Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides
A new technique of determining dispersion characteristics of the ion oscillations, excited in the hybrid plasma waveguide is elaborated (this device is a slow-wave structure, the passage channel of which is filled with plasma). This method is based on measuring changes in the shape of a single probi...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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| Цитувати: | Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides / V.S. Antipov, A.N. Antonov, V.A. Balakirev, O.F. Kovpik, E.A. Kornilov, K.V. Matyash, V.G. Svichensky // Вопросы атомной науки и техники. — 2005. — № 2. — С. 149-151. — Бібліогр.: 6 назв. — англ. |
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Antipov, V.S. Antonov, A.N. Balakirev, V.A. Kovpik, O.F. Kornilov, E.A. Matyash, K.V. Svichensky, V.G. 2015-04-04T20:09:18Z 2015-04-04T20:09:18Z 2005 Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides / V.S. Antipov, A.N. Antonov, V.A. Balakirev, O.F. Kovpik, E.A. Kornilov, K.V. Matyash, V.G. Svichensky // Вопросы атомной науки и техники. — 2005. — № 2. — С. 149-151. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 52.40.Mj https://nasplib.isofts.kiev.ua/handle/123456789/79806 A new technique of determining dispersion characteristics of the ion oscillations, excited in the hybrid plasma waveguide is elaborated (this device is a slow-wave structure, the passage channel of which is filled with plasma). This method is based on measuring changes in the shape of a single probing pulse propagating in the system. The method is tested in the process of determining the dispersion of low-frequency ion waves under the condition of the excitation of high-frequency powerful electron oscillations by an electron beam in the waveguide. The experimental data are compared with the analytical calculations. Розроблена методика визначення дисперсійних характеристик хвиль, порушуваних в гібридному плазмовому хвилеводі (уповільнююча структура, пролітний канал якої заповнений плазмою), заснована на вимірюванні зміни форми одиночного зондуючого імпульсу, що розповсюджується в системі. Випробування методу проведено при визначенні дисперсії низькочастотних іонних хвиль в умовах збудження в хвилеводі електронним пучком високочастотних електронних коливань великого рівня потужності. Проведено порівняння результатів експерименту з теоретичними розрахунками. Разработана методика определения дисперсионных характеристик волн, возбуждаемых в гибридном плазменном волноводе (замедляющая структура, пролётный канал которой заполнен плазмой), основанная на измерении изменения формы распространяющегося в системе одиночного зондирующего импульса. Испытание метода проведено при определении дисперсии низкочастотных ионных волн в условиях возбуждения в волноводе электронным пучком высокочастотных электронных колебаний большого уровня мощности. Проведено сравнение результатов эксперимента с теоретическими расчетами. The authors wish to thank J.B. Fainberg and Ju.P. Bliokh for the discussion of the results. We also gratefully acknowledge S.S. Pushkarev’s help in the elaboration of the technique of registering oscillations and pulses in plasma with the help of probes. The work fulfilled is financially supported by National Scientific Technical Center of Ukraine within the framework of the project #256. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma electronics Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides Вимірювання дисперсії низькочастотних іонних коливань в гібридних плазмових хвилеводах Измерение дисперсии низкочастотных ионных колебаний в гибридных плазменных волноводах Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| spellingShingle |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides Antipov, V.S. Antonov, A.N. Balakirev, V.A. Kovpik, O.F. Kornilov, E.A. Matyash, K.V. Svichensky, V.G. Plasma electronics |
| title_short |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| title_full |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| title_fullStr |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| title_full_unstemmed |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| title_sort |
measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides |
| author |
Antipov, V.S. Antonov, A.N. Balakirev, V.A. Kovpik, O.F. Kornilov, E.A. Matyash, K.V. Svichensky, V.G. |
| author_facet |
Antipov, V.S. Antonov, A.N. Balakirev, V.A. Kovpik, O.F. Kornilov, E.A. Matyash, K.V. Svichensky, V.G. |
| topic |
Plasma electronics |
| topic_facet |
Plasma electronics |
| publishDate |
2005 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Вимірювання дисперсії низькочастотних іонних коливань в гібридних плазмових хвилеводах Измерение дисперсии низкочастотных ионных колебаний в гибридных плазменных волноводах |
| description |
A new technique of determining dispersion characteristics of the ion oscillations, excited in the hybrid plasma waveguide is elaborated (this device is a slow-wave structure, the passage channel of which is filled with plasma). This method is based on measuring changes in the shape of a single probing pulse propagating in the system. The method is tested in the process of determining the dispersion of low-frequency ion waves under the condition of the excitation of high-frequency powerful electron oscillations by an electron beam in the waveguide. The experimental data are compared with the analytical calculations.
Розроблена методика визначення дисперсійних характеристик хвиль, порушуваних в гібридному плазмовому хвилеводі (уповільнююча структура, пролітний канал якої заповнений плазмою), заснована на вимірюванні зміни форми одиночного зондуючого імпульсу, що розповсюджується в системі. Випробування методу проведено при визначенні дисперсії низькочастотних іонних хвиль в умовах збудження в хвилеводі електронним пучком високочастотних електронних коливань великого рівня потужності. Проведено порівняння результатів експерименту з теоретичними розрахунками.
Разработана методика определения дисперсионных характеристик волн, возбуждаемых в гибридном плазменном волноводе (замедляющая структура, пролётный канал которой заполнен плазмой), основанная на измерении изменения формы распространяющегося в системе одиночного зондирующего импульса. Испытание метода проведено при определении дисперсии низкочастотных ионных волн в условиях возбуждения в волноводе электронным пучком высокочастотных электронных колебаний большого уровня мощности. Проведено сравнение результатов эксперимента с теоретическими расчетами.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/79806 |
| citation_txt |
Measurement of dispersion of low-frequency ion oscillations in hybrid plasma waveguides / V.S. Antipov, A.N. Antonov, V.A. Balakirev, O.F. Kovpik, E.A. Kornilov, K.V. Matyash, V.G. Svichensky // Вопросы атомной науки и техники. — 2005. — № 2. — С. 149-151. — Бібліогр.: 6 назв. — англ. |
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MEASUREMENT OF DISPERSION OF LOW-FREQUENCY ION
OSCILLATIONS IN HYBRID PLASMA WAVEGUIDES
V.S. Antipov, A.N. Antonov, V.A. Balakirev, O.F. Kovpik, E.A. Kornilov, K.V. Matyash,
V.G. Svichensky
NSC Kharkov Institute of Physics & Technology, Kharkov, Ukraine
A new technique of determining dispersion characteristics of the ion oscillations, excited in the hybrid plasma
waveguide is elaborated (this device is a slow-wave structure, the passage channel of which is filled with plasma). This
method is based on measuring changes in the shape of a single probing pulse propagating in the system. The method is
tested in the process of determining the dispersion of low-frequency ion waves under the condition of the excitation of
high-frequency powerful electron oscillations by an electron beam in the waveguide. The experimental data are
compared with the analytical calculations.
PACS: 52.40.Mj
INTRODUCTION
The analysis given to the processes that takes place in
beam-plasma (BP) microwave devices where hybrid
plasma waveguides (HPW) [1,2] are used indicates that
characteristics of these waveguides are prescribed not
only by the microwave field structure in HPW but also by
low-frequency (LF) ion oscillations. During the
microwave excitation and maintenance of the beam-
plasma discharge (BPD), a nonlinear coupling between
electron microwaves and LF ion oscillations is
established, which results in the augmentation of LF ion
oscillation amplitude [3]. Excitation of LF oscillations
brings substantial changes into the process of the BP
instability development as well as into spectral and energy
characteristics of the microwaves excited - even down to
the derangement of the oscillation excitation itself [1-3]. It
is impossible to understand the processes that cause the
suppression of the microwave excitation in BP devices
without studying the types of ion-plasma oscillations
excited there ( ω I) and without information about their
dispersion characteristics (DC).
The goal of our investigations is to study DC of LF
oscillations excited in HPW-chain of cavities connected
inductively (CCCI) under the condition of the plasma
maintenance due to BPD in this chain.
DETERMINATION OF LF WAVE
DISPERSION WITH THE HELP OF A SINGLE
PROBING PULSE
Impossibility of installing probing- and receiving
antennas in closed HPW hampers the measurement of DC
of the waves excited in these waveguides by the methods
available at present. The technique of determining DC of
LF oscillations excited in HPW is elaborated. It is based
on observing changes in the shape of a single probing
pulse propagating in HPW.
Duration of the pulse excited in plasma X1(t) is chosen
so that its frequency spectrum would belong to the
resonance band of LF oscillations. While propagating in
HPW, the pulse is subjected to the deformation
conditioned by the HPW DC in this frequency range.
Registering the pulse X2(t) that has passed the distance L
along the plasma column, one can get the system DC in
this frequency range:
Kz(ωņ)=1/L[arg(F(X1)n) - arg(F(X2)n)]
Here Kz(ωņ) is the wave vector projection on the pulse
propagation direction; ω=2πn/T, (1≤n≤Ν); T denotes the
selection time; Ν=T/ΧT designates discretization period;
L is the distance between the probes; F(X1) and F(X2)
mark Fourier images of the input and output pulses [5-6].
To eliminate the signal phase discontinuity in vicinity to
2πn, one must provide the realization of the condition of
smallness of the phase difference between the neighboring
frequencies in the discrete Fourier transform for both the
signals: Χφ=arg(F(Χ)n+1/F(Χ)n)<<π. For justifying this
criterion, the access time must be rather long. In practice,
the access time duration is limited by the registering
equipment capabilities. Thus, the time interval can be
prolonged only by adding zeros to the measured signals
[5-6], which introduces inevitable errors into the
frequency characteristics obtained. However, by making
use of single pulses for probing, one minimizes the errors
conditioned by complementary zeros because such pulses
are precisely localized in time.
Fig.1
In Fig.1 one can see the dispersion curves for LF
oscillations, obtained by numerical simulations of DC of
LF oscillations for T- and H-waves. In this plot, the curve
1 describes the slow magnetic-acoustic wave. The curve 2
depicts the lowest radial harmonic of ion-acoustic (IA)
oscillations. The curve 3 relates to the lowest radial
harmonic of LH oscillations. These curves correspond to
the plasma density n=1011 cm-3; the electron temperature
Te=100eV and the external magnetic field B=0.25 T. The
Problems of Atomic Science and Technology. Series: Plasma Physics (11). 2005. № 2. P. 149-151 149
Fig.4
curve 4 is plotted for LH oscillations when n=6·109 cm-3;
Te=(30-50)eV and B=0.25 T.
EXPERIMENTAL INVESTIGATIONS OF LF
ION WAVE DISPERSION IN HPW BASED ON
CCCI
The scheme of the test bench is described in [1,3].
Single pulses are sent both to a probe submerged into
plasma and to the electron beam collector. The pulses
transmitted through HPW system are registered with two
single electron probes operating in the regime of
saturation. The probes can be installed at the distance
512mm one from another, which overlaps the area of
HPW location. Signals from the probes, after passing
through the matching amplifier, are sent to the dual-
channel analogous digital transducer (ADT) input. Further
the probe signals are transmitted to PC for their
processing. For measuring DC, we have used the single
pulses of the duration 5 µs and 60 ns. The frequency
spectrum of such pulses completely overlaps the range
calculated for slow magnetic-acoustic (MA) - and low-
hybrid (LH) waves, respectively.
In the tests, the plasma density in the waveguide ranges
within (109 –2·1011) cm-3. The electron temperature makes
(25-100) eV. Microwaves are excited by the electron
beam of the power from hundreds of W and up to 40kW.
The plasma parameters are measured with double probes,
installed at the edges of HPW.
Certain specificities have been found out during the
study of the pulse propagation in the HPW plasma
column.
The probing pulse of the duration 5 µs can be for sure
registered only when microwave power is lower than
25kW. In this case, the duration of the pulse passing
through HPW is prolonged.
a
b
Fig.2
The pulse of the duration 60ns, the spectrum of which
overlaps the LH wave frequency range, is detectable only
when the microwave power is lower than 1kW and
n=1010cm-3. The pulse is subjected to the substantial
attenuation. It is significant that as the microwave power
increases, the probing pulse “scatters” to a sequence of
pulses of a shorter duration. In Fig.2, the oscillograms (a)
and (b) illustrate the evolution of pulses of the duration 5
µs and 60 ns during their passage through HPW when
microwaves are excited with the beams of the power
15kW and 0.7kW, respectively.
For LF oscillations, the dispersion characteristics (DC)
are obtained by processing oscillograms of the single
probing pulses passed through HPW according to the
above-described technique (see Fig.3).
For comparison, in the same graph (Fig.3), we have
placed DC for LH (a) and slow MA (b) waves. These
dependences are calculated analytically for the two sets of
the plasma parameters values, used in the tests: (a)
corresponds to n=6·109 cm-3 and Te=(30-50)eV; (b)
depicts the case of n=1011 cm-3 and Te=100eV. The
external magnetic field B=0.25T in both the cases. As the
given plots indicate, the curves simulated numerically
with taking into account the pulse form evolution to a high
precision coincide with the experimental results.
The dispersion characteristic of LH-waves indicates that
their wavelength is short; its maximum does not exceeding
2cm. The wave phase velocity makes several units of
108cm·s-1. This magnitude is more than by two orders
smaller than the velocity of the beam generating plasma
due to BPD.
For checking the results obtained within the shortest
wavelength range, we have measured the wavelengths by
the probing wave phase taper during the wave propagation
in HPW plasma. The measurements are carried out at the
frequencies (50, 60 and 71) MHz. In HPW, oscillations
are excited with a helical aerial, fed from the oscillator at
one of the frequencies mentioned. The probes are installed
between the spiral and HPW (in vicinity to the passage
channel) and also between HPW and the beam current
collector.
In Fig.4, one can see oscillograms of the oscillations at
the frequency 71 MHz. They are registered with probes
installed at the distance 0.5 cm from the spiral (the
waveguide input) and at the waveguide output (43 cm
from the spiral). As the oscillograms indicate, at the
distance 43 cm the oscillations are in antiphase. About
100 wavelengths can go into this distance.
150
a
b
Fig.3
The results of this series of tests also confirm that LH
wave branch does exist in HPW. However, as the data
indicate, the evaluated difference between wavelength is
twice as the deformation of the pulse propagating in
HPW. At the same time, the propagation velocity is twice
more. Discrepancies in the wave number values obtained
by the two methods are conditioned by introducing a gross
error into the measurement of the wave phase taper. These
discrepancies are both conditioned by an intricate shape
of the oscillations and smallness of the number of probes
installed in the direction of the oscillation propagation. It
is worth mentioning that the probing wave substantial
attenuates as the power of microwaves excited by the
beam increases.
CONCLUSIONS
Thus, as it is found out by analytical calculations and
numerical simulations, the three branches of LF ion
oscillations can be excited in HPW that has the form of
CCCI channel with the plasma-filled passage: SMA-, IA-
and LH ones. The existence of SMA- and LH waves is
confirmed by the analysis given to the pattern of single
pulse propagation in GPW.
The submitted method of measuring DC of HPW proper
LF waves is based on detecting deformation of the single
pulse propagating in this waveguide. This technique is
rather effective if microwaves excited are characterized by
relatively heavy power. Most probably, this method is
inapplicable just either when there takes place a
substantial attenuation of the microwaves that belong to
the probing pulse inherent spectrum or in the cases of
large amplitude of LF oscillations in plasma and that of
the pulse that stimulates the wave nonlinear interaction
development.
Very likely, the wave nonlinear interaction indicates
itself
via the emergence of a sequence of pulses, stimulated by a
single pulse. Observed in the experiment, this
phenomenon takes place when the microwave electric
field strength in the waveguide exceeds a certain threshold
value. As regards LH waves, in the experiment this
parameter has reached 300V/cm. For IA waves, the
electric field strength approaches the level 1800V/cm.
As it should be emphasized, the given technique of
determining the proper wave DC implies that the pulse
spectral composition does not get into the upper cutoff
band in the dispersion curve. In this case, the pulse during
its propagation is also transformed into a sequence of
shorter pulses, and the wave DC restoration becomes
impossible.
The authors wish to thank J.B. Fainberg and Ju.P.
Bliokh for the discussion of the results. We also gratefully
acknowledge S.S. Pushkarev’s help in the elaboration of
the technique of registering oscillations and pulses in
plasma with the help of probes.
The work fulfilled is financially supported by National
Scientific Technical Center of Ukraine within the
framework of the project #256.
REFERENCES
1. A.N. Antonov, Yu.P. Blioh, E.A. Kornilov et. al.//
Plasma Physics. 2000, v. 26, №12, p.1097-1109.
2. Yu.P, Bliox, Ya.B. Fainberg, M.G. Lubarsky et. al.
Report Conf on High-Power Particle Beams // Beams
98. HAIFA, ISRAEL 7-13, 1998, p. 286.
3. A.N. Antonov, E.A. Kornilov, O.F. Kovpik et. al.//
Plasma Physics. 2001, v. 27, №6, p. 1-5.
4. V.S. Antipov, O.F. Kovpik, E.A. Kornilov, K.V.
Matyash // Materials of the 8th International Crimean
conference. 1998, v. 2, p. 711.
5. L.S. Bennet, Dg. Ross. The Time-Impulse
Electromagnetic Processes and their Applications //
JEEE, 1978, v. 66, №3, p. 35 (in Russian).
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ИЗМЕРЕНИЕ ДИСПЕРСИИ НИЗКОЧАСТОТНЫХ ИОННЫХ КОЛЕБАНИЙ
В ГИБРИДНЫХ ПЛАЗМЕННЫХ ВОЛНОВОДАХ
В.С. Антипов, А.Н. Антонов, В.А. Балакирев, О.Ф. Ковпик, Е.А. Корнилов, К.В. Матяш, В.Г. Свиченский
Разработана методика определения дисперсионных характеристик волн, возбуждаемых в гибридном
плазменном волноводе (замедляющая структура, пролётный канал которой заполнен плазмой), основанная на
измерении изменения формы распространяющегося в системе одиночного зондирующего импульса. Испытание
метода проведено при определении дисперсии низкочастотных ионных волн в условиях возбуждения в
волноводе электронным пучком высокочастотных электронных колебаний большого уровня мощности.
Проведено сравнение результатов эксперимента с теоретическими расчетами.
ВИМІРЮВАННЯ ДИСПЕРСІЇ НИЗЬКОЧАСТОТНИХ ІОННИХ КОЛИВАНЬ
В ГІБРИДНИХ ПЛАЗМОВИХ ХВИЛЕВОДАХ
В.С. Антіпов, О.М. Антонов, В.А. Балакірєв, О.Ф. Ковпік, Є.О. Корнілов, К.В. Матяш, В.Г. Свіченський
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Розроблена методика визначення дисперсійних характеристик хвиль, порушуваних в гібридному плазмовому
хвилеводі (уповільнююча структура, пролітний канал якої заповнений плазмою), заснована на вимірюванні
зміни форми одиночного зондуючого імпульсу, що розповсюджується в системі. Випробування методу
проведено при визначенні дисперсії низькочастотних іонних хвиль в умовах збудження в хвилеводі
електронним пучком високочастотних електронних коливань великого рівня потужності. Проведено порівняння
результатів експерименту з теоретичними розрахунками.
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