Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak
The paper describes measurements of fast run-away electron beams emitted from a plasma torus in the ISTTOK tokamak, which were performed by means of a new Cherenkov-type detector equipped with four radiators made of aluminium-nitrate (AlN) crystals of 10 mm in diameter and 2.5 mm in thickness each...
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| Cite this: | Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak / L. Jakubowski, V.V. Plyusnin, K. Malinowski, M.J. Sadowski, J. Zebrowski, M. Rabinski, H. Fernandes, C. Silva, P. Duarte, M. Jakubowski // Вопросы атомной науки и техники. — 2011. — № 1. — С. 170-172. — Бібліогр.: 4 назв. — англ. |
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Jakubowski, L. Plyusnin, V.V. Malinowski, K. Sadowski, M.J. Zebrowski, J. Rabinski, M. Fernandes, H. Silva, C. Duarte, P. Jakubowski, M. 2016-01-06T16:11:46Z 2016-01-06T16:11:46Z 2011 Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak / L. Jakubowski, V.V. Plyusnin, K. Malinowski, M.J. Sadowski, J. Zebrowski, M. Rabinski, H. Fernandes, C. Silva, P. Duarte, M. Jakubowski // Вопросы атомной науки и техники. — 2011. — № 1. — С. 170-172. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 52.59.Rz, 52.70.Nc, 52.70.La https://nasplib.isofts.kiev.ua/handle/123456789/91067 The paper describes measurements of fast run-away electron beams emitted from a plasma torus in the ISTTOK tokamak, which were performed by means of a new Cherenkov-type detector equipped with four radiators made of aluminium-nitrate (AlN) crystals of 10 mm in diameter and 2.5 mm in thickness each. The measuring head was fixed to a movable support, which enabled the radiators to be placed in chosen positions along the minor radius of ISTTOK. The radiators were coated with molybdenum (Mo) layers of different thicknesses since the main aim of this study was to estimate an energy spectrum of the recorded electrons. Attention was also paid to measurements of hard X-rays emitted from ISTTOK and to their correlations with run-away electrons. The investigated correlations showed that the both emissions are strongly coupled. Описано виміри швидких втікаючих електронних пучків, що випускається з плазмового тора в токамаці ISTTOK, що було виконано за допомогою нових черенковських детекторів, оснащених чотирма радіаторами з нітратуалюмінію (AIN) із кристалами діаметром 10 і товщиною 2,5мм кожний. Вимірювальна головка була встановлена на рухливій підставі,що дозволило розміщати радіатори в обраних позиціях по малому радіусі ISTTOK. Радіатори були покриті молібденовими (Мо) шарами різної товщини ,оскільки основною метою даного дослідження було оцінити енергетичний спектр електронів, що регіструються. Увага була також приділена виміру твердого рентгенівського випромінювання з ISTTOK і його кореляції з втікаючими електронами. Досліджені кореляції показали, що обоє випромінювання сильно зв’язані. Описываются измерения быстрых убегающих электронных пучков, испускаемых из плазменного тора в токамаке ISTTOK, которые были выполнены с помощью новых черенковских детекторов, оснащенных четырьмя радиаторами из нитратаалюминия (AIN) с кристаллами диаметром 10 и толщиной 2,5 мм каждый. Измерительная головка была установлена на подвижном основании, что позволило размещать радиаторы в выбранных позициях по малому радиусу ISTTOK. Радиаторы были покрыты молибденовыми (Мо) слоями различной толщины, поскольку основной целью данного исследования было оценить энергетический спектр регистрируемых электронов. Внимание было также уделено измерению жесткого рентгеновского излучения из ISTTOK и его корреляции с убегающими электронами. Исследованные корреляции показали, что оба излучения сильно связаны. This work was supported by European Atomic Energy Community as well as by the Ministry of Science and Higher Education, Poland, and Fundacao para a Ciencia ea Tecnologia (FCT), Portugal. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Диагностика плазмы Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak Дослідження втікаючих електронних пучків і жорстокого рентгенівського випромінювання у токамаці ISTTOK Исследование убегающих электронных пучков и жестокого рентгеновского излучения в токамаке ISTTOK Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak |
| spellingShingle |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak Jakubowski, L. Plyusnin, V.V. Malinowski, K. Sadowski, M.J. Zebrowski, J. Rabinski, M. Fernandes, H. Silva, C. Duarte, P. Jakubowski, M. Диагностика плазмы |
| title_short |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak |
| title_full |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak |
| title_fullStr |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak |
| title_full_unstemmed |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak |
| title_sort |
studies of run-away electron beams and hard x-ray emission in isttok tokamak |
| author |
Jakubowski, L. Plyusnin, V.V. Malinowski, K. Sadowski, M.J. Zebrowski, J. Rabinski, M. Fernandes, H. Silva, C. Duarte, P. Jakubowski, M. |
| author_facet |
Jakubowski, L. Plyusnin, V.V. Malinowski, K. Sadowski, M.J. Zebrowski, J. Rabinski, M. Fernandes, H. Silva, C. Duarte, P. Jakubowski, M. |
| topic |
Диагностика плазмы |
| topic_facet |
Диагностика плазмы |
| publishDate |
2011 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Дослідження втікаючих електронних пучків і жорстокого рентгенівського випромінювання у токамаці ISTTOK Исследование убегающих электронных пучков и жестокого рентгеновского излучения в токамаке ISTTOK |
| description |
The paper describes measurements of fast run-away electron beams emitted from a plasma torus in the ISTTOK
tokamak, which were performed by means of a new Cherenkov-type detector equipped with four radiators made of
aluminium-nitrate (AlN) crystals of 10 mm in diameter and 2.5 mm in thickness each. The measuring head was fixed to
a movable support, which enabled the radiators to be placed in chosen positions along the minor radius of ISTTOK. The
radiators were coated with molybdenum (Mo) layers of different thicknesses since the main aim of this study was to
estimate an energy spectrum of the recorded electrons. Attention was also paid to measurements of hard X-rays emitted
from ISTTOK and to their correlations with run-away electrons. The investigated correlations showed that the both
emissions are strongly coupled.
Описано виміри швидких втікаючих електронних пучків, що випускається з плазмового тора в токамаці ISTTOK, що було виконано за допомогою нових черенковських детекторів, оснащених чотирма радіаторами з нітратуалюмінію (AIN) із кристалами діаметром 10 і товщиною 2,5мм кожний. Вимірювальна головка була встановлена на рухливій підставі,що дозволило розміщати радіатори в обраних позиціях по малому радіусі ISTTOK. Радіатори були покриті молібденовими (Мо) шарами різної товщини ,оскільки основною метою даного дослідження було оцінити енергетичний спектр електронів, що регіструються. Увага була також приділена виміру твердого рентгенівського випромінювання з ISTTOK і його кореляції з втікаючими електронами. Досліджені кореляції показали, що обоє випромінювання сильно зв’язані.
Описываются измерения быстрых убегающих электронных пучков, испускаемых из плазменного тора в токамаке ISTTOK, которые были выполнены с помощью новых черенковских детекторов, оснащенных четырьмя радиаторами из нитратаалюминия (AIN) с кристаллами диаметром 10 и толщиной 2,5 мм каждый. Измерительная головка была установлена на подвижном основании, что позволило размещать радиаторы в выбранных позициях по малому радиусу ISTTOK. Радиаторы были покрыты молибденовыми (Мо) слоями различной толщины, поскольку основной целью данного исследования было оценить энергетический спектр регистрируемых электронов. Внимание было также уделено измерению жесткого рентгеновского излучения из ISTTOK и его корреляции с убегающими электронами. Исследованные корреляции показали, что оба излучения сильно связаны.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/91067 |
| citation_txt |
Studies of run-away electron beams and hard x-ray emission in ISTTOK tokamak / L. Jakubowski, V.V. Plyusnin, K. Malinowski, M.J. Sadowski, J. Zebrowski, M. Rabinski, H. Fernandes, C. Silva, P. Duarte, M. Jakubowski // Вопросы атомной науки и техники. — 2011. — № 1. — С. 170-172. — Бібліогр.: 4 назв. — англ. |
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2025-11-24T21:13:53Z |
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| fulltext |
170 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. 1.
Series: Plasma Physics (17), p. 170-172.
STUDIES OF RUN-AWAY ELECTRON BEAMS AND HARD X-RAY
EMISSION IN ISTTOK TOKAMAK
L. Jakubowski1, V.V. Plyusnin2, K. Malinowski1, M.J. Sadowski1, J. ebrowski1,
M. Rabi ski1, H. Fernandes2, C. Silva2, P. Duarte2, M. Jakubowski1
1The Andrzej Soltan Institute for Nuclear Studies (IPJ), 05-400 Otwock-Swierk, Poland;
2Association Euratom/IST, Instituto de Plasmas e Fusão Nuclear, 1049–001 Lisboa, Portugal
E-mail: lech.jakubowski@ipj.gov.pl
The paper describes measurements of fast run-away electron beams emitted from a plasma torus in the ISTTOK
tokamak, which were performed by means of a new Cherenkov-type detector equipped with four radiators made of
aluminium-nitrate (AlN) crystals of 10 mm in diameter and 2.5 mm in thickness each. The measuring head was fixed to
a movable support, which enabled the radiators to be placed in chosen positions along the minor radius of ISTTOK. The
radiators were coated with molybdenum (Mo) layers of different thicknesses since the main aim of this study was to
estimate an energy spectrum of the recorded electrons. Attention was also paid to measurements of hard X-rays emitted
from ISTTOK and to their correlations with run-away electrons. The investigated correlations showed that the both
emissions are strongly coupled.
PACS: 52.59.Rz, 52.70.Nc, 52.70.La
1. INTRODUCTION
In tokamaks a discharge current within a ring-shaped
experimental chamber is driven initially by an externally
induced electrical field. Such a field can also lead to the
generation of so-called “runaway electrons” [1] if the
friction force (from collisions) is not compensated by the
accelerating electrical force. The runaway electrons can
influence the plasma behavior since they can carry a
substantial part of the plasma current. They are practically
collision-less, but losses of highly energetic runaway
electrons can cause heavy damages of internal walls in
fusion facilities. Therefore, the run-away electrons have
been studied in different tokamaks for many years with
various techniques. To measure run-away electrons
directly the IPJ team developed detectors using the
Cherenkov-effect in specially chosen radiators [2]. A
Polish-Portuguese team applied a Cherenkov detector in
the ISTTOK facility to detect energetic electrons (of
energy > 60 keV) and to determine their spatial and
temporal behaviour [3], but information delivered by a
single-channel detector was very limited.
The main aim of the recent experimental studies
within ISTTOK was to investigate the emission of fast
electrons in more details by means of a four-channel
Cherenkov measuring head.
2. DIAGNOSTICS OF ELECTRON BEAMS
AND HARD X-RAYS
The previous measurements of run-away electrons in
ISTTOK have been performed by means of a measuring
head equipped with four separate Cherenkov radiators [4].
The detectors were made of aluminium-nitrade (AlN)
poly-crystals of 10 mm in diameter and 1.0 mm in
thickness. They were separated by stainless-steel plates
and pressed together to improve a heat transfer. The
investigated electron streams interacted only with parts of
the detectors sides, which were coated with molybdenum
(Mo) layers of different thicknesses in order to determine
the chosen energy thresholds. The Cherenkov radiation
emitted by fast electrons (penetrating the radiators) was
transmitted through four separate optical cables to fast
photomultipliers of the Photonis XP-1918 type. An
analysis of the collected experimental data showed that
the recorded electron-induced signals were too low to
ensure an appropriate signal-to-noise ratio. During the
measurements within ISTTOK it was observed that some
parts of the Mo-filters upon the radiators were destroyed
(by plasma discharges) and the shielding of the
photomultipliers against hard X-rays was found to be
unsatisfactory. Therefore, a new version of the four-
channel measuring head was designed and manufactured
(Fig. 1).
Fig. 1. New measuring head equipped with four
Cherenkov radiators coated with Mo-filters
In the new measuring head the use was made of four
AlN crystals of 10 mm in diameter and 2.5 mm in
thickness. The increased thickness and orientation of the
radiators sides along electron trajectories made possible to
achieve almost 10-times larger effective detection surface.
During the recent experiments the detection of the
Cherenkov signals was performed by means of new
photomultipliers of the XP2010Q type, which ensured the
signal amplification equal to about 107. Those changes
made possible to obtain electron-induced signals, which
were about 2 orders of magnitude higher than those in the
previous measurements. To improve the photomultiplier
shielding against X-rays there was applied a new box
made of lead (Pb) blocks of 5.0 cm in thickness. Another
improvement was the application of the radiators with
Mo-filters deposited by electrical-arc discharges under
high vacuum conditions. It increased the adhesion of the
mailto:lech.jakubowski@ipj.gov.pl
171
Mo-filters to the radiator surfaces. The new measuring
head was fixed upon a movable probe which made
possible to locate the radiators at different position along
the ISTTOK minor radius.
To record hard X-rays (HXR) outside the ISTTOK
chamber the use was made of two measuring heads
equipped with NE102A plastic scintillators of 2.0 cm in
diameter and 1.5 cm in length. Light signals were
transmitted trough separate optical cables to XP1918
photomultipliers placed in another Pb box. The HXR
detectors were placed near the ISTTOK limiter, at a
distance of 20 cm behind the 20-mm-thick copper
chamber wall. One measuring head was additionally
shielded by a copper plate of 10 mm in thickness. An
analysis of differences in X-ray-induced signals from the
both detectors made possible to estimate HXR energies.
All the measuring channels were connected with a data
acquisition system with a 2 MHz probing.
3. EXPERIMENTAL RESULTS
The new measuring head was placed in the ISTTOK
equatorial plane, at a distance of about 20 cm from the
graphite limiter. The data were collected from four
Cherenkov radiators, which were coated with Mo-layers
of 4 (CH1), 19 (CH2), 38 (CH3) and 60 µm (CH4) in
thickness. Hence, the different channels should record
electrons of energies higher than 78, 117, 158 and 198
keV, respectively. Before the probe installation in
ISTTOK all the measuring channels (each consisting of
the Mo-coated radiator, optical cable and photomultiplier
with a supply unit) were tested at an electron accelerator
which delivered electron beams of energy up to 6 MeV.
Unfortunately, the test electron beam destroyed partially
the CH4 channel, which could not be used in further
measurements, but three measuring channels were tested
successfully.
During the experiments within ISTTOK the active
measuring channels could record electrons of energies
higher than about 80 (CH1), 120 (CH2) and 160 keV
(CH3), as shown in Fig. 2.
It should be noted that the three Cherenkov channels
recorded electron beams inside ISTTOK, while the fourth
HXR channel recorded the high-energy X-ray emission
(behind 20-mm-thick ISTTOK Cu-wall), and the fifth one
recorded still harder X-rays (penetrating the ISTTOK wall
and 10-mm-thick Cu-shield). The discharges lasted about
30 ms. The maximum discharge current was about
9.5 kA, and the highest plasma density amounted to about
4×1018 m-3. One can easily notice that electron signals
appeared usually after 2 ms (during the acceleration
phase) and during plasma density disturbances after 10
and 18 ms. Amplitudes and length of the recorded
electron-induced signals depended on discharge
parameters.
To compare the experimental data one can use
signals values integrated over the whole discharge period
(I), as given in Fig. 2. It can be easily seen that the largest
number of fast electrons was recorded in the CH1 (I =
530), while the CH2 and CH3 recorded considerably
lower electron numbers (I = 104 and 34, respectively).
These differences are even stronger when one compares
signals without those from the acceleration phase. It
means that in the run-away emission from ISTTOK is
dominated by electrons of energy below 120 keV.
Examples of HXR signals, which were obtained from
the X-ray measuring heads described above, have also
been presented in Fig. 2. In that case the integrated values
were I = 201 and 87.7, correspondingly. Since, the signals
were recorded behind different Cu-layers (20 and 30 mm,
respectively), it was possible to compute the absorption
coefficient, which might be determined from the simple
relation µ(E) =ln (I1/I2)/ (d2-d1), where is the copper
density, d2 and d1 are thicknesses of the applied copper
filters. The obtained µ(E) corresponded to X-rays of
energy equal to about 400 keV. That energy value
characterized X-rays measured behind thick Cu-filters and
corresponded to a high-energy tail of the Maxwellian
distribution of the X-ray emission.
It should be noted that temporal shapes of the
electron-induced and X-ray signals were very similar,
what was confirmed by a comparison of time-extended
traces. Similarity of these signals and their good temporal
correlations suggested that HXR was probably generated
by interactions of the fast electron beams with the limiter
and chamber walls.
Investigation of the run-away electrons within
ISTTOK was performed by means of the new Cherenkov
measuring head at different positions on the minor radius
of the experimental chamber. Those measurements were
carried out under different experimental conditions, e.g. at
various initial pressures. The obtained results were very
similar to those recorded for p0 = 0.9×10-4 mbar, which
are shown in Fig. 3.
Fig. 2. Comparison of electron-induced signals (CH1,
CH2 and CH3), hard X-rays (Xray1 and X-ray2) with
discharge current and plasma density traces
Fig. 3. Fluency of fast electrons (CH1) and X-rays
(a.u.) determined as a function of the Cherenkov probe
position. For a comparison there are shown changes
in X-ray energies (X-ray-en)
172
The diagram showed the maximum electron fluency
at r = 60…65 mm, but one should note that the deeper
insertion of the probe disturbed the plasma column. The
HXR1 and HXR2 signals became weaker when the probe
was shifted into the plasma region. In contrary, changes in
the HXR energy value showed a weak dependence on the
Cherenkov probe position. In the presented case the
computed HXR energy changed from about 300 to about
400 keV. It should be added that the maximum fast-
electron fluency, which was investigated as a function of
the initial pressure p0 at the constant probe position at r =
65 mm, was observed at po = 1.0×10-4 mbar. The same
referred to the HXR emission.
On the basis of the measurements described above it
was possible to estimate energy spectra of the runaway
electrons, as shown in Fig. 4.
It can be easily seen that the largest population of the
fast electrons has energies below 120 keV.
4. SUMMARY AND CONCLUSIONS
Although the Mo-filters on the Cherenkov radiators
have been partly destroyed during a series of ISTTOK
shots, the qualitative estimations of the measurements
seem to be reasonable. The use of the modernized
Cherenkov measuring head (with thicker AlN radiators)
and improved detection systems in ISTTOK enabled new
data about run-away electrons to be collected. It was
found that: 1 - the most run-away electrons have energies
below 120 keV, 2 – electron populations in higher energy
ranges is considerably smaller, 3 - the HXR radiation
outside the tokamak chamber has energy in the range of
300…400 keV. This radiation is well correlated with the
run-away emission, it is probably produced by
interactions of the fast electrons with the limiter and the
chamber walls, and it evidently corresponds to the high-
energy tail of the energy distribution. The maximum
emission of the run-away electrons (as well as HXR)
appears at p0 = 1.0×10-4 mbar. A dependence of the run-
away production on other ISTTOK parameters requires
further investigation.
ACKNOWLEDGEMENTS
This work was supported by European Atomic Energy
Community as well as by the Ministry of Science and
Higher Education, Poland, and Fundacao para a Ciencia e
a Tecnologia (FCT), Portugal.
REFERENCES
1. R. Jaspers, K.H. Finken, G. Mank, et al. Observation of
relativistic runaway electrons by synchrotron radiation
in TEXTOR// Proc. ICPP-1992. Innsbruck, Austria,
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2. M.J. Sadowski, L. Jakubowski, A. Szydlowski.
Adaptation of selected diagnostic techniques to
magnetic confinement fusion experiments// Czech. J.
Phys. Suppl. C. 2004, v. 54, p. C74-C81.
3. V.V. Plyusnin, L. Jakubowski, J. ebrowski, et al. Use
of Cherenkov-type detectors for measurements of
runway electrons in the ISTTOK tokamak// Rev. Sci.
Instrum. 2008, v. 79, p. 10F505.
4. L. Jakubowski, K. Malinowski, J. ebrowski, et al.
Study of electron beams within ISTTOK tokamak by
means of a multi-channel Cherenkov detector; their
correlation with hard x-rays // Nucl. Instr. Meth. A.
2010, v. 623(2), p. 689.
Article received 13.09.10.
ISTTOK
L. Jakubowski, V.V. Plyusnin, K. Malinowski, M.J. Sadowski, J. ebrowski,
M. Rabi ski, H. Fernandes, C. Silva, P. Duarte, M. Jakubowski
, ISTTOK,
,
(AlN) 10 2,5 .
,
ISTTOK. (Mo) ,
.
ISTTOK .
, .
ISTTOK
L. Jakubowski, V.V. Plyusnin, K. Malinowski, M.J. Sadowski, J. ebrowski,
M. Rabi ski, H. Fernandes, C. Silva, P. Duarte, M. Jakubowski
, ISTTOK,
, (AlN)
10 2,5 . ,
ISTTOK. (Mo)
, ,
. ISTTOK
. , .
Fig. 4. Electron energy spectra estimated for different
positions of the Cherenkov measuring head
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