Turbulent fluctuations and confinement in JET

Malacarne, M.; Duperrex, P.A.

doi:10.1088/0029-5515/27/12/011

Cited by 34 publications

(13 citation statements)

References 17 publications

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“…These turbulent filaments seen in TFTR with high power NBI are at least qualitatively similar to those reported in smaller ohmic tokamaks [1,2,13,14] and also in JET with IvT°I [16]. However, several interesting new features of these edge fluctuations could be inferred with the present 2-D optical imaging system.…”

Section: Discussionsupporting

confidence: 85%

“…A brief report of the present TFTR visible imaging observations was also given previously in the context of preliminary TFTR edge fluctuation measurements [15]. Subsequent observations of visible light fluctuations from the edge of JET [16] made with unfiltered surface barrier detectors also showed turbulent filaments similar to those in Ref. [15] The view shown schematically in Fig.…”

Section: Previous Work In Tokamakssupporting

confidence: 71%

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Visible imaging of edge fluctuations in TFTR

Zweben¹,

Medley²

1989

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Images of the visible light emission from the inner wall region of TFTR have been made using a rapidly gated, intensified TV camera. Strong "filamentation" of the neutral deuterium D^ light is observed when the camera gating time is <100 jisec during neutral-beam-heated discharges. These turbulent filaments vary in position randomly vs. time and have a poloidal wavelength of = 3-5 cm which is much shorter than their parallel wavelength of s: 100 cm. A second and new type of edge fluctuation phenomenon, which we call a "merfe," is also described. Merfes are a regular poloidal pattern of toroidally symmetric, small-scale marfes which move away from the inner midplane during the current decay after neutral beam injection. Some tentative interpretations of these two phenomena are presented.

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Section: Discussionsupporting

confidence: 85%

Section: Previous Work In Tokamakssupporting

confidence: 71%

Visible imaging of edge fluctuations in TFTR

Zweben¹,

Medley²

1989

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“…On the other hand, the level of fluctuations may become significant deeper in the plasma core [3,4]; experiments with a variable safety factor q in the TOKAPOLE tokamak [5] indicate significance of magnetic fluctuations at low q. Experiments in the ISX-B tokamak [6] at high beta (plasma pressure), Doublet III [7], and JET [8] show a correlation between confinement time and magnetic fluctuations. As the confinement time decreases, the fluctuations increase; however, causality between them was not established.…”

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confidence: 99%

“…Given the overlapping of magnetic islands, this mechanism can be responsible for the total energy transport as it was implied in Refs. [7,8]. This work has been supported by the U.S. Department of Energy.…”

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confidence: 99%

Measurement of Magnetic Fluctuation Induced Energy Transport in a Tokamak

et al. 1995

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Magnetic fluctuation induced electron energy transport is measured in the Continuous Current Tokamak [R.J. Taylor et al. , Phys. Rev. Lett. 63, 2365(1989] at 0.75 ( r/a ( 1 for fluctuations with 0 & f ( 150 kHz. The flux, produced by electrons traveling parallel to a fluctuating magnetic field, is obtained from the correlation between the fluctuations in the parallel heat flux and the radial magnetic field. It was found that the magnetic fluctuations do not contribute to the total energy transport except in the vicinity of the q = 2 magnetic surface in the presence of large amplitude Mirnov oscillation. PACS numbers: 52.55.Fa, 52.25.Fi, 52.25.Gj, 52.55.Pi The role of magnetic fluctuations in the transport of energy in a tokamak has been an unresolved question for decades. Lacking direct measurements of the energy flux driven by magnetic fluctuations, inferences have been made from measurements of the magnetic fluctuation amplitude. For example, a simple quasilinear estimate [1,2] y, = Ij,Lb, of the electron thermal conductivity is often applied to experiment (v, is the electron thermal velocity, L is the parallel correlation length for the magnetic fluctuations, and b"= B"/B is their relative amplitude).This estimate usually implies that magnetic fluctuation induced transport is small at the plasma edge, as concluded in TEXT-U [3]. On the other hand, the level of fluctuations may become significant deeper in the plasma core [3,4]; experiments with a variable safety factor q in the TOKAPOLE tokamak [5] indicate significance of magnetic fluctuations at low q. Experiments in the ISX-B tokamak [6] at high beta (plasma pressure), Doublet III [7], and JET [8] show a correlation between confinement time and magnetic fluctuations. As the confinement time decreases, the fluctuations increase; however, causality between them was not established.To determine decisively the role of the magnetic fluctuations in energy transport requires measurement of the energy flux specifically generated by the fluctuations. The radial energy flux arising from electron motion parallel to the magnetic field is given by Q"= Q~~r = (Q . b) (b r), where b and r" are unit vectors along the magnetic field and the radial direction, respectively. Separating Q and b into equilibrium and fluctuating quantities yields the ensemble-averaged radial energy flux [9] &Q~~B, &where Q~~i s the fluctuating electron heat flux parallel to the equilibrium magnetic field [i.e., Q~~= f v~~(mv /2) f(v)dv], B" is the fluctuating radial magnetic field, B is the equilibrium field, and the brackets ( ) represent the flux surface averaged product of fluctuating quantities. The key to measuring the energy flux from fluctuating magnetic field is to obtain Q~~a nd B, locally within the plasma. In this Letter we present direct measurement of magnetic fluctuation induced electron heat transport in the Continuous Current Tokamak (CCT) [10] device. This work differs from all past work in which transport is calculated using the Rechester-Rosenbluth transport model [2] with t...

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“…It is important to develop diagnostics that can detect magnetic fluctuations in a fusion plasma, especially because of the interconnection between magnetic fluctuations and transport 1 . Such a diagnostic for tokamaks must overcome a universal probem: the level of magnetic fluctuations is much lower than that of the electron density fluctuations.…”

Section: Introductionmentioning

confidence: 99%