An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam
The active charge exchange technique based upon Secondary Charge Exchange effect (SCX) is proposed for safety factor measurements in ITER. The performed numerical modeling shows that measurements of the magnetic pitch angle are possible up to the plasma center with radial resolution of 5 cm and in...
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| Опубліковано в: : | Вопросы атомной науки и техники |
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| Дата: | 2006 |
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| Мова: | Англійська |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2006
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| Цитувати: | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam / A.A. Medvedev, V.S. Strelkov // Вопросы атомной науки и техники. — 2006. — № 3. — С. 107-109. — Бібліогр.: 7 назв. — англ. |
Репозитарії
Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859471586957983744 |
|---|---|
| author | Medvedev, A.A. Strelkov, V.S. |
| author_facet | Medvedev, A.A. Strelkov, V.S. |
| citation_txt | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam / A.A. Medvedev, V.S. Strelkov // Вопросы атомной науки и техники. — 2006. — № 3. — С. 107-109. — Бібліогр.: 7 назв. — англ. |
| collection | DSpace DC |
| container_title | Вопросы атомной науки и техники |
| description | The active charge exchange technique based upon Secondary Charge Exchange effect (SCX) is proposed for
safety factor measurements in ITER. The performed numerical modeling shows that measurements of the magnetic
pitch angle are possible up to the plasma center with radial resolution of 5 cm and integration time of about
10 ms. A systematic inaccuracy amounts several milliradians. An important advantage of SCX technique is the
possibility of direct pitch angle measurements.
Активная корпускулярная методика, основанная на эффекте вторичной перезарядки (SCX), предлагается для измерения коэффициента запаса устойчивости в ITER. Проведенное численное моделирование показывает, что измерения магнитного питч-угла возможны вплоть до центра плазмы с радиальным разрешением 5 см и временем накопления информации около 10 мс. Систематическая ошибка составляет несколько миллирадиан. Важным достоинством методики является возможность проведения прямых измерений питч-угла.
Активна корпускулярна методика, заснована на ефекті вторинного перезарядження (SCX),
пропонується для виміру коефіцієнта запасу стійкості в ІTER. Проведене чисельне моделювання показує,
що виміри магнітного пітч-кута можливі аж до центра плазми з радіальним розділом 5 см і часом
накопичування інформації близько 10 мс. Систематична помилка становить кілька мілірадіан. Важливим
достоїнством методики є можливість проведення прямих вимірів пітч-кута.
|
| first_indexed | 2025-11-24T09:52:11Z |
| format | Article |
| fulltext |
AN ACTIVE CHARGE –EXCHANGE q MEASUREMENTS IN ITER
BASED UPON THE DIAGNOSTIC HYDROGEN BEAM
A.A. Medvedev, V.S. Strelkov
Russian Research Center 'Kurchatov Institute'
Kurchatov Sq. 1, Moscow, 123182, Russian Federation
E-mail: medvedev@nfi.kiae.ru
The active charge exchange technique based upon Secondary Charge Exchange effect (SCX) is proposed for
safety factor measurements in ITER. The performed numerical modeling shows that measurements of the mag-
netic pitch angle are possible up to the plasma center with radial resolution of 5 cm and integration time of about
10 ms. A systematic inaccuracy amounts several milliradians. An important advantage of SCX technique is the
possibility of direct pitch angle measurements.
PACS: 52.55.Fa; 52.70.-m
1. INTRODUCTION
Development of a technique for safety factor (q)
measurements is one of the most important and compli-
cated problems to be solved by the ITER diagnostic
community. There are a number of serious technical
problems limiting use of existed techniques at the reac-
tor relevant conditions. It compels to develop new ap-
proaches. The techniques considered in this paper can
be treated as one of them.
Fig.1 Experimental Geometry. Fig.1. Experimental geometry
The secondary charge exchange (SCX) atoms were
originally revealed during experiments on T-101. At the
same time it was proposed to use the phenomenon for q
measurements in a tokamak. Later an unfortunate at-
tempt of SCX atoms detection was made on TEXT2.
Authors know nothing about SCX experiments on
present tokamaks. In 1999-2002 renewed experiments
on T-10 proved that the technique is perspective for q
measurements in magnetic confinement plasmas3.
There are papers devoted to a similar active charge
exchange diagnostic for the plasma magnetic structure
investigation4,5,6. The approach mentioned in these pa-
pers substantially differs from SCX, as it is based on de-
tection of E/2 atoms that originate at the dissociation of
beam molecules. The SCX flux are treated in the paper-
s5,6 only as a background embarrassed measurements. It
should be noted, that use of the molecular dissociation
for measurements in the reactor is hopeless due to
strong attenuation of the molecular fraction in large
dense plasmas. Besides, the diagnostic injector of ITER
supposed to be built on the basis of negative ion source;
hence the molecular fraction of the beam is negligible.
2. PHYSICAL BASIS OF THE TECHNIQUE
The experimental geometry is exhibited in Fig.1.
The hydrogen beam (DNB) is injected along the major
radius of the machine. At this geometry the axis of the
beam is directed normally to all the flux surfaces. At in-
teractions (ionization and charge exchange) beam atoms
with plasma particles ions having energy equal to that of
the beam atoms are borne. If an ion has no longitudinal
(in relation to the magnetic field direction) velocity, the
particle gyrates along the Larmour circle. Since at least
a part of the ion’s trajectory is in the beam volume, the
ion can be charge exchanged with a beam atom. The
originated fast atom will escape plasma along straight
trajectory directed normally to the magnetic field line.
In such a manner, measuring the prevailing direction of
SCX atoms’ escape, one can get information about mag-
netic pitch angle that is immediately connected with the
safety factor (q).
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.107-109.
107
In reality, the fast ions, originated at the beam –
plasma interaction, may have some longitudinal velocity
due to the beam divergence and the transfer of the mo-
mentum at the ionization. Hence, the ions will move
along spiral trajectories. The lifetime of an ion inside
the beam volume depends on drift velocity and width of
the beam and is, in the considered condition, significant,
that leads to ‘accumulation’ of the fast ions. Their densi-
ty is well over than that of the beam atoms. The more
the longitudinal velocity of an ion the less it’s lifetime
inside the beam target, and, consequently, less the prob-
ability to be charge exchanged. That is why, the effec-
tive width of SCX atoms’ angle distribution, is signifi-
cantly less than that of the initial fast ions. The narrow
angle distribution enables to get low systematical error
of the measured pitch angle value. The trajectories of
the SCX atoms, which were borne at the same point, are
practically in one plane. That is why, the specific flux of
the particles is detectable in spite of its strong attenua-
tion in plasma.
3. RESULTS OF SIMULATIONS
At numerical simulation we modeled generation and
movement of the fast ions, charge exchange of the fast
ions with the beam atoms, attenuation of the SCX
atoms’ outflux. Besides, values of the background sig-
nals due to charge exchange of the thermalized plasma
ions both with residual neutrals and with beam atoms
were calculated. We used the plasma parameters for one
of the main scenarios of ITER performance:
Te(0)=Ti(0)=15 keV; ne=1014 cm-3; Bt=5 T; partial con-
tent of the hydrogen in plasma 5%. The used parameters
of the hydrogen beam are the following: energy of
atoms 100 keV; equivalent current 20 A; dimensions –
30×30 cm; effective divergence 7 mrad. It was supposed
that dimensions of the observation are (toroidal×radial)
10×5 cm, and detectors are arranged at 10 m from the
first wall.
The attenuation of the beam was calculated using an
effective beam-stopping cross-section that takes into ac-
count ionization at electron impact and interactions
(ionization and charge exchange) at the collisions with
hydrogen and main impurities (He, C) ions7. The densi-
ty of the residual hydrogen atoms was computed by
means of a 1D penetration code.
Fig.2 Profiles of densities of atoms
and fast ions.
Fig.2. Profiles of densities of atoms and fast ions
For the fast ions’ density calculations one has to
know the shape of their initial distribution on angle be-
tween velocity vector and magnetic field direction. This
width of the distribution, besides, strongly influences
the systematical error of the measurements. Three main
processes that determine the angle distribution are the
following: the divergence of the diagnostic beam, the
momentum transfer at the ionization, and scattering at
the plasma charged particles. The performed analysis
showed, that the main factor is the divergence of the
beam. In Fig.2 the densities of the beam and residual
atoms, as well as the concentration of the fast ions, are
shown.
Fig.3 shows the specific densities of the SCX and
background fluxes as function of the radial position
(robs) of the observed area for the beam energy 100 keV.
Fig.3 Dependencies of SCX and
background signals on radial position of
the observation region. Eb=100 keV.
Fig.3. Dependencies of SCX and background signals on
radial position of the observation region. Eb=100 keV
We supposed that the background fluxes of atoms
having this energy originated from the charge exchange
of the thermalized plasma ions both with residual neutrals
(‘passive’ background) and with beam atoms (‘active’
background). It is seen, that as the value of the ‘passive’
signal is negligible, and the ‘active’ one becomes consid-
erable for the plasma core. However, since signal-to-
noise ratio is nearly proportional to exp (-Ti/Eb), here Eb –
is the energy of the beam, Ti – ion temperature, this ratio
can be drastically improved by increasing of the beam
energy (Fig.4). The picture shows that growing of the
beam energy from 100 to 200 keV leads both to im-
provement of signal-to-noise ratio and to gain of the
SCX signal. The further increase of Eb is inexpedient
due to fast drop of the charge exchange cross-section
that leads to decrease of the SCX flux.
Fig.4 SCX and background signals versus the
beam energy. robs=0.
Fig.4. SCX and background signals versus the beam en-
ergy. robs=0
108
The systematical error of the pitch angle measure-
ments is determined by the width of the SCX atom's an-
gle distribution. The effective width of the distribution
practically does not depend on that of the fast ions and
does not exceed 5⋅10-3 rad (Fig.5).
Fig.5. The fast ions’ and SCX atoms densities versus the
angle between observation line and plane normal to
magnetic field direction. Dashed curves refers to ions,
solid ones to SCX atoms
It is due to reduce of the fast ions' lifetime inside the
beam target at the increase of the longitudinal velocity
component. It means that if the pitch angle is about 0.2
rad, we can get relative error less than few per cent. But,
it should be noted, that at large angle dispersion of fast
ions (e.g. due to inaccurate beam alignment) the friendly
signal drops, and, consequently, the statistical error of
the measurements rises.
4. CONCLUSION
A novel active charge exchange technique for q
measurements in ITER is proposed. A preliminary feasi-
bility study allows one to make the following conclu-
sions:
• The technique enables to carry out direct measure-
ments of the magnetic pitch angle. No sophisticated
data processing and calibration procedures are
needed.
• For a typical discharge scenario signal value is
enough for measurements down to ρ=0; signal to
background ratio in the plasma core is acceptable at
the beam energy of 100 keV and exceeds 104 at the
optimum Eb (200…250 keV).
• Lowest systematical error, can be achieved not ex-
ceed 0.005 rad.
• At the optimum Eb the temporal resolution of 10 ms
and the radial resolution of 5 cm seem to be achiev-
able for measurements in the plasma core.
REFERENCES
1. E.L. Berezovskij, S.L. Efremov, A.B. Izvozchikov
et al. Plasma Diagnostics. M.: “Energoatomizdat”,
Ed.5, 1986, p.157 (in Russian).
2. P.M. Valanju, L. Duraiappah, Roger D.Bengtson et
al. // Rev. of Sci. Instrum. 1995, v.66(1), p.369.
3. A.A. Medvedev, V.S. Strelkov. Advanced Diagnos-
tics for Magnetic and Inertial Fusion, Edited by
Stott et al. New York, Kluwer Academic/Plenum
Publishers, 2002, p.79-86.
4. F.C. Jobes. Proc. of the 2-nd Topical Conf. on
High-Temperature Plasma Diagnostics, Santa Fe.
1978, LA-7160-C, p.101.
5. V.I.Afanasiev et al. // Pis’ma v ZhETF. 1989, v.50,
№11, p.453 (in Russian).
6. W. Hermann // Plasma Phys. Contr. Fusion. 1990,
v.32, p.605.
7. R.K. Janev et al. // Nucl. Fusion. 1989, v.29, №12.
АКТИВНЫЕ КОРПУСКУЛЯРНЫЕ ИЗМЕРЕНИЯ q В ITER НА БАЗЕ ДИАГНОСТИЧЕСКОГО ВО-
ДОРОДНОГО ПУЧКА
А.А. Медведев, В.С. Стрелков
Активная корпускулярная методика, основанная на эффекте вторичной перезарядки (SCX), предлага-
ется для измерения коэффициента запаса устойчивости в ITER. Проведенное численное моделирование
показывает, что измерения магнитного питч-угла возможны вплоть до центра плазмы с радиальным раз-
решением 5 см и временем накопления информации около 10 мс. Систематическая ошибка составляет
несколько миллирадиан. Важным достоинством методики является возможность проведения прямых из-
мерений питч-угла.
АКТИВНІ КОРПУСКУЛЯРНІ ВИМІРИ q В ІTER НА БАЗІ ДІАГНОСТИЧНОГО
ВОДНЕВОГО ПУЧКА
А.А. Медведев, В.С. Стрелков
Активна корпускулярна методика, заснована на ефекті вторинного перезарядження (SCX),
пропонується для виміру коефіцієнта запасу стійкості в ІTER. Проведене чисельне моделювання показує,
що виміри магнітного пітч-кута можливі аж до центра плазми з радіальним розділом 5 см і часом
накопичування інформації близько 10 мс. Систематична помилка становить кілька мілірадіан. Важливим
достоїнством методики є можливість проведення прямих вимірів пітч-кута.
____________________________________________________________
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2006. № 3.
Series: Nuclear Physics Investigations (47), p.107-109.
109
2. Physical basis of the technique
3. Results of simulations
REFERENCES
|
| id | nasplib_isofts_kiev_ua-123456789-79733 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1562-6016 |
| language | English |
| last_indexed | 2025-11-24T09:52:11Z |
| publishDate | 2006 |
| publisher | Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| record_format | dspace |
| spelling | Medvedev, A.A. Strelkov, V.S. 2015-04-04T12:31:31Z 2015-04-04T12:31:31Z 2006 An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam / A.A. Medvedev, V.S. Strelkov // Вопросы атомной науки и техники. — 2006. — № 3. — С. 107-109. — Бібліогр.: 7 назв. — англ. 1562-6016 PACS: 52.55.Fa; 52.70.-m https://nasplib.isofts.kiev.ua/handle/123456789/79733 The active charge exchange technique based upon Secondary Charge Exchange effect (SCX) is proposed for safety factor measurements in ITER. The performed numerical modeling shows that measurements of the magnetic pitch angle are possible up to the plasma center with radial resolution of 5 cm and integration time of about 10 ms. A systematic inaccuracy amounts several milliradians. An important advantage of SCX technique is the possibility of direct pitch angle measurements. Активная корпускулярная методика, основанная на эффекте вторичной перезарядки (SCX), предлагается для измерения коэффициента запаса устойчивости в ITER. Проведенное численное моделирование показывает, что измерения магнитного питч-угла возможны вплоть до центра плазмы с радиальным разрешением 5 см и временем накопления информации около 10 мс. Систематическая ошибка составляет несколько миллирадиан. Важным достоинством методики является возможность проведения прямых измерений питч-угла. Активна корпускулярна методика, заснована на ефекті вторинного перезарядження (SCX), пропонується для виміру коефіцієнта запасу стійкості в ІTER. Проведене чисельне моделювання показує, що виміри магнітного пітч-кута можливі аж до центра плазми з радіальним розділом 5 см і часом накопичування інформації близько 10 мс. Систематична помилка становить кілька мілірадіан. Важливим достоїнством методики є можливість проведення прямих вимірів пітч-кута. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Ускорители заряженных частиц An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam Активные корпускулярные измерения q в ITER на базе диагностического водородного пучка Активні корпускулярні виміри q в ІTER на базі діагностичного водневого пучка Article published earlier |
| spellingShingle | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam Medvedev, A.A. Strelkov, V.S. Ускорители заряженных частиц |
| title | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam |
| title_alt | Активные корпускулярные измерения q в ITER на базе диагностического водородного пучка Активні корпускулярні виміри q в ІTER на базі діагностичного водневого пучка |
| title_full | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam |
| title_fullStr | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam |
| title_full_unstemmed | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam |
| title_short | An active charge –exchange q measurements in ITER based upon the diagnostic hydrogen beam |
| title_sort | active charge –exchange q measurements in iter based upon the diagnostic hydrogen beam |
| topic | Ускорители заряженных частиц |
| topic_facet | Ускорители заряженных частиц |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/79733 |
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