Radial electron thermal diffusivities from the perturbation of the electron temperature profile by a turbulent heating pulse in the TORTUR Tokamak

Zeeuw, W.A. de; Yousef, Nader da Fonseca; Kluiver, H. de

doi:10.1088/0741-3335/29/5/005

Cited by 6 publications

(2 citation statements)

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“…Insertion of the estimated fluctuation ratio B,iBT z 6 x lo-' in the centre, in the expression for the magnetic heat diffusivity zm = (B,/BT)2 vth,,Rq (WALTZ, 1985), yields xm = 0.07 m2 s-' for TORTUR near the plasma centre. This amounts to about 10% of the experimental value x,,,(O) = 0.6 m2 srl (DE ZEEUW et al, 1987). Clearly, to appreciate the contribution of j l m more quantitatively, direct fluctuation experiments are required.…”

Section: A Discussion Of the Fluctuation Spectrummentioning

confidence: 94%

“…The radial temperature increments, ATe,i(r), and their subsequent decreases in time have been used to derive the local heat diffusivity, l e ( r ) , by a perturbative method (DE ZEEUW et al, 1987). During the plateau stage with n,(O) = 6 x 10'' m-3, a value ~~( 0 ) = 0.6 m2 s-l has been found, slowly increasing towards the outside.…”

Section: Stage Iii: the Turbulent Heating Pulsementioning

confidence: 99%

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Current driven turbulence and microturbulent spectra in the TORTUR Tokamak

Kluiver

Barth

Donné

1988

Plasma Phys. Control. Fusion

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In the TORTUR Tokamak ( R = 0.46 m, a = 0.085 m. B, = 2.9 T, I, < 55 kAl T, P T, < 1 keV, IZ < IOzo m--3, Z,,,(imp) < 2) plasmas are heated by current driven turbulence in the build-up phase to high beta values and electron temperatures a factor of two above values retrieved from scaling law studies reported in literature for ohmically heated Tokamaks. A stationary state of current driven turbulence with the same fl value can be maintained during the plateau state by virtue of relatively high loop voltages ( 2 4 times the classical value) giving proportionally enhanced resistive dissipation.The turbulent fluctuations of the plateau state have been observed at r,'a = 0.7 by collective scattering of microwaves in a wide spectral region for I,, P 30 kA corresponding with plasmas in the safe q range: y(u) = 7. Three frequency domains of turbulence have been distinguished with rather arbitrary separation, interpreted as follows: (a) A low-frequency region (0 -0.7 MHz) containing the frequently reported electrostatic drift modes and low-frequency electromagnetic modes, which may account for a considerable fraction of the electron heat diffusivity xe(r); (b) Unstable magnetic microtearing modes driven by a supercritical electron temperature gradient characterized by real frequencies in the interval 0.7-3 MHz.Indirect ebidence for the presence of this magnetic tearing exists by the observation of distinct satellites in the Thomson scattering spectrum: (c) A magnetic fluctuation spectrum in the high-frequency region (5-55 MHz) which can be ascribed to current driven modes from non-thermal electron tails around 50 keV. All spectral domains exhibit slow time periodicities synchronous with the development of high-energy tails of the ions and with the Mirnov-type small sawteeth found on the loop voltage, electron cyclotron emission signals and soft X-rays.

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Section: A Discussion Of the Fluctuation Spectrummentioning

confidence: 94%

Section: Stage Iii: the Turbulent Heating Pulsementioning

confidence: 99%

Current driven turbulence and microturbulent spectra in the TORTUR Tokamak

Kluiver

Barth

Donné

1988

Plasma Phys. Control. Fusion

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Experimental results on current-driven turbulence in plasmas - a survey

1991

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Determination of the local current density by means of tangential Thomson scattering: Experimental setup, feasibility test, and preliminary observations

Barth

1989

Review of Scientific Instruments

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The local current density is one of the most important and most difficult parameters to be determined in a thermonuclear plasma. An experimental setup to measure the local electron drift velocity and thus, the current density, by means of tangential Thomson scattering, is presented. The drift velocity of the plasma causes a small wavelength shift of the scattered spectrum, which will be proportional to the local current density if toroidal ion rotation can be neglected. The ratio between the drift velocity and the mean thermal electron velocity is small, typically ∼0.05. A 20-channel high transmission polychromator has been constructed to observe the electron temperature and density within an accuracy of 1% and the drift velocity within 20% at a plasma density ne≊5×1019 m−3 and a laser energy of 7 J. A feasibility test on radial scattering shows that there is good agreement between the accuracy obtained from quantum statistics and observations, respectively. The high transmission and relatively high resolution of the polychromator enable the observation of irregularities in the velocity distribution which should be taken into account in the determination of the drift velocity. Preliminary observations in the tangential direction demonstrate the possibility to determine the drift velocity by a single laser shot. At ne ≊6×1019 m−3 and a laser energy of 3.5 J in the scattering volume a wavelength shift of −2.5±0.5 nm has been recorded corresponding to jφ≊1×107 A/m2.

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Radial electron thermal diffusivities from the perturbation of the electron temperature profile by a turbulent heating pulse in the TORTUR Tokamak

Cited by 6 publications

References 2 publications

Current driven turbulence and microturbulent spectra in the TORTUR Tokamak

Current driven turbulence and microturbulent spectra in the TORTUR Tokamak

Experimental results on current-driven turbulence in plasmas - a survey

Determination of the local current density by means of tangential Thomson scattering: Experimental setup, feasibility test, and preliminary observations

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