Interaction between a coaxial cavity and low beta intense electron beams
Experiments and simulations for intense relativistic electron beams with energy of <1 MeV and current of several kA that pass through a gap are carried out. A criterion is proposed for the gap length through which the beam current passes without loss, i.e. no electron is reflected by virtual ca...
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| Цитувати: | Interaction between a coaxial cavity and low beta intense electron beams / Keiichi Kamada, Takashi Nishiguchi, Keiichi Ishibana, Masaki Kamada, Ritoku Ando // Вопросы атомной науки и техники. — 2004. — № 1. — С. 28-31. — Бібліогр.: 8 назв. — англ. |
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Keiichi Kamada Takashi Nishiguchi Keiichi Ishibana Masaki Kamada Ritoku Ando 2015-03-18T14:06:46Z 2015-03-18T14:06:46Z 2004 Interaction between a coaxial cavity and low beta intense electron beams / Keiichi Kamada, Takashi Nishiguchi, Keiichi Ishibana, Masaki Kamada, Ritoku Ando // Вопросы атомной науки и техники. — 2004. — № 1. — С. 28-31. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS 52.59 Sa https://nasplib.isofts.kiev.ua/handle/123456789/78478 Experiments and simulations for intense relativistic electron beams with energy of <1 MeV and current of several kA that pass through a gap are carried out. A criterion is proposed for the gap length through which the beam current passes without loss, i.e. no electron is reflected by virtual cathode. The time evolutions of energy and current of an intense electron beam can be modified using a gap structure and a coaxial cavity. Представлено експериментальні дослідження і чисельне моделювання процесів автоприскорення при проходженні інтенсивних релятивістських електронних пучків (енергія порядку 1 МеВ і струм декілька килоампер) через коаксіальні резонатори. Знайдено критерій на довжину зазору між резонаторами для утворення віртуального катоду. Представлены экспериментальные исследования и численное моделирование процессов автоускорения при прохождении интенсивных релятивистских электронных пучков (энергия порядка 1 МэВ и ток несколько килоампер) через коаксиальные резонаторы. Найден критерий на длину зазора между резонаторами для образования виртуального катода. A part of this work is supported by a Grant-in-Aid for Scientific Research from Ministry of Education, Science, Sports and Culture, Japan. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Сильноточные импульсные ускорители Interaction between a coaxial cavity and low beta intense electron beams Взаємодія між коаксіальним резонатором і інтенсивними електронними пучками з малими бета Взаимодействие между коаксиальным резонатором и интенсивными электронными пучками с малыми бета Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Interaction between a coaxial cavity and low beta intense electron beams |
| spellingShingle |
Interaction between a coaxial cavity and low beta intense electron beams Keiichi Kamada Takashi Nishiguchi Keiichi Ishibana Masaki Kamada Ritoku Ando Сильноточные импульсные ускорители |
| title_short |
Interaction between a coaxial cavity and low beta intense electron beams |
| title_full |
Interaction between a coaxial cavity and low beta intense electron beams |
| title_fullStr |
Interaction between a coaxial cavity and low beta intense electron beams |
| title_full_unstemmed |
Interaction between a coaxial cavity and low beta intense electron beams |
| title_sort |
interaction between a coaxial cavity and low beta intense electron beams |
| author |
Keiichi Kamada Takashi Nishiguchi Keiichi Ishibana Masaki Kamada Ritoku Ando |
| author_facet |
Keiichi Kamada Takashi Nishiguchi Keiichi Ishibana Masaki Kamada Ritoku Ando |
| topic |
Сильноточные импульсные ускорители |
| topic_facet |
Сильноточные импульсные ускорители |
| publishDate |
2004 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Взаємодія між коаксіальним резонатором і інтенсивними електронними пучками з малими бета Взаимодействие между коаксиальным резонатором и интенсивными электронными пучками с малыми бета |
| description |
Experiments and simulations for intense relativistic electron beams with energy of <1 MeV and current of several kA
that pass through a gap are carried out. A criterion is proposed for the gap length through which the beam current passes
without loss, i.e. no electron is reflected by virtual cathode. The time evolutions of energy and current of an intense electron beam can be modified using a gap structure and a coaxial cavity.
Представлено експериментальні дослідження і чисельне моделювання процесів автоприскорення при
проходженні інтенсивних релятивістських електронних пучків (енергія порядку 1 МеВ і струм декілька
килоампер) через коаксіальні резонатори. Знайдено критерій на довжину зазору між резонаторами для
утворення віртуального катоду.
Представлены экспериментальные исследования и численное моделирование процессов автоускорения
при прохождении интенсивных релятивистских электронных пучков (энергия порядка 1 МэВ и ток несколько килоампер) через коаксиальные резонаторы. Найден критерий на длину зазора между резонаторами для
образования виртуального катода.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/78478 |
| citation_txt |
Interaction between a coaxial cavity and low beta intense electron beams / Keiichi Kamada, Takashi Nishiguchi, Keiichi Ishibana, Masaki Kamada, Ritoku Ando // Вопросы атомной науки и техники. — 2004. — № 1. — С. 28-31. — Бібліогр.: 8 назв. — англ. |
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INTERACTION BETWEEN A COAXIAL CAVITY AND LOW BETA
INTENSE ELECTRON BEAMS
Keiichi Kamada, Takashi Nishiguchi, Keiichi Ishibana, Masaki Kamada and Ritoku Ando
Faculty of Science, Kanazawa University, Kanazawa, 920-1192 Japan;
E-mail address:kkamada@plasma.s.kanazawa-u.ac.jp
Experiments and simulations for intense relativistic electron beams with energy of <1 MeV and current of several kA
that pass through a gap are carried out. A criterion is proposed for the gap length through which the beam current passes
without loss, i.e. no electron is reflected by virtual cathode. The time evolutions of energy and current of an intense elec-
tron beam can be modified using a gap structure and a coaxial cavity.
PACS 52.59 Sa
1. INTRODUCTION
Interactions between a coaxial cavity and an intense
relativistic electron beam (IREB) with strong self- and
induced field are not only interesting for physics but
also important for applications. As a typical application
of IREBs, intense millimeter electromagnetic wave
sources with output power of 1 GW< for nuclear fusion,
particle accelerator, etc. utilize IREBs as energy
sources. Relativistic klystron amplifiers (RKA), virtual
cathode oscillators, and backward-wave oscillators, etc.
using IREBs are intensively studied in this decade.
Moreover, a new specific mechanism of microwave ra-
diation called superradiance (SR) is proposed [1-3] us-
ing an electron beam whose length is shorter than or
comparable with interaction length. An IREB with dura-
tion of less than 1 ns is requested for millimeter wave-
band SR. However, it is technically difficult for conven-
tional pulse line system to generate an IREB with pulse
duration of less than 10 ns. We proposed multi-stage au-
toacceleration using a series of passive coaxial cavities
with decreasing lengths and obtained an IREB with du-
ration of less than 1 ns from 12 ns IREB [4,5]. The au-
toacceleration and the RKA use coaxial cavities con-
nected to the drift tube via gaps. The radius of the tube
increases suddenly at the entrance of the gap. Propaga-
tion characteristics of an IREB through a gap are impor-
tant subjects to study for autoacceleration, RKA and the
devices with a cavity or a gap.
When an electron beam propagates through a drift
tube immersed in axial magnetic field, electrostatic po-
tential in the tube due to the beam's space-charge field
limits the beam current. In the case of a cylindrical
beam propagating through a cylindrical tube, the limit-
ing current is calculated by the initial energy (γ0) of
electrons and the ratio of the beam radius (rb) to the tube
radius (rt). For an annular beam, the limiting current (IL)
is expressed as below
€
IL =I A
(γ0
2 / 3 −1)3/ 2
2 ln(rt / rb )
, (
where IA = 17 kA is the Alfven current. The limiting cur-
rent decreases where the radius of the tube increases.
Because of comparatively low energy of IREBs, the
space charge limiting current is comparable to the beam
current, so that existence of a gap affects strongly to the
propagation of the IREB. It is considered that a virtual
cathode is formed at the gap and some electrons are re-
flected when the beam current is much larger than the
space charge limiting current at the gap. However, the
above equation is derived for the beam with an infinite
axial length. In the experiments, it is not clear how long
the axial length is enough for a drift tube to apply the
above equation. In this paper, we report the length of the
gap through which the beam passes without loss and
propose the modification of time evolutions of IREB’s
energy and current using a coaxial cavity and a gap.
2. AN IREB PASSING THROUGH A GAP
We employed a simple model to start this problem.
As shown in Fig.1, a drift tube radius increases
suddenly from r1 to r2 at z (z is the distance from an
anode.) and decreases from r2 to r1 at z+d. The thicker
part of the tube with length of d is named a gap here. An
electron beam with current I which exceeds the space-
charge limiting current IL at the gap is injected from
z=0. We investigate the length d through which the
IREB current passes through without loss.
Fig.1 Simple model of a gap
]
Intense relativistic annular electron beams with ener-
gy of ~500 keV, current of 4~8 kA and duration of 12 ns
were utilized in the experiment. The beam radius and
current were changed. The beam propagated through a
drift tube with diameter of 3 cm. A gap with diameter of
12 cm was located 20 cm downstream side of the anode.
The length of the gap, d, was changed. The beam cur-
rent was detected at the end of the drift tube with diame-
ter of 3 cm by a Faraday cup. In order not to affect the
presence of the Faraday cup to the experimental results,
the Faraday cup was located 20 cm downstream side of
the gap end.
Figure 2 shows the beam current waveforms detect-
ed at the downstream side of the gap for different gap
__________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.28-31.28
lengths. The space charge limiting current at the gap
was evaluated to be 2.8 kA. Though the beam current of
8 kA was much larger than the limiting current, it passes
through the gap without loss when the gap length is less
than ~30 mm.
Fig.2. The beam current waveform passing through the
gap for different gap lengths (left). The maximum cur-
rents passing through a gap are plotted against gap
lengths
In Fig.2, the maximum beam currents detected by
the Faraday cup are also plotted against the gap length.
The beam current decreases to the space charge limiting
current at the gap gradually as the gap length increases.
The gap length through which the beam passes without
loss was also observed experimentally by changing the
beam radius and/or current. The gap length through
which the beam passes without loss increased as the
beam current decreased and it increased as the beam ra-
dius increased as expected.
PIC simulation code KARAT was used. As the code
KARAT simulated well the experimental results, we ex-
tended the range of parameters with energy of
400~1750 keV, current of 3~9 kA and gap radius of
40~90 mm in the simulation. The relation between the
gap length and the detected beam current at the down-
stream side of the gap was investigated with different
parameters. As shown in Fig.3, when the gap length is
short, the formation of a virtual cathode is incomplete
and the injected beam current can pass through the gap
without loss. On the contrary, some of the electrons are
reflected by virtual cathode, when the gap length is
long.
Dependencies of the gap length without loss on the
current, energy and radius of the beam indicated the
influence of the space-charge limiting current. In Fig.4,
the simulated and experimental gap lengths through
which the beam current passes without loss are plotted
against calculated values of 2(R -rb) for each data,
where R is the calculated maximum tube radius for the
beam with current I, energy γ0 and radius rb by eq.(1).
From the simulation results, the gap length increases
with 2(R -rb) linearly. And from the experimental
results, they also increase with 2(R -rb). We have no
physical explanation about this relation yet. The
quantitative differnce between the simulated and the
experimental results are considered to come from
precise differencies of the beam waveform parameters
between them.
In
conclusion, we propose the gap length of 2(R - rb) as a
rough criterion of the gap length through which the
beam can pass without loss.
Fig.3. KARAT simulation. Normalized axial momen-
ta of electrons are plotted against the axial position.
The formation of virtual cathode is incomplete (up) and
the beam current can pass through the gap without loss.
Virtual cathode is formed and some electrons are re-
flected (down)
__________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.28-31.29
Fig.4. The gap length through which the beam passed
without loss is plotted against 2(R - rb)
3. ENERGY AND CURRENT INCREASING
WAVEFORMS OF AN IREB
For observation of SR, it was proposed in [6] to use
an IREB with increasing energy and current in time to
increase peak power of SR pulse. As a cold cathode and
an anode are utilized for conventional IREB generator,
the voltage between diode applied by a Marx generator
and a pulse forming line is changed by the evolution of
the diode impedance caused by cathode and anode
plasmas. There is no way to control the plasmas at the
diode. The autoacceleration scheme can be a candidate
to realize the IREB with increasing energy in time after
the IREB injected from the anode. A coaxial cavity
connected to the drift tube via gap is utilized in the
autoacceleration. According to the transmission line
theory, the gap voltage of a coaxial cavity, Vg(t), is
expressed by the current at the gap, I(t), as below[7,8],
€
Vg(t)=Z×(I(t)−2I(t−T)+•••) (2)
where Z is the cavity impedance and T is the round trip
time of electromagnetic wave in the cavity. The beam is
decelerated for the first period T and accelerated for the
next period. As the initial electron energy and current
waveforms are not square shape, we have a possibility
to obtain a gradual increasing energy IREB using a
cavity with appropriate length.
Fig.5. Experimental setup
We used a gap behind the coaxial cavity for
autoacceleration in order to decrease the current in low
energy part of the IREB. As the enegy of the electrons
increases in time after the autoacceleration, we expect
that a virtual cathode that reflects only the lower energy
electrons is formed with appropriate gap length.
The experimental setup is shown in Fig.5. The
parameters of the IREB and experimental apparatus
were almost the same as the above experiment. A
Faraday cup was used to estimate the kinetic energy of
beam electrons. Aluminum foils of various thicknesses
were placed in front of the Faraday cup and a
transmitted current through aluminum foils was
measured. Using the ratio of the transmitted current to
the current detected without foil and the range-energy
relations, the maximum kinetic energy of beam
electrons was estimated.
Fig.6. Time evolution of energy with and without
coaxial cabity. The cavity length is 60 cm. Calculated
results shows good agreement with the experiment
The time evolution of energy detected downstream
side of the cavity with length of 60 cm is shown in
Fig.6. The time evolution evaluated from the sum of the
diode and gap voltages showed good agreements with
the experimental results for different cavity lengths. The
current waveform was little changed between before
and after the coaxial cavity.
Fig.7. Current waveforms after the gap
The current waveforms after the gap were modified
as shown in Fig.7. The time evolution of energy were
not changed by the gap. The current at the time with
higher energy was more decreased than lower energy
part against our expectation. Electrons with lower
energy were suspected to be included in the current at
the time when higher energy electrons were observed.
Precise experiments will be carried out for this problem.
In conclusion, the time evolutions of electron energy
and current can be changed using a coaxial cavity and a
gap within the limit of initial diode waveforms. In
connection with the design of a new diode, time
evolutions of energy and current become easier to
modify.
A part of this work is supported by a Grant-in-Aid
for Scientific Research from Ministry of Education,
Science, Sports and Culture, Japan.
REFERENCES
1. N.S. Ginzburg, I.V. Zotova // Sov. Tech Phys. Lett.
1989, v. 15, p. 573-574,
2. N.S. Ginzburg, I.V. Zotova, A.S. Sergeev,
I.V. Konoplev, A.D.R. Phelps, A.W. Cross,
S.J. Cooke, V.G. Shpak, M.I. Yalandin,
S.A. Shunailov and M.R. Ulmaskulov // Phys. Rev.
Lett. 1997, v.78, p.2365-2368,
3. S.M. Wiggins, D.A. Jaroszynsky, B.W.J. McNeil,
G.R.M. Robb, P. Alitken, A.D.R. Phelps,
A.W. Cross, K. Ronald, N.S. Ginzburg, V.G. Shpak,
M.I. Yalandin, S.A. Shunailov and M.R. Ulmaskulov
// Phys. Rev. Lett. 2000, v. 84, p.2393-2396.
__________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.28-31.
4. D. Hasegawa, K. Kamada, K. Shimizu, R. Ando
and M. Masuzaki // IEEE trans. Plasma Sci. 2000,
v.28, p.1648-1652.
5. D. Hasegawa, K. Kamada, A. Kuraku, R. Ando and
M. Masuzaki // Jpn. J. Appl. Phys. 2001, v. 40,
p.944-948.
6. N.S. Ginzburg, I.V. Zotova, R.M. Rozental,
A.S. Sergeev, M. Kamada, K. Sugawara, K. Kuri-
hara, H. Shirasaka, R. Ando, K. Kamada // Proc.
14th Int. Conf. High-Power Particles Beams. 2002,
p.291-294.
7. M. Friedman // Appl. Phys. Lett. 1982, v. 41, p.419-
421,
8. M. Kamada, R. Ando, N.S. Ginzburg and K. Kama-
da //IEEE trans. Plasma Sci. 2003, v. 31, p.297-
299.
__________________________________________________________
PROBLEMS OF ATOMIC SIENCE AND TECHNOLOGY. 2004. № 1.
Series: Nuclear Physics Investigations (42), p.28-31.31
ВЗАИМОДЕЙСТВИЕ МЕЖДУ КОАКСИАЛЬНЫМ РЕЗОНАТОРОМ И ИНТЕНСИВНЫМИ
ЭЛЕКТРОННЫМИ ПУЧКАМИ С МАЛЫМИ БЕТА
Кеичи Камада, Такаши Нишигучи, Кеичи Ишибана, Масаки Камада, Ритоку Андо
Представлены экспериментальные исследования и численное моделирование процессов автоускорения
при прохождении интенсивных релятивистских электронных пучков (энергия порядка 1 МэВ и ток несколь-
ко килоампер) через коаксиальные резонаторы. Найден критерий на длину зазора между резонаторами для
образования виртуального катода.
ВЗАЄМОДІЯ МІЖ КОАКСІАЛЬНИМ РЕЗОНАТОРОМ І ІНТЕНСИВНИМИ
ЕЛЕКТРОННИМИ ПУЧКАМИ З МАЛИМИ БЕТА
Кеичи Камада, Такаши Нишигучи, Кеичи Ишибана, Масаки Камада, Ритоку Андо
Представлено експериментальні дослідження і чисельне моделювання процесів автоприскорення при
проходженні інтенсивних релятивістських електронних пучків (енергія порядку 1 МеВ і струм декілька
килоампер) через коаксіальні резонатори. Знайдено критерій на довжину зазору між резонаторами для
утворення віртуального катоду.
31
электронными пучками с малыми бета
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