RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron
In the l=3 Uragan-3M torsatron a hydrogen plasma with the density ¬ne ~ 2×10¹² cm⁻³ is produced and heated by RF fields in the ω ≤ ωсi range of frequencies with using a frame-like antenna. Time variations are considered of (1) density ne and electron cyclotron emission at different values of the RF...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2012
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| Цитувати: | RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron / V.V. Chechkin, I.M. Pankratov, L.I. Grigor’eva, А.А. Beletskii, A.A. Kasilov, P.Ya. Burchenko, А.V. Lozin, S.А. Tsybenko, А.S. Slavnyj, A.P. Litvinov, А.Ye. Kulaga, R.O. Pavlichenko, N.V. Zamanov, Yu.K. Mironov, V.S. Romanov, V.K. Pashnev, S.M. Maznichenko, Ye.D. Volkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 3-7. — Бібліогр.: 19 назв. — англ. |
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irk-123456789-1090812018-03-21T12:35:10Z RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron Chechkin, V.V. Pankratov, I.M. Grigor’eva, L.I. Beletskii, А.А. Kasilov, A.A. Burchenko, P.Ya. Lozin, А.V. Tsybenko, S.А. Slavnyj, А.S. Litvinov, A.P. Kulaga, А.Ye. Pavlichenko, R.O. Zamanov, N.V. Mironov, Yu.K. Romanov, V.S. Pashnev, V.K. Maznichenko, S.M. Volkov, Ye.D. Магнитное удержание In the l=3 Uragan-3M torsatron a hydrogen plasma with the density ¬ne ~ 2×10¹² cm⁻³ is produced and heated by RF fields in the ω ≤ ωсi range of frequencies with using a frame-like antenna. Time variations are considered of (1) density ne and electron cyclotron emission at different values of the RF power fed to the antenna; (2) fast ion generation and loss; (3) edge electric field Er and edge turbulent transport. Obtained results are of importance for (1) subsequent production and heating of denser plasmas; (2) understanding of processes resulting in the observed transition to the H-like confinement mode. В трехзаходном торсатроне У-3М водородная плазма с плотностью ¬ne ~2×10¹² cm⁻³ создаётся и нагревается ВЧ-полями в области частот ω ≤ ωсi с использованием рамочной антенны. Рассмотрены изменения во времени: 1) плотности ne и электронного циклотронного излучения при различных значениях ВЧ-мощности, подводимой к антенне; 2) генерации быстрых ионов и их потерь; 3) краевого электрического поля Еr и краевого турбулентного пeреноса. Полученные результаты важны для последующего получения и нагрева более плотной плазмы и понимания процессов, приводящих к переходу в Н-подобную моду удержания. У тризаходному торсатроні У-3М воднева плазма зі щільністю ¬ne ~2×10¹² cm⁻³ створюється і нагрівається ВЧ-полями в області частот ω ≤ ωсi з використанням рамкової антени. Розглянуті часові зміни: 1) густини ne та електронного циклотронного випромінювання при різних значеннях ВЧ-потужності, що підводиться до антени; 2) генерації швидких іонів та їх втрат; 3) крайового електричного поля Еr та крайового турбулентного переносу. Одержані результати важливі для подальшого створення та нагріву більш щільної плазми і розуміння процесів, що призводять до переходу в Н-подібну моду утримання. 2012 Article RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron / V.V. Chechkin, I.M. Pankratov, L.I. Grigor’eva, А.А. Beletskii, A.A. Kasilov, P.Ya. Burchenko, А.V. Lozin, S.А. Tsybenko, А.S. Slavnyj, A.P. Litvinov, А.Ye. Kulaga, R.O. Pavlichenko, N.V. Zamanov, Yu.K. Mironov, V.S. Romanov, V.K. Pashnev, S.M. Maznichenko, Ye.D. Volkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 3-7. — Бібліогр.: 19 назв. — англ. 1562-6016 PACS: 52.25.Fi, 52.55.Hc, 52.55.Pi, 52.70.Pi http://dspace.nbuv.gov.ua/handle/123456789/109081 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 |
| collection |
DSpace DC |
| language |
English |
| topic |
Магнитное удержание Магнитное удержание |
| spellingShingle |
Магнитное удержание Магнитное удержание Chechkin, V.V. Pankratov, I.M. Grigor’eva, L.I. Beletskii, А.А. Kasilov, A.A. Burchenko, P.Ya. Lozin, А.V. Tsybenko, S.А. Slavnyj, А.S. Litvinov, A.P. Kulaga, А.Ye. Pavlichenko, R.O. Zamanov, N.V. Mironov, Yu.K. Romanov, V.S. Pashnev, V.K. Maznichenko, S.M. Volkov, Ye.D. RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron Вопросы атомной науки и техники |
| description |
In the l=3 Uragan-3M torsatron a hydrogen plasma with the density ¬ne ~ 2×10¹² cm⁻³ is produced and heated by RF fields in the ω ≤ ωсi range of frequencies with using a frame-like antenna. Time variations are considered of (1) density ne and electron cyclotron emission at different values of the RF power fed to the antenna; (2) fast ion generation and loss; (3) edge electric field Er and edge turbulent transport. Obtained results are of importance for (1) subsequent production and heating of denser plasmas; (2) understanding of processes resulting in the observed transition to the H-like confinement mode. |
| format |
Article |
| author |
Chechkin, V.V. Pankratov, I.M. Grigor’eva, L.I. Beletskii, А.А. Kasilov, A.A. Burchenko, P.Ya. Lozin, А.V. Tsybenko, S.А. Slavnyj, А.S. Litvinov, A.P. Kulaga, А.Ye. Pavlichenko, R.O. Zamanov, N.V. Mironov, Yu.K. Romanov, V.S. Pashnev, V.K. Maznichenko, S.M. Volkov, Ye.D. |
| author_facet |
Chechkin, V.V. Pankratov, I.M. Grigor’eva, L.I. Beletskii, А.А. Kasilov, A.A. Burchenko, P.Ya. Lozin, А.V. Tsybenko, S.А. Slavnyj, А.S. Litvinov, A.P. Kulaga, А.Ye. Pavlichenko, R.O. Zamanov, N.V. Mironov, Yu.K. Romanov, V.S. Pashnev, V.K. Maznichenko, S.M. Volkov, Ye.D. |
| author_sort |
Chechkin, V.V. |
| title |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron |
| title_short |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron |
| title_full |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron |
| title_fullStr |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron |
| title_full_unstemmed |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron |
| title_sort |
rа discharge dynamics with passing over l- and h-like mode states in the uragan-3m torsatron |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2012 |
| topic_facet |
Магнитное удержание |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/109081 |
| citation_txt |
RА discharge dynamics with passing over l- and H-like mode states in the URAGAN-3M torsatron / V.V. Chechkin, I.M. Pankratov, L.I. Grigor’eva, А.А. Beletskii, A.A. Kasilov, P.Ya. Burchenko, А.V. Lozin, S.А. Tsybenko, А.S. Slavnyj, A.P. Litvinov, А.Ye. Kulaga, R.O. Pavlichenko, N.V. Zamanov, Yu.K. Mironov, V.S. Romanov, V.K. Pashnev, S.M. Maznichenko, Ye.D. Volkov // Вопросы атомной науки и техники. — 2012. — № 6. — С. 3-7. — Бібліогр.: 19 назв. — англ. |
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Вопросы атомной науки и техники |
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MAGNETIC CONFINEMENT
ISSN 1562-6016. ВАНТ. 2012. №6(82) 3
RF DISCHARGE DYNAMICS WITH PASSING OVER L- AND H-LIKE
MODE STATES IN THE URAGAN-3М TORSATRON
V.V. Chechkin, I.M. Pankratov, L.I. Grigor’eva, А.А. Beletskii, A.A. Kasilov,
P.Ya. Burchenko, А.V. Lozin, S.А. Tsybenko, А.S. Slavnyj,
A.P. Litvinov, А.Ye. Кulaga, R.O. Pavlichenko, N.V. Zamanov, Yu.K. Mironov,
V.S. Romanov, V.K. Pashnev, S.M. Maznichenko, Ye.D. Volkov
Institute of Plasma Physics NSC “Kharkov Institute of Physics and Technology”,
Kharkov, Ukraine
In the l=3 Uragan-3M torsatron a hydrogen plasma with the density en ~ 2×1012 cm-3 is produced and heated by
RF fields in the ω ≲ ωсi range of frequencies with using a frame-like antenna. Time variations are considered of (1)
density en and electron cyclotron emission at different values of the RF power fed to the antenna; (2) fast ion
generation and loss; (3) edge electric field Er and edge turbulent transport. Obtained results are of importance for (1)
subsequent production and heating of denser plasmas; (2) understanding of processes resulting in the observed
transition to the H-like confinement mode.
PACS: 52.25.Fi, 52.55.Hc, 52.55.Pi, 52.70.Pi
INTRODUCTION
In the l=3 “Uragan-3M” (U-3M) torsatron with an
open natural helical divertor the plasma is produced and
heated by RF fields in the Alfven range of frequencies,
ω≲ωсi [1]. Enclosure of the whole magnetic system into
a large vacuum chamber and the plasma production and
heating technique result in distinctions of discharge
development during the RF pulse and after its
termination.
The time evolution of plasma parameters is
considered where the RF power is transmitted to the
plasma by means of an unshielded frame-like antenna
with a comparatively long wavelength spectrum [2].
Behaviors of the line-averaged electron density en
and electron cyclotron emission (ECE) from the central
plasma are compared at different levels of the RF power
P fed to the antenna. The link has been established
between the value of en and the level of ЕСЕ.
Two groups of ions with different temperatures are
observed in U-3М: the lower temperature (tens eV) and
higher temperature (300…600 eV) ones [3, 4]. In the
optimum conditions for plasma heating the more
energetic ion content (≳500 eV, fast ions, FI) increases
[5]. With this, a short-time enhanced FI outflow to the
divertor (burst of FI loss) occurs at a certain en value.
With the power P high enough, the FI burst triggers a
bifurcation of the edge Еr toward a more negative value
with a stronger radial Er shear and, consequently, a
stronger shear of the poloidal flux E×B. This results in
suppression of the edge turbulent transport with indications
of confinement improvement to occur (the H-like mode).
With the density en changing after discharge ignition, two
H-mode states separated by an enhanced edge turbulent
transport (the L-like state) are realized.
The results having been obtained are of interest for
(i) target plasma formation to produce and heat a denser
plasma in U-3M by means of another, shorter wave
antenna; (ii) understanding of processes being
determinative in the H-like mode formation in U-3M.
1. EXPERIMENTAL CONDITIONS
The U-3M device (fig. 1) is an l=3/m=9 torsatron with
R0=100 cm, a ≈12 cm, ι(а)/2π ≈ 0.3. The magnetic field
Вφ≲1 Т is produced with the helical coils only. The
whole magnetic system is enclosed into a large, 5 m
diameter vacuum chamber, its volume, 70 m3, being
200 times larger than the confinement volume. So, an
open natural helical divertor is realized. The fuelling gas
(hydrogen) is leaked into the chamber continuously at
the pressure p~10-5 Torr.
III
II
I
I
II
III
I
II
III
A9
A1
A8
A2 A3
A4
A5
A6A7
D2
D3
D7
D1
D4
D5
D6
D8
D9
movable probe
array
CXN energy
analyzer
microwave interferometry
ECE
divertor ion energy analyzer
Fig. 1. U-3M helical coils I, II, III. Indicated are
symmetric poloidal cross-sections А1, D1, A2, D2,…,
A9, D9 in helical periods 1, 2, …, 9. respectively. The
antenna is placed under the coils I and III between A1
and A2 (marked with dashes) with the leads in D1 on
the low field side
The plasma with en units 1012 сm-3 is RF produced
and heated at the frequency ω≲ωсi, with the local
Alfven resonance (LAR) condition N||
2=ε1 being
fulfilled for wavelengths λ|| excited by the antenna
where N|| = k||c/ω, k||=2π/λ||, ε1 ≈ ωpi
2/(ωсi
2- ω2). Parallel
with the linear Alfven heating, turbulent heating also
takes place. The RF power is transmitted into the
4 ISSN 1562-6016. ВАНТ. 2012. №6(82)
plasma by means of a twisted unshielded frame-like
antenna [1, 2] (Fig. 2). The calculated spectrum of
parallel wavelengths λ|| generated by the antenna [2]
covers 40…400 cm with the maximum generation at
λ||
max ≈ 80 cm.
0
20
40
60
80
100
120
po
w
er
, a
. u
.
0.1 1 10
λ||, m
Fig. 2. Schematic representation of the antenna. 1, 2,
connections to the oscillator. Calculated spectrum of
generated parallel wavelengths λ|| [2]
The parallel component of the RF antenna current excites
mainly slow modes of the Alfven wave [6]. In the
operating regime Вφ=0,72 Т, ω/2π=8.8 МHz
(ω=0,8ωсi(0)). The calculated λ|| spectrum in Fig. 2
corresponds to the resonance densities
ni ≈ (0,07…7)×1012 сm-3 with ni = 1.8×1012 сm-3 for
λ||
max ≈ 80 cm.
Two groups of ions, lower temperature (Ti1, tens eV
[3]) and higher temperature ones (Тi2 ≈ 300…600 eV
[4]) are formed during the heating. A possible reason for
the Тi2 group to arise turbulent processes could be [7].
Measurements are carried out of the density en , the
intensity of 2nd harmonic ECE from the central region
(“radiation temperature”), the CXN flux Гn with
different perpendicular energies W⊥, the FI component
(>500 eV) in the diverted plasma flow (DPF; a grid
analyzer with retarding potential). Spatial distributions
close to radial ones of mean and fluctuating edge
parameters are studied with the use of movable
Langmuir probes.
In the typical operating regime (Р ≈ 130 kW, the RF
pulse length 40 ms) the electron temperature in the
central region as estimated from ECE amounts
Te(0) ~ 500…700 eV.
2. DENSITY AND RADIATION
TEMPERATURE EVOLUTION
AT DIFFERENT VALUES OF RF POWER
It follows from Fig. 3 that within comparatively low
values 60 ≲ Р≲ 80 kW the en rise after discharge
ignition is slowed down near en ≈2×1012 cm-3 (“ en (t)
bend”). As P increases, the maximum en ≈ 6×1012 cm-3
shifts toward the end of RF pulse. The maximum level
of ECE is reached in the en (t) bend. An ЕСЕ drop with
a further density rise ( en >(2…3)×1012 cm-3) indicates
plasma heating reduction due to LAR shift to the
periphery.
0 20 40 60 80
0
1
2
3
4
5
6
time, ms
n e
,1
012
cm
-3
; E
C
E,
a
. u
.
RF
60 kW
_
_
ECE
ne
0 20 40 60 80
0
1
2
3
4
5
6
time, ms
n e
,1
012
cm
-3
; E
C
E,
a
. u
.
RF
ne
_
ECE
_
70 kW
0 20 40 60 80
0
1
2
3
4
5
6
time, ms
n e
,1
012
c
m
-3
; E
C
E
, a
.u
.
RF
ne
_
ÅÑÅ
_
80 kW
0 20 40 60 80
0
1
2
3
4
5
6
time, ms
n e
,1
012
cm
-3
;
EC
E,
a
. u
.
_
ne
ECE
_
110 kW
RF
0 20 40 60 80
0
1
2
3
4
5
6
time, ms
n e
,1
012
cm
-3
; E
C
E
, a
. u
.
_
1 2 3
130 kW
ne
_
ECE
RF
Fig. 3. Time behavior of density en and 2nd harmonic
ECE at different values of RF power fed to the antenna.
Vertical dashed lines separate phases 1, 2, 3 of
discharge evolution
At Р>80 kW the density achieves en ≈ 6×1012 сm-3
no more, starting to decay before the end of RF pulse
the faster the higher P is. At Р>100 kW the maximum
density becomes en max≈2×1012 сm-3 in the active stage
( en bend). After RF switched off en rises again during
~3 ms, and after reaching en ≈4×1012 cm-3 decays
finally with a characteristic time of ~15 ms. With
en ≲2×1012 сm-3 a high level of ЕСЕ is kept over all the
RF pulse, thus evidencing the optimum density for
heating.
At Р≈130…150 kW, where the value of
en ≈1.2×1012 сm-3 is attained in the slow density decrease
(the time of decay ~10 ms), some indications of the H-
mode transition [8, 9] occur. These are [10, 11] a
suspension of the en decay, speeding up of both ECE and
plasma energy content Wdia rise. Most distinctly, these
effects are displayed at Р≈130 kW. The H-mode transition
is caused by the edge Er shear strengthening and
suppression of the edge turbulent transport (see Sec. 4).
We name the initial stage of the discharge up to
emn ≈ 2×1012 сm-3 ( en bend) as phase 1 (Ph1), the stage
of the density decay to the minimum en ≈1.2×1012 сm-3
and the H-mode transition as phase 2 (Ph2), and the
subsequent state with the H-mode to the end of RF pulse
as phase 3 (Ph3; see Fig. 3 at P ≈ 130 kW).
At higher power values, Р>100 kW (see Fig. 3) in Ph2,
the rate of the en decay to the minimum and H-mode
transition increases with power so that the Ph2 length
ISSN 1562-6016. ВАНТ. 2012. №6(82) 5
reduces. This dependence is consistent with the universal
generality, power degradation of confinement [12].
At Р>80 kW a short-time ~3-fold increase en after
RF switched off (see Fig. 3) is explained [7] by plasma
flows reduction due to cooling, while the electron
temperature remains sufficiently high for some time to
ionize the neutral gas entering from the free volume of
the chamber.
3. BEHAVIOR OF FAST IONS AND THEIR
LOSS. THE LINK BETWEEN FI LOSS
AND H-MODE TRANSITION
More energetic ions from the Ti2 group (FI) seriously
affect plasma characteristics in U-3M. In particular, the
FI direct loss results in the DPF up-down asymmetry
[13]. The relative FI content increases with the RF
power [5].
0
1
2
3
4
0
1
2
3
0
1
2
3
0
1
2
3
0 20 40 60
0
1
2
3
(e)
(d)
(c)
1
n e
,1
012
cm
-3
- RF
2 3 (a)
(b)
time, ms
I i
, a
.u
.
à n
, a
. u
.
à n
, a
. u
.
à n
, a
. u
. 450 eV
1125 eV
2475 eV
>500 eV
Fig. 4. Time behavior of (а) density en ; (b, c, d) CXN
flux Гn with different perpendicular energies; (e) ion
current Ii to the analyzer collector at U=500 V
The time evolution of the CXN flux Γn with
different energies W⊥ (Fig. 4) displays variation of the
concentration of ions with such energies in the
confinement volume. At W⊥<500 eV (see Fig. 4,b) the
behavior of Гn(t) does not exhibit any distinctions
correlating with en (t). However, at W⊥≳500 eV in Ph2
Гn(t) changes in antiphase with en (t) (see Fig. 4,c,d),
attaining a maximum at the minimum
2en ≈ 1.2×1012 сm-3, where the H-like mode transition
occurs. In Ph1 with en increasing, Гn also passes over a
maximum at 1en ≈ 2en .
It is shown in Fig. 4,e how the FI outflow to the
divertor changes in time (ion current Ii to the analyzer
collector at the retarding voltage U = +500 V). In Ph1 at
en = 1en and in the end of Ph2 ( 2en ≈ 1en ) a short-time
(hundreds μs) enhanced FI outflow to the divertor
occurs, indicating a manifold rise of the FI loss (burst of
FI loss). The burst amplitude increases with RF power
[10, 11] and exhibits a resonance-like behavior
depending on Bφ at a fixed Р (Fig. 5, measured in Ph1).
0.68 0.70 0.72 0.74
0
1
2
3
4
5
I i,
a.
u.
BФ, T
Fig. 5. Fast ion burst amplitude Ii versus toroidal
magnetic field strength Bφ (measured in Ph1)
The synchronism of density decay termination at 2en ≈
1,2×1012 сm-3, the rise of ЕСЕ and Wdia in the end of
Ph2 – start of Ph3, on the one hand, and the FI content
passing over a maximum and the burst of FI ion loss, on
the other hand, suggests an idea that the H-like mode is
triggered by the non-umbipolar FI loss.
4. TIME EVOLUTION OF EDGE Еr AND Еr
EFFECT ON TURBULENT TRANSPORT
Qualitatively, the effect of the Er shear amplification
in the H-like mode transition is demonstrated by
comparison of edge floating potential profiles Vf(h)
close to radial ones (Fig. 6; h is the probe distance from
the minor vertical exis when moving 1 cm over the
midplane) before (t < 0) and after (t > 0) the transition
(t = 0 corresponds to the moment of the Ph2–Ph3
transition with the burst of FI loss).
Fig. 6. Mean edge floating potential Vf versus distance h
as measured at different moments t (indicated in ms)
before (t<0) and after (t>0) transition (t=0). The plots
measured 25 μs before and 25 μs after FI burst
maximum (shaded) are marked as -0 and +0,
respectively. Vertical dashed lines indicate LCFS
position. In the insertion the line of probe movement is
marked by dashes
a
c
b
d
e
6 ISSN 1562-6016. ВАНТ. 2012. №6(82)
The value of |Vf| near the LCFS (h = h0 ≅ 10 см)
increases with probe displacement toward both h < h0
and h > h0, while min(Vf) shifts inside the boundary.
Еr ≈ -dVf/dh becomes more negative, with Er shear
increasing. A rough estimation yields Еr ≈ -20 V/сm in
Ph2 and Еr ≈ -100 V/сm in Ph3.
Similar to other 3D systems [9] and tokamaks [14],
the radial shear of the mean flow E×B with negative Er
is formed at the plasma boundary prior to the transition.
The presence of a pre-transitional lower edge Еr is
connected with the maximum (“hump”) of the
electrostatic potential arising near the LCFS due to
formation of the “radial sheath” (Δ≲1сm) and the “ion
halo” [15].
In Ph1 a lower level of Γ% and a stronger Er shear
also set in with the burst of FI loss at 1en ≈ 2en . This
short-time (2…3 ms) H-like mode state is terminated at
emn ≈2×1012 сm-3 ( en bend) by a sudden, bifurcation-
like reduction of |Er| and Er shear with a Γ% rise and
consequent en decay due to increase of plasma loss
(Ph2). In this sense, we may say about a short-time
H-like mode state to occur in Ph1 too. Here, however,
the burst of FI loss in itself can arise at the same density
1en even at a lower power, P<100 kW, though with a
smaller amplitude where no H-mode occurs. This is an
evidence of the FI burst being a primary effect relative
to the H-like mode transition.
-120
-60
0
60
120
180
-5
0
5
10
31
n e
, 1
012
c
m
-3
2
Ã
,
a.
u
.
~
<Ã
>,
a
. u
.
~
0 5 10 15 20 25 30 35 40
time, ms
RF0.0
0.5
1.0
1.5
2.0
2.5
(c)
(b)
(a)
Fig. 7. Time behavior of (а) density en , (b) edge radial
turbulent flux Γ% (probe position h = 10.5 cm) and (c)
its value averaged over 1 ms intervals < Γ% >
The changes in Еr are momentarily displayed in the
value of the edge turbulent flux Γ% (Fig. 7). A time
correlation is well seen between the level of edge
turbulent transport (a surface process) and plasma
confinement (a volume characteristic defined here by
the rate of en decay). In Ph3 (H-like mode) <Γ% >
practically vanishes with suspension or deceleration of
the density decay.
SUMMARY AND DISCUSSION
♦ Within 60≲Р≲80 kW a cold plasma with
en ≈ (4…6)×1012 сm-3 is produced in U-3M. At
Р>100 kW the maximum density becomes
emn ≈ 2×1012 сm-3 with a high Те(0) which is kept over
all the RF pulse. Such a discharge can be used as a
target to produce and heat a denser plasma (up to
1013 сm-3) by exciting the fast mode of the Alfven wave
by a shorter wave antenna with azimuthal currents [16].
♦ In the typical operating regime (P≈130 kW),
processes developing in the active stage can be divided
in two groups by the time scale of their variation.
To the slower processes (units – 10 ms) the density
decay in Ph2 from emn ≈2×1012 сm-3 to 2en ≈1.2×1012 сm-3
(see Fig. 3,е) is related, first of all. With this, the FI
content increases (units ms) attaining a maximum at
en = 2en (see Fig. 4,с,d), with the plasma energy
content Wdia and ECE also growing monotonously.
Taking account of the FI content increasing with power
[5], optimum conditions for FI generation are supposed
to be realized at the combination ω/2π = 8.8 МHz,
Вφ = 0.72 Т and en ≈ 2en , with increasing RF power
fraction deposited in the plasma (a specific “coupling
resonance”, see also [17]). On the other hand, the rise of
this fraction results in a stronger confinement
degradation and density decrease.
Against a background of slower processes preparing
the “coupling resonance” with maximum FI content,
faster processes (tens – hundreds μs) arise, which
determine the H-like mode transition in itself. The
transition is triggered by the burst of FI loss (~500 μs,
see Fig. 4,e). The burst initiates the edge Er bifurcation
to a more negative value with the Еr shear amplified
(~50 μs, see Fig. 6). The stronger Еr shear suppresses
the edge turbulence [18] and turbulence-induced
anomalous transport Γ% (see Fig. 7). The time of the Γ%
drop is ~100 μs.
The Еr bifurcation triggered by the ion orbit loss is
considered in [19].
♦ Similar to other devices [9, 14], in U-3M a
characteristic form of the edge potential profile has been
already formed before the H-transition (see Fig. 6) and,
probably, results from the non-ambipolar ion orbit loss
[15]. With the transition, the edge Er becomes stronger,
with the potential well shifting inside the LCFS.
♦ Triggered by a single burst of FI loss, the H-like
mode state persists for a comparatively long period
without recovering the pre-transitional higher level of
the edge turbulence (see Fig. 6). It looks as if the
discharge went from one quasi-steady (L-like) state to
another (H-like) state.
REFERENCES
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Nucl. Fusion. 1986, v. 26, p. 23.
2. Y.G. Zalesski, P.I. Kurilko, N.I. Nazarov, et al. //
Fizika plasmy. 1989, v. 15, p. 1424 (in Russian).
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3. V.G. Konovalov, V.N. Bondarenko, A.N. Shapoval,
et al. // Prob. At. Sci. Techn. Ser. “Plasma Phys”. 2002,
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6. A.V. Longinov, K.N. Stepanov. High-Frequency
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Article received 01.10.12
ДИНАМИКА ВЧ-РАЗРЯДА С ПРОХОЖДЕНИЕМ L- И Н-ПОДОБНЫХ СОСТОЯНИЙ
В ТОРСАТРОНЕ УРАГАН-3М
В.В. Чечкин, И.М. Панкратов, Л.И. Григорьева, А.А. Белецкий, А.А. Касилов, П. Я.Бурченко, А.В. Лозин,
С.А. Цыбенко, А.С. Славный, A.П. Литвинов, А.Е. Кулага, Р.О. Павличенко, Н.В. Заманов,
Ю.К. Миронов, В.С. Романов, В.К. Пашнев, С.М. Мазниченко, Е.Д. Волков
В трехзаходном торсатроне У-3М водородная плазма с плотностью en ~2×1012 cм-3 создаётся и
нагревается ВЧ-полями в области частот ω≲ωсi с использованием рамочной антенны. Рассмотрены
изменения во времени: 1) плотности en и электронного циклотронного излучения при различных значениях
ВЧ-мощности, подводимой к антенне; 2) генерации быстрых ионов и их потерь; 3) краевого электрического
поля Еr и краевого турбулентного пeреноса. Полученные результаты важны для последующего получения и
нагрева более плотной плазмы и понимания процессов, приводящих к переходу в Н-подобную моду
удержания.
ДИНАМІКА ВЧ-РОЗРЯДУ З ПРОХОДЖЕННЯМ L- ТА Н-ПОДІБНИХ СТАНІВ
У ТОРСАТРОНІ УРАГАН-3М
В.В. Чечкін, І.М. Панкратов, Л.І. Григор’єва, О.О. Білецький, А.А. Касілов, П. Я.Бурченко, О.В. Лозін,
С.А. Цибенко, О.С. Славний, A.П. Литвинов, А.Є. Кулага, Р.О. Павличенко, Н.В. Заманов,
Ю.К. Миронов, В.С. Романов, В.К. Пашнєв, С.М. Мазниченко, Є.Д. Волков
У тризаходному торсатроні У-3М воднева плазма зі щільністю en ~2×1012 cм-3 створюється і нагрівається
ВЧ-полями в області частот ω≲ωсi з використанням рамкової антени. Розглянуті часові зміни: 1) густини en
та електронного циклотронного випромінювання при різних значеннях ВЧ-потужності, що підводиться до
антени; 2) генерації швидких іонів та їх втрат; 3) крайового електричного поля Еr та крайового
турбулентного переносу. Одержані результати важливі для подальшого створення та нагріву більш щільної
плазми і розуміння процесів, що призводять до переходу в Н-подібну моду утримання.
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