ICRF heating of hydrogen plasmas with two mode conversion layers
ICRF mode conversion heating regime is widely used in present-day tokamaks. The theoretically predicted mode conversion enhancement due to the constructive interference of the fast wave reflected from the evanescence layer with a wave reflected from the high-field side cutoff was first experimentall...
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irk-123456789-174522011-02-27T12:06:47Z ICRF heating of hydrogen plasmas with two mode conversion layers Kazakov, Ye.O. Van Eester, D. Lerche, E. Pavlenko, I.V. Girka, I.O. Weyssow, B. Методы создания и нагрева плазмы ICRF mode conversion heating regime is widely used in present-day tokamaks. The theoretically predicted mode conversion enhancement due to the constructive interference of the fast wave reflected from the evanescence layer with a wave reflected from the high-field side cutoff was first experimentally identified in JET in (3He)D experiments. This effect was recently tested in (3He)H plasmas, which is one of the ICRF heating scenarios considered for the non-activated phase of ITER operation. Due to the presence of the intrinsic D-like impurities in JET (e.g., C6+, 4He) the supplementary conversion layer was produced in the plasma that defined the interference conditions. The different behavior of the conversion efficiency observed at various 3He concentrations is analyzed in the paper on the basis of the theory of the fast wave mode conversion in plasmas with two evanescence layers. Высокочастотный нагрев плазмы в режиме конверсии мод широко используется в современных токамаках. Теоретически предсказанное увеличение эффективности конверсии вследствие интерференции быстрой волны, отраженной от области непрозрачности, с волной, отраженной от отсечки со стороны сильного магнитного поля, было впервые экспериментально подтверждено в (3He)D-экспериментах на токамаке JET. Данный эффект изучался в (3He)H-плазме, которая рассматривается как один из сценариев ВЧ-нагрева во время начальной стадии работы ITER. Вследствие присутствия в плазме JET дейтериеподобных примесей (C6+, 4He) образовывалась дополнительная область непрозрачности, которая определяла условия интерференции волн. Различное поведение коэффициента конверсии, наблюдаемое при разных значениях концентрации ионов 3He, анализируется в работе с помощью теории конверсии быстрых волн в плазме с двумя областями непрозрачности. Високочастотне нагрівання плазми в режимі конверсії мод широко застосовується в сучасних токамаках. Теоретично передбачене збільшення ефективності конверсії внаслідок інтерференції швидкої хвилі, що відбита від шару непрозорості, з хвилею, що відбита від відсічки з боку сильного магнітного поля, було вперше експериментально підтверджено в (3He)D-експериментах на токамаці JET. Цей ефект нещодавно апробовано в (3He)H-плазмі, яка розглядається як один із сценаріїв ВЧ-нагрівання на початковій стадії роботи ITER. Внаслідок присутності в плазмі JET дейтерієподібних домішок (C6+, 4He) утворювався додатковий шар непрозорості, що визначав умови інтерференції хвиль. Різна поведінка коефіцієнту конверсії, що спостерігалася за різної концентрації іонів 3He, аналізується в роботі на основі теорії конверсії швидких хвиль в плазмі з двома шарами непрозорості. 2010 Article ICRF heating of hydrogen plasmas with two mode conversion layers / Ye.O. Kazakov, D. Van Eester, E. Lerche, I.V. Pavlenko, I.O. Girka, B. Weyssow // Вопросы атомной науки и техники. — 2010. — № 6. — С. 37-39. — Бібліогр.: 9 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/17452 en Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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Методы создания и нагрева плазмы Методы создания и нагрева плазмы |
| spellingShingle |
Методы создания и нагрева плазмы Методы создания и нагрева плазмы Kazakov, Ye.O. Van Eester, D. Lerche, E. Pavlenko, I.V. Girka, I.O. Weyssow, B. ICRF heating of hydrogen plasmas with two mode conversion layers |
| description |
ICRF mode conversion heating regime is widely used in present-day tokamaks. The theoretically predicted mode conversion enhancement due to the constructive interference of the fast wave reflected from the evanescence layer with a wave reflected from the high-field side cutoff was first experimentally identified in JET in (3He)D experiments. This effect was recently tested in (3He)H plasmas, which is one of the ICRF heating scenarios considered for the non-activated phase of ITER operation. Due to the presence of the intrinsic D-like impurities in JET (e.g., C6+, 4He) the supplementary conversion layer was produced in the plasma that defined the interference conditions. The different behavior of the conversion efficiency observed at various 3He concentrations is analyzed in the paper on the basis of the theory of the fast wave mode conversion in plasmas with two evanescence layers. |
| format |
Article |
| author |
Kazakov, Ye.O. Van Eester, D. Lerche, E. Pavlenko, I.V. Girka, I.O. Weyssow, B. |
| author_facet |
Kazakov, Ye.O. Van Eester, D. Lerche, E. Pavlenko, I.V. Girka, I.O. Weyssow, B. |
| author_sort |
Kazakov, Ye.O. |
| title |
ICRF heating of hydrogen plasmas with two mode conversion layers |
| title_short |
ICRF heating of hydrogen plasmas with two mode conversion layers |
| title_full |
ICRF heating of hydrogen plasmas with two mode conversion layers |
| title_fullStr |
ICRF heating of hydrogen plasmas with two mode conversion layers |
| title_full_unstemmed |
ICRF heating of hydrogen plasmas with two mode conversion layers |
| title_sort |
icrf heating of hydrogen plasmas with two mode conversion layers |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2010 |
| topic_facet |
Методы создания и нагрева плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/17452 |
| citation_txt |
ICRF heating of hydrogen plasmas with two mode conversion layers / Ye.O. Kazakov, D. Van Eester, E. Lerche, I.V. Pavlenko, I.O. Girka, B. Weyssow // Вопросы атомной науки и техники. — 2010. — № 6. — С. 37-39. — Бібліогр.: 9 назв. — англ. |
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2025-07-02T18:40:29Z |
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2025-07-02T18:40:29Z |
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| fulltext |
ICRF HEATING OF HYDROGEN PLASMAS WITH TWO MODE
CONVERSION LAYERS
Ye.O. Kazakov1, D. Van Eester2, E. Lerche2, I.V. Pavlenko1, I.O. Girka1,
B. Weyssow3,4 and JET EFDA Contributors*
JET-EFDA Culham Science Centre, Abingdon, OX14 3DB, UK;
1 V.N. Karazin Kharkiv National University, Kharkiv, Ukraine;
2 Laboratory for Plasma Physics, Association EURATOM-Belgian State, Trilateral Euregio
Cluster Partner, Royal Military Academy, B-1000, Brussels, Belgium;
3 EFDA-CSU Garching, Boltzmannstr. 2, D-85748, Garching, Germany;
4 Université Libre de Bruxelles, Association EURATOM-Belgian State,
Campus Plaine, CP 231, B-1050 Brussels, Belgium
ICRF mode conversion heating regime is widely used in present-day tokamaks. The theoretically predicted mode
conversion enhancement due to the constructive interference of the fast wave reflected from the evanescence layer with
a wave reflected from the high-field side cutoff was first experimentally identified in JET in (3He)D experiments. This
effect was recently tested in (3He)H plasmas, which is one of the ICRF heating scenarios considered for the non-
activated phase of ITER operation. Due to the presence of the intrinsic D-like impurities in JET (e.g., C6+, 4He) the
supplementary conversion layer was produced in the plasma that defined the interference conditions. The different
behavior of the conversion efficiency observed at various 3He concentrations is analyzed in the paper on the basis of the
theory of the fast wave mode conversion in plasmas with two evanescence layers.
PACS: 52.55.Fa, 52.50.Qt, 52.25.Os
1. INTRODUCTION
ICRF mode conversion regime is being actively
studied within the last years [1]. The attention paid to this
scenario is caused by a number of important applications
it has beyond plasma heating. Mode conversion has
become a standard tool to do the transport analysis [2], it
is used to drive plasma rotation [3], to generate non-
inductive current drive, to pump-out impurities, to
measure the ion species mix, etc. The principle of this
scheme consists in the following. An ICRF antenna
located at the low field side (LFS) of the tokamak
launches the fast wave (FW) which propagates to the
plasma center. At the ion-ion hybrid (IIH) resonance the
FW is partially converted to short-wavelength mode
which is commonly effectively damped on the electrons.
The optimization of this heating scheme relies on the
achievement of the proper conversion conditions. The
Budden theory predicts that maximum 25% of the FW
energy can be converted to short-wavelength mode when
the FW tunnels through an isolated evanescence layer.
The interference effect described by V. Fuchs et al. [4]
allows to significantly enhance the conversion efficiency.
The conversion enhancement is caused by the additional
reflection of the FW transmitted through the evanescence
layer from the high-field side cutoff. The optimal
conversion conditions are achieved when the reflected
waves have nearly equal amplitudes and the opposite
phases. Within this model the conversion coefficient can
reach the value of 100%.
The first experimental evidence of this effect was
shown in JET for (3He)D plasmas [5]. The experimental
data of the power absorbed by electrons as a function of
minority 3He concentration, X[3He] was found to be in fair
accordance with the theoretical analysis and numerical
modeling. It was shown that the electron absorption
efficiency was an oscillatory function of X[3He].
Recently, a series of experiments at JET was
performed to test this idea in (3He)H plasma [6]. Unlike
the (3He)D scenario, the latter is an inverted one, i.e.
a scenario with a ‘heavy’ minority, (Z/A)min<(Z/A)maj. For
the inverted scenario the evanescence layer is located
between the LFS antenna and the minority cyclotron
resonance. As the minority concentration is increased, the
conversion layer shifts towards the LFS in contrast to the
HFS layer shift for the regular scenarios. Moreover, as
shown in the past experiments [7], the inverted (3He)H
scenario requires much lower X[3He] to reach the mode
conversion regime than the regular (3He)D scenario. The
aim of the (3He)H heating experiments performed earlier
at JET [7, 8] was to test the potential of this heating
scenario for the non-activated phase of ITER operation.
At this early ITER experimental stage predominantly
hydrogen plasma will be used to minimize the activation
of the tokamak components.
Before the shutdown of JET in 2009 most of the inner
wall was made of carbon tiles. It resulted in the
unavoidable presence of carbon in the plasma at a fairly
high level enough to prevent the minority heating of
deuterium in hydrogen plasmas [7, 8]. In addition,
deuterium (as the most commonly used gas in JET) and
4He (since (3He)H heating experiments were performed
after a 4He campaign) ions were present in all discharges
due to the recycling. Thus, the (3He)H plasma was
unavoidably contaminated with the D-like species, which
from RF point of view acted as a single species with
Z/A=1/2. The presence of these ions led to the production
of a second conversion layer in the plasma. This resulted
in a more complicated picture of the mode conversion
physics than for the usual case of a single resonance.
* See the Appendix of F. Romanelli et al., Proceedings of the 22nd IAEA Fusion Energy Conference 2008, Geneva, Switzerland
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2010. № 6. 37
Series: Plasma Physics (16), p. 37-39.
2. MULTIPLE MODE CONVERSION LAYERS
PHYSICS
The mode conversion coefficient in plasmas with two
evanescence layers is found to be of the form [9]:
(1)
where are the transmission coefficients through the
corresponding conversion layers. The constructive/
destructive role of the interference effects in mode
conversion is determined by the phase difference
(2)
The largest contribution to in (2) is given by the term
, which is defined by the distance between the
conversion layers.
The location and transparency properties of each of
the conversion layers strongly depend on the
concentrations of both minority species. Fig. 1 shows the
spatial dependence of the FW wavenumber, as a
function of X[3He] and X[D]. It is clearly seen that with
the increase of the minority concentration, be it X[3He] or
X[D], the corresponding conversion layer moves towards
the LFS as for the present inverted scenario. But the
mutual effect on the opposite conversion layer is inverse
for 3He and D ions. The X[3He] increase leads to a shift of
the D layer towards the HFS and to the decrease of its
width, while the increase of X[D] results in the LFS shift
of the 3He layer. It also alters the width of the 3He layer,
which results in the significant reduction of the transition
3He concentration at which the mode conversion regime is
observed [7, 9].
The (3He)H experiments referred to were performed at
the magnetic field B0 = 3.4…3.5 T and with the antenna
frequency f =32.5 MHz. This positioned the 3He cyclotron
38
Fig. 1. FW dispersion as a function of X[3He] and X[D],
B
resonance layer ~20 cm out of the plasma center to the
LFS, the D cyclotron resonance was located at the HFS at
R ≈ 2.4 m (Fig. 2). As discussed, two mode conversion
layers were present in the plasma: one layer was
associated with 3He ions, and another – with D-like ions.
Fig. 2. Tokamak poloidal cross-section with the locations
of the 3He and D cyclotron resonance and mode
conversion layers, B0=3.46 T, f=32.5 MHz
Since the position of the conversion layers depends on
the minority concentration it is important to implement
the real time control (RTC) of the 3He concentration. RTC
scheme relies on the generalized Mantsinen law. It
utilizes the definition of Zeff and links relative divertor
light intensities of species to the relative species
concentrations [5]. It was found that the experimentally
determined locations of the maxima of electron
absorption (determined from the analysis of the
temperature response to the RF power modulation) did
not coincide with the locations of the conversion layers
calculated from the dispersion study using the RTC data
for X[3He], the latter being representative for the divertor
region and not necessarily for the core. A minimization
procedure was implemented to establish the relation
between the divertor and core 3He concentrations. It
turned out that a simple multiplicative factor of 1.6 allows
to reconcile experimental and theoretical predictions.
а
For XRTC[3He]<4% there are two conversion layers in
the plasma. The conversion coefficient is defined by the
formulas (1) and (2). ICRF heating efficiency has an
oscillatory Fuchs-like dependence on X[3He] with one
clear maximum (Fig. 3). In the range 4%<XRTC[3He]<6.5%
the 3He conversion layer approaches the plasma edge.
This regime is characterized by a poor antenna-wave
coupling. Further increase of X[3He] moves the 3He
conversion layer out of the plasma, and only a single
D conversion layer remains in the plasma. In such
conditions, a change of X[3He] does not have such a
pronounced effect on the phase difference
(determined now by the distance between the
D conversion layer and the high-field side R-cutoff) for
smaller 3He concentrations. The response of the heating
efficiency to the change of X[3He] is rather flat in this
regime, which is typical of the triplet-model theory [4].
Within this model the conversion coefficient is given by
. – the transmission
coefficient through the D layer – is lower than in the two
b
B0=3.2 T, f=33 MHz
conversion layers regime due to higher 3He concentration,
which makes D conversion layer to be a semi-transparent.
The described conversion regimes have different
sensitivity not only to the plasma composition, but also to
the toroidal wavenumber, ntor. Since the location of the
high-field side cutoff depends critically on ntor, the
toroidal wavenumber dependence of the conversion
coefficient is more pronounced in the second regime.
Numerical simulations with the 1D full-wave code
confirmed the presence of two mode conversion regimes
with the different behavior to the variation of plasma
parameters [6].
Fig. 3. ICRF heating efficiency as a function of
3He concentration, XRTC[3He]
CONCLUSIONS
Recent (3He)H heating experiments at the JET
tokamak confirmed the essential role of the intrinsic
D-like species in the ICRF mode conversion scenario.
The presence of such ions leads to the generation of a
supplementary conversion layer in the plasma, which for
small 3He concentrations defines the interference pattern
in the plasma. For large X[3He] only a single conversion
layer associated with D ions is present in the plasma. The
difference in the mode conversion coefficient behavior to
the various experimental parameters observed in these
regimes can be qualitatively explained by the Fuchs
theory and its two mode conversion layers extension.
ACKNOWLEDGEMENTS
This work, supported by the European Communities
under the contract of the Association between
EURATOM and the Belgian State, was carried out within
the framework of the European Fusion Development
Agreement. The views and opinions expressed herein do
not necessarily reflect those of the European Commission.
The work of Ye.O. Kazakov was partly supported by the
Erasmus Mundus Visiting Scientist Scholarship.
REFERENCES
1. A.V. Longinov and K.N. Stepanov. High-Frequency
Plasma Heating / Ed. A.G. Litvak. New York:
“American Institute of Physics”, 1992, p. 93-238.
2. D. Van Eester, E. Lerche, P. Mantica, et al. // AIP
Conf. Proc. 2007, v. 933, p. 63-66.
3. Y. Lin, J.E. Rice, S.J. Wukitch, et al. // Physics of
Plasmas. 2009, v. 16, N 5, p. 056102.
4. V. Fuchs, A.K. Ram, S.D. Schultz, et al. // Physics of
Plasmas. 1995, v. 2, N 5, p. 1637-1647.
5. D. Van Eester, E. Lerche, Y. Andrew, et al. // Plasma
Physics and Controlled Fusion. 2009, v. 51, N 4,
p.044007.
6. D. Van Eester, E. Lerche, T. Johnson, et al. Mode
conversion heating in JET plasmas with multiple
mode conversion layers // Proc. 37th EPS
Conference on Plasma Physics (Dublin, Ireland,
2010), p. P5-163.
7. M.-L. Mayoral, P.U. Lamalle, D. Van Eester, et al. //
Nuclear Fusion. 2006, v. 46, N 7, p. S550-S563.
8. P.U. Lamalle, M.J. Mantsinen, J.-M. Noterdaeme,
et al. // Nuclear Fusion. 2006, v. 46, № 2, p. 391-400.
9. Ye.O. Kazakov, I.V. Pavlenko, D. Van Eester, et al.
// Plasma Physics and Controlled Fusion. 2010,
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Article received 13.09.2010
ВЫСОКОЧАСТОТНЫЙ НАГРЕВ ВОДОРОДНОЙ ПЛАЗМЫ С ДВУМЯ ОБЛАСТЯМИ КОНВЕРСИИ
Е.О. Казаков, D. Van Eester, E. Lerche, И.В. Павленко, И.А. Гирка, B. Weyssow
Высокочастотный нагрев плазмы в режиме конверсии мод широко используется в современных токамаках.
Теоретически предсказанное увеличение эффективности конверсии вследствие интерференции быстрой волны,
отраженной от области непрозрачности, с волной, отраженной от отсечки со стороны сильного магнитного
поля, было впервые экспериментально подтверждено в (3He)D-экспериментах на токамаке JET. Данный эффект
изучался в (3He)H-плазме, которая рассматривается как один из сценариев ВЧ-нагрева во время начальной
стадии работы ITER. Вследствие присутствия в плазме JET дейтериеподобных примесей (C6+, 4He)
образовывалась дополнительная область непрозрачности, которая определяла условия интерференции волн.
Различное поведение коэффициента конверсии, наблюдаемое при разных значениях концентрации ионов 3He,
анализируется в работе с помощью теории конверсии быстрых волн в плазме с двумя областями непрозрачности.
ВИСОКОЧАСТОТНЕ НАГРІВАННЯ ВОДНЕВОЇ ПЛАЗМИ З ДВОМА ШАРАМИ НЕПРОЗОРОСТІ
Є.О. Казаков, D. Van Eester, E. Lerche, І.В. Павленко, І.О. Гірка, B. Weyssow
39
Високочастотне нагрівання плазми в режимі конверсії мод широко застосовується в сучасних токамаках.
Теоретично передбачене збільшення ефективності конверсії внаслідок інтерференції швидкої хвилі, що відбита
від шару непрозорості, з хвилею, що відбита від відсічки з боку сильного магнітного поля, було вперше
експериментально підтверджено в (3He)D-експериментах на токамаці JET. Цей ефект нещодавно апробовано в
(3He)H-плазмі, яка розглядається як один із сценаріїв ВЧ-нагрівання на початковій стадії роботи ITER.
Внаслідок присутності в плазмі JET дейтерієподібних домішок (C6+, 4He) утворювався додатковий шар
непрозорості, що визначав умови інтерференції хвиль. Різна поведінка коефіцієнту конверсії, що спостерігалася
за різної концентрації іонів 3He, аналізується в роботі на основі теорії конверсії швидких хвиль в плазмі з двома
шарами непрозорості.
REFERENCES
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