Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode
Results of computer simulation of low-energy high-current electron beam dynamics in a low-impedance system consisting of a diode with a long plasma anode, just siding with an explosive emission cathode and an auxiliary thermionic cathode are presented. Plasma anode plays simultaneously a role of t...
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Agafonov, A.V. Tarakanov, V.P. 2017-01-09T18:36:25Z 2017-01-09T18:36:25Z 2008 Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode / A.V. Agafonov, V.P. Tarakanov // Вопросы атомной науки и техники. — 2008. — № 3. — С. 136-138. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS: 52.40.Mj https://nasplib.isofts.kiev.ua/handle/123456789/111394 Results of computer simulation of low-energy high-current electron beam dynamics in a low-impedance system consisting of a diode with a long plasma anode, just siding with an explosive emission cathode and an auxiliary thermionic cathode are presented. Plasma anode plays simultaneously a role of the transport channel providing charge neutralization of high-current beam and is created by means of the residual gas ionisation by low-current, low-voltage electron beam emitted from the auxiliary cathode in an external longitudinal magnetic field. The main peculiarities of the beam-plasma system are discussed: 1) the formation of the beam of currents exceeding the limiting Alven’s ones; 2) the formation of paramagnetic states of the beam under condition of beam charge density close to the plasma density. These peculiarities complicate beam-plasma interaction significantly due to sharp nonuniform distribution of the beam current density, significant transverse motion of the beam electrons and redistribution of ion plasma density under the influence of high-current electron beam fields. Computer simulation was performed using electromagnetic PIC code KARAT. Наведено результати чисельного моделювання динаміки низькоенергетичних потужнострумових електронних пучків у низькоімпедансній плазмовій системі, що складається з діоду з довгим плазмовим анодом, що впритул прилягає до вибухоемісійного катоду, і допоміжного термокатоду. Плазмовий анод одночасно відіграє роль каналу для транспортування пучку і створюється за допомогою іонізації залишкового газу слабкострумовим низьковольтним пучком від термокатоду в зовнішнім поздовжнім магнітному полі. Розглянуто основні особливості подібної пучково- плазмової системи: 1) формування пучків зі струмами, що перевершують граничний струм Альфвена; 2) формування парамагнітних станів пучків в умовах, коли щільність заряду пучка порівнянна із щільністю плазми. Робота виконана за підтримкою РФФД по гранту 05-02-16442. Приведены результаты численного моделирования динамики низкоэнергетичных сильноточных электронных пучков в низкоимпедансной плазменной системе, состоящей из диода с длинным плазменным анодом, вплотную прилегающим к взрывоэмиссионному катоду, и вспомогательного термокатода. Плазменный анод одновременно играет роль канала для транспортировки пучка и создается посредством ионизации остаточного газа слаботочным низковольтным пучком от термокатода во внешнем продольном магнитном поле. Рассмотрены основные особенности подобной пучково- плазменной системы: 1) формирование пучков с токами, превосходящими предельный ток Альфвена; 2) формирование парамагнитных состояний пучков в условиях, когда плотность заряда пучка сравнима с плотностью плазмы. Работа выполнена при поддержке РФФИ по гранту 05-02-16442. Work supported by RFBR under grant 05-02-16442. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Новые методы ускорения, сильноточные пучки Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode Чисельне моделювання динаміки низькоенергетичних потужнострумових електронних пучків у довгому плазмовому діоді Численное моделирование динамики низкоэнергетичных сильноточных электронных пучков в длинном плазменном диоде Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| spellingShingle |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode Agafonov, A.V. Tarakanov, V.P. Новые методы ускорения, сильноточные пучки |
| title_short |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| title_full |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| title_fullStr |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| title_full_unstemmed |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| title_sort |
computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode |
| author |
Agafonov, A.V. Tarakanov, V.P. |
| author_facet |
Agafonov, A.V. Tarakanov, V.P. |
| topic |
Новые методы ускорения, сильноточные пучки |
| topic_facet |
Новые методы ускорения, сильноточные пучки |
| publishDate |
2008 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Чисельне моделювання динаміки низькоенергетичних потужнострумових електронних пучків у довгому плазмовому діоді Численное моделирование динамики низкоэнергетичных сильноточных электронных пучков в длинном плазменном диоде |
| description |
Results of computer simulation of low-energy high-current electron beam dynamics in a low-impedance system
consisting of a diode with a long plasma anode, just siding with an explosive emission cathode and an auxiliary
thermionic cathode are presented. Plasma anode plays simultaneously a role of the transport channel providing
charge neutralization of high-current beam and is created by means of the residual gas ionisation by low-current,
low-voltage electron beam emitted from the auxiliary cathode in an external longitudinal magnetic field. The main
peculiarities of the beam-plasma system are discussed: 1) the formation of the beam of currents exceeding the
limiting Alven’s ones; 2) the formation of paramagnetic states of the beam under condition of beam charge density
close to the plasma density. These peculiarities complicate beam-plasma interaction significantly due to sharp nonuniform
distribution of the beam current density, significant transverse motion of the beam electrons and
redistribution of ion plasma density under the influence of high-current electron beam fields. Computer simulation
was performed using electromagnetic PIC code KARAT.
Наведено результати чисельного моделювання динаміки низькоенергетичних потужнострумових електронних
пучків у низькоімпедансній плазмовій системі, що складається з діоду з довгим плазмовим анодом, що впритул прилягає
до вибухоемісійного катоду, і допоміжного термокатоду. Плазмовий анод одночасно відіграє роль каналу для
транспортування пучку і створюється за допомогою іонізації залишкового газу слабкострумовим низьковольтним
пучком від термокатоду в зовнішнім поздовжнім магнітному полі. Розглянуто основні особливості подібної пучково-
плазмової системи: 1) формування пучків зі струмами, що перевершують граничний струм Альфвена; 2) формування
парамагнітних станів пучків в умовах, коли щільність заряду пучка порівнянна із щільністю плазми. Робота виконана за
підтримкою РФФД по гранту 05-02-16442.
Приведены результаты численного моделирования динамики низкоэнергетичных сильноточных электронных пучков
в низкоимпедансной плазменной системе, состоящей из диода с длинным плазменным анодом, вплотную прилегающим
к взрывоэмиссионному катоду, и вспомогательного термокатода. Плазменный анод одновременно играет роль канала
для транспортировки пучка и создается посредством ионизации остаточного газа слаботочным низковольтным пучком
от термокатода во внешнем продольном магнитном поле. Рассмотрены основные особенности подобной пучково-
плазменной системы: 1) формирование пучков с токами, превосходящими предельный ток Альфвена; 2) формирование
парамагнитных состояний пучков в условиях, когда плотность заряда пучка сравнима с плотностью плазмы. Работа
выполнена при поддержке РФФИ по гранту 05-02-16442.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/111394 |
| citation_txt |
Computer simulation of low-energy high-current electron beam dynamics in a long plasma-filled diode / A.V. Agafonov, V.P. Tarakanov // Вопросы атомной науки и техники. — 2008. — № 3. — С. 136-138. — Бібліогр.: 8 назв. — англ. |
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| fulltext |
COMPUTER SIMULATION OF LOW-ENERGY HIGH-CURRENT ELEC-
TRON BEAM DYNAMICS IN A LONG PLASMA-FILLED DIODE
A.V. Agafonov1, V.P. Tarakanov2
1P.N. Lebedev Physical Institute of RAS, Leninsky Prosp. 53, Moscow, GSP-1, 119991, Russia
2Institute for High Energy Densities of RAS, Izorskaya 13/19, Moscow, 125412, Russia
E-mail: agafonov@sci.lebedev.ru
Results of computer simulation of low-energy high-current electron beam dynamics in a low-impedance system
consisting of a diode with a long plasma anode, just siding with an explosive emission cathode and an auxiliary
thermionic cathode are presented. Plasma anode plays simultaneously a role of the transport channel providing
charge neutralization of high-current beam and is created by means of the residual gas ionisation by low-current,
low-voltage electron beam emitted from the auxiliary cathode in an external longitudinal magnetic field. The main
peculiarities of the beam-plasma system are discussed: 1) the formation of the beam of currents exceeding the
limiting Alven’s ones; 2) the formation of paramagnetic states of the beam under condition of beam charge density
close to the plasma density. These peculiarities complicate beam-plasma interaction significantly due to sharp non-
uniform distribution of the beam current density, significant transverse motion of the beam electrons and
redistribution of ion plasma density under the influence of high-current electron beam fields. Computer simulation
was performed using electromagnetic PIC code KARAT.
PACS: 52.40.Mj
1. INTRODUCTION
The main idea of low-energy high-current beam gen-
eration is based on the origin of a thin double-layer
between a cathode and adjoined anode plasma just after
the beginning of accelerating voltage pulse. Plasma-
filled diodes with explosive cathodes are used for these
purposes to generate electron beams for surface modi-
fication [1-3]. The full voltage is localised across this
layer making possible the beginning of the explosive
emission from a cathode surface. The plasma serves as
the “liquid” anode preventing the system from collapse
of the impedance. From another side it forms the chan-
nel to guide high-current beam from the cathode to a
target making sure charge neutralisation of the beam
and its transportation. We use a residual gas ionisation
by additional pulsed low-energy, low-current electron
beam to create well-defined plasma anode in a longitud-
inal magnetic field [2, 3, 7, 8].
2. CONDITIONS OF COMPUTER SIMULA-
TION
Results of computer simulation of plasma anode
formation in the residual gas by an auxiliary electron
beam and the first experiments on the generation of
high-current beams were described in [2, 3]. Additional
experimental results and the results of computer simula-
tion of the generation of low-energy high current beams
under different condition are described in [8].
Diameter of the explosive emission cathode was
chosen equals to 1 cm. At initial time the plasma
column of the same diameter along the system fills
completely space in longitudinal direction between ex-
plosive emission cathode and anode placed instead of
auxiliary gun. The density of plasma is homogeneously
distributed along longitudinal z and radial r co-ordinates
and was varied from 1×1013 cm-3 up to 7×1013 cm-3. Ini-
tial temperature of the plasma was changed from several
to tens electronvolts. Applied voltage has the given
form. It rose up to 20 kV for different time (1…10 ns)
and was constant further. Output of electrons was per-
mitted from the field-emission cathode and surfaces into
plasma if accelerating field exceeds a given value. Cal-
culations were performed for hydrogen, nitrogen and
xenon plasmas for different values of external longitud-
inal magnetic field and for different length of the
plasma diode.
3. GENERAL PECULIARITIES OF THE
BEAM-PLASMA SYSTEM
Generation and transportation of low-energy high-
current beams in such system is conditioned by several
peculiarities. First of all, if the emission of the beam
from the cathode is space charge limited, beam currents
exceed Alven’s limiting current for all considered con-
dition, if the plasma density is high enough. It manifests
the prevalence of transverse dynamics of beam elec-
trons. The second peculiarity of the system is compar-
able density of the generated electron beam and the
plasma. It means low average and large local electric
fields. The last signifies the necessity to take into con-
sideration the motion of plasma ions. Moreover beam
electrons will force out plasma electrons to the chamber
walls for a short time. As the result the exotic media
will be formed consisting of low plasma ions and fast
beam electrons. In the absence of current neutralisation
by plasma electrons the beam has to be pinched to high
local densities to the axis of the system. The density of
plasma ions will follow the electron density with a time
delay and pre-axis ion pivot will be formed. Pinching of
electron beam will create high fast alternating electro-
magnetic fields. Therefore a modification of energy
spectrum of beam electrons and stochastically acceler-
ated plasma ions must be observed. The departure of
plasma ions from the space between electrodes to walls
will limit the duration of electron beam, i.e. as heavier
ions of the residual gas as longer the duration of beam
current pulse. Beam current depends on plasma density
also and increases linearly with growth of residual gas
pressure in noted above region. It is obviously that the
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2008. № 3.
Series: Nuclear Physics Investigations (49), p.136-138.
136
behaviour and the main characteristics of the beam will
depend on the external magnetic field. If to recollect
about different time scales and multistage of processes,
then the system as a whole can be characterised as
multi-component one with alternating number of
particles and can’t be described by regular theoretical
methods.
3.1.PINCHED AND ANNULAR STATES
OF THE SYSTEM
Calculations were carried out for different levels of
external magnetic field: 0, 500 and 5000 Gs. The beha-
viour of the beam does not differ significantly for the
first two cases and for diodes of different length except-
ing the duration of the beam current. In small magnetic
fields pinched state of the beam-plasma system is
formed very likes to Bennett’s pinch. Beam electrons
force plasma electrons out to electrodes in longitudinal
direction, beam electrons are pinched to the axis of the
system by self magnetic field exceeding significantly
external one, and near axis ion pivot is formed.
Fig.1. Trajectories of several beam electrons for
different external magnetic field
Such metastable state of beam-plasma system exists for
tens nanoseconds depending on the length of the system
and ion mass. Further it goes to annular configuration of
plasma ions and electron beam.
If external magnetic field is high enough to prevent
beam electrons from focusing to the axis of the system
then pinched state is not reached at all. Plasma ions
leave pre-axis area under influence of self space charge
and annular distributions of beam electrons and plasma
ions are formed. Such state slowly expanding in radial
direction with decreasing beam current can exist for tens
nanoseconds.
Corresponding trajectories of several beam electrons
emitted from the cathode for different values of external
magnetic field (500 Gs and 5 kGs from the top to the
bottom) are shown in Fig.1 for 2-ns time interval.
3.2. BEAMS PARAMAGNETIC STATES
Usually, charged beam in an external magnetic field
behaves as a diamagnetic and forces the magnetic field
out of its volume. In [4, 5] it was shown that for some
systems, e.g. for inverted coaxial magnetic isolation di-
odes, it is possible to realise conditions under which the
magnetic field is forced inside the volume occupied by
the beam and is increased considerable as compared as
external field. About similar situation could be realised
in the beam-plasma system under consideration. In this
case the role of the internal electrode plays near axis ion
pivot. The reasons of the creation just of paramagnetic
state of the beam are not clear enough. It can be as-
sumed that just fast forced escape of plasma electrons to
the electrodes and exceeding of Alven’s limit by beam
current play the main role. As the result a “clear” sys-
tem consisting of slow plasma ions and fast beam elec-
trons is formed. This system has many commons with
so-called coupling state in moving quasi-neutral medi-
um [6] and can be considered as polarised one.
The degree of magnetic field amplification depends
on the value of the external magnetic field, plasma dens-
ity, and rise time of the applied voltage and transverse
dimensions of the system. In high external magnetic
field the amplification is smaller. In low magnetic fields
the amplification of the field can exceed 40. No special
attempts were done to find conditions of maximum
amplification. Below several results are given for short
systems to be sure in the accuracy of the calculations.
Fig.2 shows typical behaviour of beam current on the
time. Beam current on the collector decreases rapidly
because of fast escape of plasma ions to electrodes in
the system with small longitudinal dimension (see
Fig.1). The form and the duration of the current not
strongly depend on magnetic field. Beam current dura-
tion increases with increasing of the distance between
electrodes. Symbols i, e and b sign accordingly plasma
ions, plasma electrons and beam electrons.
Fig.2. Typical beam current on the collector placed at
1 cm from the cathode for magnetic field 500 Gs
Dynamics of alternating part of longitudinal magnet-
ic field near the axis in the centre of the system and lon-
gitudinal and radial distributions of complete longitud-
inal field at the moment are shown in Fig.3. For the case
of B = 5 kGs magnetic field on the axis exceeds 12 kGs.
Work supported by RFBR under grant 05-02-16442.
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2008. № 3.
Series: Nuclear Physics Investigations (49), p.136-138.
137
Fig.3. Dynamics and distributions of longitudinal
magnetic field
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ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ДИНАМИКИ НИЗКОЭНЕРГЕТИЧНЫХ СИЛЬНОТОЧНЫХ ЭЛЕК-
ТРОННЫХ ПУЧКОВ В ДЛИННОМ ПЛАЗМЕННОМ ДИОДЕ
А.В. Агафонов, В.П. Тараканов
Приведены результаты численного моделирования динамики низкоэнергетичных сильноточных электронных пучков
в низкоимпедансной плазменной системе, состоящей из диода с длинным плазменным анодом, вплотную прилегающим
к взрывоэмиссионному катоду, и вспомогательного термокатода. Плазменный анод одновременно играет роль канала
для транспортировки пучка и создается посредством ионизации остаточного газа слаботочным низковольтным пучком
от термокатода во внешнем продольном магнитном поле. Рассмотрены основные особенности подобной пучково-
плазменной системы: 1) формирование пучков с токами, превосходящими предельный ток Альфвена; 2) формирование
парамагнитных состояний пучков в условиях, когда плотность заряда пучка сравнима с плотностью плазмы. Работа
выполнена при поддержке РФФИ по гранту 05-02-16442.
ЧИСЕЛЬНЕ МОДЕЛЮВАННЯ ДИНАМІКИ НИЗЬКОЕНЕРГЕТИЧНИХ ПОТУЖНОСТРУМОВИХ ЕЛЕК-
ТРОННИХ ПУЧКІВ У ДОВГОМУ ПЛАЗМОВОМУ ДІОДІ
А.В. Агафонов, В.П. Тараканов
Наведено результати чисельного моделювання динаміки низькоенергетичних потужнострумових електронних
пучків у низькоімпедансній плазмовій системі, що складається з діоду з довгим плазмовим анодом, що впритул прилягає
до вибухоемісійного катоду, і допоміжного термокатоду. Плазмовий анод одночасно відіграє роль каналу для
транспортування пучку і створюється за допомогою іонізації залишкового газу слабкострумовим низьковольтним
пучком від термокатоду в зовнішнім поздовжнім магнітному полі. Розглянуто основні особливості подібної пучково-
плазмової системи: 1) формування пучків зі струмами, що перевершують граничний струм Альфвена; 2) формування
парамагнітних станів пучків в умовах, коли щільність заряду пучка порівнянна із щільністю плазми. Робота виконана за
підтримкою РФФД по гранту 05-02-16442.
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