Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks
The paper presents advance in a new method developed in the Institute for Nuclear Studies (IPJ) for direct detection of high-energy (super-thermal, runaway) electrons generated in tokamaks. The technique in question is based on registration of the Cherenkov radiation, emitted by energetic electron...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
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irk-123456789-909992016-01-07T03:03:10Z Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks Rabinski, M. Jakubowski, L. Malinowski, K. Mirowski, R. Sadowski, M.J. Zebrowski, J. Диагностика плазмы The paper presents advance in a new method developed in the Institute for Nuclear Studies (IPJ) for direct detection of high-energy (super-thermal, runaway) electrons generated in tokamaks. The technique in question is based on registration of the Cherenkov radiation, emitted by energetic electrons, moving through a transparent medium (radiator body) with a velocity higher than the velocity of light in this material. The main aim of the presented studies was to develop a diagnostic technique applicable for investigation of fast electron beams within magnetic confinement fusion (MCF) facilities. Представлено досягнення нового методу, розробленого в Інституті ядерних досліджень(ИЯД) для прямої реєстрації високоенергетичних (надтеплових, втікаючих) електронів, генеруємих у токамаках. Технічно задача заснована на реєстрації черенковського випромінювання, що випускається енергетичними електронами, які рухаються через прозоре середовище(випромінювальне тіло) зі швидкістю вище швидкості світла в даному матеріалі. Основною метою представлених досліджень була розробка діагностичної методики, застосованої для вивчення швидких електронних пучків у термоядерних магнітних пастках(ТМП). Представлены достижения нового метода, разработанного в Институте ядерных исследований (ИЯИ) для прямой регистрации высокоэнергетических (надтепловых, убегающих) электронов, генеруємых в токамаках. Технически задача основана на регистрации черенковского излучения, испускаемого энергитичными электронами, движущимся через прозрачную среду(излучательное тело) со скоростью выше скорости света в данном материале. Основной целью представленных исследований была разработка диагностической методики, применимой для изучения быстрых электронных пучков в термоядерных магнитных ловушках(ТМЛ). 2011 Article Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks / M. Rabinski, L. Jakubowski, K. Malinowski, R. Mirowski, M.J. Sadowski, J. Zebrowski // Вопросы атомной науки и техники. — 2011. — № 1. — С. 164-166. — Бібліогр.: 6 назв. — англ. 1562-6016 PACS: 41.75.Ht, 40.60.Bq, 52.70.La http://dspace.nbuv.gov.ua/handle/123456789/90999 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| topic |
Диагностика плазмы Диагностика плазмы |
| spellingShingle |
Диагностика плазмы Диагностика плазмы Rabinski, M. Jakubowski, L. Malinowski, K. Mirowski, R. Sadowski, M.J. Zebrowski, J. Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks Вопросы атомной науки и техники |
| description |
The paper presents advance in a new method developed in the Institute for Nuclear Studies (IPJ) for direct detection
of high-energy (super-thermal, runaway) electrons generated in tokamaks. The technique in question is based on
registration of the Cherenkov radiation, emitted by energetic electrons, moving through a transparent medium (radiator
body) with a velocity higher than the velocity of light in this material. The main aim of the presented studies was to
develop a diagnostic technique applicable for investigation of fast electron beams within magnetic confinement fusion
(MCF) facilities. |
| format |
Article |
| author |
Rabinski, M. Jakubowski, L. Malinowski, K. Mirowski, R. Sadowski, M.J. Zebrowski, J. |
| author_facet |
Rabinski, M. Jakubowski, L. Malinowski, K. Mirowski, R. Sadowski, M.J. Zebrowski, J. |
| author_sort |
Rabinski, M. |
| title |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| title_short |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| title_full |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| title_fullStr |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| title_full_unstemmed |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| title_sort |
progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2011 |
| topic_facet |
Диагностика плазмы |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/90999 |
| citation_txt |
Progress in development and applications of cherenkovtype detectors for fast electron studies in tokamaks / M. Rabinski, L. Jakubowski, K. Malinowski, R. Mirowski, M.J. Sadowski, J. Zebrowski // Вопросы атомной науки и техники. — 2011. — № 1. — С. 164-166. — Бібліогр.: 6 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| fulltext |
PLASMA DIAGNOSTICS
164 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. 1.
Series: Plasma Physics (17), p. 164-166.
PROGRESS IN DEVELOPMENT AND APPLICATIONS OF CHERENKOV-
TYPE DETECTORS FOR FAST ELECTRON STUDIES IN TOKAMAKS
M. Rabi ski, L. Jakubowski, K. Malinowski, R. Mirowski, M.J. Sadowski, J. ebrowski
The Andrzej Soltan Institute for Nuclear Studies (IPJ), 05-400 Otwock-Swierk, Poland
E-mail: rabinski@ipj.gov.pl
The paper presents advance in a new method developed in the Institute for Nuclear Studies (IPJ) for direct detection
of high-energy (super-thermal, runaway) electrons generated in tokamaks. The technique in question is based on
registration of the Cherenkov radiation, emitted by energetic electrons, moving through a transparent medium (radiator
body) with a velocity higher than the velocity of light in this material. The main aim of the presented studies was to
develop a diagnostic technique applicable for investigation of fast electron beams within magnetic confinement fusion
(MCF) facilities.
PACS: 41.75.Ht, 40.60.Bq, 52.70.La
1. INTRODUCTION
High-temperature plasmas in tokamaks and
stellarators usually contain and emit many high-energy
electrons and ions. Determination of their parameters is
indispensable part of plasma fusion studies. The IPJ team,
operating within a frame of the Association EURATOM/
IPPLM, proposed to use Cherenkov-type probes for
measurements of fast electrons escaping from tokamaks,
because of their high spatial- and temporal-resolutions.
The Cherenkov radiation is emitted by a charged
particle moving through a transparent medium with a
velocity higher than the phase velocity of light in this
medium. Emitted energy increases with an increase in a
particle velocity and it is larger for a medium with a
larger refraction coefficient. From a comparison of
refraction index values and corresponding minimal energy
values for different materials one can conclude that to
record electron beams of lower energy it is necessary to
use radiators made of diamond or rutil crystals.
The developed method enables the identification of
electron beams, the determination of their spatial
distribution, as well as the measurements of their
temporal characteristics. Research on the time-
correlations of the obtained data with the other
phenomena within tokamaks, e.g. with the generation of
X-ray pulses, the emission of neutrons and energetic ion
beams, etc., are of primary importance for the verification
of different theoretical models and for solving the plasma
engineering problems.
2. MEASUREMENT HEAD DESIGN
The realization of the Cherenkov-type diagnoctics
described above induces, however, some serious
problems. First of all the detector must be shielded by an
appropriate absorption filter protecting the radiator
against the plasma. One should note that the heat loads of
about 5 MW/m2 is deposited mainly in the radiator
surface layer of a few hundreds micrometers in the
thickness (determined by the electron range in the radiator
material). The deposited heat must be dissipated as
quickly as possible in order to eliminate local destructions
of the radiator material. Thus, the main problem is an
effective heat transfer through the radiator and a shielding
body, the formation of an appropriate heat sink as well as
keeping temperatures of the radiator and its shield below
the admissible values. The electron-induced intense heat
flux induces the use of materials resistant to high
temperature, the application of materials having high
thermal conductivity, and the performance of all
measurements during a relatively short time.
Another problem is connected with an energy
spectrum of fast electrons, and particularly with its lower
limit. Because of a threshold character of the Cherenkov
phenomenon, the detection of electrons of energy equal to
about 50 keV requires the application of a radiator
characterized by a relatively high refractive index, e.g.
diamond or aluminium nitride (AlN) crystal.
It was also decided to split the whole electron energy
spectrum into four energy channels. Each channel should
have the lower energy threshold determined by a thickness
of the applied absorption foil filter, which should be placed
in front of the radiator. Molybdenum (Mo) was chosen as
the absorption filter material, due to its high melting
temperature and resistance to the sputtering.
Computations of a heat transport and temperature
distributions inside the Mo filters, diamond radiators and
shielding body were performed, and different
constructions of the Cherenkov detector head were
considered. Results of the numerical simulations showed
that the lowest temperatures values can be achieved with
the filter deposited directly upon the diamond surface,
when the radiator is connected directly with the shielding
body (forming a heat sink). It was also decided that such
measurements should be carried out several times during
a single tokamak discharge, and the Cherenkov detector
should be introduced into a region of electron fluxes for a
short period only.
On the basis of the feasibility studies [1] some
prototypes of the one- and four-channel measuring head
have been designed, constructed and tested within several
small, medium and large devices. In particular, the
measurements have been performed within the CASTOR,
ISTTOK and TORE-SUPRA tokamaks.
3. EXPERIMENTAL RESULTS
3.1. CASTOR TOKAMAK
Preparing the use of Cherenkov detections in the
large-scale tokamaks, IPJ team designed and used
prototype detector within the CASTOR facility in Prague
mailto:rabinski@ipj.gov.pl
165
(Czech Republic). The experimental data were collected
from about 500 ohmically heated discharges, each lasting
about 25 ms. After the first series of experiments carried
out in autumn 2006 a modified version of detection
system was constructed and used for diagnostics.
The analysis of results showed that character of the
Cherenkov detector signals depends strongly on the
detector radial position as well as on the plasma density.
It was also observed that after t = 25 ms, when the
transformer primary winding was short-circuited, a strong
increase in signal intensity appeared as a result of the
plasma column destruction [2-3].
3.2. ISTTOK TOKAMAK
Fig. 1 presents a general view of Cherenkov-type
detector designed and manufactured on the basis of the
ISTTOK plasma probe console. Detector itself consists of
a measuring head equipped with a 5-mm in diameter input
window, positioned at an angle of 450 in relation to the
vacuum chamber axis. It was connected optically, through
a well-polished inner surface and thin-wall metal tube,
with an optical fiber cable. High-energy electrons
penetrating through the windowed AlN crystal with a
titanium coating caused the Cherenkov radiation
emission. The 10-µm-titanium coating layer served as a
filter for energetic electrons increasing the measuring
energy threshold.
Fig. 1. Movable support with the Cherenkov-type detector
used for measurements of fast electrons in ISTTOK
System described above allowed the detection of fast
electrons with energy of about 80 keV. A movable
support has made possible the detection of fast electrons
in different radial positions with the deepest measuring
position at the radius of 52 mm, where the detector still
did not disturb the bulk plasma considerably.
The studies of the fast electron emission as a function
of the Cherenkov probe positioning along the minor
radius showed the distinct maximum for r = 6,5 cm. The
measurements of HXR, as performed outside the tokamak
chamber, showed a relatively intense radiation for the
Cherenkov probe positioning within the radial region of
r = 6,5…9,0 cm. The HXR emission originated probably
from the fast electrons Bremsstrahlung in the limiter and
metal walls of the tokamak facility [4-5].
3.3. TORE-SUPRA TOKAMAK
Interesting results and valuable experience gained from
the experiments described above enabled the Cherenkov
detectors in the larger-scale TORE-SUPRA experiment to
be used. A scheme of the designed four-channel
Cherenkov-type detection head is presented in Fig. 2.
Fig. 2. Four-channel measuring head for TORE-SUPRA
experiment; the spatial arrangement of diamond
radiators (with metal coatings) and separate optical
fibres [6]
Fig.3. Examples of the results obtained within TORE-SUPRA tokamak [6]: changes in the vertical position of the
Cherenkov head and electron-induced signals from four measuring channels during the inward motion of the probe (on
left), and during the outward motion (on right)
166
Diamond crystals have been selected as radiator material
because of a relatively low value of the energy threshold
51 keV and high thermal conductivity (five times better
than copper). The special shape of a diamond radiator cut
was worked out to create an optical coupling with the
appropriate light pipe. All the radiator surfaces were well
polished and metal coated, except for a corner part to be
used for the coupling with an optical fibre. Only the front
part of the radiator was exposed to fast electron streams.
Therefore, the front surface of diamond radiators was
coated with the thin molybdenum layer, constituting the
light-tight protection and absorption filter. The shape and
dimensions of the radiator were chosen taking into
consideration geometrical requirements and thermal
conduction efficiency.
The example experimental results, which were
obtained with the help of the Cherenkov-type measuring
head, is presented in Fig. 3. The recorded electron-
induced signals confirm the appearance of a thin fast
electron sheath of 1…2 mm in thickness.
CONCLUSIONS
The applications of the presented diagnostics have
proved the usefulness of the one- and four-channel
versions of the detecting head for fast electron studies in
tokamaks.
The most important results, as obtained with the
described Cherenkov-type diagnostics, have proved that
the one- and four-channel versions of the detecting head
can easily be applied for studies of the fast (ripple-born
and runaway) electrons in different experiments. An
adaptation of the described solutions to other MCF
facilities is possible, and experience collected during the
studies allows to introduce some changes in the radiator
configuration and to modify the Cherenkov probe design.
In general, the use of diamond radiators seem to be the
best solution for measurements of electrons above about
60 keV, taking into account necessity to use a thin light-
tight Mo filter. For measurements of electrons of
considerably higher energy, one should take into account
different absorption filters, but they must withstand high
thermal loads during measurements, and their adhesion to
the radiators should be satisfactory all the time.
ACKNOWLEDGEMENTS
The reported studies were performed as the P3 task of the
research program supported by the EURATOM
Community under the Contract with the Association
EURATOM-IPPLM, Poland (Contract No. FU06-CT-
2004-00081). The research was also supported by the
Ministry of Education and Science, Poland, under
contract No. 47/EURATOM/2005/7.
REFERENCES
1. L. Jakubowski, M. Rabi ski, et al.// Problems of Atomic
Science and Technology. Series “Plasma physics”(13),
2007, N 1, p. 206-208.
2. L. Jakubowski, M.J. Sadowski, et al.// 34th EPS
Conference on Plasma Phys. Warsaw, 2-6 July 2007/
ECA 31F, 2007, P-5.097.
3. L. Jakubowski, M.J. Sadowski, et al.// AIP CP. 2008,
v. 996, p. 219-223.
4. V.V. Plyusnin, L. Jakubowski, et al.// 35th EPS
Conference on Plasma Phys. Hersonissos, 9-13 June
2008/ ECA 32, 2008, P-5.075
5. V.V. Plyusnin, L. Jakubowski, et al.// Rev. Sci. Instrum.
2008, v. 79, p. 10F505.
6. L. Jakubowski, M.J. Sadowski, et al.// Rev. Sci.
Instrum. 2010, v. 81, p. 0135040.
Article received 13.09.10
M. Rabi ski, L. Jakubowski, K. Malinowski, R. Mirowski, M.J. Sadowski, J. ebrowski
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