Elaboration of plasma-dielectric wakefield accelerator
Theoretical and experimental investigations of the physical principles of wakefield accelerator based on the excitation of accelerating wakefield in the plasma-dielectric structure by a long sequence of relativistic electron bunches are presented. Enhancing the wakefield intensity is supposed to b...
Saved in:
| Published in: | Вопросы атомной науки и техники |
|---|---|
| Date: | 2016 |
| Main Authors: | , , , , , , , , , |
| Format: | Article |
| Language: | English |
| Published: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2016
|
| Subjects: | |
| Online Access: | https://nasplib.isofts.kiev.ua/handle/123456789/115429 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Journal Title: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Cite this: | Elaboration of plasma-dielectric wakefield accelerator / I.N. Onishchenko, G.P. Berezina, K.V. Galaydych, R.R. Kniazev, A.F.Linnik, P.I. Markov, O.L. Omelaenko, V.I. Pristupa, G.V. Sotnikov, V.S. Us // Вопросы атомной науки и техники. — 2016. — № 6. — С. 133-139. — Бібліогр.: 21 назв. — англ. |
Institution
Digital Library of Periodicals of National Academy of Sciences of Ukraine| id |
nasplib_isofts_kiev_ua-123456789-115429 |
|---|---|
| record_format |
dspace |
| spelling |
Onishchenko, I.N. Berezina, G.P. Galaydych, K.V. Kniazev, R.R. Linnik, A.F. Markov, P.I. Omelaenko, O.L. Pristupa, V.I. Sotnikov, G.V. Us, V.S. 2017-04-04T19:45:06Z 2017-04-04T19:45:06Z 2016 Elaboration of plasma-dielectric wakefield accelerator / I.N. Onishchenko, G.P. Berezina, K.V. Galaydych, R.R. Kniazev, A.F.Linnik, P.I. Markov, O.L. Omelaenko, V.I. Pristupa, G.V. Sotnikov, V.S. Us // Вопросы атомной науки и техники. — 2016. — № 6. — С. 133-139. — Бібліогр.: 21 назв. — англ. 1562-6016 PACS: 41.75.Ht; 41.75.Lx; 41.85.Ne; 41.85.Lc https://nasplib.isofts.kiev.ua/handle/123456789/115429 Theoretical and experimental investigations of the physical principles of wakefield accelerator based on the excitation of accelerating wakefield in the plasma-dielectric structure by a long sequence of relativistic electron bunches are presented. Enhancing the wakefield intensity is supposed to be achieved by using multibunch regime of excitation for the coherent summation of wakefields of individual bunches and resonator regime for wakefields accumulation. The acceleration of bunches in the total (plasma+dielectric) wakefields is realized by detuning of bunch repetition frequency relatively to the frequency of the excited wakefield. In such a way the sequence of bunches is divided into exciting and accelerated parts due to displacing latter part of bunches into accelerating phases of wakefield excited by a former part of bunches of the same sequence. The influence of plasma in the transit channel on the amplitude of excited plasma and dielectric wakefields and focusing exciting and accelerated bunches is investigated. Представлены теоретические и экспериментальные исследования физических принципов кильватерного ускорителя, основанного на возбуждении ускоряющего кильватерного поля в плазменно-диэлектрической структуре длинной последовательностью электронных сгустков. Увеличение амплитуды возбуждаемого кильватерного поля достигается использованием мультибанчевого режима возбуждения для когерентного сложения кильватерных полей отдельных сгустков и резонаторного режима для накопления кильватерных полей. Ускорение сгустков в суммарном (плазменном+диэлектрическом) кильватерном поле реализовано расстройкой частоты следования сгустков относительно частоты возбуждаемого кильватерного поля. Таким путём последовательность сгустков разделяется на возбуждающую и ускоряемую части благодаря возника- ющему смещению второй части сгустков в ускоряющие фазы кильватерного поля, возбуждённого первой частью сгустков этой же последовательности. Исследовано влияние плазмы в пролётном канале на ампли- туду возбуждаемых плазменного и диэлектрического кильватерных полей и фокусировку возбуждающих и ускоряемых сгустков. Представлені теоретичні та експериментальні дослідження фізичних принципів кільватерного прискорюва- ча, заснованого на збудженні прискорюючого кільватерного поля в плазмово-діелектричній структурі дов- гою послідовністю електронних згустків. Збільшення амплітуди збуджуваного кільватерного поля досяга- ється використанням мультибанчевого режиму збудження для когерентного складання кільватерних полів окремих згустків і резонаторного режима для накопичення кільватерних полів. Прискорення згустків в су- марному (плазмовому+діелектричному) кільватерному полі реалізовано розстройкою частоти слідування згустків відносно частоти збуджуваного кільватерного поля. Таким шляхом послідовність згустків поділя- ється на збуджуючу і прискорювану частини завдяки виникаючому зміщенню другої частини згустків в прискорюючи фази кільватерного поля, збудженого першою частиною згустків цієї ж послідовності. Дослі- джено вплив плазми в прольотному каналі на амплітуду збуджуваних плазмового та діелектричного кільва- терних полів і фокусування збуджуючих і прискорюваних згустків. Work was supported by the complex program of the NAS of Ukraine “Perspective researches in plasma physics, controlled nuclear fusion, and plasma technologies”: Project “Development of physical principles of plasma-dielectric wakefield accelerator. Theory and experiment”. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma electronics Elaboration of plasma-dielectric wakefield accelerator Разработка плазменно-диэлектрического кильватерного ускорителя Розробка плазмово-діелектричного кільватерного прискорювача Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Elaboration of plasma-dielectric wakefield accelerator |
| spellingShingle |
Elaboration of plasma-dielectric wakefield accelerator Onishchenko, I.N. Berezina, G.P. Galaydych, K.V. Kniazev, R.R. Linnik, A.F. Markov, P.I. Omelaenko, O.L. Pristupa, V.I. Sotnikov, G.V. Us, V.S. Plasma electronics |
| title_short |
Elaboration of plasma-dielectric wakefield accelerator |
| title_full |
Elaboration of plasma-dielectric wakefield accelerator |
| title_fullStr |
Elaboration of plasma-dielectric wakefield accelerator |
| title_full_unstemmed |
Elaboration of plasma-dielectric wakefield accelerator |
| title_sort |
elaboration of plasma-dielectric wakefield accelerator |
| author |
Onishchenko, I.N. Berezina, G.P. Galaydych, K.V. Kniazev, R.R. Linnik, A.F. Markov, P.I. Omelaenko, O.L. Pristupa, V.I. Sotnikov, G.V. Us, V.S. |
| author_facet |
Onishchenko, I.N. Berezina, G.P. Galaydych, K.V. Kniazev, R.R. Linnik, A.F. Markov, P.I. Omelaenko, O.L. Pristupa, V.I. Sotnikov, G.V. Us, V.S. |
| topic |
Plasma electronics |
| topic_facet |
Plasma electronics |
| publishDate |
2016 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Разработка плазменно-диэлектрического кильватерного ускорителя Розробка плазмово-діелектричного кільватерного прискорювача |
| description |
Theoretical and experimental investigations of the physical principles of wakefield accelerator based on the excitation
of accelerating wakefield in the plasma-dielectric structure by a long sequence of relativistic electron bunches
are presented. Enhancing the wakefield intensity is supposed to be achieved by using multibunch regime of excitation
for the coherent summation of wakefields of individual bunches and resonator regime for wakefields accumulation.
The acceleration of bunches in the total (plasma+dielectric) wakefields is realized by detuning of bunch repetition
frequency relatively to the frequency of the excited wakefield. In such a way the sequence of bunches is divided
into exciting and accelerated parts due to displacing latter part of bunches into accelerating phases of wakefield excited
by a former part of bunches of the same sequence. The influence of plasma in the transit channel on the amplitude
of excited plasma and dielectric wakefields and focusing exciting and accelerated bunches is investigated.
Представлены теоретические и экспериментальные исследования физических принципов кильватерного
ускорителя, основанного на возбуждении ускоряющего кильватерного поля в плазменно-диэлектрической
структуре длинной последовательностью электронных сгустков. Увеличение амплитуды возбуждаемого
кильватерного поля достигается использованием мультибанчевого режима возбуждения для когерентного
сложения кильватерных полей отдельных сгустков и резонаторного режима для накопления кильватерных
полей. Ускорение сгустков в суммарном (плазменном+диэлектрическом) кильватерном поле реализовано
расстройкой частоты следования сгустков относительно частоты возбуждаемого кильватерного поля. Таким
путём последовательность сгустков разделяется на возбуждающую и ускоряемую части благодаря возника-
ющему смещению второй части сгустков в ускоряющие фазы кильватерного поля, возбуждённого первой
частью сгустков этой же последовательности. Исследовано влияние плазмы в пролётном канале на ампли-
туду возбуждаемых плазменного и диэлектрического кильватерных полей и фокусировку возбуждающих и
ускоряемых сгустков.
Представлені теоретичні та експериментальні дослідження фізичних принципів кільватерного прискорюва-
ча, заснованого на збудженні прискорюючого кільватерного поля в плазмово-діелектричній структурі дов-
гою послідовністю електронних згустків. Збільшення амплітуди збуджуваного кільватерного поля досяга-
ється використанням мультибанчевого режиму збудження для когерентного складання кільватерних полів
окремих згустків і резонаторного режима для накопичення кільватерних полів. Прискорення згустків в су-
марному (плазмовому+діелектричному) кільватерному полі реалізовано розстройкою частоти слідування
згустків відносно частоти збуджуваного кільватерного поля. Таким шляхом послідовність згустків поділя-
ється на збуджуючу і прискорювану частини завдяки виникаючому зміщенню другої частини згустків в
прискорюючи фази кільватерного поля, збудженого першою частиною згустків цієї ж послідовності. Дослі-
джено вплив плазми в прольотному каналі на амплітуду збуджуваних плазмового та діелектричного кільва-
терних полів і фокусування збуджуючих і прискорюваних згустків.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/115429 |
| citation_txt |
Elaboration of plasma-dielectric wakefield accelerator / I.N. Onishchenko, G.P. Berezina, K.V. Galaydych, R.R. Kniazev, A.F.Linnik, P.I. Markov, O.L. Omelaenko, V.I. Pristupa, G.V. Sotnikov, V.S. Us // Вопросы атомной науки и техники. — 2016. — № 6. — С. 133-139. — Бібліогр.: 21 назв. — англ. |
| work_keys_str_mv |
AT onishchenkoin elaborationofplasmadielectricwakefieldaccelerator AT berezinagp elaborationofplasmadielectricwakefieldaccelerator AT galaydychkv elaborationofplasmadielectricwakefieldaccelerator AT kniazevrr elaborationofplasmadielectricwakefieldaccelerator AT linnikaf elaborationofplasmadielectricwakefieldaccelerator AT markovpi elaborationofplasmadielectricwakefieldaccelerator AT omelaenkool elaborationofplasmadielectricwakefieldaccelerator AT pristupavi elaborationofplasmadielectricwakefieldaccelerator AT sotnikovgv elaborationofplasmadielectricwakefieldaccelerator AT usvs elaborationofplasmadielectricwakefieldaccelerator AT onishchenkoin razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT berezinagp razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT galaydychkv razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT kniazevrr razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT linnikaf razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT markovpi razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT omelaenkool razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT pristupavi razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT sotnikovgv razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT usvs razrabotkaplazmennodiélektričeskogokilʹvaternogouskoritelâ AT onishchenkoin rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT berezinagp rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT galaydychkv rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT kniazevrr rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT linnikaf rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT markovpi rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT omelaenkool rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT pristupavi rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT sotnikovgv rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača AT usvs rozrobkaplazmovodíelektričnogokílʹvaternogopriskorûvača |
| first_indexed |
2025-11-26T13:00:53Z |
| last_indexed |
2025-11-26T13:00:53Z |
| _version_ |
1850622126178959360 |
| fulltext |
PLASMA ELECTRONICS
ISSN 1562-6016. ВАНТ. 2016. №6(106)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2016, № 6. Series: Plasma Physics (22), p. 133-139. 133
ELABORATION OF PLASMA-DIELECTRIC WAKEFIELD
ACCELERATOR
I.N. Onishchenko, G.P. Berezina, K.V. Galaydych, R.R. Kniazev, A.F.Linnik, P.I. Markov,
O.L. Omelaenko, V.I. Pristupa, G.V. Sotnikov, V.S. Us
NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: onish@kipt.kharkov.ua
Theoretical and experimental investigations of the physical principles of wakefield accelerator based on the exci-
tation of accelerating wakefield in the plasma-dielectric structure by a long sequence of relativistic electron bunches
are presented. Enhancing the wakefield intensity is supposed to be achieved by using multibunch regime of excita-
tion for the coherent summation of wakefields of individual bunches and resonator regime for wakefields accumula-
tion. The acceleration of bunches in the total (plasma+dielectric) wakefields is realized by detuning of bunch repeti-
tion frequency relatively to the frequency of the excited wakefield. In such a way the sequence of bunches is divided
into exciting and accelerated parts due to displacing latter part of bunches into accelerating phases of wakefield ex-
cited by a former part of bunches of the same sequence. The influence of plasma in the transit channel on the ampli-
tude of excited plasma and dielectric wakefields and focusing exciting and accelerated bunches is investigated.
PACS: 41.75.Ht; 41.75.Lx; 41.85.Ne; 41.85.Lc
INTRODUCTION
In solving frontier problems of high energy physics
particle accelerators have played a main role. The pre-
sent high-energy frontier colliders producing the center-
of-mass energy of 100 GeV [1] give the possibility to
study the world of nature, of which the size can be seen
into nearly one-trillionth micron. Today we are launch-
ing forth into a new energy regime of the order of Tera
Elektron Volt [2, 3], in which profound fundamental
questions is expected to be answered on the origin of
mass, the predominance of matter over antimatter, the
existence of supersymmetry and so on. However now
elaborated CLIC [2] and ILC [3] accelerators are very
close to the limit of what we can practically afford to
build using conventional technologies, even collabora-
tively. The first understanding of this situation was stat-
ed in [4], where new approaches to particles accelera-
tion were proclaimed. In particular Ya.B. Fainberg pro-
posed to use plasma waveguides as an accelerating
structure. Later, this idea was modified by J.M. Dawson
et al. [5, 6] to a wakefield accelerating scheme, in which
high-gradient accelerating field is built up as a wake-
field excited in plasma by a short high power laser pulse
or a short bunch of the large charge.
Another potential candidate for future high gradient
particle acceleration, allowing to overcome the acceler-
ating rate limit 100 MeV/m for conventional accelera-
tors, is dielectric loaded (DL) accelerating structures
[7], in which wakefield is excited by an intense electron
bunch. As it has been shown in theoretical investiga-
tions [8] and in the recent experiments [9], the maxi-
mum accelerating gradient in dielectric structures, being
limited by the electric breakdown due to the tunneling
and collisional ionization effects, can be achieved above
1 GeV/m, i.e. on the order higher comparing to the con-
ventional metallic accelerating structures. It allows
elaborating the project of ANL 26 GHz, 3 TeV Dielec-
tric‐based Short Pulse Two Beam Linear Collider (con-
ceptual layout of one side of a 3TeV e+e‐ collider as a
Higgs Factory) [9].
As a further development of the dielectric wakefield
acceleration approach the concept of multi-bunch die-
lectric wakefield accelerator was proposed and investi-
gated [12, 13]. In the present work the hybrid “plasma-
dielectric” modification of multi-bunch dielectric wake-
field accelerator with plasma filled transit channel
(PDWA) for focusing of bunches and enhancement of
wakefield excitation is elaborated.
1. THEORY
PDWA unit under investigation is shown in Fig. 1.
In metal waveguide is inserted a dielectric tube having
inner radius a and outer radius b. The transit channel is
filled with isotropic plasma of density np. Regular se-
quence of drive bunches and witness bunch travel along
transit channel collinearly. Radius of solid drive bunch
is rb, drive bunch charge is Q0, its length is Lb (homoge-
neous bunch charge distribution), bunch repetition peri-
od is T, number of bunches in the train is Nb.
Fig. 1. Sketch of PDWA unit. The transport channel is
filled entirely with isotropic plasma
In order to determine accelerating fields we need to
solve Maxwell equations with drive bunch sequence as
a current source. Solving Maxwell equations we obtain
the equation (1) for the axial field in transit channel that
has been presented in [14] (see designations there).
Wakefield in PDWA consists of two type of waves:
dielectric waves (DW), modified by plasma, and plasma
wave (PW).
0
||2
1
4
( ) ( ) ( 1)
bN
s s
z s b z
i s
Q
E R r e r i T
a
0
||
1
4
( ) ( 1) .
bN
p p
z
ib b
Q
e r i T
r L
(1)
mailto:onish@kipt.kharkov.ua
134 ISSN 1562-6016. ВАНТ. 2016. №6(106)
At optimal focusing regime when frequency of the
first radial mode of DW is much greater than frequency
of PW the axial force behind drive bunch is mainly
formed by the dielectric wave, and the transverse force
is determined by plasma wave [15]. As the plasma den-
sity increases, the longitudinal electric field of plasma
wave increases, which could enhance the total accelerat-
ing gradient. However, firstly, the plasma wave ampli-
tude has an extremum in the plasma density [16] and,
secondly, the longitudinal electric field amplitude of the
dielectric wave on the axis of the transit channel de-
creases with increasing plasma density. Thus, the opti-
mum plasma density at which the maximum accelerat-
ing field is reached cannot be predicted in advance and
is determined below for a set of parameters close to
ones of the experimental installation “Almaz-2M”:
Outer radius of dielectric tube…………...……...4.3 cm
Inner radius of dielectric tube……………………1.1 cm
Relative permittivity…………………………………2.1
Bunch energy…………………………………… 5 MeV
Bunch charge…………………………………...0.32 nC
Bunch radius……………………………………0.95 cm
Density of drive bunch……………………..3.910
8
cm
-3
Bunch repetition rate………………………..2.71 GHz
Frequency of vacuum E01 mode……………….2.71 GHz
Single drive bunch scenario. For plasma density
np=10
10
cm
-3
the
obtained axial (a) and radial (b) de-
pendences of the total longitudinal and transverse forces
[15] are shown in Fig. 2. Hereafter F= eE.
a
b
Fig. 2. Axial profile of the longitudinal (solid curve) and
transverse (dashes curve) forces acting on a test bunch
at a distance of 0.95 cm from the waveguide axis (a);
transverse profile of the longitudinal (solid curve) and
transverse (dashes curve) forces acting on a test parti-
cle at a distance of 7.56 cm from the head of the drive-
bunch (b)
In Fig. 2,a it is seen that the accelerated witness
bunch placed at distance 7.6 or 39.1 cm from the driving
bunch head can be accelerated and focused simultane-
ously. Moreover the drive bunch is occurred in the fo-
cusing phase of the total wakefield too. In Fig. 2,b we
see the radially almost uniform accelerating wakefield
(mainly DW) and nearly linear growth of transverse
wakefield (mainly PW) providing accelerated bunch
focusing without aberration.
Sequence of drive bunches scenario. At first consid-
er PDWA unit with fixed dimensions and bunch repeti-
tion frequency (reference case) providing coherent exci-
tation of vacuum E01-mode. The results for this case are
presented in Fig. 3.
Fig. 3. Wakefield amplitude versus plasma density in the
reference case. Top figure is total wakefield (WF), mid-
dle figure is dielectric WF (first item in eq.1), bottom
figure is plasma WF (second item in eq.1)
As follows from Fig.3 for the single bunch the am-
plitude of the total wakefield is determined by DW at
low plasma density and mainly by PW at high plasma
density. The location of maximum of total wakefield is
determined by the maximum of PW which occurs under
condition kpa1. For sequences of 4 and 11 bunches
total wakefield has maximum at plasma density
np=10
11
cm
-3
. At such density dielectric wave and plas-
ma wave are summarized coherently, because their fre-
quencies are close. Wakefields from separate bunches
ISSN 1562-6016. ВАНТ. 2016. №6(106) 135
are summarized coherently too. When we use 21 bunch-
es the total wakefield at low plasma density is greater
than for the previous sequences, but at high plasma den-
sity we don’t obtain advantages in comparison with sin-
gle bunch excitation. The first reason of that behavior is
resonance destruction between bunch repetition fre-
quency and eigen frequencies of the PDWA. The se-
cond reason is resonance destruction between PW and
DW. The third reason is plasma column screening of
dielectric wave when plasma density exceeds dielectric
wave frequency so that dielectric wakefield is not excit-
ed. It looks like dielectric wave excitation in dielectric
structure is replaced by plasma wave excitation in plas-
ma column.
To avoid these resonances destruction it is needed to
beforehand change the vacuum dielectric structure pa-
rameters and bunch repetition rate so that at plasma
presence these resonances become restored.
Fig. 4. Wakefield amplitude versus plasma density in the
case of the tuning of dielectric wave frequency by
changing of inner radius of dielectric tube
The case with the frequency adjustment, when
changing the plasma density, synchronously changes
frequency of the first radial mode of dielectric wave E01
is considered. The frequency adjustment is done by
changing inner or outer radii of dielectric tube. Besides
the bunch repetition frequency is tuned up to plasma
frequency. Results of such adjustment are presented in
Fig. 4. Outer radius 4.3 cm is fixed. When changing the
plasma density from 10
11
to 10
13
cm
-3
the inner radius is
changed from 1.085 to 4.04 cm. The frequency of prin-
cipal mode of DW (simultaneously with frequency of
PW) changes from 2.84 to 28.4 GHz. At any plasma
density a bunch repetition frequency is equal to plasma
frequency. Fig. 4 shows that total wakefield in case of
tuning of eigen frequencies by inner radius change is
appreciable greater than in the reference case. Ampli-
tude of wakefield is determined by PW at most part of
plasma density interval. Input of DW is appreciable
only at plasma density np<210
11
cm
-3
. At high plasma
density dielectric wakefield becoms evanescent from
dielectric surface to the channel axis.
2. EXPERIMENT
Linear resonant electron accelerator "Almaz-2M"
produced the sequence of N = 610
3
bunches each of
energy 3.5…4.8 MeV, charge 0.26 nC, radius 0.5 cm,
duration 60ps. Bunch repetition frequency can be
changed within 2803…2807 MHz. A chamber in which
the dielectric structure of round or rectangular cross
section can be placed was attached to the accelerator.
"Multi-bunch" coherent excitation. "Multi-bunch"
issue concluded to the statement that the intense wake
field excited by a bunch with a large charge can be
achieved by a long periodic sequence of bunches with a
low charge each, but an equivalent total charge. To clar-
ify the possibility of coherent summation of individual
bunches fields it is needed to change the number of
bunches in the sequence. Because of the difficulty of
producing a set of sequences with various number of
bunches in the performed studies waveguides of various
length were used. The possibility of such a substitution
follows from the fact that due to the output of the excit-
ed wave from the waveguide of finite length with the
group velocity vg the number of bunches of the se-
quence of any duration, which contributes to the growth
of the total wakefield at the waveguide exit is limited.
Maximum number of bunches N, which wakefields dur-
ing coherent summation increase the amplitude of the
total field is directly proportional to the length of the
waveguide L: N=L/(v0/vg-1)), where is length of the
excited wave equal to the distance between the bunches,
v0 is bunch velocity. Contrary to [17] with round dielec-
tric waveguide now it was proved experimentally by
using a rectangular waveguide with two dielectric plates
the opportunity occurs to deflect e electron bunches on
the “bare” walls of the waveguide, where no dielectric
plates (Fig. 5).
Arranging magnetic field region (N-S) at different
distances from the dielectric waveguide exit we can
change the interaction length L by shifting a set of mag-
net poles (N-S) and measure the dependence of the ex-
cited wakefield amplitude upon the length of the inter-
action length. Measurements were carried out at the
same length of the whole dielectric waveguide avoiding
changes in the conditions of reflections when varying
the interaction length.
136 ISSN 1562-6016. ВАНТ. 2016. №6(106)
Fig. 5. 1 accelerator "Almaz-2M"; 2 magnetic ana-
lyzer; 3 diaphragm; 4 – waveguide; 5 dielectric;
6 dielectric plug; 7 − wavemeter VMT-10;
8 – oscilloscope
For such experiment wakefield at the dielectric wave-
guide exit linearly depends on the interaction length of
bunches with dielectric part (Fig. 6), that is consistent
with the theoretical prediction, confirming coherent
summation of wakefields of bunches.
Fig. 6. Dependence of wakefield amplitude on the length
of bunches interaction with dielectric waveguide
"Resonator" scheme of excitation [18]. The aim the
"resonator" concept is to increase the number of bunch-
es of the sequence, adding wakefields of which increas-
es the total wakefield in comparison with the case of a
waveguide case. For excitation of the wakefields in die-
lectric resonator by a sequence of bunches the resonant
conditions of the coincidence of bunch repetition fre-
quency ωm with Cherenkov radiation frequency ω0
(ωrep=ω0) and, simultaneously, with the principal eigen
frequency of the resonator ωr1, i.e. ωrep=ω0=ωr1 should
be fulfilled.
Fig. 7. Dependence of the wakefield amplitude on the
duration of bunch sequence for different Q-factors of
the resonator: 1 Q1=65; 2 Q2=268; 3 Q3=539;
4 Q4=676
In the absence of losses in the resonator (Q=) de-
clared conditions should provide coherent summation of
wakefield of all bunches and thereby increase the total
wakefield to the level of field, excited by a single bunch
with a charge equivalent to the total charge of all
bunches of the sequence. For finite Q-factor the de-
pendence of the total wakefield upon the resonator Q-
factor was experimentally investigated and presented in
Fig. 7. It is shown that in the resonator case the total
field increases with increasing duration of the sequence
and saturates, remaining constant for larger durations.
With the growth of the Q-factor the number of bunches
of the sequence contributing to the increase in the total
wakefield increases. The long sequence of 6∙10
3
bunch-
es in our experiment is practically equivalent by satura-
tion amplitude to the sequence of infinite number of
bunches.
Bunches acceleration by excited wakefield. Using
detuning between bunch repetition frequency and fre-
quency of excited wakefield allows obtaining drive and
accelerated bunches from the same sequence. Such pos-
sibility arises due to gradual shift of bunches by phase
of excited wakefield. In the performed experiments the
frequency of dielectric wakefield is fixed and deter-
mined by the Cherenkov resonance (coincidence the
velocity of bunches and the phase velocity of the excit-
ed wave of the dielectric waveguide). The bunch repeti-
tion frequency is varied by change of the frequency of
master oscillator "Rubin" of klystron amplifier. In this
concept of "excitation- acceleration" process using the
same sequence of bunches there is no need for addition-
al linac injector for bunches-witnesses production. It
simplifies the experimental demonstration of bunches
acceleration by the excited wakefield.
In the case of resonance, i.e. coincidence of bunch
repetition frequency frep and frequency of the principal
mode of excited wakefield f0 all bunches are occurred in
the decelerating phase and lose energy to excite wake-
field. If there is a frequency detuning Δf=frep-f0≠0
bunches of the first part of the sequence occurred in the
decelerating phases of excited field lose energy to the
increase in total wakefield and bunches of the next part
of the sequence, shifted to the region of the accelerating
phases of wakefield excited by the previous part of the
sequence, gain an additional energy. For point and mo-
noenergetic bunches the number of bunches N
*
of the
first part of the sequence, exciting wakefield, evaluated
from the phase shift of N
*-
th bunch on π is equal
N
*
=frep/2Δf. The next part of the sequence of bunches of
the same duration is accelerated.
Fig. 8,a,b shows obtained energy spectra [19] of the
bunch electrons passing through the resonator without
dielectric tube when there is no Cerenkov interaction of
bunches with the resonator (black spectra, which are
close to the initial ones at the resonator input) and
through the resonator with a dielectric tube (red spectra
obtained after excitation of wakefield and interaction
with it) for two cases: resonant one (zero detuning Δf=0,
Fig. 13,a) and nonresonant one (nonzero detuning
Δf=2.5 MHz, Fig. 13,b). From Fig. 8 follows that at the
presence of dielectric in the case of resonance Δf = 0 the
energy spectrum is shifted by 400 keV as a whole to
ISSN 1562-6016. ВАНТ. 2016. №6(106) 137
lower energies that is caused by the energy loss of all
the bunches on the wakefield excitation. In the case of
detuning between the bunch repetition frequency and
the frequency of wakefield Δf = frep - f0= 2.5 MHz a part
of bunches of the sequence, shifting over phase, falls
into the accelerating phase of the wakefied excited by
previous bunches of the same sequence and gain energy.
In this case, in the electron energy spectrum there are
observed both the electrons losing energy (-150 keV)
and electrons gaining additional energy (+ 150 keV).
Fig. 8. Energy spectra of electron bunches passing
through the resonator without dielectric (black curves)
and a resonator with dielectric tube (red curves):
а Δf=0; b Δf = frep - f0 = 2.5 МHz
Dependences of wakefield excitation and focusing of
bunches in plasma-dielectric structure upon plasma
density. The scheme of the experimental setup for such
investigations is shown in Fig. 9.
Fig. 9. Scheme of plasma-dielectric structure: 1 –
accelerator “Almaz-2M”; 2 titanium foil; 3 vacuum
meter; 4 dielectric waveguide; 5 dielectric micro-
wave matcher; 6 ferrite absorber; 7 microwave
probe; 8 – oscilloscope Tektronix TDS 6154C; 9 -
double Faraday cup; 10 − vacuum pump
Relativistic electron bunches produced by linac
“Almaz-2M” (1) penetrate through titanium foil (2) of
thickness 30 and enter into the dielectric waveguide
(4) of round cross section with transit channel of diame-
ter 21 mm filled with plasma.
Plasma in the transit channel of the dielectric wave-
guide is produced by the head of bunch train when it
passes through the neutral gas of the pressure regulated
by puffing and pumping. Ionization process in the trans-
it channel occurs due to the beam-plasma discharge
(BPD) [20] at pressure 1Torr and due to collisions of
bunch electrons with neutrals at higher pressures. It is
illustrated in Fig. 10 by enhancing of measured wake-
field signal in the said two regions and corresponding
beam current reduce on Faraday cup due to beam scatter-
ing [21].
Fig. 10. Dependences of wakefield signal (1) and beam
current (2) upon gas pressure in transit channel
Evolution of plasma density in time for various gas
pressure measured with a high-frequency probe of John-
sen [22] and open resonator of Moskalev [22] is shown
in Fig. 11.
Fig. 11. Dependence of plasma density on time for
various gas pressure in transit channel: а) 0.5 Тоrr,
b) 10 Тоrr
It is seen that for gas pressure P=0.5 Torr plasma
density can achieve the resonant value for which plasma
frequency is equal both wakefield frequency and bunch
repetition frequency.
Wakefield excitation by a sequence of bunches was
investigated for waveguide and resonator cases. To real-
ize the waveguide case it is needed to avoid reflections
of the excited wakefield. For this purpose, the dielectric
tube is ended with dielectric microwave matcher, and on
Teflon vacuum plug ferrite absorber is placed. For ob-
taining single bunch regime the length of the dielectric
insert was chosen equal to length of the excited dielec-
tric wave L = λ. In the case of dielectric waveguide and
a single bunch regime the dependence of the amplitude
of the excited longitudinal wakefield on the axis for the
wide range of the gas pressure is shown in Fig. 12 (red
curve).
Fig. 12. Dependence of excited wakefield Ez upon neu-
tral gas pressure in the transit channel
138 ISSN 1562-6016. ВАНТ. 2016. №6(106)
It is seen that in the pressure under which BPD de-
velops and plasma is formed the wakefield wave topog-
raphy in the channel becomes volumetric, that increases
the coupling coefficient of the bunch with the wakefield
wave and leads to the increase in the excited wakefield
amplitude compared with the case without gas injection
(see Fig. 12, horizontal red line).
In the case of dielectric resonator realized by remov-
ing matching elements and installing metal exit plug
under conditions of the double-resonance ω0 = ωrep = ωn
(coincidence of Cherenkov frequency ω0 with bunch repeti-
tion frequency ωrep and simultaneously with eigen fre-
quency of the resonator ωn) the wakefield amplitude
grows significantly (see Fig. 12, horizontal black line).
This is due to the fact that the number of bunches which
contribute to the total wakefield is limited only by Q-
factor. So it is much more compare with the case of the
waveguide, for which the number of bunches, deter-
mined by the waveguide length and the group velocity,
does not exceed tens of bunches. However in the range
of gas pressure where plasma is produced the wakefield
signal is decreased up to a single bunch level (see
Fig. 12, black curve). It is explained by destroying reso-
nances and plasma column screening.
Focusing driver-bunches. As it follows from Fig. 2,a
in the case of the waveguide and a single bunch regime
(L = λ) all driver bunches are occurred in the same own
wakefields - decelerating longitudinal dielectric (almost
uniform over radius) and focusing radial plasma (almost
linearly grows over radius) ones. Radial defocusing die-
lectric field with its almost uniform over radius longitu-
dinal field is insignificant.
Fig. 13 shows the waveform of the beam current, exper-
imentally obtained [19] with a double Faraday cup (see
(9) in Fig. 9) at vacuum Р = 10
-3
Torr (see Fig. 13,a) and
at neutral gas pressure in the transit channel of dielectric
waveguide P=0.5 Torr (see Fig. 13,b), when plasma is
intensively produced by BPD. The increase in current in
the second cup while its reducing in the first one for the
case of plasma presence (see Fig. 13,b) evidences fo-
cusing electron bunches.
а b
Fig. 13. Oscillograms of beam current taken from dou-
ble Faraday cup: top first cylinder; bottom second
cylinder; а – Р = 10
-3
Torr; б – Р = 0.5 Torr
CONCLUSIONS
The coherence at coincidence of bunch repetition
frequency and excited wakefield frequency in "multi-
bunch" regime and the accumulation of wakefields at
multiplicity of eigen frequencies of the resonator to the
bunch repetition frequency and excited wakefield fre-
quencies in "resonator" regime provides enhancement of
the total wakefield.
Enhancement of total wakefield due to summation
dielectric and plasma longitudinal wakefields doesn’t
occur because for high density plasma dielectric wake-
field dos not penetrate into plasma filled transit channel.
So dielectric wakefield excitation is replaced by plasma
wakefield excitation.
The acceleration of bunches in wakefield excited by
bunches of the same sequence at introduction of detun-
ing between bunch repetition frequency and excited
wakefield frequency is demonstrated.
The presence of plasma in the transit channel pro-
vides focusing both driving and accelerated bunches by
excited plasma wave.
Work was supported by the complex program of the
NAS of Ukraine “Perspective researches in plasma
physics, controlled nuclear fusion, and plasma technol-
ogies”: Project “Development of physical principles of
plasma-dielectric wakefield accelerator. Theory and
experiment”.
REFERENCES
1. John R. Rees, The Stanford Linear Collider, Scien-
tific American 1989, p. 36-43.
2. H.R. Braun, T. Corsini, J. D'Amico, G. Delahaye,
C.D. Guignard, A. Johnson, P. Millich, A.J. Pearce,
L. Riche, R. Rinolfi, D. Ruth, L. Schulte, M. Thorndahl,
I.H. Valentini, Wilson and W. Wuensch. The CLIC RF
power source: a novel scheme of two-beam acceleration
for electron-positron linear colliders. CLIC-Note-364,
1998.
3. J. Brau,, Y. Okada, N. Walker, A. Djouadi,
J. Lykken, K. Monig, M. Oreglia, S. Yamashita,
N. Phinney, N. Toge, T. Behnke, C. Demerell, J. Jaros
and A. Miyamoto. International Linear Collider Refer-
ence Design Report, 2007.
V.N. Veksler // Proc. Symp. CERN, Geneva, 1956, v. 1,
p. 80-83. G.I. Budker. Ibid, p. 68-75. Ya.B. Fainberg.
The use of plasma waveguides as accelerating structures
// Ibid, p. 84-92.
4. T. Tajima, J.M. Dawson. Laser electron acceleration
// Phys. Rev. Letters. 1979, v. 43, № 4, p. 267.
5. P. Chen, J.M. Dawson, R. Huff, T. Katsouleas. Ac-
celeration of electrons by the interaction of a bunched
electron beam with a plasma // Phys. Rev. Letters. 1985,
v. 54, № 7, p. 692.
6. W. Gai, P. Schoessow, B. Cole, R. Konecny,
J. Norem, J. Rosenzweig, and J. Simpson. Experimental
Demonstration of Wake-Field Effects in Dielectric
Structures // Phys. Rev. Lett. 1988, v. 61, p. 2756.
7. P. Sprangle, B. Hafizi, and R.F. Hubbard. Ionization
and pulse lethargy effects in inverse Cherenkov acceler-
ators // Phys. Rev. E. 1997, v. 55, № 5, p. 5964-5974.
8. M.C. Thompson, H. Badakov, A.M. Cook,
J.B. Rosenzweig, R. Tikhoplav, G. Travish,
I. Blumenfeld, M.J. Hogan, R. Ischebeck, N. Kirby,
R. Siemann, D. Walz, P. Muggli, A. Scott, and
R.B. Yoder. Breakdown Limits on Gigavolt-per-Meter
Electron-Beam-Driven Wakefields in Dielectric Struc-
tures. PRL 100. 30 May 2008, p. 214801.
9. E.R. Colby. Present limits and future prospects for
dielectric acceleration // 35
th
Int. Conf. on High Energy
Physics (ICHEP 2010). Paris, France. July 22-28, 2010.
ISSN 1562-6016. ВАНТ. 2016. №6(106) 139
10. T-B. Zhang, J.L. Hirshfield, T.C. Marshall, and
B. Hafizi. Stimulated dielectric wake-field accelerator //
Phys. Rev. E. 1997. v. 56, № 4, p. 4647.
11. I.N. Onishchenko, V.A. Kiselev, A.F. Linnik,
G.V. Sotnikov. “Concept of dielectric wakefield accel-
erator driven by a long sequence of electron bunches”
IPAC'13, Shanghai, China, 12-17 May, 2013.
12. R.R. Knyazev, I.N. Onishchenko, and
G.V. Sotnikov. Generation of wakefields in a dielectric
structure filled with plasma // Technical Physics. 2016,
v. 61, № 4, p. 511-516.
13. R.R. Kniazev, G.V. Sotnikov. Focusing wakefield
for accelerated bunch in a plasma-dielectric waveguide
// J. of Kharkiv University (Physical Series “Nuclei,
Particles, Fields”. 2012, № 1001, v. 54 (2), p. 64-68.
14. V.A. Balakirev, N.I. Karbushev, A.O. Ostrovskii,
and Yu.V. Tkach. Theory of Cherenkov Amplifyers and
Generators on Relativistic Beams. Kiev: “ Naukova
Dumka”, 1993.
15. G.P. Berezina, A.M. Yegorov, G.A. Krivonosov,
A.F. Linnik, O.L. Omelaenko, I.N. Onishchenko,
V.I. Pristupa, V.S. Us. Investigation of a multibanch
scheme of the wakefield excitation // Problems of
Atomic Science and Technology. Series “Nuclear Phys-
ics Investigations”. 2016, № 3(103), v. 66, p. 66-68.
16. I.N. Onishchenko. Investigations of the physical
processes in multibunch dielectric wakefield accelerator
// Problems of Atomic Science and Technology. Series
“Nuclear Physics Investigations”. 2015, № 6(100),
v. 65, p. 25-36.
17. V.A. Kiselev, A.F. Linnik, I.N. Onishchenko,
V.I. Pristupa. Acceleration and focusing of electron
bunches by wakefields in plasma produced in neutral
gas by a nonresonant sequence of bunches // Problems
of Atomic Science and Technology. Series “Plasma
Physics”. 2012, № 6(82), v. (18), р. 155-157.
18. P.M. Lebedev, I.N. Onishchenko, Yu.V. Tkach,
Ya.B. Fainberg, V.I. Shevchenko. Theory of beam-
plasma discharge // Fizika plasmy. 1976, v. 2, № 3,
p. 407-413 (in Russian).
19. V.A. Kiselev, A.F. Linnik, I.N. Onishchenko,
V.I. Pristupa. Wakefields excitation in plasma, produced
by a sequence of electron bunches in neutral gas, accel-
erating and focusing electrons by them // Problems of
Atomic Science and Technology. Series “Plasma
Physics”. 2011, № 1(71), v. 17, р. 77-79.
20. R. Johnsen. RF-probe method for measurements of
electron density in plasmas at high neutral densities //
Rev. Sci. Instrum. 1986, № 3, v. 57, p. 428-432.
21. V.A. Kiselev, A.F. Linnik, I.N. Onishchenko,
V.I. Pristupa, B.I. Ivanov, V.P. Prishchepov. Measure-
ment of plasma density formed at passing of a sequence
of relativistic electron bunches through the neutral gas //
Problems of Atomic Science and Technology. Series
“Plasma Physics”. 2013, № 1(83), v. (19), p. 143-145.
Article received 21.09.2016
РАЗРАБОТКА ПЛАЗМЕННО-ДИЭЛЕКТРИЧЕСКОГО КИЛЬВАТЕРНОГО УСКОРИТЕЛЯ
И.Н. Онищенко, Г.П. Березина, К.В. Галайдич, Р.Р. Князев, A.Ф. Линник, П.И. Марков, О.Л. Омелаенко,
В.И. Приступа, Г.В. Сотников, В.С. Ус
Представлены теоретические и экспериментальные исследования физических принципов кильватерного
ускорителя, основанного на возбуждении ускоряющего кильватерного поля в плазменно-диэлектрической
структуре длинной последовательностью электронных сгустков. Увеличение амплитуды возбуждаемого
кильватерного поля достигается использованием мультибанчевого режима возбуждения для когерентного
сложения кильватерных полей отдельных сгустков и резонаторного режима для накопления кильватерных
полей. Ускорение сгустков в суммарном (плазменном+диэлектрическом) кильватерном поле реализовано
расстройкой частоты следования сгустков относительно частоты возбуждаемого кильватерного поля. Таким
путём последовательность сгустков разделяется на возбуждающую и ускоряемую части благодаря возника-
ющему смещению второй части сгустков в ускоряющие фазы кильватерного поля, возбуждённого первой
частью сгустков этой же последовательности. Исследовано влияние плазмы в пролётном канале на ампли-
туду возбуждаемых плазменного и диэлектрического кильватерных полей и фокусировку возбуждающих и
ускоряемых сгустков.
РОЗРОБКА ПЛАЗМОВО-ДІЕЛЕКТРИЧНОГО КІЛЬВАТЕРНОГО ПРИСКОРЮВАЧА
І.М. Оніщенко, Г.П. Березіна, К.В. Галайдич, Р.Р. Князєв, A.Ф. Лінник, П.І. Марков, О.Л. Омелаєнко,
В.I. Приступа, Г.В. Сотніков, В.С. Ус
Представлені теоретичні та експериментальні дослідження фізичних принципів кільватерного прискорюва-
ча, заснованого на збудженні прискорюючого кільватерного поля в плазмово-діелектричній структурі дов-
гою послідовністю електронних згустків. Збільшення амплітуди збуджуваного кільватерного поля досяга-
ється використанням мультибанчевого режиму збудження для когерентного складання кільватерних полів
окремих згустків і резонаторного режима для накопичення кільватерних полів. Прискорення згустків в су-
марному (плазмовому+діелектричному) кільватерному полі реалізовано розстройкою частоти слідування
згустків відносно частоти збуджуваного кільватерного поля. Таким шляхом послідовність згустків поділя-
ється на збуджуючу і прискорювану частини завдяки виникаючому зміщенню другої частини згустків в
прискорюючи фази кільватерного поля, збудженого першою частиною згустків цієї ж послідовності. Дослі-
джено вплив плазми в прольотному каналі на амплітуду збуджуваних плазмового та діелектричного кільва-
терних полів і фокусування збуджуючих і прискорюваних згустків.
http://vant.kipt.kharkov.ua/CONTENTS/CONTENTS_2012_6rus.html
|