Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M"
Experimental and numerical methods were used to identify the harmonics of the RF field used for plasma production and heating in the torsatron “U-3M”.
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| Цитувати: | Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" / V.L. Berezhnyj, V.L. Ocheretenko, O.S. Pavlichenko, I.B. Pinos, A.V. Prokopenko, S.A. Tsybenko, A.V. Lozin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 53-55. — Бібліогр.: 5 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-81779 |
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Berezhnyj, V.L. Ocheretenko, V.L. Pavlichenko, O.S. Pinos, I.B. Prokopenko, A.V. Tsybenko, S.A. Lozin, A.V. 2015-05-20T15:52:00Z 2015-05-20T15:52:00Z 2006 Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" / V.L. Berezhnyj, V.L. Ocheretenko, O.S. Pavlichenko, I.B. Pinos, A.V. Prokopenko, S.A. Tsybenko, A.V. Lozin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 53-55. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.55.Hc https://nasplib.isofts.kiev.ua/handle/123456789/81779 Experimental and numerical methods were used to identify the harmonics of the RF field used for plasma production and heating in the torsatron “U-3M”. The authors are grateful to Dr. V.E.Moiseenko for theoretical substantiations of the method of identification of harmonics. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Magnetic confinement Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" 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 |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" |
| spellingShingle |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" Berezhnyj, V.L. Ocheretenko, V.L. Pavlichenko, O.S. Pinos, I.B. Prokopenko, A.V. Tsybenko, S.A. Lozin, A.V. Magnetic confinement |
| title_short |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" |
| title_full |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" |
| title_fullStr |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" |
| title_full_unstemmed |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" |
| title_sort |
identification of harmonics of rf field, which is used for production and heating of plasma in the torsatron "u-3m" |
| author |
Berezhnyj, V.L. Ocheretenko, V.L. Pavlichenko, O.S. Pinos, I.B. Prokopenko, A.V. Tsybenko, S.A. Lozin, A.V. |
| author_facet |
Berezhnyj, V.L. Ocheretenko, V.L. Pavlichenko, O.S. Pinos, I.B. Prokopenko, A.V. Tsybenko, S.A. Lozin, A.V. |
| topic |
Magnetic confinement |
| topic_facet |
Magnetic confinement |
| publishDate |
2006 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| description |
Experimental and numerical methods were used to identify the harmonics of the RF field used for plasma
production and heating in the torsatron “U-3M”.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/81779 |
| citation_txt |
Identification of harmonics of RF field, which is used for production and heating of plasma in the torsatron "U-3M" / V.L. Berezhnyj, V.L. Ocheretenko, O.S. Pavlichenko, I.B. Pinos, A.V. Prokopenko, S.A. Tsybenko, A.V. Lozin // Вопросы атомной науки и техники. — 2006. — № 6. — С. 53-55. — Бібліогр.: 5 назв. — англ. |
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| fulltext |
Problems of Atomic Science and Technology. 2006, 6. Series: Plasma Physics (12), p. 53-55 53
IDENTIFICATION OF HARMONICS OF RF FIELD,
WHICH IS USED FOR PRODUCTION AND HEATING OF PLASMA
IN THE TORSATRON "U-3M"
V.L. Berezhnyj, V.L. Ocheretenko, O.S. Pavlichenko, I.B. Pinos, A.V. Prokopenko,
S.A. Tsybenko, A.V. Lozin
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”,
61108, Akademicheskaya Str.1, Kharkov, Ukraine
Experimental and numerical methods were used to identify the harmonics of the RF field used for plasma
production and heating in the torsatron “U-3M”.
PACS: 52.55.Hc
Experiments were carried out on the plasma having an
average density en = 2⋅1012 cm-3 and a confining magnetic
field B0 = 0.72 T. The plasma was produced and heated
by the RF method with excitation of current of frequency
ω = 0.8ωBi [1] in one frame antenna. The antenna-
radiated power was PRF ≤ 200 kW.
The U-3M magnetic system is located inside a
vacuum chamber, about 70 m3 in volume. It is made up of
three helical coils. The RF antenna is arranged along one
of the coils at approximately 1cm from the inner surface.
The antenna has no screen, and the RF field radiated by it
occupies the entire chamber. The brass waveguide
systems of microwave reflectometers inside the chamber
are in essence the stub antennas for RF field reception.
One of them ends with a horn antenna 1 (X-wave) on the
outside, somewhat below the plasma bunch. The other
waveguide system ends with a horn antenna 2 (O-wave)
situated on the inside, over the plasma bunch (Fig. 1).
Fig.1. Shematic view of experiment (1, 2 – microwave
antennas)
The HF currents induced in them penetrate the
diagnostic room and thus come to the registering devices.
In the analysis of LF signals from the reflectometers, the
RF noise is easily filtered out. However, if the frequencies
of useful signals and parasitic signals are comparable in
value, their separation and identification become
complicated [2]. The spurious signals of the HF field were
taken from the reflectometer detectors in the regular way,
but without the RF filters. Therefore, the signals to be
analyzed represented the reflectometer signal proper,
which carried the information on LF plasma-density
fluctuations en∆ , and the induced RF antenna currents.
The reflectometer signals were supplied to the ADC at
the clock frequency fADC = 1428.57 kHz. The
characteristic oscillograms of the discharge are shown in
Fig. 2.
Fig.2. RF power (1), averaged electron density (2),
summarize signal of UHF reflectometer (3)
The power spectral density (PSD) of one of the signals
is shown in Fig. 3. Here three peaks with the frequencies
f1 = 194.8 kHz, f2 = 389.6 kHz and f3 = 584.4 kHz clearly
stand out against the common level of fluctuations of
en∆ . From the peak values it follows that f2 = 2 f1 and
f3 = 3 f1.
Fig.3. Spectrum of signal (X-wave, F = 19.1 GHz)
This means that the frequencies of the peaks are the
harmonics of one source. To determine this source, the
PSD was calculated for many successive windows over
the course of one discharge (Fig. 4). The harmonics
appear with the onset of the RF pulse (4 ms) and
54
disappear with its end (54 ms). During the discharge the
peak frequencies are somewhat displaced, however the
frequency ratio is retained. The presence of peaks is
independent of the electron density value (see Fig. 2).
With a two-fold increase in the clock frequency of the
ADC the occurrence of seven harmonics was observed.
Fig.4. Spectra of signal (X-wave,F = 19.1 GHz)
In principle, the generation of electromagnetic wave
harmonics is possible with the incidence of the pump
wave on the inhomogeneous plasma [3]. The comparison
between the conditions of excitation of electromagnetic-
wave harmonics by the plasma and the conditions of their
propagation [4] with the experimental data indicates that
the external RF generator, the electromagnetic field of
which is used in the U-3M for plasma production and
heating, is the source of the harmonics observed.
However, the frequency of the first harmonic fc
observed is much lower than the fundamental frequency
of the RF generator Fx. On the other hand, the frequency
Fx is substantially higher than the clock frequency of the
ADC used. For similar experimental conditions, the
authors of ref. [2] have proposed a formula relating the
RF signal frequency Fx to the frequency of “false” peaks
fc in the spectrum of signal under detection
XF = ⋅n fADC ± cf , (1)
where fADC is the clock frequency of the ADC, n = 1, 2,
3… To make use of the formula, it is necessary to find the
n value and to determine the sign before fx. To this end,
the RF generator frequency was measured in the
discharges under study by the independent method using
the frequency meter. The fc signals were registered at the
same clock frequency fADC = 1428.57 kHz. For different
ten fixed Fx values (the generator frequency could vary
from discharge to discharge within 10 kHz) the
corresponding fc values were substituted, and through a
gradual increase of n eq. (1) was solved. So it was
established that formula (1) is fulfilled provided that n = 6
and fc has the plus sign
XF = 6⋅fADC + cf . (2)
Since in our case it is necessary to calculate not only
the fundamental signal frequency but also the frequencies
of signal harmonics, the formula can be generalized to
have the following form:
XmF = ⋅⋅ nm fADC + cf , (3)
where m is the harmonic number, n = 6.
The calculations from formula (3) have proved that
harmonics is PSD observed at frequencies f1 = 194.8 kHz,
f2 = 389.6 kHz and f3 = 584.4 kHz are traces of RF
oscillator harmonics Fx1 = 8766.22 kHz,
Fx2 = 17532.44 kHz and Fx3 = 26298.66 kHz. Note that
the harmonic frequencies are reproduced within of
accuracy of to 1 kHz.
The model numerical experiment has confirmed this
conclusion (Fig. 5). At the fundamental frequency of the
RF generator Fx1 = 8775 kHz the maximum of the
spectrum is obtained at fc = 203.68 kHz, and at the
harmonics Fx2 = 17550 kHz and Fx3 = 26325 kHz the
maxima of the spectra are found at fc equal to 407.37 kHz
and 611.04 kHz, respectively.
Fig.5. Spectra of signals model for: 1- f1 = 8775 kHz,
2- f2 = 17550 kHz, 3- f3 = 26325 kHz
The excitation of harmonics means that if the
generated oscillations substantially differ from the
0 100 200 300 400 500 600 700 800
10-10
100
1010
A=0.01595
f=304.909 t= 3- 4 ms
dat 21-17
0 100 200 300 400 500 600 700 800
10-10
100
1010
A= 7.796 f=369.148 t= 4- 5 ms
dat 21-17
0 100 200 300 400 500 600 700 800
10-10
100
1010
A= 11.45 f=414.166 t= 9- 10 ms
dat 21-17
0 100 200 300 400 500 600 700 800
10-10
100
1010
A= 2.648 f=397.159 t= 30- 31 ms
dat 21-17
0 100 200 300 400 500 600 700 800
10-10
100
1010
A= 28.26 f=394.158 t= 39- 40 ms
dat 21-17
0 100 200 300 400 500 600 700 800
10-10
100
1010
A=0.005101 f=490.196
t= 55- 56 ms
dat 21-17 0 40 80 120 160 200 240 280 320 360 400 440 480 520 560 600 640 680 720 760 800
0
10
20
15.858
0
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714.2850 fxj
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55
harmonic oscillations. Such systems are called the
relaxation generators. Their generation spectrum is
extremely wide. This is confirmed by a numerical model
experiment. In Fig. 6, for the harmonic oscillation
Fx1 = 8775 kHz one peak in the PSD at fc = 203.68 kHz is
observed. If the oscillation is deviated from the harmonic
oscillation by means of an arbitrarily chosen function, the
spectrum shows the oscillations in the entire range
registered up to 700 kHz (Fig. 6). The cause of generator
oscillations deviation from the harmonic oscillations may
lie in the formation of a space-charge layer with a
nonlinear capacitance nearly the RF antenna [5]. This
nonlinearity may disturb the resonance circuit of the RF
energy input system.
Fig.6. Spectra of signals model for f = 8775 kHz :
1 – A(t)=sin(ωt), 2 – A(t)=sin((ω+0.1⋅rnd(ω/100))⋅t)
To summarize, it may be noted the following. The
observed electromagnetic-field harmonics are the
harmonics of the HF field used for plasma production and
heating in the torsatron “U-3M”. Numerical model
experiments have confirmed the possibility of generating
the harmonics by an external RF generator. It has also
been demonstrated that spurious signals can be identified
in the experiment if the ADC with a clock frequency
substantially lower than the frequency of the signal under
study is used in the registration system.
In future, it is supposed that variations in amplitudes
and frequencies of RF field harmonics during the
discharge will be investigated. The results to be obtained
may be used for optimizing the operation of the RF
generator as a source of plasma generation and heating in
the torsatron “U-3M”.
ACKNOWLEDGEMENTS
The authors are grateful to Dr. V.E.Moiseenko for
theoretical substantiations of the method of identification
of harmonics.
REFERENCES
1. A.I. Lysoivan, V.E. Moiseenko, V.A. Plusnin et al. //
Fusion Engineering and Design (26). 1995, p.185-190.
2. O.S. Pavlichenko, A.I. Skibenko, V.G. Konovalov et
al. // 15th International Stellarator Workshop, Madrid,
October 2005, p.2-17.
3. Voprosy teorii plazmy /Ed. by M.A. Leontovich.
Moscow: "Atomizdat", 1973, iss. 7. p. 187 (in Russian).
4. N.S. Yerokhin, V.E. Zakharov, S.S. Moiseyev // Zh.
Ehksp. Teor. Fiz. (56). 1969, iss. 1, p. 179-185 (in
Russian).
5. V.A. Godyak // Fizika Plasmy. 1976, 2, p.141-151
(in Russian).
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