and their mutual Coulomb influence may
be ignored. The next figures present the time history of
the beam current and microbunch particle energy along
the channel and at the linac input (output of the RF
buncher-accelerator).
30 40 50 60 70 80 90 100 110 120 130 140 150
0
10
20
30
40
50
60
C
(b)
(a)
i ar
(A
)
ϕ
Fig. 3:Bunch current pulse at the tetrode output (input of
the structure) (a);
(b) – microbunches at the output of buncher-accelerator;
ϕC − the current phase (degrees) at 178.5Hz.
45
0 1000 2000 3000 4000
0,0
0,2
0,4
0,6
0,8
1,0
Chopper in LinacColl.C3
C2
C1
L
M
eV
ϕ
Fig. 4: Time history of the microbunch energy from the
buncher-accelerator input along the channel through the
chopper, collimator, up to the linac input.
ϕL – the current phase (degrees) at 2856 MHz, C1, C2, C3
– accelerating gaps of the structure
3450 3500 3550 3600 3650 3700
0
20
40
60
80
L
(b)
(a)
i ar
(A
)
ϕ
Fig. 5: Microbunch pulse current after the chopper
before the collimator (a)
and after the collimator at the linac input (b)
3450 3500 3550 3600 3650 3700
-2
-1
0
1
2
L
(b)(a)
kV
/c
m
ϕ
Fig. 6: Distribution of the microbunch space charge
longitudinal electric field component:
(a) – before the collimator, (b) – at the linac input
CONCLUSION
All the cathode pulse current in RF electron
source is divided into 4 electron microbunch groups
with a repetition rate which is synchronous with the
frequency of the synchrotron cavities. Microbunch
repetition corresponds to the linac frequency. In this
case every microbunch is bunched and effectively
captured into the regime of further acceleration by the
linac and synchrotron without beam current losses.
Low-power RF chopper may be turned on for the
additional separation of the number of particles within
every microbunch by a phase length and cleaning the
charge between bunches down to background current
level. In this case only local bio-protection is required in
the collimator area for the energy up to 1.5 MeV at the
linac input, that is essentially cheaper than bio-
protection for the full energy of 30-200 MeV at the
synchrotron input. The length of RF gun channel is
much shorter and its vacuum value is smaller than that
of high-voltage diode gun with a subharmonic buncher,
so the amount of required vacuum pumps, adjusting
devices, and magnetic accompanying elements is
smaller, as well as their total cost is less. Moreover,
high-voltage power sources for thermogun or high-
voltage pulse modulators are not required, and there is
no need in the high-voltage gun insulation. Low-voltage
power sources with insulation up to 1000 V are used in
the tetrode for the electron beam forming.
REFERENCES
[1] Yu.I.Akchurin et al., LUE-60 accelerator as an
injector of process SR source. Voprosy atomnoj nauki I
tehniki, Harkov, 1989, vol. 5151, pp.310.
[2] V.E.Akimov et al., RF system of the racetrack
microtron. // Proc. Of ХI Conf. On Charge Part. Acc.,
Dubna, 1989, vol. 1, pp.268-270.
[3] L.Serafini, Nucl. Instr. and Meth. in Phys. Res. A
340, 1994, p.40.
[4] C.Travier, Nucl. Instr. and Meth. in Phys. Res. A
340, 1994, pp.26-39.
[5] Ch.Tang et al.,Nucl. Instr. and Meth.in Phys. Res. A
421, 1999, pp.406-10.
[6] J.Haimson, IEEE Trans. Nucl. Sci., 1996, vol NS-
12, p.966.
[7] B.V.Zverev, N.P.Sobenin, Electrodynamics
characteristics of accelerating cavities. // M.,
Energoizdat, 1993.
45
Introduction
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