Design study of the UELV-10/5-15S accelerating structure
The UELV-10/5-15S electron linear accelerator is intended for use in the sterilization applications. Electron energy can be continuously variable from 5 to 10 MeV by changing the accelerated beam current. The 2 m long accelerating structure includes a standing wave buncher, a travelling wave acceler...
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irk-123456789-789842015-03-25T03:02:35Z Design study of the UELV-10/5-15S accelerating structure Chetverikov, I.O. Kalinichenko, M.A. Ryabtsov, A.V. Zuev, Yu.V. The UELV-10/5-15S electron linear accelerator is intended for use in the sterilization applications. Electron energy can be continuously variable from 5 to 10 MeV by changing the accelerated beam current. The 2 m long accelerating structure includes a standing wave buncher, a travelling wave accelerating part and an on-axis resonant RF load. Beam dynamics calculations have been made taking into account space charge forces. Optimization of the buncher parameters permitted to achieve capture efficiencies up to 75% with no external focussing. It is expected that beam powers from 13 kW to 15 kW will be obtained in the 5 to 10 MeV energy range. 2001 Article Design study of the UELV-10/5-15S accelerating structure / I.O. Chetverikov, M.A. Kalinichenko, A.V. Ryabtsov, Yu.V. Zuev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 106-108. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS number: 29.17.+w http://dspace.nbuv.gov.ua/handle/123456789/78984 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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The UELV-10/5-15S electron linear accelerator is intended for use in the sterilization applications. Electron energy can be continuously variable from 5 to 10 MeV by changing the accelerated beam current. The 2 m long accelerating structure includes a standing wave buncher, a travelling wave accelerating part and an on-axis resonant RF load. Beam dynamics calculations have been made taking into account space charge forces. Optimization of the buncher parameters permitted to achieve capture efficiencies up to 75% with no external focussing. It is expected that beam powers from 13 kW to 15 kW will be obtained in the 5 to 10 MeV energy range. |
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Chetverikov, I.O. Kalinichenko, M.A. Ryabtsov, A.V. Zuev, Yu.V. |
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Chetverikov, I.O. Kalinichenko, M.A. Ryabtsov, A.V. Zuev, Yu.V. Design study of the UELV-10/5-15S accelerating structure Вопросы атомной науки и техники |
| author_facet |
Chetverikov, I.O. Kalinichenko, M.A. Ryabtsov, A.V. Zuev, Yu.V. |
| author_sort |
Chetverikov, I.O. |
| title |
Design study of the UELV-10/5-15S accelerating structure |
| title_short |
Design study of the UELV-10/5-15S accelerating structure |
| title_full |
Design study of the UELV-10/5-15S accelerating structure |
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Design study of the UELV-10/5-15S accelerating structure |
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Design study of the UELV-10/5-15S accelerating structure |
| title_sort |
design study of the uelv-10/5-15s accelerating structure |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2001 |
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http://dspace.nbuv.gov.ua/handle/123456789/78984 |
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Design study of the UELV-10/5-15S accelerating structure / I.O. Chetverikov, M.A. Kalinichenko, A.V. Ryabtsov, Yu.V. Zuev // Вопросы атомной науки и техники. — 2001. — № 5. — С. 106-108. — Бібліогр.: 4 назв. — англ. |
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Вопросы атомной науки и техники |
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2025-07-06T03:06:50Z |
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2025-07-06T03:06:50Z |
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| fulltext |
DESIGN STUDY OF THE UELV-10/5-15S ACCELERATING STRUCTURE
I.O. Chetverikov, M.A. Kalinichenko, A.V. Ryabtsov, Yu.V. Zuev
NIIEFA D.V. Efremov Scientific Research Institute of Electrophysical Apparatus
St-Petersburg, Metallostroy, av. Sovetsky 1, Russia
e-mail: NPK LUTS @ NIIEFA. SP.SU
The UELV-10/5-15S electron linear accelerator is intended for use in the sterilization applications. Electron energy
can be continuously variable from 5 to 10 MeV by changing the accelerated beam current. The 2 m long accelerat-
ing structure includes a standing wave buncher, a travelling wave accelerating part and an on-axis resonant RF load.
Beam dynamics calculations have been made taking into account space charge forces. Optimization of the buncher
parameters permitted to achieve capture efficiencies up to 75% with no external focussing. It is expected that beam
powers from 13 kW to 15 kW will be obtained in the 5 to 10 MeV energy range.
PACS number: 29.17.+w
1 INTRODUCTION
The UELV-10/5-15S electron linear accelerator with
a combined accelerating structure [1] is designed for
different irradiation uses, in particular for sterilization
applications. The electron energy may be continuously
varied from 5 to 10 MeV by changing the accelerated
beam current from 0.58 to 0.33 A. The average beam
power is 13-15 kW. The beam focusing in all modes is
accomplished by the accelerating RF-field.
The klystron KIU-147A with parameters 6 MW,
25 kW, 2856 MHz is used as an accelerator RF-source.
The peak and average RF-powers supplied to the accel-
erating structure are 4.7 MW and 22.5 kW, respectively.
The repetition rate is 300 Hz, the pulse duration is
16 μs. The electron source is a 50 kV diode gun with a
maximum beam peak current of 0.9 A. High voltage is
applied to the gun from the klystron modulator. Magnet-
ic coil is placed in the 200 mm gap between the gun and
the input collimator of the structure. Choice of the coil
current and coil position determines the necessary cur-
rent of the injected beam and optimum matching of the
input transverse phase ellipse with structure acceptance.
The 2054.8 mm accelerating structure consists of 82
cells. The structure can be divided into three sections: a
buncher, an accelerating part and a resonant RF-load.
2 BUNCHER
The buncher consists of 11 cells, including the #11
coupler cell. The buncher operates in the π/2 standing
wave mode. The cell dimensions and field amplitudes
have been found as a result of transverse and longitudi-
nal particle dynamics optimization. The purpose of this
optimization was to achieve a narrow electron energy
spectrum (3-4%), with the bunch phase width of about
20˚. The narrow energy spectrum facilitates beam con-
trol problems and allows the beam to be used more ef-
fectively in the technological processes. Furthermore,
the moderate bunch phase width supports repulsive
space charge forces at the acceptable level. The initial
optimization of the transverse beam dynamics (with no
space charge forces) has been made to arrange the over-
focusing in the region where the electron energy is from
2 to 3 MeV. Coulomb forces in the subrelativistic in-
tense beam counteract to the overfocusing and are capa-
ble to increase the current fraction passing through the
structure provided that small correction of the buncher
parameters were made.
The specific feature of a buncher in the combined
structure is the weak dependence of the field amplitudes
and phases on the beam current. High- quality accelerat-
ed beams in the energy range from 5 to 10 MeV should
be obtained due to this feature.
3 ACCELERATING PART
The accelerating part operates in the travelling wave
π/2 mode and comprises the cells from the 12th to the
70th inclusive. The part geometry is of quasi- constant
gradient design. Compared to more traditional cylindri-
cal geometry U-shape cells have higher Q-factors and
shunt-impedances. The accelerating part contains four
uniform π/2 mode segments of increasing impedance in-
terconnected by transition groups of 3 cells each. Table
1 lists neighbor coupling coefficients kn,n+1, quality fac-
tors Qn and shunt-impedances rs,n for cells of each seg-
ment.
Table 1
Cell num-
bers kn,n+1 Qn rs,n,МΩ, m
12÷28 0.035 11260 1.030
32÷46 0.020 11224 1.084
50÷56 0.012 11208 1.118
60÷66 0.0063 11198 1.138
4 RESONANT LOAD
A build-in on-axis resonance load consisting of 12
cylindrical π/2-mode cells coated by Al-Si-Fer is used in
the UELV-10/5-15S electron linear accelerator. A uni-
form power dissipation per cell has been assumed at
zero beam current. The endurance of coating is deter-
mined by the surface density of RF-losses q. To reduce
q it is necessary to increase coating area. It results, in
turn, in the lowering of field amplitude in the load. The
latter has been obtained by increasing the coupling coef-
ficient up to k = 0.027. The Q-values of load cells have
been calculated by the method described in [2] and are
listed in Table 2.
Table 2
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 106-108.
106
cell № 71 72 73 74 75 76
Q 889 747 735 605 580 463
cell № 77 78 79 80 81 82
Q 426 322 273 181 121 45
Comparison shows that the q value in the
UELV-10/5-15S accelerator is twice as less than that in
the operating UELV-8-2D-30 linear accelerator. How-
ever, average RF-losses in the UELV-10/5-15S
(10.53 kW) are five times higher than that in the
UELV-8-2D-30 (2.14 kW). Excessive heating should be
taken away by water flow cooling the accelerating part
of the structure. In this case the temperature drop be-
tween the load walls and water increases by a factor of
2.5, but the frequency detuning caused by this drop will
not considerably affect the load operation because of
low Qs of the load cells.
These measures have to provide the reliable load op-
eration especially as zero beam-loading mode is not
nominal for the structure. The data of table 3 compare
RF-power losses in the accelerating part and resonant
load for three operational modes.
Table 3
Pulse beam current, А 0 0.33 0.58
Average RF-losses power on the
accelerating part, kW 11.97 5.50 3.4
Average RF-losses power on the
load, kW 10.53 0.43 3.4
Note, that Joule losses in the load are negligible for
10 MeV mode, and are three times less for 5 MeV mode
than that for the zero beam-loading mode.
It is essential that RF-field in the build-in load af-
fects the electron energy. In particular, an addition ener-
gy gain in 10 MeV mode is 0.2 MeV while deceleration
in the load in 5 MeV mode gives an electron energy loss
of 1.1 MeV. So, the range of beam current variation at
injection becomes narrower to provide the accelerated
beams of high quality in all modes.
5 STRUCTURE CHARACTERISTICS
The cells connecting uniform segments of accelerat-
ing waveguide define the frequency band properties of
the combined accelerating structure. Calculations show,
that the VSWR values at zero beam current do not ex-
ceed β0≤1.2 over the frequency band of 2856±0.45 MHz
(Fig. 1). That is quite sufficient to ensure the normal op-
eration of accelerator because of high- frequency stabili-
ty of the RF-field (∆f/f0≈1∙10-6) and when using the au-
tomatic frequency control system.
The final optimization of beam dynamics of the ac-
celerator has been made taking into account the
Coulomb forces. The beam continuously injected has
been simulated by 3000 large charged particles. The op-
timization goal was to maximize the number of particles
passing through the structure. To achieve this goal it
was necessary to correct the buncher parameters and to
inject into the structure a converging beam of a rather
large diameter. The latter permits to relax the transverse
Coulomb repulsion forces in the beginning of the
buncher, where the electron bunches are formed. The
maximum accelerated beam current has been obtained
at the injected beam diameter of 7 mm and initial con-
vergence angles of (-25) mrad and (-10) mrad in the 5
and 10 МeV operational modes, respectively.
Fig. 1. VSWR-frequency dependence of
UELV-10/5-15S.
Generally, space charge effects are considered as
parasitic ones, which deteriorate beam parameters.
However, in this case the space charge was included
from the very beginning of optimization, and it results
in the improvement of beam current passing through the
structure while increasing injected current from 0.5 to
0.9 А (75.4% and 78.7%, respectively). Particularly,
90% of accelerated electrons were found inside the spot
of 9.6 mm diameter (5 MeV mode) and 11.5 mm diame-
ter (10 MeV mode). The beam at the accelerator output
is divergent in all modes.
The nonlinear distortions of phase volume of accel-
erated beam are minimum because of high operational
buncher quality (Figs. 2, 3). The beam diameter at the
output foil window is estimated of 15-20 mm taking
into account the beam divergence and relevant drift
space. It diminishes the foil heating and, therefore, ex-
tends its lifetime and improves the uniformity of object
irradiation.
Fig. 2. The beam phase portrait at the accelerating
structure output (10 МeV mode).
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 107-108.
107
Fig. 3. The beam phase portrait at the accelerating
structure output (5 МeV mode).
The beam energy spectra at the nominal modes are
shown in Figs. 4, 5.
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0
0.0
5.0
10.0
15.0
20.0
25.0
W,MeV
(dI/dW)/(I/Wmax)
Fig. 4. The beam energy spectrum (10 МeV).
0.0 1.0 2.0 3.0 4.0 5.0 6.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
22.0
24.0
26.0
28.0
W,MeV
(dI/dW)/(I/Wmax)
Fig. 5. The beam energy spectrum (5 МeV).
The beam loading and beam power characteristics of
the UELV-10/5-15S accelerator are shown in Fig. 6.
The curves are calculated for the pulse duration of
14 μs.
0
2
4
6
8
10
12
14
16
18
0 0.1 0.2 0.3 0.4 0.5 0.6
I, A
P, кВт W, МэВ
Fig. 6. The load and power characteristics of the
UELV-10/5-15S accelerator.
The maximum of beam average power of 15.5 kW
was found at 8.5 MeV. Suggesting the average RF-pow-
er fed into the structure was 22.6 kW the maximum
electron efficiency of π/2-structure has been found as
68%. The average beam powers amount to 14.3 kW and
13.0 kW when the electron energies are 10.3 MeV and
5.2 MeV, respectively.
6 CONCLUSION
The optimization of the accelerating structure per-
mits to achieve the required beam characteristics with-
out external focusing. Calculated capture efficiencies
are about 75% for both nominal modes. The total length
of the structure is 2.05 m.
The accelerating structure of the UELV-10/5-15S
linear electron accelerator is now in fabrication.
REFERENCES
1. Yu.P.Vakhrushin, A.V.Ryabtsov, V.L.Smirnov,
V.V.Terent’ev. Combined Accelerating Structure
With Optimized Multicavity Buncher // Proc. XIII
All-Russia Workshop on Charged Particle Acceler-
ators, Dubna, 1992, v 1, p. 249 (in Russian).
2. A.V.Ryabtsov. Calculating of Resonant Loads in
The Traveling Running Wave Linear Electron Ac-
celerator // Proc. XVII All-Russia Workshop on
Charged Particle Accelerators, Protvino, 2000 (in
Russian).
The measured bandwidth at VSWR<2 is about oc-
tave. HOM damping efficiency was measured by S-pa-
rameters method using P2-83 network analyser and low-
coupling antennas. Figure 3 presents the measurement
results for S21 parameter within a frequency range.
HOM quality factors within 0.9–2.2 GHz frequency
range (i.e. within the range where HOMs with large R/Q
value are located) do not exceed 100 for the most
HOMs. The fundamental mode (E110) quality factor de-
creasing when connecting the loads to the wave-to-coax
transition is about 7.5%.
4 CAVITY TESTING
After assembling, the cavity was heated at work-
bench during 24 hours at a temperature of 150oC, and
then inserted into the damping ring and connected to the
systems of RF power supply, water cooling, and control.
Vacuum 160 l/s ion pump provided 10-9 Torr vacuum
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 108-108.
108
without RF. Conditioning was started in pulsed mode,
which prevented discharge path memorizing, limited
discharge energy, and allowed us to provide the re-
quired pressure level by varying the relative pulse dura-
tion. After 2 hour conditioning the nominal voltage of
300 kV in continuous mode was obtained in the cavity
at pressure of 10-8 Torr. The reflection coefficient in the
cavity power supply feeder line corresponded to the one
measured at low power level. The maximal heating was
observed at a place of waveguide connection. Frequency
detuning at 20 kW dissipating power level was –
150 kHz. The general view of the cavity is shown in
Fig. 4.
Fig. 1. General view of the cavity.
REFERENCES
1. N.S.Dikansky et al. // Proc. of EPAC'94, Jule 1,
1994, London, p. 482–484.
2. V.V.Parkhomchuk et al. Status of the injector com-
plex for c/τ-factory at Novosibirsk // Proc.
APAC'98, March 23–27, Tskuba, Japan, 1998.
3. A.Alinovsky et al. RF system for VEPP-5 damping
ring // Proc. of PAC'98, 22–28 June, 1998, Stock-
holm.
4. D.Myakishev and V.Yakovlev // Proc. PAC'91,
May 6–9, San-Francisco, p. 3002.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №5.
Серия: Ядерно-физические исследования (39), с. 109-108.
109
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