High pressure plasma confinement and stability in gas dynamic trap
The paper reviews recent results obtained in the studies of high beta plasma confinement in Gas-Dynamic Trap (GDT) device. Successful application of Ti -gettering and increase of NB injection power and duration enable to obtain a plasma as high as 30%. Enery balance and stability of this high beta p...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2000
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| Цитувати: | High pressure plasma confinement and stability in gas dynamic trap / A.A. Ivanov, A.V. Anikeev, P.A. Bagryansky, A.N. Karpushov, S.A. Korepanov, V.N. Kornilov, A.A. Lizunov, V.V. Maximov, S.V. Murakhtin // Вопросы атомной науки и техники. — 2000. — № 3. — С. 51-53. — Бібліогр.: 6 назв. — англ. |
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irk-123456789-823682015-05-30T03:01:37Z High pressure plasma confinement and stability in gas dynamic trap Ivanov, A.A. Anikeev, A.V. Bagryansky, P.A. Karpushov, A.N. Korepanov, S.A. Kornilov, V.N. Lizunov, A.A. Maximov, V.V. Murakhtin, S.V. Мagnetic Confinement The paper reviews recent results obtained in the studies of high beta plasma confinement in Gas-Dynamic Trap (GDT) device. Successful application of Ti -gettering and increase of NB injection power and duration enable to obtain a plasma as high as 30%. Enery balance and stability of this high beta plasma with a density of ~3 10¹³ cm⁻³ were thoroughly studied. Confinement of more dense plasma with steeper density gradients was also studied in the experiment with on-axis gas puff in the central cell. 2000 Article High pressure plasma confinement and stability in gas dynamic trap / A.A. Ivanov, A.V. Anikeev, P.A. Bagryansky, A.N. Karpushov, S.A. Korepanov, V.N. Kornilov, A.A. Lizunov, V.V. Maximov, S.V. Murakhtin // Вопросы атомной науки и техники. — 2000. — № 3. — С. 51-53. — Бібліогр.: 6 назв. — англ. 1562-6016 http://dspace.nbuv.gov.ua/handle/123456789/82368 533.9 en Вопросы атомной науки и техники 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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English |
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Мagnetic Confinement Мagnetic Confinement |
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Мagnetic Confinement Мagnetic Confinement Ivanov, A.A. Anikeev, A.V. Bagryansky, P.A. Karpushov, A.N. Korepanov, S.A. Kornilov, V.N. Lizunov, A.A. Maximov, V.V. Murakhtin, S.V. High pressure plasma confinement and stability in gas dynamic trap Вопросы атомной науки и техники |
| description |
The paper reviews recent results obtained in the studies of high beta plasma confinement in Gas-Dynamic Trap (GDT) device. Successful application of Ti -gettering and increase of NB injection power and duration enable to obtain a plasma as high as 30%. Enery balance and stability of this high beta plasma with a density of ~3 10¹³ cm⁻³ were thoroughly studied. Confinement of more dense plasma with steeper density gradients was also studied in the experiment with on-axis gas puff in the central cell. |
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Article |
| author |
Ivanov, A.A. Anikeev, A.V. Bagryansky, P.A. Karpushov, A.N. Korepanov, S.A. Kornilov, V.N. Lizunov, A.A. Maximov, V.V. Murakhtin, S.V. |
| author_facet |
Ivanov, A.A. Anikeev, A.V. Bagryansky, P.A. Karpushov, A.N. Korepanov, S.A. Kornilov, V.N. Lizunov, A.A. Maximov, V.V. Murakhtin, S.V. |
| author_sort |
Ivanov, A.A. |
| title |
High pressure plasma confinement and stability in gas dynamic trap |
| title_short |
High pressure plasma confinement and stability in gas dynamic trap |
| title_full |
High pressure plasma confinement and stability in gas dynamic trap |
| title_fullStr |
High pressure plasma confinement and stability in gas dynamic trap |
| title_full_unstemmed |
High pressure plasma confinement and stability in gas dynamic trap |
| title_sort |
high pressure plasma confinement and stability in gas dynamic trap |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2000 |
| topic_facet |
Мagnetic Confinement |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/82368 |
| citation_txt |
High pressure plasma confinement and stability in gas dynamic trap / A.A. Ivanov, A.V. Anikeev, P.A. Bagryansky, A.N. Karpushov, S.A. Korepanov, V.N. Kornilov, A.A. Lizunov, V.V. Maximov, S.V. Murakhtin // Вопросы атомной науки и техники. — 2000. — № 3. — С. 51-53. — Бібліогр.: 6 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
UDC 533.9
Problems of Atomic Science and Technology. 2000. N 3. Series: Plasma Physics (5). p. 51-53 51
Fig.1 The GDT layout: 1-central cell vacuum vessel; 2-expander end tank; 3-cusp end tank; 4-end tank; 5-mirror coils; 6-
cusp coils; 7- central cell coils; 8-plasma gun; 9-additional plasma gun; 10-plasma dump; 11-neutral beam injectors; 12-
beam dumps; 13-first wall liner; 14-expander coils; 15-cryopumps; 16-Ti-getter pumps.
HIGH PRESSURE PLASMA CONFINEMENT AND STABILITY IN GAS
DYNAMIC TRAP
A.A. Ivanov, A.V. Anikeev, P.A. Bagryansky, A.N. Karpushov, S.A. Korepanov, V.N.Kornilov,
A.A. Lizunov, V.V. Maximov, S.V. Murakhtin
Budker Institute of Nuclear Physics, Prospect Lavrent'eva 11, 630090, Novosibirsk, Russia
The paper reviews recent results obtained in the studies of high beta plasma confinement in Gas-Dynamic Trap
(GDT) device. Successful application of Ti -gettering and increase of NB injection power and duration enable to
obtain a plasma as high as 30%. Enery balance and stability of this high beta plasma with a density of ~3 1013 cm-3
were thoroughly studied. Confinement of more dense plasma with steeper density gradients was also studied in the
experiment with on-axis gas puff in the central cell.
INTRODUCTION
One of the key issues to be studied in the
experiments on GDT device is the MHD and micro-
stability of multi-component plasma with high β. It is
essential that for the GDT-based neutron source plasma
confinement is to be nearly classical one. Successful
application of Ti -gettering and increase of NB injection
power and duration provided excess to obtaining plasma
with β value as high as 30%. It enable us to study
plasma energy balance and stability in these regimes
with a bulk plasma density of ~3 1013 cm-3 and fast ion
density of up to 1013 cm-3 in the turning points and
compare the plasma parameters with the code
predictions. Additionally, confinement of more dense
plasmas with steeper density gradients was studied in
the experiment with on-axis gas puff in the central cell.
EXPERIMENTAL SETUP
The experimental setup is schematically shown in
Fig.1. The vacuum chamber consists of a cylindrical
central cell 7 m long and 1 m in diameter (1) and two
expander tanks attached to the central cell at both ends
(2,3). GDT has an axisymmetric magnetic field
configuration that is produced by a set of coils
mounted on the vacuum chambers (4). Both mirror
coils of the GDT are composed of two parts inserted
one into another (5). The outer coil is supplied in
series with central cell coils whereas the inner coil is
powered independently and produces an additional field
of up to 10 T. These inserts provide a variable mirror
ratio ranging from 12.5 to 100 when the central
magnetic field is set to be up to 0.22 T.
In the recent years remote anchor cells of two
different types were experimentally tested. The first is
an expander end cell in which the plasma from the
mirror throat freely expands along decreasing magnetic
field to the end walls. By energizing the proper coils of
the end tank we were able to perform experimental runs
that switched between expander and cusp end cell
configurations without opening the device to air.
Plasma start-up is initiated by injection of the
hydrogen plasma along the field lines from one end
during ~2.9 ms by making use of a gas-puffed washer-
stack plasma gun installed inside the end tank.
Subsequently, the target plasma column with an initial
temperature of 3−5 eV and a density of 6−20×1013 cm-
3 is heated up by the Neutral Beam injection which at
the same time provides the fast ions. The total time of
plasma gun operation is up to 4.0 ms. an additional
plasma gun was installed behind the cusp end cell to
vary the plasma parameters in the cusp independently. A
more detailed description of the GDT device is given
in [1-4]. The GDT NB-system consists of six injectors
that are azimutally arranged in two groups on opposite
sides of the central cell. The azimuthal angle between
the injectors of one group is 300. The neutral beams are
injected at 450 to the axis. The current of each neutral
beam amounts to 48-55 equivalent Amps, the energy of
neutrals is in the range of 12.5−17.5 keV, the duration
of the NB pulse is 1−1.2 ms, and the total injected
power exceeds 4 MW. The angular divergence of the
neutral beams is: α⊥≈10 in the direction perpendicular
to the machine axis, and α| | ≈2.50 along the axis. In
order to
decrease the charge-exchange losses of fast ions it is
essential to reduce the neutral gas recycling at the
chamber wall.
52
FAST ION RELAXATION AND CONFINEMENT
Hot ion confinement in high-ß regimes was studied
by comparison of the global and local parameters of the
fast ions measured experimentally with those predicted
by computer simulations. To realize this approach a
self-sufficient set of diagnostic methods for studying
the fast ions has been developed [5]. As an example of
application of this approach, Fig. 2, 3 show calculated
and measured parameters of the fast ions in the GDT
central cell. The fast ion energy and angular
distributions were inferred from the energy spectrum
of charge-exchange neutrals with spatial resolution of
~4 cm. For comparison the results of FIT [5] code
simulation are also shown.
The experimental data and estimated values of the
fast ion angular spread for the given experimental
conditions are presented in
Fig. 2 as functions of ion energy. These data allow
to conclude that the measured angular spread of the
ions is quite well explained by their Coulomb
interaction with the bulk plasma particles. From this
observation it can be further concluded that within the
measurements accuracy (~15%) micro-instabilities
which could cause significant additional scattering of
fast ions were not yet observed in GDT experiment in
these high beta shots.
The global energy distribution functions of the fast
ions were obtained by integration of experimentally
measured functions over pitch-angles and the central
cell volume. These are shown in Fig. 3 as measured
during and after the NB injection. It is seen that the
distribution evolves over time so that ions accumulate
in the low energy range as provided by the dominant
process of the ion slowing down on bulk plasma
electrons. Comparison of these distributions with those
simulated by the numerical codes show that losses to
the radial limiters and to the loss cone are not
significant. Classical character of the fast ion
relaxation in high-β plasma was also confirmed by the
measurements of the angular distributions of the fast
ions shown in Fig. 4 together with the distributions
simulated by the FIT code. Note that the angular spread
at high energy (14-18 keV) is close to that in the main
NBs. The angular spread of the ions with energies 3-
5 keV was approximately 3 times larger than that for
the injection energy. Therefore the conclusion can be
drawn that confinement of the fast ions is good enough
that was also confirmed by measurements of their
energy balance which are summarized in the table.
Fast ion energy content, within the measurement
accuracy (about 15%), is in reasonable agreement with
the simulation results and do not exhibit any significant
differences compared to the case of low β shots.
Generally, the measurements indicate that the fast
ions have relatively narrow angular spread. Therefore
the longitudinal fast ion density profile (and the
resulted neutron flux) is to be peaked near the turning
points. This is one of the basic features of the GDT-
based neutron source [6]. This peaking was additionally
studied by the measurements of axial profile of D-D
fusion products in the shots with deuterium neutral
beams with the energy 13-17 keV and total power up to
3 MW. It was observed that the decay time of
accumulated fast deuterons is ~1.5 time longer than for
H+ ones. The fusion products (2.45 MeV neutrons and
3.02 MeV protons) emission were measured by an
array of scintillation detectors equipped with
retractable collimators. While not collimated the
detector sees ~2π solid angle. When collimated by a
mask with slits oriented perpendicularly to the machine
axis, the detector essentially measures the DD proton
linear specific yield with a spatial resolution ~ 20 cm.
The measured proton flux profile is presented in Fig. 5
in which the estimated flux for 30 angular spread of the
fast D+ ions is also shown for comparison. Reasonable
agreement between experiment and simulation results
was noted that is considered to be an additional
important argument supporting the main conclusions
about classical character of fast ion relaxation in the
GDT-experiment with high-ß plasma.
The hot ions with maximum density of about 1013
cm-3 and mean ion energy of about 8 keV was produced
in GDT with the 4 MW neutral beam injection. At the
same time plasma ß reaches almost 30%.
GLOBAL ENERGY BALANCE OF THE HIGH-β
TWO-COMPONENT PLASMA
The results of the global energy balance studies for
high-β regimes at 0.6 ms after NBI start shown that
about 60% of injected fast atoms were trapped and
transformed into sloshing ions. The dominant fast ions
energy losses channel was electron drag. The main
channel of the plasma energy losses was the
longitudinal losses through the mirrors (43% of
electron drag power). The losses to the limiters were
about 26%. Heat sink to the plasma gun muzzle (27%)
significantly contributes to the energy losses in near-
axis region.
The following conclusions can be drawn from the
measured energy balance measurements in the high-β
shots:
• fast ions energy losses are dominated by classical
Parameter Value
NB injected power 3.1−3.7 MW
Trapped power 1.6−2.2 MW
Fast ion energy contents 520−650 J
Charge-exchange losses 150±30 kW
Losses to loss cone <50 kW
Electron drag power: 1.15±0.1 MW
in plasma core ~930 kW
in plasma halo ~220 kW
Energy confinement time:
global energy balance data 550−750 µs
test ions relaxation [7] 774±36 µs
estimated value ~700 µs
Fast ion energy balance data
53
electron drag and charge-exchange losses as it was
previously measured in low plasma-β regimes;
• the measurements of the angular and energy
distribution functions are explained quite well by
Coulomb interaction with the target plasma particles;
• enhanced scattering or energy losses due to micro-
instabilities were not observed in the GDT experiment;
• for electron temperatures ~100 eV the energy
losses from the target plasma are increased in the near-
axis region presumably due to heat sink to plasma gun
located in the expander;
• for the radii 8-12 cm longitudinal losses from the
target plasma are dominated by collisional outflux
through the mirrors;
• the measured transverse lifetime of the plasma
exceeds 40 Bohm transverse lifetime.
CONCLUSIONS
Confinement of a plasma β in GDT central cell
with beta up to 30% was studied. Measurements of
local distribution of fast ions over energies and pitch
angels indicate that there were no noticeable anomalies
in fast ion slowing down and scattering. For mirror
ratio of 12.5, energy losses from the target plasma are
dominated by longitudinal ones. With increasing mirror
ratio to 45 it was observed that energy lifetime of the
target plasma is about 2 time less than that determined
by longitudinal losses through the mirrors. Additional
channel of energy losses can be characterized by
corresponding lifetime which is estimated to be ≈ 30-
40 Bohmτ for the representative shot parameters.
In this estimate of the effective plasma
temperature is calculated including contribution from
fast ions. Exact mechanism of enhanced transverse
losses is not identified so far. It is believed that the
extra energy losses during NB injection would be
caused by residual asymmetry of beam current of
injectors installed at different azimuths that still exists.
Nevertheless, it should be emphasized that these losses
are tolerable when scaled to the operational parameters
of the GDT-based neutron source [6].
REFERENCES
1. A.A.Ivanov, A.V.Anikeev, P.A.Bagryansky, et al, Phys.
Plasmas, 1(5),p.1529(1995)
2. A.V. Anikeev, P.A. Bagryansky, P.P. Deichuli, et al,
Phys. of Plasmas, v.4(2), pp.347-354 (1997)
3. P.A.Bagryansky, E.D.Bender, A.A.Ivanov,
A.N.Karpushov, S.V.Murakhtin, K.Noack, St.Krahl, S.Collatz,
J. Nucl. Mat. No.265/1-2, p.p.124-133 (1999)
4. A.V.Anikeev, P.A.Bagryansky, A.A.Ivanov,
A.N.Karpushov, S.A.Korepanov, V.V. Maximov, S.V.
Murakhtin, A.Yu. Smirnov, K. Noack, G. Otto, Nuclear Fusion,
Vol.40, No. 4, pp.753-765 (2000)
5. K.Noack, G.Otto, S.Collatz, Transactions of Fusion
Technology, Vol. 35, No 1T, p.p. 218-222 (1999).
6. A.A.Ivanov, D.D.Ryutov, Nucl. Sci. and Eng., v.106, p.235
(1990)
Fig. 4. Angular distribution of fast ions for various
energy intervals at 0.6-0.9 ms
Fig. 5. Axial profile of 3.02 MeV proton flux
Fig. 2. Angular spread of fast ions vs. energy
Fig. 3. Global energy distribution functions
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