18 research outputs found
Improved confinement transition in high density deuterium discharges at the FT-2 tokamak accompanied by onset of negative triangularity
Poloidal inhomogeneity of the particle fluctuation induced fluxes near of the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak
This paper deals with the new spectral and microturbulence experimental data
and their analysis, which show, that the radial electric field Er generated at
the LH heating (LHH) in the FT-2 is high enough to form the transport barriers.
The ETB is formed when LHH is switched off. The radial fluctuation-induced
EB drift flux densities near LCFS in SOL are measured at two different
poloidal angles. For this purpose two Langmuir probes located at low and high
field sides of the torus are used. Registration of the poloidal and radial
components of the electric field and density fluctuations at the same time
during one discharge permits to measure the poloidal asymmetry of the transport
reduction mechanism of the radial and poloidal particle fluxes in the SOL. The
absolute E(~) fluctuation levels show dependence on the sign of Er
shear. The modification of the microscale turbulence by the poloidal Er x B
rotation shear EB at the L - H transition near LCFS is also
studied by X-mode fluctuation Reflectometry. The new data were obtained by
spatial spectroscopic technique.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Role of turbulence and electric fields in the formation of transport barriers and the establishment of improved confinement in tokamak plasmas through inter-machine comparison
Over the past decade new regimes of tokamak operation have been identified, whereby electrostatic and magnetic turbulence
responsible for anomalous transport, can be externally suppressed, leading to improved confinement. Although turbulence
measurements have been performed on many confinement devices, the insight gained from these experiments is relatively
limited. To make further progress in the understanding of plasma turbulence in relation to improved confinement and transport
barriers, an extensive experimental and theoretical research programme should be undertaken. The present INTAS project
investigates the correlations between on the one hand the occurrence of transport barriers and improved confinement in the
tokamaks TEXTOR & T-10 and Tore Supra as well as on the smaller-scale tokamaks FT-2, TUMAN-3M and CASTOR, and on
the other hand electric fields, modified magnetic shear and electrostatic and magnetic turbulence using advanced diagnostics with
high spatial and temporal resolution. This is done in a strongly coordinated way and exploiting the complementarity of TEXTOR
and T-10 and the backup potential of the other tokamaks, which together have all the relevant experimental tools and theoretical
expertise. Advanced theoretical models and numerical simulations are used to check the experimental results.За останні десять років було отримано нові режими роботи токамаків, у яких електростатична і магнітна
турбулентність, відповідальна за аномальний перенос, могла заглушатися шляхом зовнішнього впливу, і тим самим
досягалося поліпшене утримання. Незважаючи на те, що дослідження турбулентності проводилися на багатьох установках,
розуміння цих процесів залишається досить обмеженим. Для досягнення подальшого прогресу в розумінні плазмової
турбулентності з погляду поліпшеного утримання і транспортних бар'єрів необхідні інтенсивні експериментальні і
теоретичні дослідження. Проект INTAS спрямовано на з'ясування кореляції між виникненням транспортних бар'єрів і
поліпшеного утримання в токамаках TEXTOR, Т-10 і Tore Supra, а також у токамаках малих розмірів ФТ-2, ТУМАН-3М и
CASTOR, з одного боку, і електричними полями, модифікованим магнітним широм і електростатичною і магнітною
турбулентністю, з іншого боку, з використанням передових діагностичних засобів з високим просторовим і тимчасовим
розділенням. Дослідження проводяться з високим ступенем координації робіт і використанням взаємодоповнюваності
установок TEXTOR і Т-10, і можливостей інших токамаків, що в сукупності забезпечить необхідну експериментальну і
теоретичну перевірку. Для перевірки експериментальних результатів буде використано нові теоретичні моделі і чисельне
моделювання.В последние десять лет были получены новые режимы работы токамаков, в которых электростатическая и магнитная
турбулентность, ответственная за аномальный перенос, могла подавляться путём внешнего воздействия, и тем самым
достигалось улучшенное удержание. Несмотря на то, что исследования турбулентности проводились на многих установках,
понимание этих процессов остаётся весьма ограниченным. Для достижения дальнейшего прогресса в понимании
плазменной турбулентности с точки зрения улучшенного удержания и транспортных барьеров необходимы интенсивные
экспериментальные и теоретические исследования. Проект INTAS направлен на выяснение корреляции между
возникновением транспортных барьеров и улучшенного удержания в токамаках TEXTOR, Т-10 и Tore Supra, а также в
токамаках малых размеров ФТ-2, ТУМАН-3М и CASTOR, с одной стороны, и электрическими полями, модифицированным
магнитным широм и электростатической и магнитной турбулентностью, с другой стороны, с использованием передовых
диагностических средств с высоким пространственным и временным разрешением. Исследования проводятся с высокой
степенью координации работ и использованием взаимодополняемости установок TEXTOR и Т-10, и возможностей других
токамаков, что в совокупности обеспечит необходимую экспериментальную и теоретическую проверку. Для проверки
экспериментальных результатов будут использованы новые теоретические модели и численное моделирование
Role of turbulence and electric fields in the establishment of improved confinement in tokamak plasmas
An extensive (INTAS) research programme started in 2002 to investigate the correlations between on the one hand the occurrence of
transport barriers and improved confinement in the medium-size tokamaks TEXTOR and T-10 and on the smaller tokamaks FT-2,
TUMAN-3M and CASTOR, and on the other hand electric fields, modified magnetic shear and electrostatic and magnetic turbulence
using advanced diagnostics with high spatial and temporal resolution and of various active means to externally control plasma transport .
This has been done in a strongly coordinated way and exploiting the complementarity of TEXTOR and T-10 and the backup potential of
the three other tokamaks, which together have all the relevant experimental tools and theoretical expertise
Test of a periodic multipass-intracavity laser system for the TEXTOR multiposition Thomson scattering diagnostics
A multipass intracavity laser probing system operating in a burst mode has been tested for the Torus Experiment for Technology Oriented Research Thomson scattering diagnostics. The parameters tested were the probing pulse energy and power as well as pulse repetition frequency. The system is to be applied for the dynamic study of fast plasma phenomena (e.g., transport barrier formation and filaments) requiring both high time and spatial resolutions of the electron temperature measurements. (C) 2001 American Institute of Physics
10 kHz repetitive high-resolution TV Thomson scatatering on TEXTOR
In December 2003 a new 10 kHz multiposition Thomson scattering diagnostic with high spatial resolution has become operational on the TEXTOR tokamak. The system is the follow up of the high-resolution double-pulse Thomson scattering diagnostic. The conventional ruby laser has been replaced by a 10 kHz intracavity laser system and the spectrometer detector has been upgraded with two ultrafast complementary metal-oxide-semiconductor cameras combined with a special image intensifier stage. In the initial phase of operation, a burst of 18 pulses decaying from 17 to 8 J, with a repetition rate of 5 kHz, could be extracted from the laser. At a laser energy up to 12 J per pulse, ten electron temperature and density profiles were measured with an observational error of 10% on the electron temperature (T-e) and 5% on the electron density (n(e)) at n(e)=2.5x10(19) m(-3) per spatial element of 12 mm. The resolution of the detection optics enables to sample either the full plasma diameter of 900 mm with 120 spatial channels of 7.5 mm each, or a 160 mm long edge chord with 98 spatial channels of 1.7 mm each. (C) 2004 American Institute of Physics
Improved confinement transition in high density deuterium discharges at the FT-2 tokamak accompanied by onset of negative triangularity
Turbulence and anomalous tokamak transport control by Geodesic Acoustic Mode
The elementary process of turbulence control by Geodesic Acoustic Modes (GAMs) leading to modulation of its level at the GAM frequency is for the first time supported by experimental observations at the FT-2 tokamak. The modulation effect is confirmed by the global total-distribution-function gyrokinetic modelling of the tokamak discharge, predicting strong modulation of the electron thermal diffusivity induced by GAMs, which propagates inward and possesses the GAM temporal and spatial structure