Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them
Experiments on wakefield excitation by a long sequence of relativistic electron bunches in plasma, formed by head bunches of the same sequence in neutral gas of various pressure are presented. The ranges of pressure are found, in which beam-plasma discharge is developed, that leads to intensificat...
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| Zitieren: | Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them / V.A. Kiselev, A.F. Linnik, I.N. Onishchenko, V.I. Pristupa // Вопросы атомной науки и техники. — 2011. — № 1. — С. 77-79. — Бібліогр.: 7 назв. — англ. |
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Kiselev, V.A. Linnik, A.F. Onishchenko, I.N. Pristupa, V.I. 2016-01-04T19:33:54Z 2016-01-04T19:33:54Z 2011 Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them / V.A. Kiselev, A.F. Linnik, I.N. Onishchenko, V.I. Pristupa // Вопросы атомной науки и техники. — 2011. — № 1. — С. 77-79. — Бібліогр.: 7 назв. — англ. 1562-6016 PACS: 29.17.+w; 41.75.Lx https://nasplib.isofts.kiev.ua/handle/123456789/90826 Experiments on wakefield excitation by a long sequence of relativistic electron bunches in plasma, formed by head bunches of the same sequence in neutral gas of various pressure are presented. The ranges of pressure are found, in which beam-plasma discharge is developed, that leads to intensification of plasma generation. Acceleration and focusing of bunches electrons that is determined by ratio of the bunch length to its diameter and detuning between bunches repetition frequency and wakefield frequency, are investigated. Представлено експерименти по збудженню кільватерних полів довгою послідовністю релятивістських електронних згустків у плазмі, яка створена головними згустками тієї ж послідовності в нейтральному газі різного тиску. Знайдено області тиску газу, в яких розвивається пучково-плазмовий розряд, що приводить до інтенсифікації генерації плазми. Досліджені прискорення та фокусировка електронів згустків, які визначаються відношенням довжини згустку до його діаметру і розстройкою між частотою слідування згустків і частотою збуджуваного кільватерного поля. Представлены эксперименты по возбуждению кильватерных полей длинной последовательностью релятивистских электронных сгустков в плазме, образуемой головными сгустками этой же последовательности в нейтральном газе различного давления. Найдены области давлений газа, в которых развивается пучково- плазменный разряд, приводящий к интенсификации генерации плазмы. Исследованы ускорение и фокусировка электронов сгустков, определяемые отношением длины сгустка к его диаметру и расстройкой между частотой следования сгустков и частотой возбуждаемого кильватерного поля. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Плазменная электроника Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them Збудження кільватерних полів у плазмі, яка створена послідовністю електронних згустків у нейтральному газі, прискорення та фокусировка ними електронів Возбуждение кильватерных полей в плазме, образуемой последовательностью электронных сгустков в нейтральном газе, ускорение и фокусировка ими электронов Article published earlier |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| spellingShingle |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them Kiselev, V.A. Linnik, A.F. Onishchenko, I.N. Pristupa, V.I. Плазменная электроника |
| title_short |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| title_full |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| title_fullStr |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| title_full_unstemmed |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| title_sort |
wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them |
| author |
Kiselev, V.A. Linnik, A.F. Onishchenko, I.N. Pristupa, V.I. |
| author_facet |
Kiselev, V.A. Linnik, A.F. Onishchenko, I.N. Pristupa, V.I. |
| topic |
Плазменная электроника |
| topic_facet |
Плазменная электроника |
| publishDate |
2011 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Збудження кільватерних полів у плазмі, яка створена послідовністю електронних згустків у нейтральному газі, прискорення та фокусировка ними електронів Возбуждение кильватерных полей в плазме, образуемой последовательностью электронных сгустков в нейтральном газе, ускорение и фокусировка ими электронов |
| description |
Experiments on wakefield excitation by a long sequence of relativistic electron bunches in plasma, formed by head
bunches of the same sequence in neutral gas of various pressure are presented. The ranges of pressure are found, in
which beam-plasma discharge is developed, that leads to intensification of plasma generation. Acceleration and
focusing of bunches electrons that is determined by ratio of the bunch length to its diameter and detuning between
bunches repetition frequency and wakefield frequency, are investigated.
Представлено експерименти по збудженню кільватерних полів довгою послідовністю релятивістських
електронних згустків у плазмі, яка створена головними згустками тієї ж послідовності в нейтральному газі
різного тиску. Знайдено області тиску газу, в яких розвивається пучково-плазмовий розряд, що приводить до
інтенсифікації генерації плазми. Досліджені прискорення та фокусировка електронів згустків, які визначаються
відношенням довжини згустку до його діаметру і розстройкою між частотою слідування згустків і частотою
збуджуваного кільватерного поля.
Представлены эксперименты по возбуждению кильватерных полей длинной последовательностью
релятивистских электронных сгустков в плазме, образуемой головными сгустками этой же последовательности
в нейтральном газе различного давления. Найдены области давлений газа, в которых развивается пучково-
плазменный разряд, приводящий к интенсификации генерации плазмы. Исследованы ускорение и фокусировка
электронов сгустков, определяемые отношением длины сгустка к его диаметру и расстройкой между частотой
следования сгустков и частотой возбуждаемого кильватерного поля.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/90826 |
| citation_txt |
Wakefields excitation in plasma, produced by a sequence of electron bunches in neutral gas, accelerating and focusing electrons by them / V.A. Kiselev, A.F. Linnik, I.N. Onishchenko, V.I. Pristupa // Вопросы атомной науки и техники. — 2011. — № 1. — С. 77-79. — Бібліогр.: 7 назв. — англ. |
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2025-11-24T03:54:52Z |
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PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. № 1. 77
Series: Plasma Physics (17), p. 77-79.
WAKEFIELDS EXCITATION IN PLASMA, PRODUCED BY A SEQUENCE
OF ELECTRON BUNCHES IN NEUTRAL GAS, ACCELERATING
AND FOCUSING ELECTRONS BY THEM
V.A. Kiselev, A.F. Linnik, I.N. Onishchenko, V.I. Pristupa
National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: onish@kipt.kharkov.ua
Experiments on wakefield excitation by a long sequence of relativistic electron bunches in plasma, formed by head
bunches of the same sequence in neutral gas of various pressure are presented. The ranges of pressure are found, in
which beam-plasma discharge is developed, that leads to intensification of plasma generation. Acceleration and
focusing of bunches electrons that is determined by ratio of the bunch length to its diameter and detuning between
bunches repetition frequency and wakefield frequency, are investigated.
PACS: 29.17.+w; 41.75.Lx;
1. INTRODUCTION
Acceleration of charged particles by wakefields
excited in plasma by a relativistic electron bunch or a
sequence of bunches, is a promising method to accelerate
electrons with the acceleration rate of several orders of
magnitude higher than used in conventional accelerators
[1-3]. Besides wakefields provide focusing of the
accelerated electrons by orders of magnitude greater than
focusing by magnetic systems [4].
In this paper we study the excitation of wakefield in
plasma by a long sequence of bunches as they pass
through the neutral gas at different pressures, unlike to
[1], where plasma was produced by a plasma gun. We
have previously shown [5] that during the injection of a
sequence of bunches in the neutral gas at atmospheric
pressure plasma is created with the resonant density, for
which the plasma frequency ωp coincides with the
frequency of bunches ωm. We study the acceleration and
focusing of electron bunches by excited plasma wakefield
in the presence of detuning Δω= ωp-ωм arising from the
change plasma density. To enhance the focusing effect
bunches were made of elongated shape by means of
aperture, that led, as we have shown in [6], to the
prevalence of radial component of the wakefield [7].
2. EXPERIMENTAL SETUP
Experimental study were carried out with setup,
scheme of which is shown in Fig.1
Fig. 1. 1 – sequence of bunches , 2 - electron accelerator,
3 – interaction chamber, 4 - diaphragm, 5 - plasma
column, 6 - movable plug, 7 - microwave probe,
8 – oscilloscope
Relativistic electron beam produced by a linear
resonant accelerator. Beam parameters: energy –
4.5 MeV, pulsed current – 0.5 A, pulse duration – 2 μs,
modulation frequency – 2805 MHz.
Each pulse consists of 6×103 bunches with a duration of
each one – 60 ps and the time interval between them –
300 ps. Beam diameter at the exit from the accelerator
10 mm, bunch length – 17 mm, charge of bunch –
0.16 nC.
Beam was injected into a rectangular waveguide of
cross-section (72×34) mm2 and length of 25 cm. Neutral
gas pressure in the waveguide can be varied from 760 to
5×10-2 Torr. As the neutral gas was air. The waveguide
was pumped through the pipe, and was filled with neutral
gas through the leak. When closing the exit end of the
waveguide with a metal plate in the center of which the
probe was mounted, the cavity was formed. To measure
the beam current passing through the waveguide, the
probe was replaced by Faraday cup with a diameter of
15 mm. The energy loss of electrons bunches were
determined using a magnetic analyzer. The transverse size
of bunches was estimated by the beam portrait on a glass
plate.
3. RESULTS OF EXPERIMENT
3.1. EXCITATION OF WAKEFIELD
The dependence of the amplitude of Ez-component of
the excited wakefield on neutral gas pressure is shown in
Fig. 2 (curve 1). Two ranges of pressure was observed -
10-2…10 and 400…760 Torr, in which the intense
wakefield are excited. In these ranges more efficient
generation of plasma is explained by fact that in addition
to collisional ionization of the gas a beam-plasma
discharge (BPD) is developed. In the first range there is
an avalanche-like increase of the plasma density in the
microwave field of beam-plasma instability (classic BPD)
is developed. Unlike classic ERP using beams with
energies of tens of keV and observed at gas pressures of
10-3…10-4 Torr, in our experiments with a beam of
4.5 MeV this pressure range is shifted to higher pressures.
This is due to a decrease in the ionization cross-section
for the electron beams of relativistic energies, that
requires a higher density of gas to generate the critical
plasma density, at which BPD starts developing. In the
second area of higher pressure collisional ionization is
intensified, as well as BPD is developed on the base of
beam-dissipative instability. In both ranges, the growth of
plasma density stabilizes at a level when resonance of
frequency of bunches repetition and plasma frequency is
satisfied (ωp = ωm).
78
Fig. 2 (curve 2) shows the change in the beam current
which passed through the system and was measured by
Faraday cup diameter of 1.5 cm. It is seen that the beam
current, registered by Faraday cup, decreases in the
pressure range where the wakefield amplitude increases.
This decrease is the result of spread of the electrons by
transverse component of the exciting wakefield.
Fig. 2. Dependence of amplitude of the Ez-component
of the excited wakefield (curve 1) and magnitude of the
beam current (curve 2) on neutral gas pressure
In the pressure range where the amplitude of Ez-
wakefield is small, it is required more time to reach
resonant plasma density ωp ≈ ωм. It is concluded from
oscillograms of Ez wakefield, shown in Fig. 3. At
atmospheric pressure, the maximum amplitude of the
excited wakefield is achieved in a short time. At pressure
300 Torr maximum field is achieved only by the middle
of the current pulse (Fig. 3, b), and at pressure 40 Torr
wakefield amplitude not at al reaches its maximum value
(see Fig. 3, b).
Fig. 3. Oscillograms of Ez-component of the excited
wakefield at different pressures: a) 760 Torr,
b) 300 Torr, c) 40 Torr
The slow growth of wakefield and its small value in
Fig. 3,b,c indicates that the plasma density is below the
resonant value ωp ≈ ωм, i.e. there is a detuning between
bunches repetition frequency ωм and plasma frequency
ωр in this pressure range.
Detuning Δω= ωp-ωm caused by change in the plasma
frequency at plasma density reducing can be obtained
both at a decrease in gas pressure, and at a decrease in the
beam current.
3.2. ACCELERATION BY WAKEFIELD
The presence of the detuning leads to that part of the
sequence of bunches, the shifting along phase, fall into
the accelerating phase of the excited wakefield and take
the energy of the wakefield excited by previous bunches.
Electrons which lost their energy on wakefield excitation
and the electrons accelerated by wakefield (up to 6 MeV)
were observed using a magnetic analyzer, which is
located at the waveguide exit (see electron energy spectra
in Fig 4).
Fig. 4. Energy spectra of electrons
(1-input, 2-after interaction with plasma)
3.3. FOCUSING BY WAKEFIELD
In the presence of detuning at pressure in the range
from 200 to 40 Torr the various parts of the sequence of
bunches, shifting on phase, are occurred in defocusing or
focusing radial wakefield. Bunches, which fell in
defocusing phase, radially diverse and do not reach the
chamber exit. The passage focused bunches is improved.
This leads to the beats of the beam current, registered by
Faraday cup at the exit (Fig. 5, b). At atmospheric
pressure (Fig. 5, a) the beats are absent because in this
case there is no detuning.
Fig. 5. Oscilograms of beam current at chamber exit
(a-250 Torr, b - 40 Torr)
Studies of focusing were carried out at gas pressure
f = 760 Torr for two cases: 1) the current Ib = 0.5 A,
diameter of the bunch a and its length l are comparable
(a = 10 mm, l = 17 mm) and 2) the current Ib = 0.25 A,
diameter of the bunch appreciably less than its length
(a = 10 mm, l = 17 mm). The second case was realized by
diaphragming of the bunch and provided preferential
excitation of the radial component of the wakefield. In the
second case the current was decreased to create a
detuning and moving of bunches along phase, and bunch
shape was changed to emphasize the focusing effect.
Fig. 6 shows oscillogram of excited wakefield for the
first case. It is seen that the amplitude of the excited field
is growing during the whole pulse, that indicates that all
bunches are in the decelerating phase of the excited field.
At that, as it is evident from the measurements of beam
diameter on the darkening of the glasses (Fig. 7), part of
electrons of each bunch are in the focusing phase of the
excited field and keep within the same transverse
dimension, and the other part are defocused.
Fig. 6. Oscillogram of Ez wakefield in the absence of
detuning (Ib = 0.5 A, a = 10 mm, l = 17 mm)
a b c
ba
79
Fig. 7. Beam diameter at different distances from the exit
foil (Ib = 0,5 A, a = 10 mm, l = 17 mm):
1)0 cm, 2) 5 cm, 3)7cm, 4) 9cm, 5)11cm, 6)13cm, 7)15 cm
When reducing the beam diameter to 4 mm,
accompanied by a decrease in the current two times,
oscillograms of the wakefield showed beats (Fig. 8),
which are connected with the fact that at decrease in
current nonresonant plasma is created, that is caused by
weakening ionization process.
Fig. 8. Oscillogram Ez wakefield in the presence of
detuning (Ib = 0,25 A, a = 4mm, l = 17mm)
Fig. 9. Beam diameter at different distances from the exit
foil (Ib = 0,25 A, a = 4 mm, l = 17 mm):
1)0 cm, 2) 5 cm, 3)7cm, 4) 9cm, 5)11cm, 6)13cm, 7)15 cm
Appeared detuning leads to that various part of the
sequence of bunches gets into focusing or defocusing
phase of wakefield. This is proved by measurements of
the bunches diameter on the darkening portraits on the
glass plate (Fig. 9), on which is observed focusing and
defocusing effect is observed.
4. CONCLUSIONS
1. Studies of wakefield excitation in plasma produced by
a sequence of bunches of relativistic electrons as they
pass through the neutral gas at different pressures have
shown that there are two ranges of pressure –
400…760Тorr and 10-2…10Тorr, in which the maximum
amplitude of the wakefield and plasma frequency is close
repetition frequency of bunches.
2. The energy spectrum of electrons at exit shows both
energy loss by exciting electrons and the tail of f
accelerated electrons.
3. Focusing of bunches by excited plasma wakefield is
investigated in the resonant case and in the case of
detuning between the repetition frequency of bunches
and plasma frequency.
4. The beats of wakefield amplitude and beam current
associated with the detuning are revealed
REFERENCES
1. А.К. Berezin, et al. // JETPh. 1972, v. 63, N 3(9),
p. 861; Plasma Phys. Rep. 1994, v. 20. p. 596.
2. J.M.Chen, et al. // Phys. Rev. Lett. 1985, v. 54, N 7,
p. 693.
3. I. Blumenfeld, et al. // Nature, 2007, v. 445, p. 741.
4. P. Muggli. EPAC’06 06/28/06
5. V.A. Kiselev, et al. // VANT. Ser. "Plasma Physics".
2003, N 1, p. 105.
6. N. Ayzatskiy, et al. ECA V.22C. 1998, p. 1554.
7. R. Keinigs, M.E. Jones // Phys. Fluids. 1987, v.30, N 1,
p. 252.
Article received 26.09.10
ВОЗБУЖДЕНИЕ КИЛЬВАТЕРНЫХ ПОЛЕЙ В ПЛАЗМЕ,
ОБРАЗУЕМОЙ ПОСЛЕДОВАТЕЛЬНОСТЬЮ ЭЛЕКТРОННЫХ СГУСТКОВ В НЕЙТРАЛЬНОМ ГАЗЕ,
УСКОРЕНИЕ И ФОКУСИРОВКА ИМИ ЭЛЕКТРОНОВ
В.А. Киселёв, А.Ф. Линник, И.Н. Онищенко, В.И. Приступа
Представлены эксперименты по возбуждению кильватерных полей длинной последовательностью
релятивистских электронных сгустков в плазме, образуемой головными сгустками этой же последовательности
в нейтральном газе различного давления. Найдены области давлений газа, в которых развивается пучково-
плазменный разряд, приводящий к интенсификации генерации плазмы. Исследованы ускорение и фокусировка
электронов сгустков, определяемые отношением длины сгустка к его диаметру и расстройкой между частотой
следования сгустков и частотой возбуждаемого кильватерного поля.
ЗБУДЖЕННЯ КІЛЬВАТЕРНИХ ПОЛІВ У ПЛАЗМІ, ЯКА СТВОРЕНА ПОСЛІДОВНІСТЮ
ЕЛЕКТРОННИХ ЗГУСТКІВ У НЕЙТРАЛЬНОМУ ГАЗІ, ПРИСКОРЕННЯ ТА ФОКУСИРОВКА НИМИ
ЕЛЕКТРОНІВ
В.О. Кисельов, А.Ф. Лінник, І.М. Онищенко, В.І. Приступа
Представлено експерименти по збудженню кільватерних полів довгою послідовністю релятивістських
електронних згустків у плазмі, яка створена головними згустками тієї ж послідовності в нейтральному газі
різного тиску. Знайдено області тиску газу, в яких розвивається пучково-плазмовий розряд, що приводить до
інтенсифікації генерації плазми. Досліджені прискорення та фокусировка електронів згустків, які визначаються
відношенням довжини згустку до його діаметру і розстройкою між частотою слідування згустків і частотою
збуджуваного кільватерного поля.
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