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ABSTRACT: The propagation and damping of waves excited by a poloidal antenna in a hydrogen plasma at the ion cyclotron resonance (ICR)
frequency were investigated. The longitudinal wavenumber and damping length of waves excited in the ohmically heated plasma
of the L-2M stellarator, the dependence of the damping length of fast magnetosonic waves on the magnetic field strength, and
the dependence of the antenna load resistance on the plasma density were measured. It is the first time that such complex
measurements were performed in experiments on ICR heating of a hydrogen plasma at the fundamental harmonic of the ion gyrofrequency
in toroidal magnetic confinement systems.
PACS numbers52.50.Qt–52.70.Gw
Plasma Physics Reports 04/2012; 34(3):203-211. · 0.65 Impact Factor
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G. S. Voronov,
D. K. Akulina,
G. M. Batanov,
M. S. Berezhetskii,
D. G. Vasil’kov,
I. Yu. Vafin,
E. V. Voronova,
S. E. Grebenshchikov,
I. A. Grishina,
L. V. Kolik, [......],
A. I. Meshcheryakov, Yu. I. Nechaev,
A. E. Petrov,
K. A. Sarksyan,
V. V. Saenko,
N. N. Skvortsova,
O. I. Fedyanin,
N. K. Kharchev,
Yu. V. Khol’nov,
S. V. Shchepetov
[show abstract]
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ABSTRACT: A plasma confinement mode characterized by the formation of an edge transport barrier (ETB) was discovered in the L-2M stellarator
after boronization of the vacuum vessel wall. The transition into this mode is accompanied by a jump in the electron temperature
by 100–200 eV at the plasma edge and a sharp increase in the gradient of the electron temperature T
e
in this region. The threshold power for the transition into the ETB confinement mode with an increased electron temperature
gradient is P
thr▿Te
= (60 ± 15)n
e
[1019 m−3] kW. The formation of the ETB manifests itself also in a substantial change in the electron density profile. A density peak
with a steep gradient at the outer side forms at the plasma edge. The threshold power for the transition into the ETB confinement
mode corresponding to a substantial increase in the plasma density gradient near r = a is P
thr▿Te
= (67 ± 9)n
e
[1019 m−3] kW, which agrees to within experimental error with the threshold power for the transition into the ETB confinement mode
determined from the sharp increase in the gradient of the electron temperature T
e
. The value of P
thr for the L-2M stellarator agrees to within 25% with that obtained from the tokamak scaling. In the ETB confinement mode, the
plasma energy W and the energy confinement time τ
E
determined from diamagnetic measurements increase by 20–30% as compared to those obtained from the stellarator scaling for
the confinement mode without an ETB. When the heating power increases by a factor of 2–3 above the threshold value, the effects
related to improved energy confinement disappear.
Plasma Physics Reports 04/2012; 36(7):551-557. · 0.65 Impact Factor
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D. K. Akulina,
G. M. Batanov,
M. S. Berezhetskiĭ,
D. G. Vasil’kov,
I. Yu. Vafin,
G. S. Voronov,
E. V. Voronova,
G. A. Gladkov,
S. E. Grebenshchikov,
I. A. Grishina, [......], Yu. I. Nechaev,
A. E. Petrov,
A. A. Pshenichnikov,
V. V. Saenko,
K. A. Sarksyan,
N. N. Skvortsova,
O. I. Fedyanin,
N. K. Kharchev,
Yu. V. Khol’nov,
S. V. Shchepetov
[show abstract]
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ABSTRACT: Results are presented from experimental studies of variations in the plasma parameters during the excitation of a multiaxis
magnetic configuration by the induction current (up to 17 kA) in the basic magnetic configuration of the L-2M stellarator
in the regime of ECR heating at a microwave power of ∼200 kW (∼1 MW m−3) and an average plasma density of (1–2) × 1019 m−3. The current direction was chosen to reduce the net rotational transform (the so-called “negative“ current). The current
was high enough for the rotational transform to change its sign inside the plasma column. Computer simulations of the L-2M
magnetic structure showed that the surface with a zero rotational transform is topologically unstable and gives rise to magnetic
islands, i.e., to a multiaxis magnetic configuration. Magnetic measurements showed that, at negative currents above 10 kA,
intense bursts of MHD oscillations with a clearly defined toroidal mode number n = 0 were observed in the frequency range of several kilohertz. Unfortunately, the experimental data are insufficient to draw
the final conclusion on the transverse structure of these oscillations. The radial temperature profiles along the stellarator
major radius in the equatorial plane were studied. It is found that the electron temperature decreases by a factor of 1.3
in the plasma core (r/a ≤ 0.6) and that the temperature jump is retained near the boundary. A change in turbulent fluctuations of the plasma density
during the excitation of a negative current was studied using wave scattering diagnostics. It is found that the probability
density function of the increments of fluctuations in the plasma core differs from a Gaussian distribution. The measured distribution
is heavy-tailed and broadens in the presence of the current. It is found that the spectrum of turbulent fluctuations and their
Doppler shift near the plasma boundary are nonuniform in the radial direction. This may be attributed to the shear of the
poloidal velocity. The experimental results indicate that the formation of regions with a zero rotational transform in the
plasma core somewhat intensifies plasma transport.
Plasma Physics Reports 04/2012; 34(12):979-990. · 0.65 Impact Factor
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[show abstract]
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ABSTRACT: In the course of experiments on electron-cyclotron resonance heating of plasma in the L-2M stellarator, it was found that,
at high specific heating powers, the SXR spectrum was distorted in the entire photon energy range under study (from 1.5 to
15 keV). To determine the character of this distortion, a procedure was proposed for recovering the electron energy distribution
function (EEDF) from soft X-ray (SXR) measurements. The SXR spectra were analyzed for different values of the specific heating
power. Numerical calculations show that the edge plasma contributes insignificantly to the chord-averaged SXR spectrum. A
conclusion is drawn on the applicability and accuracy of the procedure for recovering the EEDF at high specific heating powers.
Plasma Physics Reports 11/2008; 34(12):1016-1021. · 0.65 Impact Factor
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O. I. Fedyanin,
D. K. Akulina,
G. M. Batanov,
M. S. Berezhetskiĭ,
D. G. Vasil’kov,
I. Yu. Vafin,
G. S. Voronov,
E. V. Voronova,
G. A. Gladkov,
S. E. Grebenshchikov, [......],
A. A. Letunov,
V. P. Logvinenko,
N. I. Malykh,
A. I. Meshcheryakov, Yu. I. Nechaev,
K. A. Sarksyan,
N. N. Skvortsova,
S. V. Shchepetov,
N. K. Kharchev,
Yu. V. Khol’nov
[show abstract]
[hide abstract]
ABSTRACT: Results are presented from studies of the effect of the discharge parameters (in particular, plasma density and heating power)
and the characteristics of the magnetic configuration (e.g., rotational transform) on the confinement of a low-pressure plasma
during electron-cyclotron resonance heating in the L-2M stellarator. An analysis shows that the plasma energy in the steady-state
phase of a discharge is fairly well described by the product of power functions of the plasma density, heating power, and
rotational transform:
W = W0 nean Pap iai W = W_0 n_e^{\alpha _n } P^{\alpha _p } \iota ^{\alpha _\iota }
. The energy scalings constructed in terms of the parameters in the initial stage of free plasma decay and those in the steady-state
phase are close to one another. The dynamic analysis of the plasma energy decay is now under way.
Plasma Physics Reports 01/2007; 33(10):805-815. · 0.65 Impact Factor
