Wall conditioning and density control in the reversed field pinch RFX-mod

Puiatti, M. E.; Spizzo, G.; Auriemma, F.; Carraro, L.; Cavazzana, R.; Gobbin, M.; Innocente, P.; Predebon, I.; Scarin, P.; Agostini, M.; Canton, A.; Bello, S. Dal; Fassina, A.; Franz, P.; Grando, L.; Mansfield, D. K.; Marrelli, L.; Martin, P.; Mazzitelli, G.; Munaretto, S.; Roquemore, L.; Ruzzon, A.; Terranova, D.; Valisa, M.; Vertkov, А.V.; Zaniol, B.

doi:10.1088/0029-5515/53/7/073001

Cited by 19 publications

(22 citation statements)

References 40 publications

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“…Since the RFP heating is ohmic, multiplying equation ( 1) by n G , we get (V − V dyn ) I p = V G πa 2 n 0 , which is a linear dependence of the central density on heating power (input power minus the dynamo term). This dependence has indeed been reported for RFX [23]: with larger input power, larger densities can be accessed. This is a result reminiscent of the Sudo scaling, and it has been shown in the past also in the TEXTOR tokamak [24].…”

Section: Density Limit Phenomenology In the Rfx Rfpsupporting

confidence: 76%

“…This is a result reminiscent of the Sudo scaling, and it has been shown in the past also in the TEXTOR tokamak [24]. In the same paper [23], it was reported that, with lithization, the power required to get to the same density is half as much as in standard RFX discharges. According to equation (1), this means that also V G can be greatly reduced with wall conditioning.…”

Section: Density Limit Phenomenology In the Rfx Rfpmentioning

confidence: 71%

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Density limit studies in the tokamak and the reversed-field pinch

Spizzo¹,

Pucella²,

Tudisco³

et al. 2015

Nucl. Fusion

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The ITER scenarios and the project of DEMO involve stable operation above the Greenwald density, which justifies efforts to understand and overcome the density limit, this last observed as a disruptive termination of tokamak discharges and a thermal crash (with no disruption) of stellarator and reversed-field pinch (RFP) ones. Both in the tokamak and the RFP, new findings show that the high density limit is not governed by a unique, theoretically well-determined physical phenomenon, but by a combination of complex mechanisms involving two-fluid effects, electrostatic plasma response to magnetic islands and plasma-wall interaction. In this paper we will show new evidence challenging the traditional picture of the 'Greenwald limit', in particular with reference to the role of thermal instabilities and the edge radial electric field E r in the development of this limit.

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Section: Density Limit Phenomenology In the Rfx Rfpsupporting

confidence: 76%

Section: Density Limit Phenomenology In the Rfx Rfpmentioning

confidence: 71%

Density limit studies in the tokamak and the reversed-field pinch

Spizzo¹,

Pucella²,

Tudisco³

et al. 2015

Nucl. Fusion

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“…On the other hand, as the density is increased, its profile becomes hollow, due to the lack of continuous core fuelling (the only central fuelling is by pellet injection, whose effectiveness is limited by the short particle confinement time [42]), combined with an outward pinch and a high recycling [6]. In order to improve density control, in addition to boronization, lithization by different techniques has been applied, including evaporation and lithization by a liquid lithium limiter [43] and, recently, solid Li multi-pellet injection [44]. The latter technique allowed a more uniform Li deposition on the plasma wall, as shown in figure 12, where Li influxes at different toroidal positions as obtained after Li evaporation and by multipellet injection are compared.…”

Section: Density Control and Pwi Studiesmentioning

confidence: 99%

Overview of the RFX-mod contribution to the international Fusion Science Program

Puiatti¹,

Bello²,

Marrelli³

et al. 2015

Nucl. Fusion

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The RFX-mod device is operated both as a reversed field pinch (RFP), where advanced regimes featuring helical shape develop, and as a tokamak. Due to its flexibility, RFX-mod is contributing to the solution of key issues in the roadmap to ITER and DEMO, including MHD instability control, internal transport barriers, edge transport and turbulence, isotopic effect, high density limit and three-dimensional (3D) non-linear MHD modelling. This paper reports recent advancements in the understanding of the self-organized helical states, featuring a strong electron transport barrier, in the RFP configuration; the physical mechanism driving the residual transport at the barrier has been investigated. Following the first experiments with deuterium as the filling gas, new results concerning the isotope effect in the RFP are discussed. Studies on the high density limit show that in the RFP it is related to a toroidal particle accumulation due to the onset of a convective cell. In the tokamak configuration, q(a) regimes down to q(a) = 1.2 have been pioneered, with (2,1) tearing mode (TM) mitigated and (2,1) resistive wall mode (RWM) stabilized: the control of such modes can be obtained both by poloidal and radial sensors. Progress has been made in the avoidance of disruptions due to the (2,1) TM by applying q(a) control, and on the general issue of error field control. The effect of externally applied 3D fields on plasma flow and edge turbulence, sawtooth control and runaway electron decorrelation has been analysed. The experimental program is supported by substantial theoretical activity: 3D non-linear visco-resistive MHD and non-local transport modelling have been advanced; RWMs have been studied by a toroidal MHD kinetic hybrid stability code.

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“…In RFX-mod, the carbon wall, due to its high hydrogen retention, dominates the behaviour of the plasma density, leading to uncontrolled H release in the presence of a strong plasma-wall interaction (PWI). Experiments testing several techniques of first wall lithization led to the reduction of recycling and improvement of density control [4] (section 3.2). (b) Feedback control of MHD stability.…”

Section: Advances In Active Controlmentioning

confidence: 99%

Overview of the RFX-mod fusion science programme

et al. 2013

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This paper reports the highlights of the RFX-mod fusion science programme since the last 2010 IAEA Fusion Energy Conference. The RFX-mod fusion science programme focused on two main goals: exploring the fusion potential of the reversed field pinch (RFP) magnetic configuration and contributing to the solution of key science and technology problems in the roadmap to ITER. Active control of several plasma parameters has been a key tool in this endeavour. New upgrades on the system for active control of magnetohydrodynamic (MHD) stability are underway and will be presented in this paper. Unique among the existing fusion devices, RFX-mod has been operated both as an RFP and as a tokamak. The latter operation has allowed the exploration of edge safety factor qedge < 2 with active control of MHD stability and studies concerning basic energy and flow transport mechanisms. Strong interaction has continued with the stellarator community in particular on the physics of helical states and on three-dimensional codes.

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Wall conditioning and density control in the reversed field pinch RFX-mod

Cited by 19 publications

References 40 publications

Density limit studies in the tokamak and the reversed-field pinch

Density limit studies in the tokamak and the reversed-field pinch

Overview of the RFX-mod contribution to the international Fusion Science Program

Overview of the RFX-mod fusion science programme

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