Turbulence and transport characteristics of a barrier in a toroidal plasma

Fujisawa, A.; Shimizu, A.; Nakano, H.; Ohsima, S.; Itoh, K.; Iguchi, H.; Yoshimura, Y.; Minami, Takashi; Nagaoka, K.; Takahashi, C.; Kojima, M.; Nishimura, Satoshi; Isobe, M.; Suzuki, C.; Akiyama, Tsuyoshi; Nagashima, Yoshihiko; Ida, K.; Toi, K.; Ido, T.; Itoh, Sanae–I.; Matsuoka, K.; Okamura, S.; Diamond, P. H.

doi:10.1088/0741-3335/48/4/s15

Cited by 33 publications

(38 citation statements)

References 29 publications

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“…The effect of the E × B velocity shear on the growth of the turbulence plays a significant role for the transport reduction, see a review paper by Burrell [17] and references therein. Also it has been shown experimentally that the suppression of the turbulence-driven transport by the E × B velocity shear results in the transport barrier in helical devices [18]. As described above, the considerable reduction of the transport accomplished in the CERC plasma is realized with the spontaneous formation of the electron-root E r with the large shear.…”

Section: The Radial Electric Field Formation In Cerc Plasmamentioning

confidence: 88%

Formation of Electron-Root Radial Electric Field and its Effect on Thermal Transport in LHD High Te Plasma

Matsuoka

Satake

Takahashi

et al. 2013

Plasma and Fusion Research

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Neoclassical transport analyses have been performed for a high electron temperature LHD plasma with steep temperature gradient using a neoclassical transport simulation code, FORTEC-3D. It is shown that the large positive radial electric field is spontaneously formed at the core along with the increase in the electron temperature, while the neoclassical heat diffusivity remains almost unchanged. This indicates that the 1/ν-type increase expected in the neoclassical transport in helical plasmas can be avoided by the spontaneous formation of the radial electric field. At the same time, it is found that the experimentally estimated heat diffusivity is significantly reduced. This suggests that the formation process of the transport barrier in the high electron temperature plasma can be caused by the spontaneous formation of the radial electric field.

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Section: The Radial Electric Field Formation In Cerc Plasmamentioning

confidence: 88%

Formation of Electron-Root Radial Electric Field and its Effect on Thermal Transport in LHD High Te Plasma

Matsuoka

Satake

Takahashi

et al. 2013

Plasma and Fusion Research

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“…This table covers the LCO in the L-H transition dynamics as well as that related with internal transport barrier. Owing to the neoclassical mechanism, which drives the radial electric field, the observed phenomena in TJ-II should have a deep commonality with internal transport barrier phenomena in CHS [50], which has clearly demonstrated the impact of zonal flow on turbulence intensity in conjunction with the formation/decay of transport barriers.…”

Section: Observations Of Limit Cycle Oscillations Near Transition Boumentioning

confidence: 91%

An Assessment of Limit Cycle Oscillation Dynamics Prior to L-H Transition

Itoh

Fujisawa

2013

Plasma and Fusion Research

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In this article, experimental observations of limit cycle oscillations (LCO) that precede L-to-H transition are discussed. Issues are: (1) the existence of zonal flows, (2) spatio-temporal evolutions of turbulence intensity, and (3) periodic generations/decays of mean radial electric field and density. The role of Reynolds stress to accelerate the LCO flow is also addressed. The propagation of changes of the density gradient and turbulence amplitude into the core is commented. Varieties in experimental reports on these issues are explained, and possible origins of different interpretations are discussed. Problem definitions for the future research for resolution are presented.

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“…The ZFs have been identified in the CHS plasma, 24 and the temporal evolution of the intensities of the microfluctuations and the ZFs have been measured simultaneously. 25 Figure 2 shows the intensity of the ZFs, ͉E ZF ͉ 2 , and the normalized fluctuation amplitude, ͉eẼ r / ٌT 0 ͉ 2 , during the period of the e-ITB and in the case without the barrier. ٌ͑T 0 is the gradient of the mean electron temperature.͒ Data in the time window of 10 ms before the ITB-to-L transition ͑e-ITB͒ and those after the transition ͑L͒ are shown.…”

Section: ͑4͒mentioning

confidence: 99%

“…͓R =1 m, a = 0.2 m, B = 0.88 T, n =5 ϫ 10 18 m −3 , T e ͑0͒Ӎ1 keV and details of the discharges are given in Ref. 25.͔ The ZFs intensity is given by the integral of the power spectrum of the fluctuating electric field in the interval of 0.25 kHzϽ /2 Ͻ 2.5 kHz, and those in the interval of 25 kHzϽ /2 Ͻ 250 kHz are integrated for ͉eẼ r / ٌT 0 ͉ 2 . The error in the estimate of ͉eẼ r / ٌT 0 ͉ 2 ͑shown by an error bar͒ is mainly due to the uncertainty in ٌT 0 .…”

Section: ͑4͒mentioning

confidence: 99%

Physics of internal transport barrier of toroidal helical plasmas

et al. 2007

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The role of zonal flows ͑ZFs͒ in the formation of an internal transport barrier in a toroidal helical plasma is analyzed. The turbulent transport coefficient is shown to be suppressed when the plasma state changes from the branch of a weak negative radial electric field to the strong positive one. This new transition of turbulent transport is caused by the change of the damping rate of the ZFs. It is clearly demonstrated, theoretically and experimentally, that the damping rate of the ZFs governs the global confinement of toroidal plasmas. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2435310͔The turbulence-driven transport and the structural formation in confined plasmas are one of the principal issues of modern plasma physics.1 In particular, the transport barriers in toroidal plasmas 2 have attracted attention, in which the turbulent transport coefficient shows a steep gradient at a particular radius after the onset of the transition. 3-5 One thread of thought to explain transport barriers is the structural transition in the profile of the radial electric field, E r , and suppression of turbulence by its gradient through the sheared advection of fluctuations. 3,[6][7][8][9] For the study of turbulent structural transitions, toroidal helical plasmas provide unique opportunities: That is, the bifurcation of the radial electric field is influenced by the neoclassical ripple transport, 10 and the resultant electric field interface ͑by which the radial domains with positive E r and negative E r are separated͒ was predicted to induce the internal transport barrier. The E r interface was found on the compact helical system ͑CHS͒, 11 and the improvement of the electron confinement was found inside of the E r interface 12 ͓hereafter called the electron internal transport barrier ͑e-ITB͔͒. Observations on Wendelstein 7AS ͑W7AS͒, 13 LHD, 14 and other experiments followed. 5,15 The appearance and location of the E r interface were analyzed. [16][17][18] However, the essential issue of e-ITB formation has been unexplained, i.e., the turbulent transport coefficient was found to be suppressed not only near the interface but also in the whole region of strong positive E r ͑where the gradient dE r /dr is not strong enough to suppress turbulent transport͒. Therefore the fundamental problem remains unresolved. In this article, we study the role of zonal flows ͑ZFs͒ ͑Ref. 19͒ in the formation of an e-ITB. The turbulent transport coefficient, in which the screening influence of ZFs is included, is shown to be suppressed when the plasma state changes from the branch of weak negative E r to that of strong positive E r . This new transition of turbulent transport is induced by the change of the damping rate of the ZFs, which is strongly influenced by the neoclassical ripple transport. The analytic theory is explained first. Then the transport analysis is shown. Finally, the experimental verification based on the CHS plasmas is demonstrated. This is the first report to clarify that the collisional damping rate of the ZFs gover...

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Turbulence and transport characteristics of a barrier in a toroidal plasma

Cited by 33 publications

References 29 publications

Formation of Electron-Root Radial Electric Field and its Effect on Thermal Transport in LHD High <i>T</i><sub>e </sub>Plasma

Formation of Electron-Root Radial Electric Field and its Effect on Thermal Transport in LHD High <i>T</i><sub>e </sub>Plasma

An Assessment of Limit Cycle Oscillation Dynamics Prior to L-H Transition

Physics of internal transport barrier of toroidal helical plasmas

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