RFX

Figure 1:Consorzio RFX Padua (Italy)

The history of RFX
RFX Milestones
RFX Objectives and Achievements

The history of RFX

Fusion research in Padua started in 1958 with a small University Group. In the seventies, the research moved from the initial Theta-pinch experiments in a linear magnetic confinement device, which confines the plasma in cylindrical geometry by using a poloidal current and an axial magnetic field, towards the study of the Reversed Field Pinch (RFP) configuration with the Eta Beta I and Eta Beta II experiments.

The RFP is a toroidal magnetic confinement device, similar to a tokamak, in which the poloidal and the toroidal magnetic fields are of comparable magnitude. It is capable of higher plasma current and pressure for a given external magnetic field.

Eta Beta II, in particular, allowed a "quiescent phase" to be obtained in the discharge. This was first discovered 22 years before on the ZETA and other Harwell (UK) devices but was never reproduced in further experiments on other machines. These encouraging results prompted further research on the Reversed Field Pinch configuration and consolidated the collaboration with the laboratories operating in this field at that time.

In 1984 the Padua Group was entrusted with the Reversed Field Experiment (RFX) Project, which received EURATOM priority support. This project aims at confining and studying plasma rings in a Reverse Field Pinch configuration of large size, with currents of up to 2 MA and a pulse duration of up to 0.25 s. The RFX machine started operation in 1992, and has been working intensively in subsequent years. With RFX, the study of the RFP configuration has been extended to high current regimes (up to 1.2 MA) by sustaining the discharge in stationary conditions for more than 100 ms. Due to the device’s sophisticated diagnostic equipment, a wide range of physics phenomena has been analysed and accurate comparisons to theoretical predictions have been made. New interpretative tools have also been developed.

Since 13 May 1996, the Padua Research Unit of the Association EURATOM-ENEA has been formally incorporated into Consorzio RFX, whose members are CNR, ENEA, University of Padua and a local company.

On 17 December 1999 a fire destroyed parts of the RFX power supplies, causing a long shutdown of the experimental activities. Since then, most efforts have been devoted to the reconstruction of the experimental facility and the implementation of several improvements, which aim at further widening the scientific scope of RFX. The modified RFX experiment became operational at the end of 2004.

Figure 2:RFX Machine

RFX Milestones

1958	The study on plasma linear confinement starts in Padua at the University Institute of Electrical Engineering, with the collaboration of the Physics Institute.
Early 1970’s	Toroidal plasma studies begin on Eta Beta I and Eta Beta II experiments, built with EURATOM priority support.
1976	Eta Beta I results (together with results from other laboratories) confirm Taylor's theory.
1979	Eta Beta II reproduces the so called "quiescent" plasma conditions.
1979-1982	Experimental results stimulate further the research on Reversed Field Pinches; a larger machine (RFX) is designed in collaboration with Culham (UK) and Los Alamos Laboratories (USA).
1984	The RFX experiment, to be built in Padua, is approved with EURATOM priority support.
1985-1991	Construction of RFX.
1992	RFX enters into operation.
1996	Consorzio RFX is set up by CNR, ENEA, University of Padua and a local company.
1992 - 1996	Experimental activities on RFX.
1999	On 17 December 1999, a fire destroys part of the RFX power supplies, causing a long shutdown.
2000 - 2001	Restoration and design of new components.
2001 - 1003	Reconstruction and implementation of machine modifications.
2004	RFX restarts experimental activities.

Figure 3:RFX Inside - First Wall

RFX Objectives and Achievements

RFX-mod is the largest RFP device in the world. It is run by Consorzio RFX, which is the Padova Research Unit of the Euratom-ENEA Association. It is equipped with the best system for active control of MHD stability ever realized in a fusion device. The system is composed by 192 independently driven active coils, allowing the optimization of the plasma magnetic boundary by feedback control. The RFX-mod experiment is based in a fertile academic environment and is one of the European excellence centers for education. The University of Padova, one of the oldest in the world, is tightly connected with RFX. Fusion is taught both at the undergraduate and graduate level, and a number of professors and students are involved in the RFX project. More than 200 diploma, master and Ph.D. thesis have been produced at RFX in the last 10 years. In the same time period, 43 young scientists have been recruited at RFX and 25 people, who had their undergraduate or graduate education at RFX, joined other international fusion laboratories.

The objective of Consorzio RFX is to drive forward the scientific and technological research activities in the field of thermonuclear fusion as a possible future energy source.It aims to contribute to the design and development activities essential for the realisation of new technologies, equipment and devices, which will promote research and industrial evolution. A trainee programme for young physicists and engineers ensures a close collaboration with the Universities.

The most significant scientific results can be summarised as follows:

• Improvement of the energy confinement by reducing the magnetic turbulence via current profile control.
• Reduction of the particle transport in the outer region by reducing the electrostatic turbulence via velocity profile shaping.
• Demonstration that external rotating fields can drag the Magnethydrodynamic (MHD) perturbations via non-linear coupling among MHD modes.
• Discovery of "Quasi-Single Helicity" regimes where the MHD mode spectrum is strongly reduced, giving rise to regular magnetic surfaces and significant temperature gradients in the plasma core.
• Demonstration that the "dynamo" effect that sustains the RFP configuration has a MHD origin and that it is not necessarily associated with a chaotic magnetic field.
• Discovery of intermittency phenomena, later observed also in Tokamaks and Stellarators, that permits an understanding of the energy transfer from large to small scales and allows the identification of coherent structures emerging from the turbulences; development of tools for acting on those coherent structures.