G. Mazzitelli

Heating in Toroidal Plasmas (Report on the 4th International Symposium, Rome, 21–28 March, 1984)

The Fourth International Symposium of the Varenna-Grenoble series, held in Rome from March 21 to 28, 1984, was organized by the Italian Commission for Nuclear and Alternative Energy Sources (ENEA) and the International School of Plasma Physics (Varenna).

The Fusion Advanced Studies Torus (FAST): a proposal for an ITER satellite facility in support of the development of fusion energy*

FAST is a new machine proposed to support ITER experimental exploitation as well as to anticipate DEMO relevant physics and technology. FAST is aimed at studying, under burning plasma relevant conditions, fast particle (FP) physics, plasma operations and plasma wall interaction in an integrated way. FAST has the capability to approach all the ITER scenarios significantly closer than the present day experiments using deuterium plasmas. The necessity of achieving ITER relevant performance with a moderate cost has led to conceiving a compact tokamak (R = 1.82m, a = 0.64m) with high toroidal field (BT up to 8.5T) and plasma current (Ip up to 8MA). In order to study FP behaviours under conditions similar to those of ITER, the project has been provided with a dominant ion cyclotron resonance heating system (ICRH; 30MW on the plasma). Moreover, the experiment foresees the use of 6MW of lower hybrid (LHCD), essentially for plasma control and for non-inductive current drive, and of electron cyclotron resonance heating (ECRH, 4MW) for localized electron heating and plasma control. The ports have been designed to accommodate up to 10MW of negative neutral beams (NNBI) in the energy range 0.5‐1MeV. The total power input will be in the 30‐40MW range under different plasma scenarios with a wall power load comparable to that of ITER ( P/ R∼ 22MWm −1 ). All the ITER scenarios will be studied: from the reference H mode, with plasma edge and ELMs characteristics similar to the ITER ones (Q up to ≈1.5), to a full current drive scenario, lasting around 170s. The first wall (FW) as well as the divertor plates will be of tungsten in order to ensure reactor relevant

Edge properties with the liquid lithium limiter in FTU—experiment and transport modelling

Liquid lithium as a plasma-facing material was tested for the first time on a high field medium size tokamak, FTU. A liquid Li reservoir supplies a mesh of capillaries that is movable from shot to shot in the scrape-off layer (SOL) plasma to act as a secondary limiter. An almost complete lithization of the vacuum vessel walls is obtained in about three discharges. Plasmas cleaner than boronization and titanization, with lower radiation losses and smaller impurity content are produced. The SOL electron temperature increases, ΔTe ~ 10 eV, while density (ne) is less affected. The 2D multifluid code TECXY explains this only if a strong reduction of plasma recycling on the walls and main limiter occurs, consistent with the high Li hydrogen pumping capability. This property also permits a much tighter control of the plasma density. With the Li limiter inserted inside the vessel poloidal asymmetries develop in the SOL that TECXY explains with a local increase of radiation, caused by enhanced evaporation/sputtering of Li. New regimes can be produced in such conditions with a clear increase in |∇ne/ne| and of the peaking factor ne0/

Lithization of the FTU tokamak with a critical amount of lithium injection

FTU plasma discharges with an extremely high amount of Li injection have been performed using a poloidal liquid lithium limiter acting as the principal Li source in the shadow of the main TZN toroidal limiter. Very peculiar of these discharges is the formation of a ‘virtual’ toroidal lithium limiter that redistributes the energy flux to the tokamak vessel first wall by radiative processes and therefore decreases the heat load onto the Mo limiter. These experiments contribute to the investigation of a more complex scenario that will possibly be faced by a project of a liquid lithium divertor in a tokamak with high additional power (or high power load on to the targets).

Conference Report on the 2nd International Symposium on Lithium Applications for Fusion Devices

The 2nd International Symposium on Lithium Applications for Fusion Devices (ISLA-2011) was held on 27–29 April 2011 at the Princeton Plasma Physics Laboratory (PPPL) with broad participation from the community working on aspects of lithium research for fusion energy development. This community is expanding rapidly in many areas including experiments in magnetic confinement devices and a variety of lithium test stands, theory and modeling and developing innovative approaches. Overall, 53 presentations were given representing 26 institutions from 10 countries. The latest experimental results from nine magnetic fusion devices were given in 24 presentations, from NSTX (PPPL, USA), LTX (PPPL, USA), FT-U (ENEA, Italy), T-11M (TRINITY, RF), T-10 (Kurchatov Institute, RF), TJ-II (CIEMAT, Spain), EAST (ASIPP, China), HT-7 (ASIPP, China), and RFX (Padova, Italy). Sessions were devoted to: I. Lithium in magnetic confinement experiments (facility overviews), II. Lithium in magnetic confinement experiments (topical issues), III. Special session on liquid lithium technology, IV. Lithium laboratory test stands, V. Lithium theory/modeling/comments, VI. Innovative lithium applications and VII. Panel discussion on lithium PFC viability in magnetic fusion reactors. There was notable participation from the fusion technology communities, including the IFE, IFMIF and TBM communities providing productive exchanges with the physics oriented magnetic confinement lithium research groups. It was agreed to continue future exchanges of ideas and data to help develop attractive liquid lithium solutions for very challenging magnetic fusion issues, such as development of a high heat flux steady-state divertor concept and acceptable plasma disruption mitigation techniques while improving plasma performance with lithium. The next workshop will be held at ENEA, Frascati, Italy in 2013.

EXPERIMENTS IN FTU WITH DIFFERENT LIMITER MATERIALS

Over the last few years, a great deal of effort has been devoted to solving the problem of power and particle handling in divertors, which has been recognized as a critical issue for the operation of a magnetic fusion reactor. In particular, the choice of materials for plasma facing components has been examined with a view to developing heat and erosion resistant materials for divertor target plates. A large database on the behaviour of low-Z (carbon or beryllium) materials in tokamaks is available, while for high-Z materials there is little experience in the present generation of magnetic fusion devices. Frascati Tokamak Upgrade (FTU), a high field compact tokamak, has devoted part of its experimental campaign to studying the plasma characteristics when its limiter material is changed from the usual Inconel (nickel) to molybdenum and tungsten. Siliconization of the machine has also allowed the comparison of plasma performance when a relatively low-Z (silicon) ion is the dominant impurity. In this article, results are reported concerning the plasma operation, the differences in plasma characteristics and radiation losses, the impurity generation mechanisms and the relative impurity concentrations in the core plasma. A simulation of the experimental results, made with a self-consistent edge-core coupled model is presented, in order to provide evidence of the main physics mechanisms responsible for the observed behaviour

Reduction of the electron thermal conductivity produced by ion Bernstein waves on the Frascati Tokamak Upgrade tokamak

Operating with a high frequency and a wave guide antenna, the ion Bernstein wave (IBW) experiment on the Frascati Tokamak Upgrade is not dominated, as expected, by nonlinear plasma edge phenomena. By coupling IBW power, a simultaneous increase of plasma density and central electron temperature (⩾2 keV) is produced when the confinement magnetic field is adjusted to set an ion cyclotron resonant layer in the plasma bulk. Transport analysis indicates a reduction of the electron thermal transport inside the internal resonant layer larger than a factor of 2.

Plasma characteristics in FTU with different plasma facing materials

Experiments with different dominant impurities (C, Si, Ni, Mo) have been carried out on the FTU tokamak. Density limit, marfe, Zeff and radiation losses are compared and discussed. An analytical model that couples in a self consistent way the parameters of the SOL and the transport of the impurities generated at the limiter to the bulk plasma parameters has been used to reproduce the experimental data.

First Steps in the FTU Migration Towards a Modular and Distributed Real-Time Control Architecture Based on MARTe

The Fusion Advanced Studies Torus (FAST) experiment is being proposed by the Italian laboratories as a European satellite Tokamak that will enhance and facilitate the exploitation of ITER like scenarios and technologies. Its size and complexity is comparable to the largest fusion machine in the world: JET. As such, its real time control system will have to meet basic requirements such as a modular and distributed architecture, where different control subsystems can be easily integrated at different times and can operate either independently or in cooperation with other subsystems. Another important feature, which has to be taken into account, is the transparency regarding both the hardware interfacing and the adopted platform. As a test bed, we are currently planning to upgrade the architecture of the Frascati Tokamak Upgrade (FTU) real-time system in order to improve its flexibility and modularity and have decided to adopt the MARTe package to reach our goal. Currently, there are four systems under development at FTU: the LH-Power system; the gas puffing control system; the ODIN Equilibrium Reconstruction system; and the position and current feedback control system (currently in a design phase). This paper will describe the current status and first results of the previously referred systems integration.

Updating of ionization data for ionization balance evaluations of atoms and ions for the elements hydrogen to germanium

Atomic data for electron impact ionization of all the elements from H to Ge are reviewed, the rates for these processes needing to be regularly updated following the publication of new experimental data and new theoretical calculations. Experimental cross sections, along with specific theoretical calculations when experimental data are missing, are fitted as functions of the electron energy, and from these fits ionization rate coefficients can be evaluated. It has been possible to take into account all elements but not all charge states of every element. Since the purpose of the paper is to update the ionization data evaluated and proposed in previous review papers, it is discussed if modifications are needed for the ions not considered. For highly ionized ions starting from the Ne-like iso-electronic sequence corrections do not appear necessary. On the other hand, except for Fe, for slightly ionized ions, specifically below the S-like iso-electronic sequence, the previously proposed data often underestimate the total ionization cross section, since only direct ionization channels have been considered and indirect processes have been neglected. Multiplicative correction coefficients are given to agree with recently published theoretical calculations. Experimental ionization data are considered, even when the presence of populated metastable levels (related to the electron density inside the source) is reported in the ion beams involved in the cross-section data measurements. We deem such a procedure acceptable when the proposed rates have to be included in codes that simulate the impurity behaviour in magnetic-confinement fusion devices, i.e., when radial transport is added to ionization and recombination to predict spatially resolved charge-state distributions. On the other hand, for astrophysical plasmas the contributions of metastable levels to the experimental data may represent a serious problem since, generally, the values of the electron densities that are involved are much lower than those in the ion sources. However, we critically investigated this problem and we found that the presence of metastables does not significantly modify the rates of most of the ions apart from a dozen. For this set of ions we provide different, corrected rates. Recombination is not considered since a review has been recently published.