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The Crowbar System is a key protection system for the Super Conducting Magnet Power Supplies (SCMPSs) of JT-60SA, it is a Safety Relevant component and it is designed to be seismic resistant. The Crowbar System is operated in case of faults, quench of superconducting coils, plasma disruption or earthquake event, and it has to carry the current flowing through the superconducting coils in order to protect them and the SCMPS from over-voltages. The circuit configuration is based on a hybrid-making-switch, composed by a bidirectional-static-switch with a mechanical-switch and a varistor in parallel. The static-switch is composed by eight thyristors in bidirectional configuration (four connected in parallel and four in antiparallel), and it is designed to be able to safely intervene even if one thyristor or the mechanical-switch is not operating. The mechanical-switch (rated 50 kA making capacity) takes some tens of milliseconds to close, limiting the conduction time of thyristors. The overvoltage protection is performed by a voltage transducer, a Break-Over-Diode (BOD) and a varistor assuring a fast intervention with a high redundancy protection level.

This paper presents the development and testing of the prototype of a hybrid mechanical-static dc circuit breaker (CB) for quench protection of superconducting magnets based on a mechanical switch paralleled to a static CB. In normal operation, the mechanical switch is closed and it handles the continuous flow of dc current, minimizing the on-state losses. In case of intervention, the mechanical switch opens, commutating the current into the static CB that quickly interrupts and transfers the current into a discharge resistor, withstanding the reapplied voltage. This paper was carried out to face and solve some issues of this design solution being not available in the literature examples of similar applications rated for significant power levels. The operation of the hybrid CB has been successfully tested up to a current of 10 kA with a recovery voltage of about 1 kV. Special tests have been dedicated to characterize the reliability and the repeatability of the current commutation from the mechanical switch to the static CB and to characterize the arc voltage under different conditions.

The paper describes the main features of the Superconducting Magnets Power Supply to generate the toroidal and poloidal magnetic fields in JT-60SA tokamak, with special regard to coil current regulation mode and magnets protection.

The paper presents an overview on the power supply (PS) systems for plasma instabilities control in fusion experiments, based on active control coils. First, the MHD instabilities and the approach to their control in Tokamaks and Reversed Field Pinches (RFPs) are described. Then, the features of MHD modes controls presently used in fusion experiments are reviewed. For the control systems based on active coils fed by fast power supplies, the typical requirements in terms of power, dynamics, accuracy and delay are summarized and discussed. Then, a survey on the technology available to design these types of PSs is given, together with the most suitable circuit topologies and guidelines for the design, on the basis of solutions adopted in existing experiments.

Considering its widespread distribution in marine environments, its fast replication times and low infectious doses and the rapid spread of its strains in recent years, intensive and continuous monitoring of potentially pathogenic Vibrio parahaemolyticus is strongly recommended in order to assess the human health risk arising from shellfish consumption. The lack of epidemiological data points to the need to develop specific methods for detecting V. parahaemolyticus. In this note, the authors compare two plating media currently available for isolating V. parahaemolyticus in shellfish. Both approaches involve pre-enrichment of V. parahaemolyticus. One uses thiosulphate-citrate-bile salt sucrose (TCBS) as the isolation medium, while the other uses a chromogenic medium (CHROMagar Vibrio). Next, biochemical identification of isolates was performed with API 20E, followed by PCR assay aimed at the toxR gene to confirm the cultural and biochemical identification. Comparison of the two methods highlighted that CHROMagar Vibrio is more accurate and specific than TCBS. The analysis of data from 160 shellfish samples showed an accuracy and specificity of just 51% and 71% for TCBS compared with 88% and 95% for CAV.

The identification of the maximum amplitude of the currents circulating in the circuits is a useful indication for the design both of magnet and power supply components in fusion experiments. This paper evaluates the maximum level of coil overcurrents in the poloidal superconducting magnets of JT-60SA, the satellite tokamak that will be built in Naka, Japan, in the framework of EU-JA “Broader Approach” Agreement and that is expected to perform first plasma on 2016. To derive these information, a complete model capable to take into account all the mutually coupled elements was worked out, including the poloidal superconducting coils, the plasma position control in-vessel coils, the vacuum vessel, the stabilizing plates and the plasma. The model was utilized to analyze plasma disruption and quench protection circuit intervention in a large variety of different conditions to identify the possible overcurrent levels. The paper describes the model and the analyses performed, and presents and discusses the results.

Summary This study provides data on the prevalence of potentially pathogenic Bacillus cereus in foods from catering kitchens by evaluating the occurrence of B. cereus and the presence of virulence-associated genes. B. cereus was detected in 72/250 (28.8%) food samples. Specifically, B. cereus was highlighted in 34/74 (45.9%) pastries, 16/40 (40%) rice samples, 4/38 (10.5%) potato meals, 6/54 (11.1%) mozzarella samples and 12/44 (27.3%) meat meals. PCRs aimed at the hbl (C, D, A, B), nhe (A, B, C), bceT and cytK genes demonstrated a widespread distribution of the toxin-encoding genes among B. cereus isolates. The results highlight the frequent failure of control measures in catering kitchens and the need for intensive and continuous monitoring in order to assess the human health risk, as proposed by Regulation (EC) no. 1441/2007 on microbiological criteria for foodstuffs.

Toxoplasma gondii infection is a parasitological antropozoonoses widely distributed in the world. Toxoplasmosis is mainly followed by serious disease in fetuses and immunocompromised people. Wild boars represent an important source for this parasite and evisceration, handling and consumption of raw or undercooked meat are important risk factors. The study confirms the presence of potentially infectious cysts in wild boars muscles, detected by histological and biomolecular methods.

In the framework of the strategy for the development and the procurement of the NB systems for ITER, it has been decided to build in Padova a test facility, including two experimental devices: a full size plasma source with low voltage extraction and a full size NB injector at full beam power (1 MV). These two different devices will separately address the main scientific and technological issues of the 17 MW NB injector for ITER. In particular the full size plasma source of negative ions will address the ITER performance requirements in terms of current density and uniformity, limitation of the electron/ion ratio and stationary operation at full current with high reliability and constant performances for the whole operating time up to 1 h. The required negative ion current density to be extracted from the plasma source ranges from 290 A/m2 in D2 (D−) and 350 A/m2 in H2 (H−) and these values should be obtained at the lowest admissible neutral pressure in the plasma source volume, nominally at 0.3 Pa. The electron to ion ratio should be limited to less than 1 and the admissible ion inhomogeneity extracted from the grids should be better than 10% on the whole plasma cross-section having a surface exposed to the extraction grid of the order of 1 m2. The main design choices will be presented in the paper as well as an overview of the design of the main components and systems.

In JT-60SA, the new satellite tokamak to be built in Naka, Japan, the magnetic field for plasma generation and confinement is produced by a number of superconducting coils whose rated current ranges from 20 kA to 25.7 kA, with a nominal voltage up to 5 kV. This paper deals with the conceptual design of the Quench Protection Circuits (QPC) of JT-60SA, which must provide a fast removal of the energy stored in the superconducting coils in case of quench. The core of the QPC units is based on a dc current breaker, which diverts the coil current into a discharge resistor. Different concepts of dc circuit breaker for QPC were considered, including vacuum and static circuit breakers; then, a hybrid solution, composed of a mechanical bypass switch paralleled to a static switch based on Integrated Gate Commutated Thyristor (IGCT) technology, has been worked out. A pyrobreaker is added in series to the hybrid switch as a backup protection. The resulting design allows benefiting from the fast breaking and very low maintenance requirement of the static switches, besides maintaining the advantage of the much lower power losses of the mechanical bypass in normal operation. After a brief presentation of the preliminary studies, the selected design solution for JT-60SA is presented in detail.

This study provides data on the prevalence of pathogenic Vibrio parahaemolyticus in shellfish from some coastal areas in southern Italy. The approach involved isolating V. parahaemolyticus strains by cultural and biochemical analysis and molecular assays, which highlighted the presence of TDH-positive V. parahaemolyticus. The results confirmed the need for a specific shellfish inspection plan to detect the presence of Vibrio species in order to eliminate public health risks associated with shellfish consumption.

The modified RFX is a very flexible device used for a variety of control schemes for MHD instabilities and for advanced reverse field pinch scenarios. Relative to the previous machine, RFX-mod has a thin Cu shell with vertical field penetration time τS, lowered from 450 to 50 ms and shell/plasma proximity from b/a ≤ 1.24-1.1. Toroidal equilibrium is feedback-controlled and new power supplies provide better Bφ control. Newly designed graphite tiles protect the vessel from localized power deposition. A mesh of 192 external saddle coils, supervised by a digital feedback system, controls radial fields due to field errors and MHD modes. The paper presents an overview of the very encouraging results obtained using both new and 'standard' advanced operational modes in the current range 0.3-1 MA. A dramatic improvement of plasma performance was obtained by using the saddle coils to cancel all the radial field components, an operation mode dubbed virtual shell (VS). The toroidal voltage was lowered by more than 25% and the pulse length was tripled, up to 7 times the τS. Steady-state RFP pulses are now limited only by the applied volt-seconds. The improved magnetic boundary also has an effect on the tearing modes underlying the sustainment of the RFP, whose core amplitude is more than halved. The VS combined with new schemes for the active rotation of the MHD dynamo modes has allowed us to obtain reliable and well-controlled long RFP pulses in the MA current range. This results in a 100% increase in the particle and energy confinement time relative to the previous experiment and opens the possibility of exploring the machine performance in the 2 MA design range. © 2007 IAEA.

The authors used a polymerase chain reaction (PCR) assay on buffalo mozzarella, a typical Italian dairy product, from the Apulia markets to evaluate the presence of cow milk and verification of the mozzarella label. The results obtained from 30 mozzarella samples demonstrated the presence of the cow genome in 22/30 samples, highlighting contamination as probable fraudulent adding of cow's milk or use of the same equipments in both working cycles.

This paper first recalls the main characteristics, design criteria, and strong points of the ac/dc conversion system of RFX-mod. Then, after having described some innovative experimental scenarios and performance improvements which have been devised, the corresponding impact on the ac/dc conversion system and the compatibility with the present design are discussed. Some possible upgrades are identified and the pros and cons are evaluated, also through dedicated simulations.

This paper firstly recalls the main characteristics, design criteria and strong points of the ac/dc conversion system of RFX-mod. Then, after having described some innovative experimental scenarios and performance improvements which have been devised, the corresponding impact on the ac/dc conversion system and the compatibility with the present design are discussed. Some possible upgrades are identified and the pros and cons are evaluated, also through dedicated simulations.

This paper presents the experimental qualification of the Hybrid Circuit Breaker developed for the full scale prototypes of the Quench Protection Circuit (QPC) used for Poloidal Field Coils (PFC) and Toroidal Field Coils (TFC) of JT-60SA within a contract placed to Ansaldo Sistemi Industriali S.p.A.. JT-60SA will be built in Naka, Japan, as a satellite tokamak of ITER in the framework of the Broader Approach Agreement; it is a complementary facility which accelerates the development of magnetic confinement fusion reactors. It is designed to perform long lasting plasma pulses up to 5.5 MA, with a flat-top duration of 100 seconds thanks to additional heating systems. In order to limit the power dissipation it will be equipped with both toroidal and poloidal magnets manufactured with low temperature superconductors and protected against quench by means of QPCs, which are capable of interrupting and diverting the current into a dump resistor avoiding major damages to the coils. The heart of the QPC is the Hybrid mechanical-static Circuit Breaker (HCB) an innovative concept which has no similar applications either industrialor laboratory at such power values. HCB is a device which combines a mechanical bypass switch (BPS) and a static circuit breaker (SCB): It takes advantage of the low power losses during normal operation while the BPS is closed, and the fast, reliable, arch-less current interruption of the SCB when it is operated. The SCB does not need a counterpulse network to turn-OFF the SCBthanks to the selection of static devices (IGCTs) which can be controlled both at turn-ON andturn-OFF. The HCB has been developed by Consorzio RFX team since 2007, starting from the conceptual design and the feasibility studies [1] which allowed to explore and solve open issues such as the reliable turn-ON of single and paralleled static switches with a very low voltage. The 10 kA unidirectional HCB prototype [2] has been a major step through the adoption of this solution for QPC, because it highlighted the suitability and reliability of the arc voltage to divert the current into the static devices in few ms. The final step has been the development and construction of the full scale prototypes for toroidal and poloidal HCBs which match JT-60SA requirements in terms of current polarity, current value, reapplied voltage and intervention time. In particular HCB for PFC is rated for a bidirectional current up to 21 kA and a maximum voltage of 5 kV, while the HCB for TFC is rated for a unidirectional current up to 25.7 kA and a maximum voltage of 2.8 kV; the operational time for both HCBs is 350 ms. Since the QPC is a safety component a full qualification process, based on a complete set of tests, has been designed and performed during 2012. It allowed to highlight the commutation between BPS and SCB which is one key aspect of the HCB and also the robustness of solutions and technologies employed for the HCB prototypes. The performances of the prototypes during the tests proved the compliance with the requirements and verified also the goodness of the electrical and thermal models developed during the design phase. [1] Novello et al. "Feasibility Study of a Hybrid Mechanical-Static DC Circuit Breaker for Superconducting Magnet Protection" IEEE Transactions on applied superconductivity, vol. 19, no. 2, April 2009, pages 76-83 [2] Novello et al. "Development and Testing of a 10-kA Hybrid Mechanical-Static DC Circuit Breaker" IEEE Transactions on applied superconductivity, vol. 21, no. 6, December 2011, pages 3621-3627

The RFX-mod fusion science program has made significant progress since the last 2010 IAEA Fusion Energy Conference. The activities focused on the goal of exploring the fusion potential of the RFP magnetic configuration and that of 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 program. New upgrades on the system for active control of MHD stability are under way and will be presented here. Unique in the portfolio of existing fusion devices, RFX-mod has been operated both as a RFP and as a tokamak. The latter operation has allowed the exploration of qedge

This paper describes the detailed design of the quench protection circuits (QPCs) for the superconducting toroidal field (TF) and poloidal field (PF) magnets of the satellite tokamak JT-60SA, which will be installed in Naka, Japan. The nominal currents to be interrupted and the maximum reapplied voltages are 25.7 kA and 2.8 kV for the TF QPCs and 20 kA and 5 kV for the PF QPCs. The innovative solution proposed in the QPC design is based on a hybrid circuit breaker (CB) composed of a mechanical bypass switch for conducting the continuous current, in parallel to a static CB for current interruption. The main choices of the final design are presented and discussed, either to confirm or to update and complete the study performed at the conceptual design level.

This paper presents the analyses carried out to address the impact on the power quality of the Extra High Voltage Italian network due to the operation of thermonuclear fusion experiments located in Padova, north-east of Italy. In particular, the impact of a full scale prototype of the 1MV Neutral Beam Injector (NBI) of the ITER experiment, which is currently under development, will be analyzed. The simultaneous operation of both NBI and the RFX-mod experiment, already existing and in operation at the same site since 2004, will be assessed. A detailed frequency model of the high voltage grid surrounding the facilities supplying node has been setup and simulated using ATP-EMTP program to support the analyses, in particular on the harmonics.

Given the considerable economic loss to beekeepers worldwide and the possible public health implications related to the presence of antibiotics in honey, an American Foulbrood (AFB) monitoring/prevention program for Paenibacillus larvae is regarded as essential. This study investigates the occurrence and distribution of P. larvae genotypes in honey and brood combs from Apulia (Italy). Genotyping of P. larvae isolates using ERIC-PCR generated a total of four different ERIC banding patterns (ERIC-A, ERIC-B, ERIC-C, ERIC-D), including fragments ranging from 200 to 3000 bp. Considering that the genotype has an influence on P. larvae infections and multi-genotype infections of colonies or apiaries may increase the complexity of P. larvae infections by influencing the type and speed of the development of clinical symptoms, the findings of the present study could be helpful for training veterinarians, bee inspector’s extension staff, and beekeepers, thus improving the detection of AFB infections in the field.

Veterinary surgeons in Italy were surveyed about their current practice with regard to the use of propofol and intravenous opioids during anaesthesia and for treatment of acute pain in small animals. Questionnaires were e-mailed to all 171 members of the Italian Society of Veterinary Regional Anaesthesia and Pain Medicine. Information was requested on the type of practice the veterinarians worked in, the administration techniques used and the perceived benefit of pumps with target-controlled infusion (TCI) capability implementing small animal pharmacokinetic models. A total of 168 responses were received (response rate 98.2 per cent). Of the respondents, 121 (72.0 per cent) worked in a first-opinion private practice, 25 (14.9 per cent) worked in a 24/7 private practice, 11 (6.5 per cent) worked in a referral private practice, eight (4.8 per cent) worked in a university hospital, two (1.2 per cent) were not currently practising with small animals and one (0.6 per cent) had retired. Of the 130 (78.8 per cent) practising respondents who reported using a syringe pump, eight (4.8 per cent) used a TCI system, 31 (18.8 per cent) used manual TCI, 40 (24.2 per cent) used a bolus-elimination-transfer scheme and 51 (31 per cent) used a constant-rate infusion. As a result, 79 of 165 (47.9 per cent) practising respondents used a pharmacokinetic model-driven method of drug delivery. The majority of respondents (81.2 per cent) believed that the use of pumps with TCI capability would improve practice and patient care.

An interesting result of magnetic chaos reduction in RFX-mod high current discharges is the development of strong electron transport barriers. An internal heat and particle transport barrier is formed when a bifurcation process changes the magnetic configuration into a helical equilibrium and chaos reduction follows, together with the formation of a null in the q shear. Strong temperature gradients develop, corresponding to a decreased thermal and particle transport. Turbulence analysis shows that the large electron temperature gradients are limited by the onset of micro-tearing modes, in addition to residual magnetic chaos. A new type of electron transport barrier with strong temperature gradients develops more externally (r/a = 0.8) accompanied by a 30% improvement of the global confinement time. The mechanism responsible for the formation of such a barrier is still unknown but it is likely associated with a local reduction of magnetic chaos. These external barriers develop primarily in situations of well-conditioned walls so that they might be regarded as attempts towards an L–H transition. Both types of barriers occur in high-current low-collisionality regimes. Analogies with tokamak and stellarators are discussed.

This paper summarizes the main achievements of the RFX fusion science program in the period between the 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is the largest reversed field pinch in the world, equipped with a system of 192 coils for active control of MHD stability. The discovery and understanding of helical states with electron internal transport barriers and core electron temperature >1.5 keV significantly advances the perspectives of the configuration. Optimized experiments with plasma current up to 1.8 MA have been realized, confirming positive scaling. The first evidence of edge transport barriers is presented. Progress has been made also in the control of first-wall properties and of density profiles, with initial first-wall lithization experiments. Micro-turbulence mechanisms such as ion temperature gradient and micro-tearing are discussed in the framework of understanding gradient-driven transport in low magnetic chaos helical regimes. Both tearing mode and resistive wall mode active control have been optimized and experimental data have been used to benchmark numerical codes. The RFX programme also provides important results for the fusion community and in particular for tokamaks and stellarators on feedback control of MHD stability and on three-dimensional physics. On the latter topic, the result of the application of stellarator codes to describe three-dimensional reversed field pinch physics will be presented. © 2011 IAEA, Vienna.

New promising and versatile materials for the development of in situ sustained release systems consisting of thin films of either poly(2-hydroxyethyl methacrylate) or a copolymer based on poly(ethylene-glycol diacrylate) and acrylic acid were investigated. These polymers were electrosynthesized directly on titanium substrates and loaded with ciprofloxacin (CIP) either during or after the synthesis step. X-ray photoelectron spectroscopy was used to check the CIP entrapment efficiency as well as its surface availability in the hydrogel films, while high-performance liquid chromatography was employed to assess the release property of the films and to quantify the amount of CIP released by the coatings. These systems were then tested to evaluate the in vitro inhibition of methicillin-resistant Staphylococcus aureus (MRSA) growth. Moreover, a model equation is proposed which can easily correlate the diameter of the inhibition haloes with the amount of antibiotic released. Finally, MG63 human osteoblast-like cells were employed to assess the biocompatibility of CIP-modified hydrogel coatings.

The recent start-up improvements brought to RFX-mod have allowed increasing the plasma current in the range 1.7–1.9 MA, but still they proved to be not sufficient to routinely and reliably reach higher values of plasma current that would be very useful for the present studies on enhanced confinement. The need for higher poloidal flux variation together with the overabundant available toroidal flux has led to the study of a rearrangement of the power supply system with the aim of increasing the first at the expenses of the latter. Thanks to the flexibility of the power supply system, composed of modular thyristor converters, the rearrangement has been easily obtained and the resulting enhanced poloidal flux capability scenario described in the paper allows a two step plasma current ramp-up. In order to increase as much as possible the plasma current up to the nominal value of 2 MA it is necessary to fully exploit the thyristor converter power capability, in particular in the first ramp-up phase. In the paper a detailed verification of their maximum performance is presented. The first results obtained after power supply reconfiguration are very good, with plasma current kept constant at about 2 MA for 100 ms. The enabled operation at very high plasma current requires also an optimization of the magneto hydro dynamics (MHD) mode coil power supplies that are required to provide higher current values. Therefore a dedicated study of their control system has been worked out, which allowed understanding how to increase as much as possible the output current without losing the dynamic performance, so keeping the efficiency in the control of dominant and secondary modes, which is essential to obtain good and reproducible discharges.

IAEA Fusion Energy Conference 2010 Proceedings of the 23rd IAEA Fusion Energy Conference Daejeon, 11-16 October 2010 Organized by the International Atomic Energy Agency and hosted by the Government of the Republic of Korea IAEA-CN-180 (EXC/P4-10) Internal and Edge Electron Transport Barriers in the RFX-Mod Reversed Field Pinch M.E. Puiatti1), M. Valisa1), A. Alfier1), M. Agostini1), L. Apolloni1), F. Auriemma1), M. Baruzzo1), T. Bolzonella1), D. Bonfiglio1), F. Bonomo1), A. Canton1), S. Cappello1), L. Carraro1), R. Cavazzana1), S. Dal Bello1), G. De Masi1), D.F. Escande2), A. Fassina1), P. Franz1), E. Gazza1), M. Gobbin1), S. Guo1), P. Innocente1), R. Lorenzini1), G. Marchiori1), L. Marrelli1), P. Martin1), E. Martines1), S. Martini1), S. Menmuir1), B. Momo1), L. Novello1), R. Paccagnella1), P. Piovesan1), L. Piron1), I. Predebon1), A. Ruzzon1), F. Sattin1), A. Scaggion1), P. Scarin1), A. Soppelsa1), G. Spizzo1), S. Spagnolo1), M. Spolaore1), D. Terranova1), M. Veranda1), N. Vianello1), P. Zanca1), B. Zaniol1), L. Zanotto1), M. Zuin1) 1) Consorzio RFX, Associazione EURATOM-ENEA sulla Fusione, Padova, Italy 2) Laboratoire PIIM, UMR 6633 CNRS-Aix Marseille Université, France Abstract. An interesting result of the self-organization processes in RFX-mod high current discharges is the development of strong electron transport barriers. An internal heat and particle transport barrier is formed when a bifurcation process changes the magnetic configuration into a helical equilibrium (SH) and chaos reduction follows, together with the formation of a null in the q shear. Turbulence analysis shows that the large electron temperature gradients are likely limited by the onset of micro-tearing modes. A new type of electron transport barrier with strong temperature gradients develops more externally (r/a = 0.8), independently on the presence of the helical equilibrium, accompanied by a 30% improvement of the global confinement time. Both types of barriers occur in high current low collisionality regimes. Analogies with Tokamak and Stellarators are discussed.

The full three-dimensional (3D) approach is now becoming an important issue for all magnetic confinement configurations. It is a necessary condition for the stellarator but also the tokamak and the reversed field pinch (RFP) now cannot be completely described in an axisymmetric framework. For the RFP the observation of self-sustained helical configurations with improved plasma performances require a better description in order to assess a new view on this configuration. In this new framework plasma configuration studies for RFX-mod have been considered both with tools developed for the RFP as well as considering codes originally developed for the stellarator and adapted to the RFP. These helical states are reached through a transition to a very low/reversed shear configuration leading to internal electron transport barriers. These states are interrupted by MHD reconnection events and the large Te gradients at the barriers indicate that both current and pressure driven modes are to be considered. Furthermore the typically flat Te profiles in the helical core have raised the issue of the role of electrostatic and electromagnetic turbulence in these reduced chaos regions, so that a stability analysis in the correct 3D geometry is required to address an optimization of the plasma setup. In this viewtheVMECcode proved to be an effectiveway to obtain helical equilibria to be studied in terms of stability and transport with a suite of well tested codes. In this work, the equilibrium reconstruction technique as well as the experimental evidence of 3D effects and their first interpretation in terms of stability and transport are presented using both RFP and stellarator tools. © 2010 IOP Publishing Ltd.

With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and promising perspectives for the Reversed Field Pinch (RFP). A big leap with respect to previous knowledge and expectations on RFP physics and performance has been made by RFX-mod since the last 2006 IAEA Fusion Energy Conference. We present results, which are relevant for the understanding of the RFP physics and confinement performance, and contribute to the solution of issues for the optimization of ITER construction and operation. RFX-mod is a large ohmically heated RFP (R = 2 m, a = 0.457 m, volume 10 m3), equipped with an advanced system for feedback control of MHD instabilities, based on 192 independently driven coils covering the whole plasma boundary. An axisymmetric magnetic boundary is produced, with differential rotation of tearing modes and full stabilization of multiple RWM. The operation above 1 MA (up to 1.6 MA reported at this conference) has revealed a new self-organised helical equilibrium (the Single Helical Axis - SHAx - state), which is the preferred state at high current. This regime is characterized by strong core electron transport barriers, with electron temperature gradients comparable to those achieved in tokamaks, and by a factor four improvement in confinement time with respect to the standard RFP. The electron temperature shows peak values in the 1 keV range, linearly increasing with plasma current with no degradation of beta. The RFP dominated by magnetic chaos belongs to the past, and the new findings open an exciting and clear path, which deserved to be explored. The achievements in the field of MHD stability real-time control have been of high quality. Progresses in control of tearing modes and RWM have been reported. Besides providing an improved magnetic boundary for the high current operation, the feedback experiments address general issues like multi-mode control, tools for mode unlocking and for forcing mode rotation, implementation of advanced control theory, development of a plant model including features of the plasma, wall, sensors, actuators, field error environment, noise environment and controller dynamics, incorporation of 3-d effects due to a non-axisymmetric wall, benchmarking of numerical stability codes also used for ITER. All these results give strong confidence in the RFX-mod future programme.

The reversed field pinch configuration is characterized by the presence of magnetic structures both in the core and at the edge: in the core, at high plasma current the spontaneous development of a helical structure is accompanied by the appearance of internal electron transport barriers; at the edge strong pressure gradients, identifying an edge transport barrier, are observed too, related to the position of the field reversal surface. The aim of this paper is the experimental characterization of both the internal and edge transport barriers in relation to the magnetic topology, discussing possible analogies and differences with other confinement schemes. © 2009 IOP Publishing Ltd.

With the exploration of the MA plasma current regime in up to 0.5 s long discharges, RFX-mod has opened new and very promising perspectives for the reversed field pinch (RFP) magnetic configuration, and has made significant progress in understanding and improving confinement and in controlling plasma stability. A big leap with respect to previous knowledge and expectations on RFP physics and performance has been made by RFX-mod since the last 2006 IAEA Fusion Energy Conference. A new self-organized helical equilibrium has been experimentally achieved (the Single Helical Axis - SHAx - state), which is the preferred state at high current. Strong core electron transport barriers characterize this regime, with electron temperature gradients comparable to those achieved in tokamaks, and by a factor of 4 improvement in confinement time with respect to the standard RFP. RFX-mod is also providing leading edge results on real-time feedback control of MHD instabilities, of general interest for the fusion community. © 2009 IAEA, Vienna.

This paper describes the feasibility studies of a hybrid DC circuit breaker (CB) for quench protection of superconducting magnets rated for current up to some tens of kiloamperes (kA) and voltage of several kilovolts (kV). The proposed scheme is based on a mechanical switch paralleled to a fully controlled static CB; integrated gate commutated thyristors (IGCTs) were selected. In normal operation, the mechanical switch handles the continuous flow of DC current minimizing the on-state losses. When protection against quench is requested, the current is diverted into the static breaker that quickly interrupts the current, withstanding the reapplied voltage of several kV. The reliable turn-ON of several IGCTs in parallel with low voltage applied between anode and cathode is an issue to be assessed to confirm the feasibility of this design solution. The paper highlights that the components commonly used as snubber or protection circuit can guarantee the turn-ON of all the devices in parallel and that the IGCTs can be turned-ON with few volts applied; this latter aspect was proved by means of specific tests. Finally, a comparison between a static only and a hybrid CB is performed, highlighting the benefits introduced by the hybrid solution.

JT-60SA is a fully superconducting coil tokamak to be built under the framework of the EU-JA Broader Approach Agreement, and it aims to contribute to the complement of the ITER experiments and to the DEMO reactor design by the study of steady-state high-beta plasma experiments. The conceptual design of the JT-60SA tokamak and the peripheral systems has been carried out in close collaboration of EU and Japan from middle of 2006, and the JT-60SA Conceptual Design Report which involves an analysis of plasma physics and engineering design is summarized in May 2007. This paper intends to present an overall view of the JT-60SA project, and the latest design status of the key engineering issues such as superconducting magnets, divertor target, plasma heating devices, and magnet power supplies.

Optimization of machine operation, including plasma position control, density control and especially feedback control on multiple magnetohydrodynamic modes, has led RFX-mod to operate reliably at 1.5 MA, the highest current ever achieved on a reversed field pinch (RFP). At high current and low density the magnetic topology spontaneously self-organizes in an Ohmical helical symmetry, with the new magnetic axis helically twisting around the geometrical axis of the torus. The separatrix of the island disappears leaving a wide and symmetric thermal structure with large gradients in the electron temperature profile. The new topology still displays an intermittent nature but its overall presence has reached 85% of the current flat-top period. The large gradients in the electron temperature profile appear to be marginal for the destabilization of ion temperature gradient modes on the assumption that ions and electrons have the same gradients. There are indications that higher currents could provide the conditions under which to prove the existence of a true helical equilibrium as the standard RFP configuration. © 2008 IOP Publishing Ltd.

In this paper, the conceptual design of a hybrid DC circuit breaker for quench protection (QP) of superconducting magnets in fusion experiments is presented. In this applications currents of the order of tens of kilo-ampere have to be sustained in steady state and interrupted in case of quench with reapplied voltage of several kilo-volt. The scheme proposed for the QP is based on a mechanical switch to handle the current in steady state operation paralleled to a static circuit breaker for the current interruption. IGCTs available on the market have been selected to analyse the obtainable performance; the relationship among the current to be interrupted, the IGCT junction temperature rise, the opening time of the mechanical switch and the number of devices in parallel, as well as between the reapplied voltage and the number of devices in series are reported and discussed.

In reversed-field pinch (RFP) devices the magnetic configuration is characterized by a toroidal magnetic field whose direction in the plasma edge is opposite that in the core. With an edge safety factor qa? - 0.02 ( q = aBt/RBp), the toroidal magnetic field in the RFP is much smaller than in the Tokamak and stability is ensured by the large magnetic shear (r/q dq/dr). Since in the RFP the safety factor is everywhere less than one, a large number of MHD modes are resonant and their amplitude largely affect the confinement. In RFX, as usual in RFP devices, MHD modes amplitude had been controlled by the use of a passive thick conductive shell that vanish the radial magnetic field at the surface. In RFX-mod a different approach has been followed: radial magnetic field control is obtained by external magnetic field coils and a close fitting thin conductive shell. In the so-called Virtual Shell operation (VS), radial field zeroing at the thin shell radius is stationary provided by the externally controlled coils. First experiments of RFX-mod proved the capability of the active scheme to control the radial magnetic field at any time. Furthermore it has been found that such edge magnetic field control extends its beneficial effects to the whole plasma, leading to a stationary 2 to 3-fold reduction of the core Br field amplitude. The reduction of field fluctuations positively reflects on confinement. In fact, a strong reduction of the loop voltage is observed and correspondingly a 3-fold increase in pulse length is achieved by using the same poloidal flux swing. Temperature and particle measurements confirm the improved confinement properties of the virtual shell operation. With a lower ohmic input power, higher electron temperature in the plasma core and a steeper profile is measured. Particle and heat transport have been studied by means of a 1-d code. Local power balance was used to compute the heat conductivity profile: for the VS discharges a lower conductivity over a significant region of the plasma is found. The improved properties of RFX-mod VS operation provide a better confinement scaling both in terms of plasma current and density. The results show that compared to the thick shell solution, a significant confinement improvement can be obtained under stationary conditions by actively controlling the plasma magnetic boundary.