Edge plasma physics modifications due to magnetic ripple in RFX-mod

Scarin, P.; Agostini, M.; Carraro, L.; Cavazzana, R.; Ciaccio, G.; Spizzo, G.; Spolaore, M.; Vianello, N.

doi:10.1016/j.jnucmat.2014.10.052

Cited by 4 publications

(7 citation statements)

References 21 publications

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“…it reproduces a perfect helical shape. This was reported in the past on RFX, based on measurements performed on the equatorial plane, only [8][9][10][11][12][13][14][15]. The new pattern of L c,w reproduces quite well experimental data: in figure 9 black triangles are the position (in u 1,7 ) of the minimum of the floating potential V f , measured with a poloidal array of 5 internal probes belonging to the ISIS system [48], and averaged over ∼20 discharges.…”

Section: Connection Lengthssupporting

confidence: 79%

“…In previous RFX studies, a very good agreement was found between a helical 1/7 edge topology and measurements of floating potential, edge electron pressure and E × B flow [8][9][10][11][12][13][14][15]: the conclusion was that plasma kinetic quantities are indeed shaped as the 1/7 dominant helix. The theoretical reason for this is that electrons follow closely the magnetic field lines, so that even a small amount of chaos can influence electron density and temperature [16][17][18][19].…”

Section: Introductionsupporting

confidence: 52%

“…Despite this tangled topology, in the past a very good agreement has been found between a simple, helical 1/7 symmetry and measurements of floating potential, edge electron pressure and E × B flow [8][9][10][11][12][13][14][15]. Nevertheless, those measurements were performed along the toroidal angle φ, at two fixed poloidal locations θ = 0, π (the same as in figure 2).…”

Section: Mode Spectra and Basic Properties Of The Rfp Helical Topologymentioning

confidence: 90%

“…Our case study is the topology of the RFX-mod helical edge (r/a 0.85), which is dominated by a 1/7 modulation. In the past, this base mode was found to dominate measurements of electron pressure, floating potential and plasma flow [8][9][10][11][12][13][14][15]. New measurements show that m = 0 effects are strong [21,22], the 0/7 mode being the main sideband toroidally coupled to the base mode [23].…”

Section: Discussionmentioning

confidence: 99%

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Toroidal coupling in the kinetic response to edge magnetic perturbations

et al. 2017

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The magnetic topology of the stochastic edge of a helical reversed-field pinch, with helicity m/n, shows to be deeply influenced by higher harmonics (m ± 1)/n, with the same n, due to toroidal coupling. As a consequence, by measuring kinetic quantities in a particular θ, φ location, one can incur in substantial errors or mis-interpretations of the kinetic plasma response: only a full 3D coverage of θ, φ angles can reveal the real topology of the plasma. This can be a caveat for MP application in tokamaks, because it shows that toroidal and poloidal sidebands, though smaller than the base mode by a factor ∼ = a/R, can have a sizable effect on the kinetic response of the edge plasma, and thus on related issues (for example, ELM stabilization and suppression).

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Section: Connection Lengthssupporting

confidence: 79%

Section: Introductionsupporting

confidence: 52%

Section: Mode Spectra and Basic Properties Of The Rfp Helical Topologymentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

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Toroidal coupling in the kinetic response to edge magnetic perturbations

et al. 2017

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“…By evaluating the crosscorrelation between toroidally spaced floating potential probes it is possible to obtain an estimate of the propagation velocity of V f fluctuations; since the probes are also installed at different poloidal angles, ( ) θ φ v t, is evaluated. In previous papers [10,29,30] it was observed that the spatial structure of φ v reflects the magnetic field topology, but detailed analyses along the poloidal direction are missing. Here we show in figure 12 the fluctuation of the toroidal velocity δ = − φ φ φ v v v as a function of the helical angle for four different poloidal angles.…”

Section: D Edge Perpendicular Velocitymentioning

confidence: 99%

Edge plasma properties with 3D magnetic perturbations in RFX-mod

Agostini¹,

Scarin²,

Spizzo³

et al. 2017

Nucl. Fusion

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The response of the edge plasma to a magnetic perturbation (MP) is studied in the RFXmod device, in both reversed field pinch (RFP) and tokamak discharges. The use of spatially distributed diagnostics, in particular along the poloidal direction, allows a direct 3D characterization of the plasma. It is shown that there is a difference between the spectrum of the MP and that of different properties of the edge plasma, such as the floating potential, the electron pressure and the flow, for both RFP and tokamak plasmas. In particular, for RFP cases, even if the magnetic perturbation is mainly m = 1, with the amplitude of the m = 0 and m = 2 sidebands negligible, the connection length to the wall of the magnetic field L cw has a more complex structure. The ergodic regions, with L cw larger than the Kolmogorov length, are due to the interaction of both m = 1 and m = 0 modes, showing a complex and non-monochromatic behaviour along the poloidal angle. This structure of L cw is responsible for the impure m = 1 behaviour of the plasma wall interaction, floating potential and electron pressure. Thus the helicity of the edge plasma is quite different from that of the dominant MP.

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