Mechanism of the transport barriers formation at lower hybrid heating in the FT-2 tokamak experiments

Lashkul, S. I.; Budnikov, V.N.; Borevich, A A; Chechik, E. O.; Dyachenko, V. V.; Goncharov, P. R.; Esipov, L. A.; Its, E. R.; Kantor, M. Yu.; Kouprienko, D. V.; Popov, A. Yu.; Podushnikova, K.A.; Sackharov, I E; Shatalin, S. V.; Yermolaev, V B

doi:10.1088/0741-3335/42/5a/318

Cited by 11 publications

(9 citation statements)

References 5 publications

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“…Most experiments have achieved internal transport barriers (ITBs) by adding auxiliary heating 2,3,4,5,6 beyond some threshold value resulting in distinct changes in the heat, momentum, or particle transport from one region of the plasma to another. It has also been demonstrated that reversal of magnetic shear by use of current modification by lower hybrid current drive 7 or electron cyclotron current drive 8 encourages ITB development. These are thought to occur when the effects of pressure profile gradient driven instabilities are reduced by the introduction of rotational shear into the unstable region or by providing a region of reversed magnetic shear 9 .…”

Section: Introductionmentioning

confidence: 99%

Control of internal transport barriers on Alcator C-Mod

et al. 2004

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Recent studies of internal transport and double transport barrier regimes in Alcator C-Mod [I. H. Hutchinson, et al., Phys. Plasmas 1, 1511] have explored the limits for forming, maintaining, and controlling these plasmas. C-Mod provides a unique platform for studying such discharges: the ions and electrons are tightly coupled by collisions and the plasma has no internal particle or momentum sources. The double-barrier mode comprised of an edge barrier with an internal transport barrier (ITB) can be induced at will using off-axis ion cyclotron range of frequency (ICRF) injection on either the low or high field side of the plasma with either of the available ICRF frequencies (70 or 80 MHz). When enhanced D α high confinement mode (EDA H-mode) is accessed in Ohmic plasmas, the double barrier ITB forms spontaneously if the Hmode is sustained for ~2 energy confinement times. The ITBs formed in both Ohmic and ICRF heated plasmas are quite similar regardless of the trigger method. They are characterized by strong central peaking of the electron density, and reduction of the core particle and energy transport. Control of impurity influx and heating of the core plasma in the presence of the ITB have been achieved with the addition of central ICRF power in both Ohmic H-mode and ICRF induced ITBs. The radial location of the particle transport is dependent on the toroidal magnetic field but not on the location of the ICRF resonance. A narrow region of decreased electron thermal transport, as determined by sawtooth heat pulse analysis, is found in these plasmas as well. Transport analysis indicates that reduction of the particle diffusivity in the barrier region allows the neoclassical pinch to drive the density and impurity accumulation in the plasma center. Examination of the gyrokinetic stability at the trigger time for the ITB suggests that the density and temperature profiles are inherently stable to ion temperature gradient (ITG) and trapped electron (TEM) modes in the core inside of the ITB location.

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Section: Introductionmentioning

confidence: 99%

Control of internal transport barriers on Alcator C-Mod

et al. 2004

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“…Furthermore, the increase of T e (r = 2 cm) from 400 eV up to 650 eV during LHH is followed by a further heating up to 700 eV in the post-heating stage. The persisting high values of T e (r) after the RF pulse indicate that electron heating is not only due to RF power absorption but also due to ICC (see figure 1 in [2], where the first scenario is described in detail. )…”

Section: Methodsmentioning

confidence: 99%

“…The LCFS is the last of the closed flux surfaces to touch the poloidal limiter at the same point. The L-H transition has been observed in experiments with additional plasma heating by lower hybrid (LH) waves [1,2]. The working gas is hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Processes in SOL plasma at the transition into improved confinement mode in FT-2 tokamak

Lashkul

Budnikov

Dyachenko

et al. 2002

Plasma Phys. Control. Fusion

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Studies of processes in the scrape-off layer (SOL) of the tokamak show a direct influence of periphery effects on confinement parameters of the plasma core. This paper illustrates experimentally observed transport barrier formation initialized by the low hybrid (LH) heating of the hydrogen plasma. The experimental data near last close flax surface (LCFS) and in SOL were obtained by means of an enhanced movable multielectrode Langmuir probe and spatially resolved spectroscopic technique retooled with additional helium puffing. The edge diagnostics show a strong change of a radial electric field and plasma parameters near LCFS. The alteration at the plasma edge is generated by high LH ion heating. It was found that the L-H transition is accompanied by a noticeable reconstruction of the poloidal and radial plasma parameters profiles in the SOL and in the limiter shadow region.

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“…Other techniques use radio frequency waves to alter the internal magnetic configuration of the plasma to obtain magnetic shear stabilization of microturbulence. These include lower hybrid current drive [18,19], electron cyclotron heating [20] and ion Bernstein wave injection [21]. A comprehensive review of the internal transport barrier (ITB) experiments and analysis can be found in papers by Wolf [22] and Connor [23].…”

Section: Introductionmentioning

confidence: 99%

Rotation and transport in Alcator C-Mod ITB plasmas

et al. 2010

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Internal transport barriers (ITBs) are seen under a number of conditions in Alcator C-Mod plasmas. Most typically, radio frequency power in the ion cyclotron range of frequencies (ICRF) is injected with the second harmonic of the resonant frequency for minority hydrogen ions positioned off-axis at r/a > 0.5 to initiate the ITBs. They also can arise spontaneously in ohmic H-mode plasmas. These ITBs typically persist tens of energy confinement times until the plasma terminates in radiative collapse or a disruption occurs. All C-Mod core barriers exhibit strongly peaked density and pressure profiles, static or peaking temperature profiles, peaking impurity density profiles, and thermal transport coefficients that approach neoclassical values in the core. The strongly co-current intrinsic central plasma rotation that is observed following the H-mode transition has a profile that is peaked in the center of the plasma and decreases towards the edge if the ICRF power deposition is in the plasma center.When the ICRF resonance is placed off-axis , the rotation develops a well in the core region.The central rotation continues to decrease as long as the central density peaks when an ITB develops. This rotation profile is flat in the center(0

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Mechanism of the transport barriers formation at lower hybrid heating in the FT-2 tokamak experiments

Cited by 11 publications

References 5 publications

Control of internal transport barriers on Alcator C-Mod

Control of internal transport barriers on Alcator C-Mod

Processes in SOL plasma at the transition into improved confinement mode in FT-2 tokamak

Rotation and transport in Alcator C-Mod ITB plasmas

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