The isotope effect in the RFX-mod experiment

Lorenzini, R.; Agostini, M.; Auriemma, F.; Carraro, L.; Fassina, A.; Franz, P.; Gobbin, M.; Innocente, P.; Puiatti, M. E.; Scarin, P.; Zaniol, B.; Zuin, M.

doi:10.1088/0029-5515/55/4/043012

Cited by 16 publications

(20 citation statements)

References 53 publications

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“…The particle influx is significantly reduced and the particle confinement time shows a scaling ∼Mi 0.45 . Such effect on confinement has been mainly associated to the mitigation of transport at the edge, internally to the scrape-off layer where long range correlations have been detected [31]. 3D magnetic fields have been applied both in H and D [32].…”

Section: Internal Transport Barriers and Helical State Formationmentioning

confidence: 99%

Overview of the RFX-mod fusion science activity

Zuin¹,

Bello²,

Marrelli³

et al. 2017

Nucl. Fusion

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This paper reports the main recent results of the RFX-mod fusion science activity. The RFX-mod device is characterized by a unique flexibility in terms of accessible magnetic configurations. Axisymmetric and helically shaped Reversed-field pinch equilibria have been studied, along with tokamak plasmas in a wide range of q(a) regimes (spanning from 4 down to 1.2 values). The full range of magnetic configurations in between the two, the so-called ultra low-q ones, has been explored, with the aim of studying specific physical issues common to all equilibria, such as, for example, the density limit phenomenon. The powerful RFX-mod feedback control system has been exploited for MHD control, which allowed to extend the range of experimental parameters, as well as to induce specific magnetic perturbations for the study of 3D effects. In particular, transport, edge and isotope effect in 3D equilibria have been investigated, along with runaway mitigations through induced magnetic perturbations. The first transitions to an improved confinement scenario in circular and D-shaped tokamak plasmas have been obtained thanks to an active modification of the edge electric field through a polarized electrode. The experiments are supported by intense modelling with 3D MHD, gyrokinetic, guiding center and transport codes. Proposed modifications to the RFX-mod device, which will enable further contributions to the solution of key issues in the roadmap to ITER and DEMO, are also briefly presented.

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Section: Internal Transport Barriers and Helical State Formationmentioning

confidence: 99%

Overview of the RFX-mod fusion science activity

Zuin¹,

Bello²,

Marrelli³

et al. 2017

Nucl. Fusion

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“…In Tokamaks and RFPs, Deuterium is almost always noted to have better confinement than Hydrogen [1,2]. However, the main scaling law for confinement, so-called Bohm or GyroBohm scaling laws predict that Deuterium should have worse confinement due to a larger gyro-radius [3].…”

Section: Introductionmentioning

confidence: 99%

“…The differences of confinement of H and D plasmas, the so-called "isotope effect" in Tokamaks, reversed-field pinches (RFPs) and Stellarators/Heliotrons has long been a largely theoretically unresolved problem. In Tokamaks and RFPs, Deuterium is almost always noted to have better confinement than Hydrogen [1,2]. However, the main scaling law for confinement, so-called Bohm or Gyro-Bohm scaling laws predict that Deuterium should have worse confinement due to a larger gyro-radius [3].…”

Section: Introductionmentioning

confidence: 99%

Role of Helium–Hydrogen ratio on energetic interchange mode behaviour and its effect on ion temperature and micro-turbulence in LHD

et al. 2018

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In the Large helical device, a change of energetic particle mode is observed as He concentration is varied in ion-ITB type experiments, having constant electron density and input heating power but with a clear increase of central ion temperature in He rich discharges. This activity consists of bursty, but damped energetic interchange modes (EICs, X Du et al., Phys. Rev. Lett. 114 p.155003 (2015)), whose occurrence rate is dramatically lower in the He-rich discharges. Mechanisms are discussed for the changes in drive and damping of the modes with He concentration. These EIC bursts consist of marked changes in the radial electric field, which is derived from the phase velocity of turbulence measured with the 2D phase contrast imaging (PCI) system. Similar bursts are detected in edge fast ion diagnostics. Ion thermal transport by gyro-Bohm scaling is recognised as a contribution to the change in ion temperature, though fast ion losses by these EIC modes may also contribute to the ion temperature dependence on He concentration, most particularly controlling the height of an "edge-pedestal" in the Ti profile. The steady-state level of fast ions is shown to be larger in Helium rich discharges on the basis of a compact neutral particle analyser (CNPA), and the fast-ion component of the diamagnetic stored energy. These events also have an influence on turbulence and transport. The large velocity shear induced produced during these events transiently improves confinement and suppresses turbulence, and has a larger net effect when bursts are more frequent in Hydrogen discharges. This exactly offsets the increased gyro-Bohm related turbulence drive in Hydrogen which results in the same time-averaged turbulence level in Hydrogen as in Helium.

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“…Contrary to what is to be expected from gyro-Bohm classical and neoclassical transport estimates, experiments show that heavier hydrogen isotopes produce enhanced plasma confinement in tokamaks [14,15,16,17]. Recently, improved confinement for increased ion mass has also been observed in a reversed field-pinch configuration [18]. It has been suggested that enhanced shear-flow activity for heavier hydrogen isotopes may suppress edge turbulence favorably.…”

Section: Introductionmentioning

confidence: 99%

Isotope effect on blob-statistics in gyrofluid simulations of scrape-off layer turbulence

Meyer

Kendl

2017

Nucl. Fusion

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Abstract. We investigate time-series obtained from gyrofluid simulations in coupled edge/scrape-off layer turbulence characteristic for fusion edge-region plasmas. Blob birth near the separatrix produces intermittent signals whose statistics depend on the ion mass of the reactor fuel, pointing towards overall slower dynamics for heavier isotopes. We find that a recently established shot-noise stochastic model for scrape-off layer fluctuations coincides reasonably well with the numerical simulations performed in this contribution.

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The isotope effect in the RFX-mod experiment

Cited by 16 publications

References 53 publications

Overview of the RFX-mod fusion science activity

Overview of the RFX-mod fusion science activity

Role of Helium–Hydrogen ratio on energetic interchange mode behaviour and its effect on ion temperature and micro-turbulence in LHD

Isotope effect on blob-statistics in gyrofluid simulations of scrape-off layer turbulence

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