Prototype of the S-band buncher for the VEPP-5 preinjector
The buncher system of the VEPP-5 preinjector consists of two subharmonic cavities at operating frequency of 180 MHz (the 16-th subharmonic of the operating frequency f₀ = 2856 MHz), S-band buncher, and the first accelerating structure with the operating frequency of 2856 MHz. By now a prototype of...
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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: | Prototype of the S-band buncher for the VEPP-5 preinjector / A.V. Antoshin, V.V. Podlevskih, V.V. Tarnetsky // Вопросы атомной науки и техники. — 1999. — № 3. — С. 41-43. — Бібліогр.: 3 назв. — англ. |
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irk-123456789-813502015-05-15T03:02:04Z Prototype of the S-band buncher for the VEPP-5 preinjector Antoshin, A.V. Podlevskih, V.V. Tarnetsky, V.V. The buncher system of the VEPP-5 preinjector consists of two subharmonic cavities at operating frequency of 180 MHz (the 16-th subharmonic of the operating frequency f₀ = 2856 MHz), S-band buncher, and the first accelerating structure with the operating frequency of 2856 MHz. By now a prototype of the buncher, presented in the paper, has been manufactured. Measurements carried out are in a good agreement with simulation results. A new version of the buncher, which will allow us to control not only an amplitude, but also phase ratio in accelerating cavities is under development now. 1999 Article Prototype of the S-band buncher for the VEPP-5 preinjector / A.V. Antoshin, V.V. Podlevskih, V.V. Tarnetsky // Вопросы атомной науки и техники. — 1999. — № 3. — С. 41-43. — Бібліогр.: 3 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/81350 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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The buncher system of the VEPP-5 preinjector consists of two subharmonic cavities at operating frequency of 180 MHz (the 16-th subharmonic of the operating frequency f₀ = 2856 MHz), S-band buncher, and the first accelerating structure with the operating frequency of 2856 MHz.
By now a prototype of the buncher, presented in the paper, has been manufactured. Measurements carried out are in a good agreement with simulation results. A new version of the buncher, which will allow us to control not only an amplitude, but also phase ratio in accelerating cavities is under development now. |
| format |
Article |
| author |
Antoshin, A.V. Podlevskih, V.V. Tarnetsky, V.V. |
| spellingShingle |
Antoshin, A.V. Podlevskih, V.V. Tarnetsky, V.V. Prototype of the S-band buncher for the VEPP-5 preinjector Вопросы атомной науки и техники |
| author_facet |
Antoshin, A.V. Podlevskih, V.V. Tarnetsky, V.V. |
| author_sort |
Antoshin, A.V. |
| title |
Prototype of the S-band buncher for the VEPP-5 preinjector |
| title_short |
Prototype of the S-band buncher for the VEPP-5 preinjector |
| title_full |
Prototype of the S-band buncher for the VEPP-5 preinjector |
| title_fullStr |
Prototype of the S-band buncher for the VEPP-5 preinjector |
| title_full_unstemmed |
Prototype of the S-band buncher for the VEPP-5 preinjector |
| title_sort |
prototype of the s-band buncher for the vepp-5 preinjector |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
1999 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81350 |
| citation_txt |
Prototype of the S-band buncher for the VEPP-5 preinjector / A.V. Antoshin, V.V. Podlevskih, V.V. Tarnetsky // Вопросы атомной науки и техники. — 1999. — № 3. — С. 41-43. — Бібліогр.: 3 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT antoshinav prototypeofthesbandbuncherforthevepp5preinjector AT podlevskihvv prototypeofthesbandbuncherforthevepp5preinjector AT tarnetskyvv prototypeofthesbandbuncherforthevepp5preinjector |
| first_indexed |
2025-07-06T06:04:02Z |
| last_indexed |
2025-07-06T06:04:02Z |
| _version_ |
1836876400549691392 |
| fulltext |
PROTOTYPE OF THE S-BAND BUNCHER FOR THE VEPP-5
PREINJECTOR
A.V. Antoshin, V.V. Podlevskih, V.V. Tarnetsky
Budker Institute of Nuclear Physics, Novosibirsk, Russia
INTRODUCTION
The buncher system of the VEPP-5 preinjector
consists of two subharmonic cavities at operating
frequency of 180 MHz (the 16-th subharmonic of the
operating frequency fo = 2856 MHz), S-band buncher,
and the first accelerating structure with the operating
frequency of 2856 MHz [1].
Numerical simulations of the buncher system shows
that space charge factor has a great influence on the
beam dynamics, and interaction between the bunch and
RF channel units is of a complicated character. Under
these circumstances the buncher system should provide
an ability to tune its elements during the system setup.
A possible variant of the S-band buncher with the
operating frequency of 2856 MHz is presented in the
paper. It is our belief that this buncher can provide the
system's adaptability and required bunch parameters at
the input of the first accelerating structure. The couplers
of the accelerating structure which have already been
produced are used as main elements of the buncher, that
allowed us to decrease the manufacturing time and total
cost of the whole system.
BUNCHER DESIGN
The S-band buncher was designed as a three-coupled
cavity structure. The input coupler of the buncher is
connected with the RF power source (5045 klystron)
through the SLED system and the 25 dB directional
coupler [1]. The buncher is coupled with the rectangular
waveguide by the inductive iris.
The interaction between the electrons and
electromagnetic field occurs within the first and third
resonators (accelerating cavities) of the buncher. The
second resonator (coaxial cavity) is used as a connecting
cavity between them. The general layout of the S-band
buncher is shown in Fig.1.
Fig. 1: The S-band buncher.
Geometrical parameters of the buncher cavities are
listed in Table 1.
Table 1
D1,mm L1,mm d2,mm D2,mm L2,mm D3,mm L3,mm
83 34 32 85 102 83 34
Here Di, Li (i=1,3) are the diameters and lengths of
the first and third cavities;
d2, D2, L2 are the internal diameter, the external
diameter, and the length of the coaxial cavity.
The buncher operates at 2856 MHz. The operational
mode, which corresponds to the operating frequency,
provides the equality of the field phases in both
accelerating resonators. Centers of the accelerating
cavities are 14.6 cm distant from one another (see
Tab.1).
Thus the interaction of the 200 keV electrons (
ν ≈ 0 7. c ) with the electromagnetic field occurs in
equal phases for both accelerating cavities.
The first and the third cavities have the tuner,
designed as a plunger (see Fig.1). The resonant
frequencies of the accelerating cavities may be changed
by changing the plunger position, by this means a new
ratio of field amplitudes can be set.
The standard couplers from the accelerating
structure are used as accelerating cavities (the first and
third cavities, Fig.1). Such a design after the minor
changes provides RF power input, vacuum pumping,
and possibility to tune the resonant frequencies of the
both cavities. Each of the accelerating cavities is a high
quality copper resonator operating at E010 fundamental
mode.
The second resonator was designed as a coaxial
cavity operating at TEM012 mode with two field
variations along the axis. It couples accelerating cavities
with one another. This resonator was made of 12X18H
special stainless steel with low conductivity within S-
band, that allowed us to decrease the transient process
characteristic time down to 0.2 µs and therefore increase
its stability to external factors (i.e. RF pulse instability,
temperature regime, etc.). It should be noted that RF
power level according to the preinjector project is more
than enough for the buncher operating, so low quality
does not reduce the bunching efficiency.
BASIC EQUATIONS AND COMPUTER
SIMULATION
The equivalent circuit of the buncher is shown in
Fig.2.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 1999. №3.
Серия: Ядерно-физические исследования. (34), с. 41-43.
41
Fig. 2: Electric circuit representation of the buncher.
The first cavity is connected with the power
transmission waveguide by an iris, which is represented
in Fig.2 as a transformer with transformer ratio m. In
terms of our model the value of m may be expressed by
coupling coefficient β between the first cavity and
input waveguide by the following equation: β = m Z
r
2
0
1
,
where 0Z is the rectangular waveguide characteristic
impedance.
Let us consider that the circuit is driven by a
harmonic signal: U = U ei ft
0
2π , where U const0 =
(steady-state regime). In this case we can write:
−−+−
−
−−+−
−
+
−−
0, = 3
3
13
2
2
3122
2
(1.1) 0 = 32
2
2
2
12
2
2
2112
1
01
12
2
0 = 22
1
1
1
111
2
2
11
X
Qf
f
i
f
f
X
k
X
k
X
Qf
f
i
f
f
X
k
ZQ
f
fi
U
X
k
X
Qf
f
i
f
f βπ
π
β
where Xn = J Ln n , Jn is the current in the n-th
oscillation circuit cell;
fn , Qn are the resonant frequency and quality factor
of the n-th cavity;
kn is the coupling coefficient between the n-th and
(n+1)-th cavities;
f is the drive frequency.
The incident wave power Pin at the buncher input is
connected with the equivalent generator voltage U0 by
the following equation:
P U U
Zin = 0 0
08
*
, (1.2)
so we can deduce the electromagnetic field energy
W nn ( )= 1 2 3, , stored in each cavity from the system
(1.1):
W X Xn n n= 1
2
* . (1.3)
The accelerating voltage in the first and third cavity
is:
U X f R
Qn n n
sh
n
= 2π , n=1,3 , (1.4)
where Rsh is the cavity shunt impedance for the space
harmonic with phase velocity ν = 0 7. c (that
corresponds to the speed of 200 keV electrons).
The reflection coefficient of the buncher may be
found directly from the matrix composed from the
coefficients of system (1.1):
Γ ∆
∆
= − −1 2 1
1
i f
f Q
β '
, (1.5)
where ∆ is the determinant of the matrix (1.1);
′∆ is the determinant of the same matrix without the
first row and first column.
We can estimate how the field amplitudes in the
accelerating cavities depend on electrotechnical
parameters of the system. Let us consider the solution of
the system (1.1), which corresponds to the normal mode
with the lowest resonant frequency for the case β = 0
(free oscillations) to estimate the dependence of the
field amplitudes in accelerating cavities, from the
system parameters. In this case we can obtain:
X
X
k
k
f
f
i f
f Q
f
f
i f
f Q
1
3
1
2
1
2
0
2
1
0 1
3
2
0
2
3
0 3
1 1
1 1
=
− −
− −
. (1.6)
From (1.6) we can see, that if the resonant
frequencies of the first and third cavities are the same (
f f1 3= ), and their Q-factors are sufficiently high (i.e.
11
1
< <
Q and
1 1
3Q
< < ), the ratio of the field amplitudes
in accelerating cavities is determined only by their
coupling coefficients with the coaxial cavity:
X k
k
X1
1
2
3= . (1.7)
If we change the resonant frequencies of the first and
third cavities by the value of ∆ f and − k
k
f1
2
∆
correspondingly, the resonant frequency of the buncher
f0 remains the same (that can be shown either from
Eqs. (1.1) or from Boltzmann/Ehrenfest theorem), and
the ratio of the fields will be equal to:
X
X
k
k
f
f
k
k
f
f
f
f
f
f
1
3
1
2
3
2
0
2
1
2 0
1
2
0
2
0
1 2
1 2
=
− +
− −
∆
∆
. (1.8)
It is also followed from (1.1) that if the all three
cavity resonant frequencies are the same, the following
equation holds:
1
2
1 3
2
0
2
1
2
2
3
− =
+f
f
k k, . (1.9)
Let us define: ∆ ∆
f
f
f
≡
0
, γ ≡ − = +1
2
1 3
2
0
2
1
2
2
2f
f
k k, .
In this terms the equation (1.6) can be written as:
X
X
k
k
k
k f
f
1
3
1
2
1
2
2
2
=
+
−
γ
γ
∆
∆
, (1.10)
and for the coaxial cavity:
X
X k
k
k f
2
1 2
1
2
2 2= +( )γ ∆ . (1.11)
From equations (1.1) − (1.11) we can make the
following important conclusions:
a) Any desired ratio of the field amplitudes in the
accelerating cavities can be obtained by choosing the
proper coupling coefficients.
b) This ratio may be changed by varying the
resonant frequencies of the accelerating cavities, so that
the structure resonant frequency remains the same.
42
c) Sensitivity of the field amplitudes in the
accelerating cavities to their resonant frequency
changing depends mainly on the absolute value of the
coupling coefficient between the cavities.
After extended simulations the following parameters
of the buncher elements were chosen (see Table 2):
Table 2
f1, MHz Q1 k1 f2,MHz Q2 k2 f3,MHz Q3
2872 7000 0.012 2864 950 0.006 2872 7000
The initial ratio of the accelerating fields has been
chosen of 1/2 (that corresponds to
k
k
1
2
2= ) and may be
changed during the buncher setup.
The exact electromagnetic field axial distribution
was calculated by SLANS code [1] for each of the
cavities individually. The absolute value of the
electromagnetic field was obtained by the energy stored
in each cavity, determined by Eqs. (1.1) and (1.3). A
phase shift between the field amplitudes in the cavities
is determined by Eqs. (1.1) and is equal to:
∆ φ = arg( )
arg( )
X
X
1
3
. (1.12)
The numerical simulations shown that for the
parameters listed in Tab.2 ∆ φ ≈ 1 (i.e. the oscillations
in the both cavities are of the same phase, and an
additional phase shift due to a finite quality of the
cavities is practically zero).
The field distribution along the buncher axis for
different parameters of its elements is shown in Fig. 3.
Fig. 3: Axial field distributions.
It should be noted that the described method allows
us to measure fields on the structure axis with a high
enough accuracy, because the coupling slots are located
near the shell and do not disturb the axial fields.
TRANSIENT PROCESS IN THE BUNCHER
All equation listed above are valid only for the case
when the amplitude of the input RF pulse changes
during a time interval much longer than the transient
time of the buncher. The buncher transient process must
be considered because the RF pulse duration after the
SLED system is 0.5 µs, that is a value of the same order
as the buncher transient time.
Transient regime of buncher operation was
simulated by the VIT 032 special computer code,
developed by one of the authors [2]. That program was
intended for simulations of the RF process in the whole
preinjector system (SLED system, accelerating
structure, buncher system etc.), as well as ion its
individual elements. The brief explanation of the code
algorithm as well as the calculation results is presented
below.
Results of simulations carried out by VIT 030 code
[3] are presented in Fig.4.
Fig. 4: Time dependencies of the filed amplitude.
CONCLUSIONS
By now a prototype of the buncher, presented in the
paper, has been manufactured. Measurements carried
out are in a good agreement with simulation results. A
new version of the buncher, which will allow us to
control not only an amplitude, but also phase ratio in
accelerating cavities is under development now. It may
be done in a transient regime by varying the coupling
cavity parameters, according to Eq. (1.1).
REFERENCES
[1] M.S. Avilov et al., Electron-Positron Preinjector of
Vepp-5 Complex. Proc. of The Xviii Int. Linear Acc.,
Geneva, Switzerland, 1996, Pp. 821-823.
[2] Myakishev D.G., Yakovlev V.P., An Interactive
Code SuperLANS for Evaluation of RF Cavities and
Acceleration Structures. − IEEE Particle Accelerator
Conference, May 6−9, 1991, San Francisco, California,
91CH3038-7, Conference Record, V-5, pp.3002-3004.
[3] V.V.Podlevskih, VIT 030 – the special code for
computer simulation of the RF process in linear
accelerator. − Proc. of PAC’99, New York, USA,
pp.736−739.
42
INTRODUCTION
BUNCHER design
Basic equations and computer simulation
Transient process in the buncher
Conclusions
References
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