Long-range spatial correlations in the turbulent edge plasma of the L-2M stellarator
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LongRange Spatial Correlations in the Turbulent Edge Plasma of the L2M Stellarator D. G. Vasil’kov, Yu. V. Kholnov, and S. V. Shchepetov Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia email:[email protected] Received July 19, 2012; in final form, December 12, 2012
Abstract—Longrange spatial correlations in the turbulent plasma of the L2M stellarator were revealed experimentally, and their relation to the geometry of magnetic surfaces was analyzed (Plasma Phys. Control. Fusion 50, 045001 (2008)). The operation modes of the facility in which fast transport transitions in plasma are possible were studied. Upon these transitions, the turbulence level is found to decrease substantially. It is shown that longrange spatial correlations are typical of relatively narrow frequency ranges. In particular, before a transport transition, such frequency ranges are f ~ 30–40 kHz and f ~ 1–3 kHz. After the transition, longrange spatial correlations in the frequency range of f ~ 30–40 kHz disappear due to a significant decrease in the turbulence level in this frequency range. At the same time, correlations in the low frequency range are retained and new correlations at frequencies of f ~ 6–12 kHz occur. It is found that global electromagnetic oscillations in the frequency range of f ~ 1–3 kHz are related to the m/n = 0/0 perturbation and its toroidal satellites (here, m and n are the poloidal and toroidal mode numbers, respectively). It is also shown that, after the transport transition, a threedimensional localized electromagnetic mode at the frequency of the geodesic acoustic mode governed by the average magnetic field curvature is excited. At higher frequencies typical of a geodesic acoustic mode related to the threedimensional curvature of the magnetic field, no longrange spa tial correlations were observed both before and after the transport transition. DOI: 10.1134/S1063780X13080072
1. INTRODUCTION It is commonly accepted that heat and particle transport in the edge plasma is determined by turbu lent processes. It turns out that the characteristic properties of the turbulent edge plasma in different magnetic confinement systems (tokamaks, stellara tors, and reversed pinches) are often very similar (see, e.g., [1–3]). Plasma turbulence has been studied using various approaches. However, in spite of a large num ber of mathematical models, a noncontradictory self consistent theory of anomalous transport is still lack ing [4–6]. This is partially due to the fact that, in tur bulent plasma, there can exist very different objects that can hardly be described in the framework of a uni fied statistical approach. For example, largescale structures with longrange spatial correlations can exist in a system with differentorder rational mag netic surfaces. In this case, a priori, there are several processes that can lead to the appearance of such cor relations. For example, quasilinear modes (with all possible satellites) localized in the vicinity of
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