Beam dynamics in an initial part of a high brightness electron linac
The paper is focused on problems of obtaining a bright electron beam in a system that includes a grid-controlled electron gun, a klystron type subharmonical buncher, a standing wave fundamental buncher with increasing accelerating field and a short travelling wave accelerating section. Beam focusing...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Zitieren: | Beam dynamics in an initial part of a high brightness electron linac / M.I. Ayzatsky, D.E. Gutovsky, A.N. Dovbnya, V.A. Kushnir, V.V. Mytrochenko, S.A. Perezhogin // Вопросы атомной науки и техники. — 2001. — № 3. — С. 141-143. — Бібліогр.: 8 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859968837191991296 |
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| author | Ayzatsky, M.I. Gutovsky, D.E. Dovbnya, A.N. Kushnir, V.A. Mytrochenko, V.V. Perezhogin, S.A. |
| author_facet | Ayzatsky, M.I. Gutovsky, D.E. Dovbnya, A.N. Kushnir, V.A. Mytrochenko, V.V. Perezhogin, S.A. |
| citation_txt | Beam dynamics in an initial part of a high brightness electron linac / M.I. Ayzatsky, D.E. Gutovsky, A.N. Dovbnya, V.A. Kushnir, V.V. Mytrochenko, S.A. Perezhogin // Вопросы атомной науки и техники. — 2001. — № 3. — С. 141-143. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The paper is focused on problems of obtaining a bright electron beam in a system that includes a grid-controlled electron gun, a klystron type subharmonical buncher, a standing wave fundamental buncher with increasing accelerating field and a short travelling wave accelerating section. Beam focusing is provided by a longitudinal solenoidal magnetic field. It was shown that the proposed system can provide electron bunches with a peak current more than 100 A and normalized r.m.s. emittance no more than 12 π∙mm∙mrad.
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| first_indexed | 2025-12-07T16:21:36Z |
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BEAM DYNAMICS IN AN INITIAL PART OF A HIGH BRIGHTNESS
ELECTRON LINAC
M.I. Ayzatsky, D.E. Gutovsky, A.N. Dovbnya, V.A. Kushnir,
V.V. Mytrochenko, S.A. Perezhogin
National science center "Kharkov Institute of Physics and Technology"
1, Akademicheskaya Str., Kharkov, 61108 Ukraine
e-mail: mitvic@kipt.kharkov.ua
The paper is focused on problems of obtaining a bright electron beam in a system that includes a grid-controlled
electron gun, a klystron type subharmonical buncher, a standing wave fundamental buncher with increasing acceler-
ating field and a short travelling wave accelerating section. Beam focusing is provided by a longitudinal solenoidal
magnetic field. It was shown that the proposed system can provide electron bunches with a peak current more than
100 A and normalized r.m.s. emittance no more than 12 π⋅mm⋅mrad.
PACS numbers: 41.85
1 INTRODUCTION
It is planned to create several free electron lasers un-
der implementation of Dubna synchrotron radiation
source [1] on the base of its linac. To obtain laser radia-
tion in visible and ultraviolet ranges of wavelength it is
necessary to upgrade an injector part of the linac. After
upgrading of the injector the linac should provide the
following beam performances: normalized r.m.s. emit-
tance of the beam no more than 20 π⋅mm⋅mrad; peak
current no less than 100 A; energy spread no more than
0.1%. Lasers radiating at a wavelength of about 300 nm
can de obtained with using a convenient injector that
consists of a triode electron gun and subharmonic and
fundamental harmonic bunchers [2].
Our paper is devoted to simulation of a convenient
injector that can be used to upgrade the linac of the
Dubna synchrotron radiation source. Simulations of
bunching and accelerating elements as well as a focus-
ing system of the injector were performed with SUPER-
FISH/POISSON [3]. Simulation of beam dynamics in
the injector was performed with PARMELA [4].
2 INJECTOR OUTLINE
An outline of the injector is shown in Fig. 1. As an
electron source it is planned to use an 100 kV electron
gun that will be designed on the base of the CPI Eimac
cathode – grid unit. An enough low subharmonic fre-
quency of 142.8 MHz (20th subharmonic of the funda-
mental linac frequency) was chosen to diminish a cath-
ode load.
2
43
1
5
Fig. 1. Injector outline.
1 – triode electron gun, 2 – windings of the solenoid, 3 –subharmonic buncher, 4 – fundamental frequency buncher,
5 – short travelling wave section.
To provide efficient bunching the triode gun will
generate a train of cut cosine current pulses that will be
phase locked to the RF field in the subharmonic bunch-
er. Bunch length will be 1.75 ns and each bunch will
contain a charge of 1 nC. An average current of the gun
will be 143 mA while the maximal current will be about
1 A. Needed beam characteristics at the gun exit are
summarized in the Table 1.
A quote wave coaxial cavity was chosen as the sub-
harmonic buncher. A general outline of the buncher is
similar to the buncher that was described in [5]. A
length of a modulation gap taken into account fringing
fields will be 60 mm.
Table 1
W, keV 100
τpulse, ns 1.75
Qpulse, nC 1
Fpulse, MHz 142.8
εn rms, π⋅mm⋅mrad 2
To decrease wake fields that will be excited by a
bunched beam in the cavity and to diminish a time of a
transient response the buncher will be made of stainless
steel. SUPERFISH evaluated characteristics of the cavi-
ty are presented in Table 2.
The beam, preliminary bunched in the subharmonic
buncher, undergoes the additional acceleration bunching
in the fundamental frequency buncher. It is known that
beam acceleration in the electromagnetic field increas-
ing along the buncher allows to diminish a phase length
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 141-143.
141
mailto:mitvic@kipt.kharkov.ua
of bunches effectively [6, 7].
Table 2
F0, MHz 142.8
Q0 960
Rs, kOhm 126
Prf (Еz max =1.4 МВ/м), kW 25
Emax on the surface, MV/m 10
We propose to use a chain of inhomogeneous on-
axis coupled cylindrical cavities to create such field dis-
tribution. Characteristics of the cavities are chosen in
that way to obtain the π⁄2 mode at the operating fre-
quency so the five-cavity buncher consists of three ac-
celerating cavities and two coupling cavities. Needed
on-axis field distribution is reached by variation of iris
diameters and length of cavities on the base of the best
bunching. Initial configuration of the buncher was syn-
thesized on a base of results of PARMELA beam dy-
namics simulations in a simplified model that consisted
of separated cells and drifts.
This initial configuration was slightly changed dur-
ing optimization of the injector. The main electrody-
namics characteristics of the buncher are presented in
Table 3.
Table 3
f0, MHz 2856
Q0 10800
Rs, kOhm 301
Prf (Еz max =20.5 МВ/м), kW 153
Emax on the surface, MV/m 30
Stability of a field configuration under frequency
variation of a RF supply generator is a very important
for a resonant system that is used for accelerating the in-
tensive current. This variation is necessary to compen-
sate a beam loading effect [8]. Fig. 2 shows a family of
on-axis field distribution in the buncher for several fre-
quencies within a range of ±3 MHz relatively to the res-
onant frequency. Field amplitudes were normalized to
obtain an average on-axis field equal to 1 MV/m for
each frequency. One can see that curves almost over-
lapped and look like as a single curve. This is evidence
of good field stability. Estimation shows that the maxi-
mal deviation of the average field amplitude in the first
cell is no more than 6.5% as well as it is no more than
2.5% in the last one.
0 2 4 6 8 10 12
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
Z (cm)
E
z
(M
V/
m
)
Fig. 2. A family of on-axis field distribution in the
buncher.
Final beam bunching is realized in a drift space be-
tween the buncher and the accelerating section as well
as in the accelerating section. As the accelerating sec-
tion we are going to use a part of a 2π⁄3 disc loaded
waveguide with constant impedance and phase velocity
that is equal to the velocity of the light. Characteristics
of the accelerating section is given in Table 4.
Table 4
f, MHz 2856
Mode 2π/3
βph 1
a/λ 0.1013
t/λ 0.0191
βg 0.0123
α, 1/m 0.166
Rs, MOhm/m 64.4
Number of cells 19
P, MW 2
3 BEAM DYNAMICS
The research of beam dynamics in the injector was
conducted in several stages. At the first stage the opti-
mized values of amplitude and phase of a field of a sub-
harmonic buncher and value of drift space were deter-
mined. Optimization was carried out by minimization of
a product of beam emittance on bunch phase length. Ob-
taining the minimal value of the product that depends on
the drift space length and phase and amplitude of field
in a modulating gap of the subharmonic buncher allows
to determine the optimal length of the drift space
(70 cm) and average field amplitude (0.9 MV/m). Inves-
tigation shows that values obtained are stable with re-
spect to the change of the solenoid magnetic field in the
range from 0.02 to 0.05 T. It was also found that at opti-
mal injection the phase average energy of particles de-
creases by 20 keV after interaction with the field of the
subharmonic buncher that allows effective bunching at
an enough short distance.
Needed configuration of on-axis field distribution in
the fundamental frequency buncher was determined at a
next stage of beam dynamics simulation. After defini-
tion of a necessary configuration of the field in the
buncher the simulation of dynamics of particles was car-
ried out at different values of strength and phase of the
field in it. That has allowed finding their optimal values
for obtaining a maximum brightness of a beam at a
buncher exit. The analysis of beam characteristics at a
buncher exit has shown a capability of a further bunch-
ing of a beam in the drift space therefore the accelerat-
ing section was established apart 17 cm from the bunch-
er exit. Amplitude of accelerating field in the section
was chosen enough low (E0 = 6.5 MV/m) that allowed
additional bunching of a beam. Study of longitudinal
motion of particles in bunchers has shown that at opti-
mum phases of a field the center of a bunch is injected
in a slowing phase of a field. It results in an effective
bunching of a beam and reduces sensitivity of the char-
acteristics of a beam against changes of amplitudes and
phases of fields in the bunchers. The research of longi-
tudinal motion of particles shows that in a homogeneous
magnetic field of particles betatron oscillations occur
because of change of space charge forces during bunch-
ing and acceleration. Therefore at an injector exit with a
homogeneous magnetic field it was not possible to re-
142
ceive the normalized root mean square emittance (1σ)
of a beam less than ~18 π⋅mm⋅mrad at 100% passing of
particles through the injector. Application of an inhomo-
geneous magnetic field with taking into account the
change of forces of a space charge [2] has allowed re-
ducing the effective emittance growth of a beam during
its bunching and acceleration. Beam performances at the
exit of the injector with inhomogeneous magnetic field
are presented in the Table 5.
Table 5
εn rms, π⋅mm⋅mrad (1σ) 11
4σx,у, mm 3.4
∆φ, ° (90% of particles) 10
∆W/Wav , % (90% of particles) 7
Wmax, MeV 6
Wav, MeV 5.58
Maximal Instant Brightness, A/m2/rad2 1.3⋅1010
Maximal Instant Current, A 252
Illustration of bunching process in injector is pre-
sented in Fig. 3 that shows variation of a maximal in-
stant current of bunches along the injector. Variations of
root mean square emittance and radius of a beam along
the injector are presented in Fig. 4. Probably it is possi-
ble to improve beam emittance using more complicated
magnetic system that provides sharp magnetic field
changing in a region of the fundamental frequency
buncher.
0 5 0 1 0 0 1 5 0 2 0 0
0
5 0
1 0 0
1 5 0
2 0 0
2 5 0
3 0 0
Z ( c m )
M
a
xi
m
a
l i
ns
ta
nt
c
ur
re
nt
(
A
)
Fig. 3. Variation of maximal instant current of bunches
along the injector.
0 5 0 1 0 0 1 5 0 2 0 0
0
0 . 2
0 . 4
0 . 6
0 . 8
1
1 . 2
1 . 4
Z ( c m )
R
b (
c
m
),
ε n rm
s (
c
m
*m
ra
d
) 1
2
Fig. 4. Variations of root mean square normalized emit-
tance (1σ) and radius of a beam along the injector. 1 –
emittance, 2 – beam radius (70% of particles).
4 CONCLUSION
The research carried out has shown that the offered
configuration of the injector provides the characteristics
of a beam that are suitable for a short-wavelength free
electron laser.
The search of minimum value of the product of a
phase length of bunches on an emittance of a beam al-
lows to receive optimal values of amplitude and phase
of the field in a subharmonic buncher as well as lengths
of the drift space.
The injection of bunch centers in a slowing phase of
an electrical field in the subharmonic buncher and a fun-
damental frequency of buncher provide an effective
bunching of a beam and reduce the sensitivity of beam
characteristics with respect to small changes of phases
and amplitudes in bunchers.
The calculations performed allow to proceed to de-
signer development of the injector.
REFERENCES
1. V.A.Archipov, V.K.Antropov, N.I.Balalykin, et. al.
Project of Dubna Electron Synchrotron // Proc. of
the III workshop devoted to the mamory of
V.P. Sarantcev. Dubna, 22 – 23 of September 1999,
Dubna: JINR, 2000, p. 7 – 23.
2. T.Tomimasu, Y.Morii, E.Oshita et al. Strong focus-
ing system of FELI 6 MeV electron injector used
for ultraviolet range FEL oscillation // Nucl. Instr.
Meth. 1998, A 407, p. 370-373.
3. J.H.Billen and L.M.Young. POISSON/SUPER-
FISH on PC compatibles // Proc. 1993 Particle Ac-
celerator Conff. –Washington (USA). 1993,
p. 790-792.
4. L.M.Young. PARMELA // LA-UR-96-1835, Los
Alamos. 1996.
5. Yu.S.Pavlov. Device for bunching electrons on a
subharmonic to the accelerating frequency of a
linac // Uskoriteli, M., Atomizdat. Vyp. 17, 1979,
p. 32 – 37. (In Russian).
6. M.S.Avilov, A.V.Novochatsky. Single bunch com-
pression in exponent field // XIV Workshop on
charged particle accelerators, Protvino, 1994, Vol.
3, p. 181 – 183. (In Russian).
7. A.A.Zavadtsev, B.V.Zverev, V.E.Kaluzhny. Manu-
facturing and adjusting of a buncher of a 5 MeV
resonant linac // Uskoriteli, M., Atomizdat, Vyp. 17,
1979, p. 93 – 98. (In Russian).
8. R.J.Bakker, C.A.J. van der Geer, A.F.G. van der
Meer et al. GHz modulation of a high-current elec-
tron gun // Nucl. Instr. Meth., North-Holland, 1991,
A 307, p. 543-552.
143
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| id | nasplib_isofts_kiev_ua-123456789-79259 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:21:36Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Ayzatsky, M.I. Gutovsky, D.E. Dovbnya, A.N. Kushnir, V.A. Mytrochenko, V.V. Perezhogin, S.A. 2015-03-30T08:05:34Z 2015-03-30T08:05:34Z 2001 Beam dynamics in an initial part of a high brightness electron linac / M.I. Ayzatsky, D.E. Gutovsky, A.N. Dovbnya, V.A. Kushnir, V.V. Mytrochenko, S.A. Perezhogin // Вопросы атомной науки и техники. — 2001. — № 3. — С. 141-143. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS numbers: 41.85 https://nasplib.isofts.kiev.ua/handle/123456789/79259 The paper is focused on problems of obtaining a bright electron beam in a system that includes a grid-controlled electron gun, a klystron type subharmonical buncher, a standing wave fundamental buncher with increasing accelerating field and a short travelling wave accelerating section. Beam focusing is provided by a longitudinal solenoidal magnetic field. It was shown that the proposed system can provide electron bunches with a peak current more than 100 A and normalized r.m.s. emittance no more than 12 π∙mm∙mrad. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Beam dynamics in an initial part of a high brightness electron linac Динамика пучков электронов в начальной части линейного ускорителя с высокой яркостью пучка Article published earlier |
| spellingShingle | Beam dynamics in an initial part of a high brightness electron linac Ayzatsky, M.I. Gutovsky, D.E. Dovbnya, A.N. Kushnir, V.A. Mytrochenko, V.V. Perezhogin, S.A. |
| title | Beam dynamics in an initial part of a high brightness electron linac |
| title_alt | Динамика пучков электронов в начальной части линейного ускорителя с высокой яркостью пучка |
| title_full | Beam dynamics in an initial part of a high brightness electron linac |
| title_fullStr | Beam dynamics in an initial part of a high brightness electron linac |
| title_full_unstemmed | Beam dynamics in an initial part of a high brightness electron linac |
| title_short | Beam dynamics in an initial part of a high brightness electron linac |
| title_sort | beam dynamics in an initial part of a high brightness electron linac |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79259 |
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