Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator
Wakefield excitation in a cylindrical dielectric waveguide or resonator by a regular sequence of electron bunches for application to high-gradient particle acceleration has been investigated theoretically and experimentally using an electron linac «Almaz-2» (4.5 МeV, 6.103 bunches of duration 60...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2006
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| Цитувати: | Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator / I.N. Onishchenko,V.A. Kiselev, A.F. Linnik, N.I. Onishchenko, G.V Sotnikov, V.V. Uskov // Вопросы атомной науки и техники. — 2006. — № 2. — С. 79-81. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-787722015-03-21T03:02:23Z Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator Onishchenko, I.N. Kiselev, V.A. Linnik, A.F. Onishchenko, N.I. Sotnikov, G.V. Uskov, V.V. Линейные ускорители заряженных частиц Wakefield excitation in a cylindrical dielectric waveguide or resonator by a regular sequence of electron bunches for application to high-gradient particle acceleration has been investigated theoretically and experimentally using an electron linac «Almaz-2» (4.5 МeV, 6.103 bunches of duration 60 ps and charge 0.32 nC each). Исследовано возбуждение кильватерных полей в цилиндрическом диэлектрическом волноводе или резонаторе регулярной последовательностью электронных сгустков для целей высокоградиентного ускорения частиц как теоретически, так и в эксперименте на линейном электронном ускорителе «Алмаз-2» (4,5 МэВ, 6•103 сгустков длительностью 60 пс и зарядом 0,32 нКл каждый). Досліджено збудження кільватерних полів у циліндричному діелектричному хвилеводі або резонаторі регулярною послідовністю електронних згустків для цілей високоградієнтного прискорення часток як теоретично так і в експерименті на лінійному електронному прискорювачі «Алмаз-2» (4,5 МеВ, 6•103 згустків тривалістю 60 пс і зарядом 0,32 нКл кожний). 2006 Article Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator / I.N. Onishchenko,V.A. Kiselev, A.F. Linnik, N.I. Onishchenko, G.V Sotnikov, V.V. Uskov // Вопросы атомной науки и техники. — 2006. — № 2. — С. 79-81. — Бібліогр.: 9 назв. — англ. 1562-6016 PACS: 41.75.Lx, 41.85.Ja, 41.60.Bq http://dspace.nbuv.gov.ua/handle/123456789/78772 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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English |
| topic |
Линейные ускорители заряженных частиц Линейные ускорители заряженных частиц |
| spellingShingle |
Линейные ускорители заряженных частиц Линейные ускорители заряженных частиц Onishchenko, I.N. Kiselev, V.A. Linnik, A.F. Onishchenko, N.I. Sotnikov, G.V. Uskov, V.V. Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator Вопросы атомной науки и техники |
| description |
Wakefield excitation in a cylindrical dielectric waveguide or resonator by a regular sequence of electron bunches
for application to high-gradient particle acceleration has been investigated theoretically and experimentally using an
electron linac «Almaz-2» (4.5 МeV, 6.103
bunches of duration 60 ps and charge 0.32 nC each). |
| format |
Article |
| author |
Onishchenko, I.N. Kiselev, V.A. Linnik, A.F. Onishchenko, N.I. Sotnikov, G.V. Uskov, V.V. |
| author_facet |
Onishchenko, I.N. Kiselev, V.A. Linnik, A.F. Onishchenko, N.I. Sotnikov, G.V. Uskov, V.V. |
| author_sort |
Onishchenko, I.N. |
| title |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| title_short |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| title_full |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| title_fullStr |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| title_full_unstemmed |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| title_sort |
experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2006 |
| topic_facet |
Линейные ускорители заряженных частиц |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/78772 |
| citation_txt |
Experimental and theoretical researches of a resonator concept of a dielectric wakefield accelerator / I.N. Onishchenko,V.A. Kiselev, A.F. Linnik, N.I. Onishchenko, G.V Sotnikov, V.V. Uskov // Вопросы атомной науки и техники. — 2006. — № 2. — С. 79-81. — Бібліогр.: 9 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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2025-07-06T02:49:32Z |
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| fulltext |
EXPERIMENTAL AND THEORETICAL RESEARCHES
OF A RESONATOR CONCEPT OF A DIELECTRIC WAKEFIELD
ACCELERATOR
I.N. Onishchenko,V.A. Kiselev, A.F. Linnik, N.I. Onishchenko, G.V Sotnikov, V.V. Uskov
NSC Kharkov Institute of Physics and Technology, Kharkov, Ukraine
E-mail: onish@kipt.kharkov.ua
Wakefield excitation in a cylindrical dielectric waveguide or resonator by a regular sequence of electron bunches
for application to high-gradient particle acceleration has been investigated theoretically and experimentally using an
electron linac «Almaz-2» (4.5 МeV, 6.103 bunches of duration 60 ps and charge 0.32 nC each).
PACS: 41.75.Lx, 41.85.Ja, 41.60.Bq
1. INTRODUCTION
Along with laser acceleration in plasma and vacuum,
a dielectric wakefield acceleration (DFWA) is one of
the novel methods of high gradient acceleration of
charged particles. Three issues arise in connection with
intense wakefield excitation in a dielectric. A wakefield
in a dielectric (Cherenkov radiation) excited by charged
particles can be enhanced by using a regular sequence
of relativistic electron bunches (multi-bunch operation)
[1], an interference of many transverse modes to enlarge
peak amplitude (multi-mode operation) [2], and a reso-
nant accumulation of wakefield in a cavity resulting
from many bunches (resonator concept) [3]. We wish to
exploit the third approach while retaining working the
other two. In the present work we attempt to clarify by
theory and experiments the process of wakefield excita-
tion in a cylindrical dielectric waveguide and resonator
using a long sequence of relativistic electron bunches.
The temporal evolution and spatial distribution of the
excited wakefield are investigated by HF probes for
both waveguide and resonator cases and comparison
was made. Electron energy loss measured by a magnetic
analyzer and the total energy of the excited HF wake-
field measured by a calorimeter were compared to deter-
mine the energy balance.
2. THEORY
For a semi-infinite dielectric waveguide the problem
of wakefield excitation was solved analytically [4].
There are two new peculiarities compared to the case of
the infinite waveguide: an appearance of transition radi-
ation and wakefield removal with group velocity from
the waveguide entrance. As a result, the net field ampli-
tude grows from the entrance to the trailing edge of the
first bunch field and then decreases to the position of the
first bunch. The field amplitude at a given cross-section
grows and after the passage of several bunches it satu-
rates; however, the saturation level does not depend on
the total number of bunches but is determined by the
distance to the entrance.
The more complicated problem with a hole for the
bunches was solved in cylindrical geometry for a
waveguide of finite length [5] and for a resonator [6].
Due to wakefields moving along the system with group
velocity, the number of bunches whose wakefields can
be coherently added giving maximum amplitude at the
waveguide exit, is restricted in the first case by
( )1//1 0max −∆+≈ gvvzLN , (1)
where L is a waveguide length, ∆z is a distance between
bunches, v0 and v g are the bunch velocity and group ve-
locity, respectively. The presence of the hole results in
an appearance of oscillations with the group velocity of
light in vacuum. These oscillations move ahead of
bunch and form a weak field precursor. For the res-
onator, a single bunch excites a multibunch wakefield
which is the same as the field in a semi-infinite waveg-
uide [4] until it is reflected from the resonator exit. Ex-
citation by a sequence of bunches results, first in the ex-
citation of only the resonant fundamental mode, the fre-
quency of which coincides with the bunch repetition fre-
quency (mode-locking) and, secondly, in the linear
growth of the field amplitude with time in proportion to
the number of injected bunches. The saturation level is
determined by a nonlinear electron-wave interaction for
the NSC KIPT experiment with 4 MeV bunches [6]. It
might be supposed that for higher energy (e.g. an exper-
iment with 0.5 GeV bunches) the saturation could be
caused the Q-factor of the resonator.
To demonstrate both multimode and multibunch
regimes in a resonator case, a rectangular dielectric res-
onator (still without a vacuum channel) which provides
equidistant resonant modes, was theoretically investigat-
ed [7]. It was shown that multimode operation is real-
ized under the condition:
2
0 0 01, /L Na v cβ ε β= − = , (2)
i.e., the length of the resonator L should be a multiple N
of half-integer wave lengths of the resonant fundamen-
tal mode; a is the transverse size; the other transverse
size b is supposed much larger, ε is the permittivity. For
coherent summing of wakefields from injected bunches
the coincidence of the fundamental mode frequency and
the frequency f of bunch repetition should be fulfilled.
This condition sets the transverse size of the resonator
2
0 0/ 2 1a v f β ε= − . (3)
Conditions (5) and (6) are the basis of the resonator
concept of the rectangular DWFA.
3. EXPERIMENT
Experiments to study the excitation of wakefields in
a cylindrical dielectric structure (waveguide or res-
onator) were performed using the linear resonant elec-
tron accelerator “Almaz-2” at the NSC KIPT.
___________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.79-81. 79
3.1. EXPERIMENTAL SETUP
The scheme of the installation is described in [8].
An electron beam had the following parameters: energy
4.5 MeV, current 0.5 A, impulse duration 2 µsec, modu-
lation frequency 2820 MHz. Therefore, we had a regular
sequence of 6⋅103 bunches, 60 ps duration each spaced
by 300 ps. The diameter and length of each bunch were
1.0 cm and 1.7 cm, respectively.
This sequence of electron bunches was injected into
a dielectric structure made from Teflon (permittivity ε
=2.1, tgδ=1.5⋅10-4 at a frequency f=3⋅109 Hz). The length
of the dielectric structure was varied up to 65 cm, the
outer diameter was 8.6 cm and the diameter of the hole
was 2.2 cm. The dielectric structure was placed into a
copper tube of length 100 cm.
3.2. WAKEFIELD SPATIAL DISTRIBUTION
The transverse topography of the excited field is
found to be almost azimuthally symmetric. The radial
dependence of the Er – component of the field shows a
small value on the axis and a maximum near the tube
wall. The radial dependence of the longitudinal Ez –
component shows a maximum it on the axis and a small
value near the wall. Such topography of the excited field
demonstrates that in the present experiment E0n – waves
are excited. Beyond-cutoff waveguides were used to es-
timate the contribution of higher radial modes. It was
found that their total contribution is less than half of the
fundamental mode. This result confirms theoretical con-
clusion [5] that a coincidence of the bunch repetition
frequency with the fundamental frequency but not with
the difference frequency between the non-equidistant
frequencies of the higher modes results in survival of
the resonant fundamental mode and suppression of the
other modes.
The longitudinal distribution of the excited fields in
the waveguide of finite length was measured in the fol-
lowing way. The dielectric structure was cut into several
pieces of various length (1, 2, 5, and 10 cm) and the
electric field was measured at exit of the structure,
which is composed of a number of dielectric pieces to
assemble the required length. The results of measure-
ments of Ez after passing of 6⋅103 bunches are depicted
in Fig.2 (curve 1). A linear growth of amplitude of the
longitudinal component of the field along the dielectric
waveguide was observed. This proves the theoretical re-
sult [5] according to which at the time when Nmax bunch-
es have passed through the structure a linear stationary
longitudinal distribution of Ez has been established.
Fig.2. Ez dependence on dielectric length
In the case of the resonator, the longitudinal distribu-
tion of Ez obtained by measuring Ez at the exit end of
each dielectric insertion consisting of a certain number
of pieces is shown in Fig.2 (curve 2). As seen from
Fig.2, the resonator electric field amplitude is larger
than for the waveguide. Besides, the longitudinal depen-
dence has a resonant character. Accumulation of wake-
field in a dielectric resonator of appropriate length was
proposed in [3] with the aim of enlarging the number of
coherently contributing bunches. If the amplitude is pro-
portional to the number of contributing bunches, we
conclude that the resonator allows one to increase the
number of contributing bunches approximately 4 times
for length 10 cm and 2 times for length 65 cm. Resonant
behavior is explained by the effective excitation at a co-
incidence (multiplicity) of resonator and bunch repeti-
tion frequencies.
3.3. WAKEFIELD TEMPORAL EVOLUTION
To determine the increase in the number of coher-
ently contributing bunches for the resonator case, we
changed the duration of the beam current macro-pulse.
This was achieved by using a time delay of the HF-
pulse of the master oscillator of the klystron feeding the
linac, with respect to the high voltage pulse applied to
the klystron. This results in beam duration in the range τ
=0.1…2.0 µsec without changing other beam parame-
ters. In this way we could compose trains with a number
of bunches 3⋅102 up to 6⋅103.
The results of measuring the dependence of the ex-
cited field amplitude upon beam pulse duration, i.e.,
upon the number of bunches, are shown in Fig.3 at a di-
electric length 30 cm. It is seen that for the waveguide
case (curve 1) the amplitude achieves saturation caused
by the group velocity effect [4,5] at a time <0.1µsec (i.e.
Nmax<300). According to theory (1) for experimental
conditions v0 /vg=2, Nmax
theory
=3. For the resonator case
(curve 2) the saturation time is much longer and occurs
at 0.3µsec (i.e. N= 900 bunches). The number of con-
tributing bunches in the waveguide case can be estimat-
ed from Fig.2 by amplitudes ratio 4 for L=30 cm, and it
makes Nmax =225. This greatly exceeds the theoretical
value and such a discrepancy must be explained in fur-
ther research. Also, the physical mechanism of ampli-
tude saturation is not revealed yet. Provisionally, we
suppose that for low electron energy the reason for satu-
ration is a nonlinear particle-wave interaction, but for
super-relativistic bunches it might be the Q-factor. For
smaller beam current 0.25 A (curve 3) the amplitude
grows slower and does not achieve saturation.
Fig.3. Ez dependence on pulse duration
70
3.4. ENERGY LOSS OF ELECTRON BUNCHES
To find the dependence of bunch energy loss on
wakefield excitation, an electron energy spectrum was
measured by magnetic analyzers at the accelerator exit
(initial spectrum) and after passing the dielectric struc-
ture at a distance 100 cm from the linac exit (spectrum
after excitation). In Fig.4 initial spectrum (curve 1) and
spectrum after excitation (curve 2) for a dielectric length
of 65 cm are presented. We find that the electron energy
loss is 3% for waveguide (Fig.4,a) and 12% for res-
onator (Fig.4,b). For the resonator case accelerated elec-
trons are observed.
3.0 3.5 4.0 4.5 5.0 5.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
dN
/d
W
, a
. u
.
W, MeV
12
a
3 4 5 6
0
1
2
3
dN
/d
W
, a
.u
.
W, MeV
b
1
2
b
Fig.4. Electron energy spectra
3.5. CALORIMETER MEASUREMENTS
The total energy of excited wakefields was mea-
sured by a specially constructed sensitive calorimeter
[9]. Electron bunches were deflected by a magnetic field
or passed through a hole in the calorimeter. It was found
that the total excited energy in the waveguide case is
1.4% of the initial beam energy. The dependence upon
the number of bunches in the train is similar to one ob-
served in amplitude measurements (Fig.3, curve 1). To
explain this discrepancy of the calorimeter data with re-
spect to the energy spectrum loss, we measured the
damping of an excited field in the metal tube. It oc-
curred 3 dB, i.e., 2 times. Thus we conclude that the en-
tire beam energy loss of about 3% is expended on wake-
field excitation, within reasonable energy balance.
CONCLUSIONS
1. The radial topography of excited wakefields was
studied and it was established that the excited modes are
predominantly of E0n-type.
2. By changing the number of bunches it was shown
that in the waveguide case the wakefield amplitude is
built up by a small number of bunches (less 300), that is
explained by a wakefield removal with group velocity.
3. The resonator concept was verified, so that at
right choice of resonator parameters and bunch repeti-
tion frequency, more bunches contribute coherently and
the amplitude of the wakefield grows considerably.
4. The electron energy spectra for waveguide and
resonator cases were measured, from which it was con-
cluded that for an electron energy of 4.5 MeV and cur-
rent 0.5 A, and dielectric length of 65 cm, the energy
loss during the interaction was 12% for the resonator
and 3% for the waveguide.
5. Calorimeter measurements were found to be in
agreement with results from the HF-probes and allow
one to determine the overall excited wakefield energy.
Research supported by CRDF UP2-2569-KH-04 and
Ukr DFFD 02.07/325.
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B. Hafizi // Phys. Rev. 1997, E56, p.4647.
3. T.C. Marshall, J.-M. Fang, J.L. Hirshfield,
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// Phys. Rev. 2002, E65, p. 066501-1-11.
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// Ukr. Fiz. Zh. 2003, v.48, p.16.
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D.Yu. Sidorenko, G.V. Sotnikov // Technical Phys.
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7. N.I. Onishchenko, G.V Sotnikov. Coherent summa-
tion of wake fields excited by electron bunch se-
quence in planar multimode dielectric resonator //
this issue, p.73-75.
8. V.A. Kiselev, A.F. Linnik, I.N. Onishchenko et al.
The experimental stand for research of wakefield
method of charged particles acceleration // this is-
sue, p.76-78.
9. V.A. Kiselev, A.F. Linnik, I.N. Onishchenko,
V.V. Uskov // Instruments and Experimental Tech-
niques. 2005, №2, p.103-106.
ЭКСПЕРИМЕНТАЛЬНЫЕ И ТЕОРЕТИЧЕСКИЕ ИССЛЕДОВАНИЯ РЕЗОНАТОРНОЙ
КОНЦЕПЦИИ КИЛЬВАТЕРНОГО ДИЭЛЕКТРИЧЕСКОГО УСКОРИТЕЛЯ
И.Н. Онищенко, В.А. Киселев, А.Ф. Линник, Н.И. Онищенко, Г.В. Сотников, В.В. Усков
Исследовано возбуждение кильватерных полей в цилиндрическом диэлектрическом волноводе или резо-
наторе регулярной последовательностью электронных сгустков для целей высокоградиентного ускорения
частиц как теоретически, так и в эксперименте на линейном электронном ускорителе «Алмаз-2» (4,5 МэВ,
6·103 сгустков длительностью 60 пс и зарядом 0,32 нКл каждый).
ЕКСПЕРИМЕНТАЛЬНІ ТА ТЕОРЕТИЧНІ ДОСЛІДЖЕННЯ РЕЗОНАТОРНОЇ КОНЦЕПЦІЇ
КІЛЬВАТЕРНОГО ДІЕЛЕКТРИЧНОГО ПРИСКОРЮВАЧА
І.М. Оніщенко, В.О. Кисельов, А.Ф. Лінник, М.І. Оніщенко, Г.В. Сотніков, В.В. Усков
Досліджено збудження кільватерних полів у циліндричному діелектричному хвилеводі або резонаторі
регулярною послідовністю електронних згустків для цілей високоградієнтного прискорення часток як
___________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 2.
Series: Nuclear Physics Investigations (46), p.79-81. 79
теоретично так і в експерименті на лінійному електронному прискорювачі «Алмаз-2» (4,5 МеВ, 6·103
згустків тривалістю 60 пс і зарядом 0,32 нКл кожний).
72
ЭКСПЕРИМЕНТАЛЬНЫЕ И ТЕОРЕТИЧЕСКИЕ ИССЛЕДОВАНИЯ РЕЗОНАТОРНОЙ КОНЦЕПЦИИ кильватерного диэлектрического ускорителя
ЕКСПЕРИМЕНТАЛЬНІ ТА ТЕОРЕТИЧНІ ДОСЛІДЖЕННЯ РЕЗОНАТОРНОЇ КОНЦЕПЦІЇ кІльватерного дІЕлектричНОГО ПРИСКОРЮВАЧА
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