Since the 2012 IAEA-FEC Conference, FTU operations have been largely devoted to runaway electrons generation and control, to the exploitation of the 140 GHz electron cyclotron (EC) system and to liquid metal limiter elements. Experiments on runaway electrons have shown that the measured threshold electric field for their generation is larger than predicted by collisional theory and can be justified considering synchrotron radiation losses. A new runaway electrons control algorithm was developed and tested in presence of a runaway current plateau, allowing to minimize the interactions with plasma facing components and safely shut down the discharges. The experimental sessions with 140 GHz EC system have been mainly devoted to experiments on real-time control of magnetohydrodynamic (MHD) instabilities using the new EC launcher with fast steering capability. Experiments with central EC injection have shown the onset of 3/2 and 2/1 tearing modes, while EC assisted breakdown experiments have been focused on ITER start-up issues, exploring the polarization conversion at reflection from inner wall and the capability to assure plasma start-up even in presence of a large stray magnetic field. A new actively cooled lithium limiter has been installed and tested. The lithium limiter was inserted in the scrape-off layer, without any damage to the limiter surface. First elongated FTU plasmas with EC additional heating were obtained with the new cooled limiter. Density peaking and controlled MHD activity driven by neon injection were investigated at different plasma parameters. A full real-time algorithm for disruption prediction, based on MHD activity signals from Mirnov coils, was developed exploiting a large database of disruptions. Reciprocating Langmuir probes were used to measure the heat flux e-folding length in the scrape-off layer, with the plasma kept to lay on thea internal limiter to resemble the ITER start-up phase. New diagnostics were successfully installed and tested, as a diamond probe to detect Cherenkov radiation produced by fast electrons and a gamma camera for runaway electrons studies. Laser induced breakdown spectroscopy measurements were performed under vacuum and with toroidal magnetic field, so demonstrating their capability to provide useful information on the surface elemental composition and fuel retention in present and future tokamaks, such as ITER.

FTU is operating since 1989, thus its hardware and software infrastructure must be continuously updated to preserve its efficiency and reliability. This issue can be addressed by means of two distinct approaches: (i) the migration to an emulated environment enabling the use of modern hardware on virtualized standard servers to keep the operating systems full functionality and the application environment; (ii) the porting of the complete system architecture to new hardware, new operating systems, and new programming languages. This paper reports on the upgrades implemented on FTU in the last two years using both these approaches including the new system to acquire and store the image frames of FTU plasma discharges through a Photron FASTCAM SA4 camera. Regarding data handling, a small Linux high performance computing system (1TFlops) with a high performance data storage system (100 TB) in InfiniBand DDR infrastructure has been installed as data analysis, modelling and archive cluster for the next three years of FTU experimental activities. (C) 2014 EURATOM-ENEA. Published by Elsevier B.V. All rights reserved.

New FTU ohmic discharges with a liquid lithium limiter at I P = 0.7–0.75 MA, B T = 7 T and n e0 ⩾ 5 × 10 20 m −3 confirm the spontaneous transition to an enhanced confinement regime, 1.3–1.4 times ITER-97-L, when the density peaking factor is above a threshold value of 1.7–1.8. The improved confinement derives from a reduction of electron thermal conductivity (χ e ) as density increases, while ion thermal conductivity (χ i ) remains close to neoclassical values. Linear microstability reveals the importance of lithium in triggering a turbulent inward flux for electrons and deuterium by changing the growth rates and phase of the ion-driven turbulence, while lithium flux is always directed outwards. A particle diffusion coefficient, D ∼ 0.07 m 2 s −1 , and an inward pinch velocity, V ∼ 0.27 m s −1 , in qualitative agreement with Bohm–gyro-Bohm predictions are inferred in pellet fuelled lithized discharges. Radio frequency heated plasmas benefit from cleaner plasmas with edge optimized conditions. Lower hybrid waves penetration and current drive effects are clearly demonstrated at and above ITER densities thanks to a good control of edge parameters obtained by plasma operations with the external poloidal limiter, lithized walls and pellet fuelling. The electron cyclotron (EC) heating system is extensively exploited in FTU for contributing to ITER-relevant issues such as MHD control: sawtooth crash is actively controlled and density limit disruptions are avoided by central and off-axis deposition of 0.3 MW of EC power at 140 GHz. Fourier analysis shows that the density drop and the temperature rise, stimulated by modulated EC power in low collisionality plasmas are synchronous, implying that the heating method is the common cause of both the electron heating and the density drop. Perpendicularly injected electron cyclotron resonance heating is demonstrated to be more efficient than the obliquely injected one, reducing the minimum electric field required at breakdown by a factor of 3. Theoretical activity further develops the model to interpret high-frequency fishbones on FTU and other experiments as well as to characterize beta-induced Alfvén eigenmodes induced by magnetic islands in ohmic discharges. The theoretical framework of the general fishbone-like dispersion relation is used for implementing an extended version of the HMGC hybrid MHD gyrokinetic code. The upgraded version of HMGC will be able to handle fully compressible non-linear gyrokinetic equations and 3D MHD.

As in any other long-lasting experiment, new and standard activities on Frascati Tokamak Upgrade may require technological updates, especially on the control and data acquisition domain.The present paper will deal with a set of experiences arising from the necessity to replace ageing systems that turned out to be an interesting test-bed for new technologies.The first case study deals with FTU slow control, which is based on a standard three-layer model. The lower layer has been updated in the G1 power supply of the toroidal field, replacing the old Westinghouse PLC with a Siemens-S7. To integrate the new PLC in FTU control system, the open source LibNodave package under Linux operating system has been used. The results are compared to those obtained using the Siemens-S7 commercial library.The second case study regards FTU magnetic measurements. The system proposed will lead to the replacement of the old CAMAC system with a PXI embedded controller, acquiring hundreds of signals.Finally it will be shown how, taking advantage of those technologies, an ITER relevant control and data acquisition architecture can be designed. (C) 2010 Elsevier B.V. All rights reserved.

Spontaneous increases in plasma density, up to ∼1.6 times the Greenwald value, are observed in FTU with lithized walls. These plasmas are characterized by profile peaking up to the highest obtained densities. The transport analysis of these discharges shows a 20% enhancement of the energy confinement time, with respect to the ITER97 L-mode scaling, correlated with a threshold in the peaking factor. It has been found that 0.4 MW of ECRH power, coupled at q = 2 surface, are sufficient to avoid disruptions in 0.5 MA discharges. Direct heating of magnetic islands produced by MHD modes determines current quench delay or avoidance. Supra-thermal electrons generated by 0.5 MW of lower hybrid power are sufficient to trigger precursors of the electron-fishbone instability. Evidence of spatial redistribution of fast electrons, on the ∼100 µs typical mode timescale, is shown by the fast electrons bremsstrahlung diagnostic. From the presence of new magnetic island induced accumulation points in the continuous spectrum of the shear Alfvén wave spectrum, the existence of new magnetic island induced Alfvén eigenmodes (MiAE) is suggested. Due to the frequency dependence on the magnetic island size, the feasibility of utilizing MiAE continuum effects as a novel magnetic island diagnostic is also discussed. Langmuir probes have been used on FTU to identify hypervelocity (10 km s−1), micrometre size, dust grains. The Thomson scattering diagnostic was also used to characterize the dust grains, present in the FTU vacuum chamber, following a disruption. Analysis of the broad emitted light spectrum was carried out and a model taking into account the particle vaporization is compared with the data. A new oblique ECE diagnostic has been installed and the first results, both in the presence of lower hybrid or electron cyclotron waves, are being compared with code predictions. A time-of-flight refractometer at 60 GHz, which could be a good candidate for the ITER density feedback control system, has also been tested.

Steady internal transport barriers (ITBs) are obtained in FTU at ITER-relevant magnetic field and density (n(eo) >= 1. 3 x 10(20) m(-3)) in almost full non-inductive discharges, sustained by lower hybrid (LH) and electron cyclotron (EC) RF waves sources. Similarly to ITER, only electrons are directly heated which in turn heat ions via collisions and no momentum is injected. Collisions do not affect the mechanisms of turbulence suppression and energy transport. At the highest densities the ion thermal conductivity remains <= the ohmic level, while the energy confinement time exceeds the ITER 97-L scaling by about 1.6 times. The ITB radius can be varied in the range 0.2 <= r/a <= 0.65 modifying the radial profile of the LH driven current, acting mainly on the safety factor q. A liquid lithium limiter (LLL) of innovative design, composed of a mesh of porous capillaries, has been tested successfully for the first time on a medium size tokamak. The LLL surface showed no damage up to the maximum 2 thermal load of 5 MW m(- 2). With LLL cleaner plasmas are obtained and the particle recycling strongly drops; new interesting regimes of particle transport arise at high density, with highly peaked profiles. Significant progress in disruption mitigation by means of EC power has shown that they can be avoided when absorption occurs directly on the MHD islands driving the disruption. Feedback control/suppression of MHD tearing modes (TM, m = 2) with EC waves has been achieved relying on a real-time detection of the TM and of its radial location. Testing the collective Thomson scattering in ITER-relevant configuration has stressed that avoiding backscattered radiation to the source is very crucial. The theory of the evolution of fishbone-like instabilities driven by LH generated supra-thermal electrons in FTU is outlined, and its relation to the trapped alpha particles dynamics is stressed.

In the second half of 2005, a liquid lithium limiter (LLL) with capillary porous system (CPS) configuration was installed to test on Tokamak FTU. The liquid lithium flows through capillaries from a reservoir to the side faced to the plasma to form a thin lithium film as wall coating. The system includes three stainless steel cases, which contain two thermocouples each one. A heating system brings the Li temperature about 200 degrees C to allow the liquid to flow. This temperature, monitored by thermocouples, needs to be controlled.To carry out this experimental procedure, some new features have been introduced in the existent control system based on Opto22(TM) modules and a CORBA/PHP/MySQL software architecture. The historical data storage to keep the lithium temperature evolution has been added. Two graphical tools - developed in MATLAB(TM) and Java environments, respectively, to monitor the lithium temperature coming from thermocouples - have been also implemented. The LLL control system allows to regulate the heater temperature in each unit to reach operational conditions, where the temperature adjustment can be performed either automatically through a specific control law or manually by the operator. During the plasma shot the System switches off the limiter power supply to prevent instruments damage. Moreover, in the same experimental context, a first approach to automatically obtain executable code - starting from control laws designed by Simulink(TM) tool - has been realized. (C) 2007 Elsevier B.V. All rights reserved.

The Frascati Tokamak Upgrade (FFU) continuous (slow) data acquisition system has been redesigned to allow easy monitoring of the status of the plant. In the new system "Opto22 (TM)" modules, which use Ethernet as fieldbus, substitute the old "programmable logic controller (PLC)" devices allowing easy access to and display of many continuous measurements. Data collected by "Opto22" modules are stored in a "MySQ12" database via a driver written in C++ language. A "CORBA" server, running on the same machine hosting the "MySQ12" server, allows the database access from any remote client regardless of the local platform. A remarkable aspect looks out for the use of totally free software packages. This new architecture overcomes the limitations of the previous monitoring system:an interface based on internet browser allows to easily configure Opto22 modules and MySQL database;a graphical interface, developed in Java, allows data management and visualization;the above operations are completely platform independent. In addition the CORBA server introduces the advantages of:hardware independence, thus allowing maximum flexibility in the choice of platforms and system components;both network and programming languages being completely transparent. This paper will present the new system architecture, last results and future developments. (c) 2005 Elsevier B.V. All rights reserved.

A tokamak plasma with internal transport barriers (ITBs) is the best candidate for a steady ITER operation, since the high energy confinement allows working at plasma currents (Ip) lower than the reference scenario. To build and sustain an ITB at the ITER high density (⩾1020 m−3) and largely dominant electron (e−) heating is not trivial in most existing tokamaks. FTU can instead meet both requests, thanks to its radiofrequency heating systems, lower hybrid (LH, up to 1.9 MW) and electron cyclotron (EC up to 1.2 MW). By the combined use of them, ITBs are obtained up to peak densities ne0 > 1.3 × 1020 m−3, with central e− temperatures Te0 ≈ 5.5 keV, and are sustained for as long as the heating pulse is applied (>35 confinement times, τE). At ne0 ≈ 0.8 × 1020 m−3 Te0 can be larger than 11 keV. Almost full current drive (CD) and an overall good steadiness is attained within about one τE, 20 times faster than the ohmic current relaxation time. The ITB extends over a central region with an almost flat or slightly reversed q profile and qmin ≈ 1.3 that is fully sustained by off-axis lower hybrid current drive. Consequent to this is the beneficial good alignment of the bootstrap current, generated by the ITB large pressure gradients, with the LH driven current. Reflectometry shows a clear change in the turbulence close to the ITB radius, consistent with the reduced e− transport. Ions (i+) are significantly heated via collisions, but thermal equilibrium with electrons cannot be attained since the e−–i+ equipartition time is always 4–5 times longer than τE. No degradation of the overall ion transport, rather a reduction of the i+ heat diffusivity, is observed inside the ITB. The global confinement has been improved up to 1.6 times over the scaling predictions. The ITB radius can be controlled by adjusting the LH power deposition profile that is affected mostly by the q value of the discharge, while the ITB strength can be varied through central EC heating. FTU experiments have shown that ITER-like e-ITBs are achievable.

In this paper the results of the experiments of combined injection of LH waves and EC waves performed in the FTU tokamak are reported. Such experiments were mainly devoted to study and to control the access to the advanced tokamak scenarios in plasma conditions close to ITER parameters (Bt≈5T or higher, ne,line≈1020 m−3). Two different absorption mechanisms were used for the EC waves. In the first one the cold resonance absorption of EC waves launched with a toroidal angle was used to induce small modification of the current profile mainly maintained by LH waves. In the second one the absorption through Doppler shift due to the fast electron tails generated by LHCD was used.

An overview of the FTU results during the period 2003–4 is presented. A prototype ITER-relevant lower hybrid current drive (LHCD) launcher, the passive active multijunction, has been successfully tested (f = 8 GHz) showing high power handling and good coupling properties and current drive comparable to those of a conventional launcher. Effective electron and ion heating (via collisions) have been achieved with the 140 GHz ECRH systems up to 1.5 MW, as well as current drive (25 kA at ne0 = 8 × 1019 m−3). The mitigation of disruptions has been studied with on-axis ECRH. Ion Bernstein wave studies have shown the importance of recycling in achieving improved confinement plasmas. Advanced tokamak scenarios are presented including repetitive pellet enhanced plasmas and electron internal transport barriers (e-ITBs). Very peaked density profiles have been achieved with a low speed vertical pellet injector located at about mid-radius on the high field side. The performance is comparable to that achieved with a high-speed horizontal pellet injector. Possible reasons for this behaviour are discussed, among them the presence of an ‘MHD’ drift once particles reach the q = 1 surface. The effect of peaked density profiles on confinement is discussed. Electron ITBs can be produced at high density in FTU with LHCD only and with the combined use of LHCD and ECRH: Te0 = 6 keV with ne0 = 1.4 × 1020 m−3 and H97 = 1.6. Turbulence is strongly reduced. Ions are heated by collisions with ΔTi/Ti up to 35% showing that e-ITBs are not degraded by the electron–ion collisions. Particle pinch studies have been made at high densities in full current drive conditions where the Ware pinch plays no role. An anomalous inward pinch exists even at these high densities (ne0 = 1.5 × 1020 m−3). Despite the absence of energetic particles in FTU, MHD spectroscopy has revealed high frequency modes (30–80 kHz) that might have consequences for burning plasmas.

The Frascati Tokamak Upgrade (FTU) has been operating for more than 12 yr since its first plasma in 1990 and has played an important role in several aspects of the tokamak research. As the first paper of this special issue containing papers on all aspects of FTU, this paper briefly summarizes the main dates, the general description of the facility, the objectives, and the major achievements in FTU.

New experiments with the ion Bernstein waves (IBWs) have been performed in the Frascati Tokamak Upgrade (FTU) both in hydrogen and deuterium plasmas at higher power level, operation at higher density, higher plasma current and lower effective ion charge values than in the previous campaign. Improved confinement in a region with larger radius is obtained when operating in deuterium. Transport analysis shows a uniform decrease of the electron thermal conductivity by 40% over the radial region bounded by the absorption layer.

New experiments with the ion Bernstein waves (IBW) has been performed on FTU both in Hydrogen (H) and Deuterium (D) majority plasmas, at higher radio‐frequency power level, plasma density, current, lower effective ion charge than in previous campaign of 1999. Also in these conditions, no role is played by non‐linear edge physics, which prevented, instead, the RF penetration in the plasma bulk of DIII‐D. With resonant toroidal magnetic field (≈8T), improved confinement occurs inside a radial region of 1/3 of the minor radius operating in H‐plasma, and 2/3 of the minor radius operating in D‐majority plasma. Such behavior is consistent with the model of turbulence suppression by locally‐induced‐IBW‐sheared flow expected to occur close the resonant layer. The FTU results provide support for active control of the pressure profile by IBW which is of relevance for advanced tokamaks .

This paper will present the experience with Ethernet as fieldbus for monitoring and controlling FTU (Frascati Tokamak Upgrade) subplants, particularly the process control based on bolometric and gyrotron vacuum measurements of ECRH (Electron Cyclotron Radiofrequency Heating), and on the antenna temperature and gyrotron vacuum measurements of LH (Lower Hybrid). So ne methods of getting data from Opto22 I/O modules will be described.A MySQL database has been adopted to store the field measurements acquired by means of an Opto22 software driver. The Apache/PHP/MySQL tern allows the data access and management by providing a simple web-based graphical interface to monitor every field signal; such a solution makes possible to obtain data directly into a browser on every platform, to show real-time trends, stored data for comparisons, elaboration, etc.Another approach both to communicate with the Opto22 modules and to access and manage the MySQL database is based on a CORBA server with an appropriate set of me-hods. By means of CORBA clients running on many platforms and utilizing a graphical interface developed in MATLAB environment, users can start data acquisition and storage and in addition visualize required physical quantities in progress or previously archived.A lava application called jScope queries directly the MySQL database and quickly presents diagrams for prompt check during operations.

The growth of data warehouse in tokamak experiment is leading fusion laboratories to provide new IT solutions in data handling. In the last three years, the Frascati Tokamak Upgrade (FTU) experimental database was migrated from IBM-mainframe to Unix distributed computing environment. The migration efforts have taken into account the following items: (1) a new data storage solution based on storage area network over fibre channel; (2) andrew file system (AFS) for wide area network file sharing; (3) ‘one measure/one file’ philosophy replacing ‘one shot/one file’ to provide a faster read/write data access; (4) more powerful services, such as AFS, corba and MDSplus to allow users to access FTU database from different clients, regardless their O.S.; (5) large availability of data analysis tools, from the locally developed utility show to the multi-platform Matlab, interactive data language and jScope (all these tools are now able to access also the Joint European Torus data, in the framework of the remote data access activity); (6) a batch-computing cluster of Alpha/CompaqTru64 CPU based on CODINE/GRD to optimize utilization of software and hardware resources.

An overview of the FTU results during the period 2000-2002 is presented. Long duration Internal Transport Barriers have been obtained on FTU with combined injection of Lower Hybrid and Electron Cyclotron waves in 5T/0.5MA discharges. The ITB phase lasts about ten energy confinement times and is characterised by an energy confinement time up to 1.6 times the ITER97L-mode scaling. Up to 11keV are achieved at 0.9×1020m-3 central density. ITB studies using IBW injection have been also continued up to 8T/0.8MA. The Lower Hybrid system has operated at full power allowing to complete the current drive studies at ITER relevant densities. At these density values the electrons and ions are coupled and an increase in the ion temperature is clearly observed. Preliminary sign of enhanced Current Drive efficiency has been obtained in combined injection of Electron Cyclotron and Lower Hybrid waves at magnetic field values lower than the resonant field. Pellet optimisation studies have been performed in order to test the conditions under which a quasi steady state confinement improvement can be obtained and impurity accumulation can be avoided. Ohmic discharges generally exhibit a confinement time in agreement with the ITER97 L-mode scaling. Transient confinement improvement is observed for duration less than one energy confinement time. Radiation Improved mode studies have been started thanks to the recently inserted boronisation system which has allowed to reduce the radiated power. Confinement improvement with Neon injection has been observed in 6T/0.9MA discharges. Transport studies on profile stiffness and MHD studies of fast reconnection and snakes will be also presented.

The Electron Cyclotron Radio Frequency Heating (ECRH) system is mainly used to control the temperature profile of the plasma in a tokamak through sharp focusing of the RF power for bulk heating. Some experiments on tokamak devices have shown that Electron Cyclotron Current Drive (ECCD) can reduce the growth of rotating magnetic islands, thus controlling magnetohydrodynamic (MHD) resistive instabilities in steady-state operation. On Frascati Tokamak Upgrade (FTU), 1.6 MW 140 GHz Electron Cyclotron (EC) waves are injected using four gyrotrons, each emitting 0.4 MW for 0.5 s. A crucial point of the whole system is the fast control of the RF power output through a Digital Waveform Reference (DWR). This paper describes the new implementation of the DWR on FTU with a PXI-embedded controller and two PXI DAC boards by National Instruments. DWR control code integrates synthesized waveforms and graphic display, validity test on reference outputs, fully hardware-driven analog output, network process communication with ECRH plant PLC and the FTU Supervisor Control System. The validity test on the working parameters takes into account hardware constraints, system configuration and tetrode dissipation. The off-line calculations select the reference voltage using a wide choice of pulse shapes, while the real-time analog output is fully hardware-driven by the FTU central timing and trigger system. Because of the FIFO and DMA transfer data of the PXI DAC board, the 1 MHz update rate of the reference output has been successfully tested, largely matching the system requirements (up to 500 kHz). The high reliability shown by the present DWR gives us the chance to implement a 50 kHz closed-loop feedback system to control the growth of the plasma instabilities by EC waves.

In its early stages, Frascati tokamak upgrade DAS was essentially devoted to acquiring data from experiments in CAMAC standard, using a software system (code and database) entirely written by domestic professionals. In 15 years of life DAS has been growing in size and complexity, still preserving its original structure; at the same time new standards were introduced (VME, PCI) to take into account users’ ever increasing demands for amount of data and acquisition frequency with which the existing code couldn't cope. Moreover, machines were getting old and the maintenance became troublesome. Finally, the data archive porting to Unix has definitely shown that the DAS system was ageing and a thorough redesign was needed. The system we are planning to introduce is founded on a standard corba bus: (i) to integrate heterogeneous platforms and define a standard layer for interactions between the different acquisition units; (ii)to grant, with open source tools (MySql) and interfaces (Html and Java), unified access to hardware and software configuration data. So, a dedicated PC server, connected via a suitable PCI serial highway driver card, will perform the CAMAC access for all the clients interacting through the corba layer. Up to now we have successfully tested CAMAC access, and we designed an acquisition unit, which will be the building block of the new system. The next step will be migrating to Alpha/VMS the software related to CAMAC data acquisition, which has been so far the cornerstone of the whole DAS; it will be completely redesigned to fit the ‘acquisition unit’ paradigm we have defined. Finally we will have a fully distributed data acquisition system with VME (at present six such units have been operating since 1999) and PCI stations, an Alpha/VMS client of the CAMAC/PC server and any possible platform interacting through a corba bus for getting data configuration, synchronisation and data archiving.

Recent ECRH experiments in FTU have provided new results in two plasma scenarios, both characterized by the absence of the sawtooth activity and by flat or reversed q profiles. The first is the current ramp-up phase where low density plasmas have been heated up to high electron temperature. When the heating is localized on the plasma axis, the high additional power density has produced the evidence of a deformation of the bulk of the local electron distribution function, which is in agreement with the results of a detailed kinetic simulation. When off-axis heating is applied, no clear evidence of non-diffusive energy transport has been found. In the second scenario, ECRH has been applied on the high density plasma produced by pellet injection, resulting in strong ion heating as shown by the increase of the neutron yield. The analysis of this scenario shows that, when the post pellet phase is MHD quiescent, an enhanced energy confinement regime can be obtained with ECRH as found previously in ohmically heated post-pellet plasmas.