Ion accelerator based on plasma vircator
Based on previous fundamental and experimental research [1, 2] the conception of a collective ion accelerator is proposed to be developed in the frameworks of STCU project #1569 (NSC KIPT, Ukraine) in coordination with the ISTC project #1629 (VNIIEF, Russia). The main processes of acceleration are s...
Збережено в:
| Опубліковано в: : | Вопросы атомной науки и техники |
|---|---|
| Дата: | 2001 |
| Автори: | , |
| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2001
|
| Онлайн доступ: | https://nasplib.isofts.kiev.ua/handle/123456789/79229 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| Цитувати: | Ion accelerator based on plasma vircator / I.N. Onishchenko, S.S. Pushkarev // Вопросы атомной науки и техники. — 2001. — № 3. — С. 41-43. — Бібліогр.: 8 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860034844631760896 |
|---|---|
| author | Onishchenko, I.N. Pushkarev, S.S. |
| author_facet | Onishchenko, I.N. Pushkarev, S.S. |
| citation_txt | Ion accelerator based on plasma vircator / I.N. Onishchenko, S.S. Pushkarev // Вопросы атомной науки и техники. — 2001. — № 3. — С. 41-43. — Бібліогр.: 8 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | Based on previous fundamental and experimental research [1, 2] the conception of a collective ion accelerator is proposed to be developed in the frameworks of STCU project #1569 (NSC KIPT, Ukraine) in coordination with the ISTC project #1629 (VNIIEF, Russia). The main processes of acceleration are supposed to be consisted of two stages. First one is the plasma assistance virtual cathode (VC) in which plasma ions are accelerated in a potential well of VC. Along with ion acceleration the relaxation oscillations, caused by diminishing the potential well due to ion compensation, arise that provides the low-frequency (inverse ion transit time) temporal modulation of an intense relativistic electron beam (IREB) current. At the second stage temporally modulated IREB is injected into the spatially periodic magnetic field. The further ion acceleration is realized by the slow space charge wave that arises in IREB due to its simultaneous temporal and spatial modulation.
|
| first_indexed | 2025-12-07T16:53:07Z |
| format | Article |
| fulltext |
ION ACCELERATOR BASED ON PLASMA VIRCATOR
I.N. Onishchenko, S.S. Pushkarev
National Science Center “Kharkov Institute of Physics and Technology”
Kharkov, 61108, Ukraine
E-mail: onish@kipt.kharkov.ua
Based on previous fundamental and experimental research [1, 2] the conception of a collective ion accelerator is
proposed to be developed in the frameworks of STCU project #1569 (NSC KIPT, Ukraine) in coordination with the
ISTC project #1629 (VNIIEF, Russia). The main processes of acceleration are supposed to be consisted of two
stages. First one is the plasma assistance virtual cathode (VC) in which plasma ions are accelerated in a potential
well of VC. Along with ion acceleration the relaxation oscillations, caused by diminishing the potential well due to
ion compensation, arise that provides the low-frequency (inverse ion transit time) temporal modulation of an intense
relativistic electron beam (IREB) current. At the second stage temporally modulated IREB is injected into the spa-
tially periodic magnetic field. The further ion acceleration is realized by the slow space charge wave that arises in
IREB due to its simultaneous temporal and spatial modulation.
PACS numbers: 29.17.+w
1 INTRODUCTION
Acceleration of ions in the potential well of the VC
space charge [I], and in the field of a space charge slow
wave, which arises in IREB due to its modulation both
in space and time are the physical processes that allow
to develop the conception of a collective accelerator
with high acceleration gradient and intense current. Its
possible applications are the followings:
- electronuclear method of energy production (energy
amplifier) [3], ion deep implantation [4], material modi-
fication with ion beams [5]. Besides the ion beams, gen-
erated on the accelerator proposed, can be used for the
following goals: nuclear transmutation purposes, ra-
dioactive scrap demolishing, research on inertial ther-
monuclear fusion, radiation damage imitation, electron -
ion beam transportation, etc.
In the present paper the preliminary investigations of
a two-stage scheme of collective ion acceleration that
uses consecutively both mechanisms [1] and [2] are rep-
resented. At the first stage VC with plasma assistance is
used. Plasma ions are accelerated by the VC electric
field and along with this ions IREB are modulated in
time by means of repeated compensation of VC space
charge. At the second stage IREB modulated at low fre-
quency (determined by ion transit time), are injected
into a drift chamber with a spatially periodic magnetic
field [6], where the spatial modulation of IREB takes
place. In the drift chamber the preliminary accelerated
in a VC region are being accelerated by a slow wave of
IREB space charge to the energy determined by the resi-
dence time in Cherenkov synchronism with the wave.
2 PRELIMINARY RESULTS [6]
2.1 Simulation
We represent the results of theoretical consideration
of the low-frequency (LF) modulation of IREB current
at ion acceleration by VC with plasma presence. In the
scheme under consideration two goals are gained: the
ion acceleration up to energies of the order of the initial
energy of the IREB particles and the LF modulation of
the IREB current, which is necessary for the subsequent
excitation of the slow wave during the beam injection
into a spatially modulated magnetic field. To elucidate a
mechanism for LF modulation of the IREB and to deter-
mine its characteristic frequencies, we developed a nu-
merical model that adequately describes the experiment.
The self-consistent dynamics of the ion flow and the
VC, which is formed by the IREB, is studied by the par-
ticle-in-cell method in an electrostatic approximation.
For the simulation of axisymmetric annular beams
we used a planar model. The two-dimensional calcula-
tions used a 32x32 grid. We assumed the following
boundary conditions: the potential vanished at both the
side boundaries and the left (entrance) boundary, and
the right boundary was open. Thin symmetrical electron
and ion beams were injected into the system from the
left.
The transverse sizes of the beams (which correspond
to the beam diameters in the axisymmetric statement of
the problem) and their thickness, the initial electron and
ion energies, as well as the injection currents could be
independently varied in the calculations. We assumed
that electrons were magnetized and moved only along
the magnetic field lines, whereas the ion motion was
two-dimensional.
The calculations were performed with the following
model parameters: injection electron current J
50-500 A/cm, ion current 0-50 A/cm, initial electron en-
ergy 200-500 keV, initial ion energy 50-100 keV, ion
mass was 25-30 electron masses, the beam width (diam-
eter) 0-3 cm, and the system length 7 cm.
Calculation results:
In the absence of ions, we observed VC formation
accompanied by the high-frequency (HF) modulation of
the reflected and transmitted currents. When the ion cur-
rent was injected near the axis of the system, this effect
was similar up to the ratio of the ion- to electron cur-
rents equal to 0.25. When the ion-beam "radius" was
larger than the electron-beam "radius" (Ri/Re = 3.5), we
observed LF modulation of both the transmitted and re-
flected electron current even for the ratio of the ion- to
electron currents equal to 0.1. When the LF modulation
of IREB takes place, the transverse ion motion plays an
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 41-43.
41
important role in VC dynamics. Moving in the two-di-
mensional potential well produced by the electron beam,
the ions accelerate along the axis and, at the same time,
displace toward the axis; as a result, they are focused
behind the VC. When a sufficient amount of ions is ac-
cumulated, the neutralization of the IREB space charge
causes the VC to displace inward the chamber and then
to disappear. In this case, the entire electron-beam cur-
rent flows through the system. The ion acceleration by
the VC field and their arrival into the IREB ceases.
Then, the previously accumulated ions drift into the
chamber, and the VC is restored at the left end of the
chamber. Further, this process repeats. The estimates
show that the frequency of the LF beam modulation is
of the order of the frequency of the transverse ion oscil-
lations in the VC field.
In the second stage of the accelerator, when the
IREB with the LF-modulated density enters the spatially
periodic magnetic field, spatial modulation of the beam
along the drift chamber occurs. As a result of the spatial
and temporal modulation, a slow wave is formed in the
beam. The phase velocity of this wave is v ph, = ω m / km,
where ω m is the time-modulation frequency, and
k m = 2n/L is the wave number of the spatial beam mod-
ulation (L is the period of the external magnetic field).
As follows from this relationship, for the synchronism
between the wave and accelerated ions to be main-
tained, it is necessary that either the spatial period of the
magnetic field or the modulation frequency ω m should
be increased.
We consider the magnetic field in the form
H r = hI1(k mr)sin(k mzz),
H z = H 0 + hI0(k mr)sin(k mz),
where I0,1 are the modified Bessel functions. The current
of the annular beam at the entrance of the system is har-
monically modulated in time. Then, for the accelerating
field near the axis, we obtain the following expression:
Ez =(Jα kmh/2νHo)sin(ω mt- kmz)
where J is the electron-beam current, v is the electron-
beam velocity, and α is the amplitude of the time modu-
lation of the beam. As follows from the latter expres-
sion, the accelerating-field amplitude is proportional to
the product of amplitudes of the magnetic field and
beam current modulation and linearly depends on the
beam current.
2.2 Experiment
The experiments were carried out in the AGAT ac-
celerator, which is a microsecond diode with a magnetic
insulation [7]. The accelerator produced an annular elec-
tron beam with the following parameters: E = 280 keV,
J= 3.5 kA, τ = 1 µ s, and the beam energy 350 J. The
beam was injected into a drift chamber 4.9 cm in diame-
ter which was placed in an external magnetic field of 4-
4.5 T. In the first acceleration stage, the acceleration is
related to the formation of the VC near the diode in the
regime of the overlimiting IREB current. We studied
experimentally the conditions of the VC formation and
measured both the space and time distributions of the
electric potential in the drift chamber for different val-
ues of the beam diameter, gas pressure, and external
magnetic field. It was found that, when the magnetized
IREB with a current higher than the limiting current was
injected into the drift chamber filled by a gas at a pres-
sure of 2×10–5 - 4×10–4 Torr, the relaxing VC was
formed near the anode. Simultaneous measurements
were made by a set of the capacious probes located
along the drift chamber. The dimensions of the region
occupied by the VC were determined by comparing the
signals from the probes located at distances of 3, 5, 7,
and 11 cm from the cathode. It was shown that, at a dis-
tance of 3 cm from the cathode, the potential is higher
than the voltage applied to the diode. As the distance in-
creases, the potential drops rapidly, and then, at a dis-
tance of 11 cm, it becomes constant. The magnitude of
magnetic field in the region of the IREB injection was
chosen such that a portion of the beam escapes to the
walls of the chamber. Thereby, a plasma was produced
near the anode; in the experiment, this plasma acted as
an ion source. The maximum ion current was observed
for Hα / H0 = 0.6, where Hα is the magnetic field near
the anode, and H0 is the guiding magnetic field.
In the experiments, we studied the structure of ion
pulses for different geometry of the diode and also for
different values of the electron beam diameter, magnetic
field magnitude and gradient, and gas pressure. To mea-
sure the ion-beam parameters, we used collimated and
wide-aperture collectors, negatively biased Faraday
cylinders, Rogowski loops, magnetic analyzer, and track
detectors made from the cellulose nitrate. It was found
that the accelerated ions appeared behind the VC when
the injection current J was either comparable or higher
than the limiting current. The ion current reaches its
maximum of 200 A when the radius of the beam propa-
gating through the drift chamber is 14 mm. When the
injection current is smaller than the limiting current, the
ion current was noticeably smaller. Most of the nitrogen
ions of the wall plasma, which were accelerated by the
potential well of the VC, had energies of the order of
300 keV. From the energy spectrum and potential distri-
bution, we found that ion energy was governed by the
depth of the potential well of the VC.
In the VC regime, we observed LF modulation of
the electron beam; the modulation characteristics were
determined from the measurements of the
bremsstrahlung X radiation and beam-collector current
and from the signals of the magnetic loop probes in-
stalled along the drift chamber. From the correlation
analysis of the measured signals, we could determine
the fluctuation parameters. It was found that the fre-
quency spectra of the signals, which were measured by
three independent diagnostics, coincide quite well over
the entire transportation channel. The LF fluctuations of
the electron current were quite regular and were ob-
served over all the IREB-transportation channel. The
frequency spectrum has a maximum at a frequency of
20 MHz; the modulation amplitude reaches 40%. As
follows from the above theoretical analysis, the trans-
verse oscillations of ions in the VC field are responsible
42
for LF modulation.
In the second acceleration stage, the spatial modula-
tion of the beam was produced by the periodic magnetic
field. The space-modulation period was chosen such
that the slow wave in the IREB was synchronized with
the accelerated ions. Spatial modulation occurred during
IREB propagation in the external magnetic field through
a set of iron and aluminum coils placed around the cir-
cular waveguide. In the experiments, the modulation
amplitude h, which dependeds on the coil thickness,
could be varied within 12-40%. The modulation period
could be either constant or increasing along the system;
the space periods were chosen in such a way that the
ions were accelerated continuously and synchronously
in our system. We studied the acceleration of the ion
beam that was preliminarily accelerated in the first ac-
celerator stage. The maximum energy of the nitrogen
ions reached 1.5 MeV after passing five space-modula-
tion periods whose length was changed from 6 to
7.8 cm. The current of the accelerated ions was 20 A;
the pulse duration was 400 ns.
The experimental study of the time modulation of
the REB current revealed an increase in the time-mod-
ulation frequency during acceleration: as the beam prop-
agated through the modulated magnetic field, the maxi-
mum of the frequency spectrum of LF fluctuations of
the REB current shifted to higher frequencies (from 20
to 60 MHz). This increase in the time-modulation fre-
quency during the acceleration process causes a corre-
sponding increase in wave phase velocity, which en-
ables ion acceleration even when the space-modulation
period is constant. A more complete understanding of
this effect requires further study.
3 PLANNED INVESTIGATIONS
The further investigations are determined in the pro-
posals of the projects that are purposed for physical in-
vestigations and elaboration of the recommendations on
the construction of intense ion accelerator of a new type,
based on the vircator with a plasma anode and space-pe-
riodic magnetic field.
The main important problems, which are supposed
to be solved in the frame of project #1569 [8] are the
followings:
• theoretical study and numerical simulation of the
mechanism of low-frequency modulation of the
REB current and the dependence of LF modulation
frequency on the REB parameters, the current of
accelerated ion flow and the geometry of system;
• theoretical study of the maintenance of synchro-
nism conditions for the charge density wave of
REB and accelerated ions of various kinds by
changing the period of a magnetic field or modula-
tion frequency, research of radial and phase stabili-
ty of ions in field of acceleration;
• a choice of geometry of the high current diode and,
accordingly, IREB configuration in the field of ac-
celeration and drift space;
• experimental research of modes and parameters of
the non-stationary ion flow;
• investigation of conditions of ion trapping with the
help of compulsory creation and configuration of a
dense plasma bunch with a necessary ion structure;
• study of dynamic characteristics of the virtual cath-
ode and parameters of ion flow at the output of the
first step of acceleration at presence of a focusing
magnetic field of a various configuration and am-
plitude;
• elaboration of the diagnostic equipment for deter-
mination of final and intermediate parameters of ac-
celerated ion currents and diagnostics of a slow
wave of REB spatial charge;
• experimental research of spatial - temporary char-
acteristics of high current REB depending on REB
and plasma parameters;
• investigation of energy gain by ions in dependence
on the length of the second section with a spatially
periodic magnetic field;
• determination of the REB configuration optimum
from the point of view of efficiency of ion accelera-
tion and their radial and longitudinal stability.
REFERENCES
1. J.S.Luce, H.L.Sahlin, T.R.Crites. // IEEE Trans. on
N.S. NS-20, 1973, p.306.
2. A.G.Lymar, N.A.Khizhnyak, V.V.Belikov //
VANT. Issue: High Energy Physics (5). 1973, # 3,
p. 78.
3. Carlo Rubbia. A comparison of the safety and envi-
ronmental advantages of the energy amplifier and
of magnetic confinement fusion // CERN/AT/95-58
(ET), 1995.
4. T.Horsky, Indirectly heated cathode arc discharge
source for ion implantation of semiconductors //
Proc. of 7 Int. Conf. On Ion Sources ICIS’97 (Sept.
7-13, 1997), O-D.01, p. 78.
5. Proc. of the 10th Int. Conf. on Ion Beam Modifica-
tion of Materials, Albuquerque, NM, 1996. Nucl.
Instrum. &Methods in Physics Research, Sec. B,
v. 127/128, 1997.
6. V.A.Balakirev, A.M.Gorban, I.I.Magda et al //
Plasma Phys. Reports. 1997, v. 23, # 4, p. 323.
7. S.S.Pushkarev, V.A.Bondarenko, N.I.Gadetski, et.
al // Prib. Techn. Exp. 1989, # 3, p. 31.
8. STCU Project 1569. Development of the collective
ion accelerator, based on plasma vircator and peri-
odic magnetic field.
This work was partly supported by STCU grant
#1569.
ВОПРОСЫ АТОМНОЙ НАУКИ И ТЕХНИКИ. 2001. №3.
Серия: Ядерно-физические исследования (38), с. 43-43.
43
|
| id | nasplib_isofts_kiev_ua-123456789-79229 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-12-07T16:53:07Z |
| publishDate | 2001 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Onishchenko, I.N. Pushkarev, S.S. 2015-03-30T06:40:58Z 2015-03-30T06:40:58Z 2001 Ion accelerator based on plasma vircator / I.N. Onishchenko, S.S. Pushkarev // Вопросы атомной науки и техники. — 2001. — № 3. — С. 41-43. — Бібліогр.: 8 назв. — англ. 1562-6016 PACS numbers: 29.17.+w https://nasplib.isofts.kiev.ua/handle/123456789/79229 Based on previous fundamental and experimental research [1, 2] the conception of a collective ion accelerator is proposed to be developed in the frameworks of STCU project #1569 (NSC KIPT, Ukraine) in coordination with the ISTC project #1629 (VNIIEF, Russia). The main processes of acceleration are supposed to be consisted of two stages. First one is the plasma assistance virtual cathode (VC) in which plasma ions are accelerated in a potential well of VC. Along with ion acceleration the relaxation oscillations, caused by diminishing the potential well due to ion compensation, arise that provides the low-frequency (inverse ion transit time) temporal modulation of an intense relativistic electron beam (IREB) current. At the second stage temporally modulated IREB is injected into the spatially periodic magnetic field. The further ion acceleration is realized by the slow space charge wave that arises in IREB due to its simultaneous temporal and spatial modulation. This work was partly supported by STCU grant #1569. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Ion accelerator based on plasma vircator Ускоритель ионов, основанный на плазмонаполненном виркаторе Article published earlier |
| spellingShingle | Ion accelerator based on plasma vircator Onishchenko, I.N. Pushkarev, S.S. |
| title | Ion accelerator based on plasma vircator |
| title_alt | Ускоритель ионов, основанный на плазмонаполненном виркаторе |
| title_full | Ion accelerator based on plasma vircator |
| title_fullStr | Ion accelerator based on plasma vircator |
| title_full_unstemmed | Ion accelerator based on plasma vircator |
| title_short | Ion accelerator based on plasma vircator |
| title_sort | ion accelerator based on plasma vircator |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79229 |
| work_keys_str_mv | AT onishchenkoin ionacceleratorbasedonplasmavircator AT pushkarevss ionacceleratorbasedonplasmavircator AT onishchenkoin uskoritelʹionovosnovannyinaplazmonapolnennomvirkatore AT pushkarevss uskoritelʹionovosnovannyinaplazmonapolnennomvirkatore |