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Yanovskiy V.V.,Consorzio RFX
Physics of Plasmas | Year: 2016

On the example of the plasma and mode parameters relevant, e.g., to the experiments on the rotational stabilization of resistive wall modes (RWMs) reported in Reimerdes et al. [Phys. Rev. Lett. 98, 055001 (2007)], it is shown that the plasma resistivity can have a strong impact on the stability of RWMs. The stability criteria for kinetic RWMs derived in Hu and Betti [Phys. Rev. Lett. 93, 105002 (2004)] has been complemented by the restriction on the maximum mode damping rate. © 2016 Author(s).

Agency: European Commission | Branch: FP7 | Program: CP | Phase: SPA-2007-2.2-01;SPA-2007-2.2-02 | Award Amount: 5.36M | Year: 2008

The main objective of the HiPER project is to initiate technological and programmatic consolidation in the development of innovative electric propulsion technologies (and of the related power generation) to fulfill future European space transportation needs. The objective will be pursued by conceiving and substantiating a long term vision for European space transportation and exploration, considering realistic developments in the state-of-the-art, and by performing basic research and proof-of-concept experiments on the key technologies identified by such a vision.

Cavenago M.,Viale Delluniversita N2 | Veltri P.,Consorzio RFX
Plasma Sources Science and Technology | Year: 2014

Deflection of negative ion beamlets due to the magnets embedded in the first extraction electrode for the purpose of dumping the co-extracted electrons is a serious issue for multiaperture ion accelerators of neutral beam injectors. Several kinds of magnet arrays which offer the possibility of cancelling ion deflection, employing crossed rows of magnets or even more compact parallel row arrangements, are discussed. A general equation for beamlet deflection is presented here, and the interference of the magnetic deflection and the electrostatic lens steering is carefully calculated; this equation may also include beamlet-beamlet interactions and image charge effects. Analytical expressions are given for the field and the line integrals for the magnet arrays, and these are simplified for beam optics calculations, but still retain an excellent agreement with numerical values. Optimization formulas for the filling fraction xy of the magnets are given, for cancellation of deflection both after the first electrode or after the second accelerating electrode. The latter case is of direct interest for the design of small accelerators (e.g., NIO1), for which compact solutions are proposed, while the former case may approximate well the design of a large accelerator such as MITICA, with a predicted xy = 0.1015 against a numerical optimized value of 0.0975 ±0.005 in normal conditions. The detailed comparison between simulation results and theory shows that thin lens models are suitable approximations for calculating beam steering. Stability of optimal xy prediction with respect to the first accelerating gap length is shown, and the variation of xy with the voltage is discussed. © 2014 IOP Publishing Ltd.

The cylindrical MHD model integrated with a feedback system is applied to the study of resistive wall mode (RWM) in reversed field pinch (RFP) plasmas. The model takes into account the compressibility, longitudinal flow, viscosity and resistive wall with a finite thickness. The study, via both analytical and numerical analyses, provides a physical understanding on the following subjects: firstly, on the nature of the instability spectrum of the RWM observed in RFP plasmas; specifically, the growth rates of the two groups of the RWMs (internally non-resonant and externally non-resonant) have opposite dependence on the variation of the field reversal. Secondly, on the response of the unstable plasmas to the feedback control in RFPs, the mode behaviour in plasmas under the feedback is clarified and discussed in detail. Finally, the linear solutions of time evolution of RWM instability in various feedback scenarios are given. The effects of the wall proximity, the sensor location and the system response time are discussed, respectively. © 2011 IAEA, Vienna.

Pasqualotto R.,Consorzio RFX
Journal of Instrumentation | Year: 2012

ITER nuclear fusion experiment requires additional heating via neutral beams by means of two injectors, delivering 16.5 MW each, up to one hour. This power level results from the neutralization of negative deuterium ions generated by an RF source and accelerated to 1 MeV. Such specifications have never been simultaneously achieved so far and therefore a test facility is being constructed at Consorzio RFX, to demonstrate the feasibility of a prototype neutral beam injector. The facility will host two experimental devices: SPIDER, a 100 kV negative hydrogen/deuterium RF source, full size prototype of the ITER source, and MITICA, a prototype of the full ITER injector. SPIDER will be devoted to optimize the extracted negative ion current density and its spatial uniformity and to minimize the co-extracted electron current. Negative hydrogen is mainly produced by conversion of hydrogen particles at the cesium coated surface of the plasma grid. The interplay of these two species is fundamental to understand and optimize the source performance. Two laser-aided diagnostics play an important role in measuring the negative hydrogen and cesium density: cavity ring down spectroscopy and laser absorption spectroscopy. Cavity ring down spectroscopy will use the photo-detachment process to measure the absolute line-of-sight integrated negative ion density in the extraction region of the source. Laser absorption spectroscopy will be employed to measure the line integrated neutral cesium density, allowing to study the cesium distribution in the source volume, during both the plasma and the vacuum phases. In this paper, the design of the laser-aided diagnostic systems on SPIDER is presented, supported by a review of results obtained in other operating experiments. © 2012 IOP Publishing Ltd and Sissa Medialab srl.

Predebon I.,Consorzio RFX | Sattin F.,Consorzio RFX | Veranda M.,Consorzio RFX | Bonfiglio D.,Consorzio RFX | Cappello S.,Consorzio RFX
Physical Review Letters | Year: 2010

In the reversed field pinch RFX-mod strong electron temperature gradients develop when the single-helical-axis regime is achieved. Gyrokinetic calculations show that in the region of the strong temperature gradients microtearing instabilities are the dominant turbulent mechanism acting on the ion Larmor radius scale. The quasilinear evaluation of the electron thermal conductivity is in good agreement with the experimental estimates. © 2010 The American Physical Society.

Gobbin M.,Consorzio RFX | Spizzo G.,Consorzio RFX | Marrelli L.,Consorzio RFX | White R.B.,Princeton Plasma Physics Laboratory
Physical Review Letters | Year: 2010

Test particle evaluation of the diffusion coefficient in a fusion plasma in the reversed-field pinch (RFP) configuration shows distinct similarities with stellarators when the plasma spontaneously evolves towards a helical shape. The almost total absence of superbanana particles at the levels of helical deformation seen in experiment (Bh/B=10%) causes transport to be proportional to collision frequency (at low collisions). This fact excludes the possibility that the minimum conceivable transport could be inversely proportional to collision frequency, which is typical of unoptimized stellarators. This result strengthens the perspectives of the helical RFP as a fusion configuration. © 2010 The American Physical Society.

Sartori E.,Consorzio RFX | Veltri P.,Consorzio RFX
Vacuum | Year: 2013

A code for efficient and accurate gas pressure calculation named AVOCADO is described in this paper. The non-collisional gas flow is resolved at steady-state considering only the solid boundaries of the domain (gas-wall interaction), where the gas pressure is defined. The mutual interactions between elements of the three-dimensional discretized surfaces are evaluated in terms of fluxes considering the cosine law as scattering operator. A coefficient matrix, which describes the geometry of the model, is parallel computed using view factors; correction factors accounting for gas species and specified boundary conditions are then applied, before the degree of freedom inversion is carried out. The developed tool includes also an efficient BiCGstab (biconjugate gradient stabilized method) implementation for sparse matrix inversion, to solve the system of equations. This surface finite element method reduces the degrees of freedom of the linear system and allows for fast solution of gas pressure distributions in both well-detailed and complex geometries. Overall results and pressure distribution obtained with the application of the code on typical analytical cases are presented and discussed. © 2012 Elsevier Ltd. All rights reserved.

In the framework of innovative feedback schemes for control of dynamo tearing modes (TMs) in reversed field pinch (RFP) devices, the possibility of placing active coils between a non-conducting first wall and the vacuum vessel is investigated with a MHD based model. In this formulation the vacuum vessel plays the role of a stabilizing shell. With active coils placed outside the vacuum vessel and magnetic sensors located inside it, a previous study (Zanca 2009 Plasma Phys. Control. Fusion 51 015006) has shown that the ratio between the TM radial field amplitudes at the sensors' radius and at the resonant surface can be made close to but not smaller than the ideal-shell limit. This analysis considered a continuous-time modelling of the feedback. The same model admits a very appealing solution when applied to the in-vessel coil configuration: For high gains the radial field measured by sensors located between the first wall and the coils is reduced virtually to zero and the TM rotation frequency approaches the unperturbed natural value. In this case the feedback would mimic the stabilizing action of an ideal shell placed at the sensor radius. An improvement which makes the model closer to a realistic digital feedback is also presented. This is realized by introducing a discretetime feedback action which includes a non-zero latency time. Unfortunately, the nice solution for in-vessel coils becomes unstable for realistic TM amplitudes when passing to the discrete-time feedback. In contrast the feedback of outvessel coils is robust to time discretization, except when the vacuum vessel time constant becomes very small. This analysis indicates that future RFPs should rely on feedback systems of out-vessel coils. © 2010 IOP Publishing Ltd.

Consorzio RFX | Date: 2013-05-31

A method for making junctions between a first body (A) made of a first material includes a tube (A1) and a second body (B) made of a second material and having a hole (B1) for the insertion of the tube (A1). The method includes the threading (A3) of the tube (A1) for screwing in a corresponding threaded portion (B3) of the hole (B1) in the second body (B), the creation of a recess (B2) in the opening of the hole (B1) in the second body (B) and the creation of a ring (A5) at the end (A2) of the tube (A1), wherein the ring (A5) and the recess (B2) have such a shape and size that the ring (A5) is forced in the recess (B2) producing a plastic deformation and thus a seal through interference between the first and second body.

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