Energy flux driven by electrostatic turbulence in the RFX edge plasma

Martines, E.; Antoni, V.; Desideri, Daniele; Serianni, G.; Tramontin, L.

doi:10.1088/0029-5515/39/5/302

Cited by 31 publications

(33 citation statements)

References 16 publications

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“…The mechanism which drives energy transport in this region has not been completely identified yet [29], but the present measurements, which suffer by a poorer spatial resolution than in the core, indicate that it has a weaker scaling with S. (ii) a core region, where magnetic turbulence is dominating both particle [30] and energy transport. In low-S regimes the core does not give an appreciable contribution to confinement, but when S is increased either in stationary state or transiently by fluctuations control techniques like PPCD, significant energy confinement is achieved.…”

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confidence: 63%

Scaling of Local Core Transport with Lundquist Number in the Reversed Field Pinch

Intravaia¹,

Marrelli²,

Martin³

et al. 1999

Phys. Rev. Lett.

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We investigate the scaling of the core energy transport with the magnetic Lundquist number S in the reversed field pinch. We analyze for the first time the electron temperature and thermal conductivity profiles and the dynamo magnetic fluctuations in a wide range of stationary plasmas produced in the RFX device at plasma current ranging between 0.2 and 1.1 MA. When S increases we measure an improvement of core confinement associated with the strengthening of the internal electron temperature profiles gradient and with the decrease of magnetic turbulence. This shows that core energy transport is related with magnetic fluctuations and can be ameliorated in high S regimes. PACS numbers: 52.25.Fi, 52.25.Gj, 52.55.Hc The role of self-generated internal electric currents is crucial to control the plasma dynamic evolution in the reversed field pinch (RFP), a magnetic configuration studied for the confinement of thermonuclear plasmas. These currents are driven by the continuous action of a magnetic field regeneration mechanism, often called "dynamo." This mechanism can be powered by magnetic fluctuations due to a wide spectrum of m 1 resistive tearing modes [1,2], which are thought to be the cause of anomalous energy and particle transport in the RFP core. This makes a well diagnosed laboratory plasma like the RFP resemble geophysical and astrophysical systems. Moreover, it offers a unique experimental opportunity to study the role of resistive magnetohydrodynamics (MHD) magnetic fluctuations in driving anomalous energy transport in magnetized plasmas [3] and how this mechanism scales to more collisionless, reactor relevant conditions. The role of turbulence in controlling transport is in fact still the subject of active investigation, in particular, in the plasma core where measurements are difficult.According to MHD theory, the relevant dimensionless parameter to scale the amplitude of normalized magnetic fluctuationsb B is the magnetic Lundquist number S, defined as the ratio of the resistive diffusion time t R m 0 a 2 h to the Alfvén time t A a y a , where a is the minor radius, h is the plasma electrical resistivity, and y A is the Alfvén velocity. Besides the simplest theoretical prediction based on the dimensionless Ohm's law,b B~S 21͞2 , quite a wide effort has been dedicated to investigate the behavior of magnetic fluctuations in the RFP [4-12]: exponents a for theb B~S 2a scaling law have been found ranging from a ഠ 0.07 to a ഠ 0.5. In particular, in a recent paper Stoneking et al. [11] have extended the range of S over which the scaling is experimentally studied and they have proposed a narrow range of measured exponents a, i.e., 0.07 # a # 0.18, depending on the density regime. Given these scaling laws, an improvement of the core energy confinement as S increases is expected, for example, on the basis of the quasilinear RechesterRosenbluth model [13]. This prediction has been only partially verified up to now: direct probe measurements of heat transport induced by magnetic fluctuations have been performed ...

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confidence: 63%

Scaling of Local Core Transport with Lundquist Number in the Reversed Field Pinch

Intravaia¹,

Marrelli²,

Martin³

et al. 1999

Phys. Rev. Lett.

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“…As already reported elsewhere [5], it is difficult to unfold directly the density fluctuations from light emission fluctuations, but from Langmuir measurements in old RFX [6] of edge electron density and temperature, density fluctuations are about two times those of temperature. The He flux injected for the measurements is 10 19 -10 20 atoms/s and it does not seem to influence the turbulence properties as evidenced by other edge diagnostic systems close to GPI in presence or absence of the He puff.…”

Section: Introductionmentioning

confidence: 98%

Edge turbulence in RFX-mod virtual-shell discharges

Scarin

Agostini

Cavazzana

et al. 2007

Journal of Nuclear Materials

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“…It has been experimentally shown that in some cases the fluctuating flux can account for an important part of the total particle flux in the edge region. [2][3][4] In particular, the level of fluctuation-induced transport at the limiter radius was of a comparable magnitude and scaled in a similar way with discharge conditions as the particle fluxes inferred from H ␣ measurements and global particle balance in tokamak plasmas. 2 However, it should be noted that in some cases fluctuation fluxes appear too high to be consistent with global particle balance.…”

Section: Introductionmentioning

confidence: 54%

“…In this respect, it is worth noting that experiments carried out in the Reversed Field Experiment device have shown a clear maximum in the fluctuation flux near the velocity shear layer location and then a decrease towards the inner plasma. 3 This result is also in clear disagreement with the interpretation of probe measurements based on the influence of the probe's pre-sheath region. Rev.…”

Section: Resultsmentioning

confidence: 74%

On the interpretation of fluctuation and E×B turbulent transport measured by Langmuir probes in fusion plasmas

Calderón¹,

Hidalgo²,

Pedrosa³

et al. 2004

Review of Scientific Instruments

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Plasma fluctuations and fluctuation-induced particle fluxes have been investigated in the plasma edge of the TJ-II stellarator using Langmuir probes. Simultaneous measurements of plasma fluctuations carried out by probes located in and out of the probe body sheath show similar results in the normalized level of fluctuations in the ion saturation current. However, floating potential fluctuations measured in the co and counter direction of the magnetic field on the sheath probe body show slight but significant differences. The local radial electrostatic turbulent driven transport measured in and out of the probe body sheath shows consistent results, within the errors bars due to uncertainties in the determination of the effective probe collecting area; the normalized local radial transport to the average ion saturation current (the effective velocity which is not affected by uncertainties in the probe area) show consistent results. These results and previous findings call into question the recent interpretation of probe measurements on the basis of the influence of the probe's pre-sheath zone [B. Labombard, Phys. Plasmas. 9, 1300 (2002)].

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Energy flux driven by electrostatic turbulence in the RFX edge plasma

Cited by 31 publications

References 16 publications

Scaling of Local Core Transport with Lundquist Number in the Reversed Field Pinch

Scaling of Local Core Transport with Lundquist Number in the Reversed Field Pinch

Edge turbulence in RFX-mod virtual-shell discharges

On the interpretation of fluctuation and E×B turbulent transport measured by Langmuir probes in fusion plasmas

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