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The TJ-II stellarator presently in operation at the National Laboratory of Fusion is subject to radiological surveillance in compliance with the Spanish Nuclear Regulation. During its pulsed operation hard X-rays are emitted by the runaway electrons, and soft X-rays are generated by bremsstrahlung of thermalized electrons. Inside the experimental hall, the plasma heating systems and some active diagnostics are additional sources of radiation. Outside the experimental hall, some auxiliary systems, such as high-voltage power supplies, must be checked for radiological influence. In order to verify the adequate radiological classification of the different working areas, 15 dosemeters are distributed in radiologically controlled areas close to the machine, as well as in areas of public use in the TJ-II building. The integrated dose equivalent is analyzed to help establish the range of radiological influence of the stellarator. The results of the period 2015–20 are presented and analyzed.

TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.

The International Fusion Materials Irradiation Facility (IFMIF) is a planned high-energy neutron source for the testing of candidate materials for future fusion power plants. Safety studies performed during the various stages of the conceptual design of IFMIF have been brought together in a preliminary assessment of the safety of IFMIF, identifying the principal hazards and the means to prevent or mitigate them. The design is based on dual high-energy deuteron accelerators delivering beams onto a flowing lithium target, in which neutrons are produced through a d-Li stripping reaction. The neutrons irradiate material samples in controlled conditions in a test cell. In all these systems, potential hazards arise, but analyses show that no postulated off-normal event can result in a significant risk of harm to the public. However, care must be taken in forthcoming detailed design development to minimise occupational radiation exposure during IFMIF operation and maintenance.

Events, such as fire, have been considered in ITER documentation of low probability and a general approach has been defined in [Technical basis for the ITER final design, EDA Documentation Series I, No. 22, IAEA, Vienna, 2001] to be developed later for the ITER specific site. It was said that “these hazards will be treated according to the industrial safety regulations and practices of the host country”. In the framework of studies for the European ITER site in Cadarache, an assessment of fire hazard has been done in order to ensure compliance with French safety requirements. In this report, a summary of existing laws is presented and an example of the deterministic approach to be followed for the preliminary safety report (PSR) is given on the analysis of tritium building design.

The licensing procedure for ITER in Europe in the framework of the French regulations is a non-prescriptive approach based on a continuous dialogue between the nuclear installation owner (or its representative) and the safety authority. In this paper, the licensing procedure and main safety issues, which are being studied in this process, are presented.

This paper describes a series of experiments performed in TJ-II stellarator with the aim of studying the influence of magnetic configuration on stability and transport properties of TJ-II plasmas. Plasma potential profiles have been measured in several configurations up to the plasma core with the heavy ion beam probe diagnostic. Low-order rational surfaces have been positioned at different plasma radii observing the effect on transport features. Plasma edge turbulent transport has been studied in configurations that are marginally stable due to decreased magnetic well. Results show a dynamical coupling between gradients and turbulent transport. Experiments on the influence of magnetic shear on confinement are reported. Global confinement issues as well as enhanced confinement regimes found in TJ-II are discussed as well.

The TJ-II is a four period, low magnetic shear stellarator, with high degree of configuration flexibility (rotational transform from 0.9 to 2.5) which has been operating in Madrid since 1998 (R=1.5 m, a

TJ-II is a four period, low magnetic shear stellarator (R = 1.5 m, a < 0.22 m, B0 ≤ 1.2 T) which was designed to have a high degree of magnetic configuration flexibility. In the most recent experimental campaign, coupling of the full ECRH power (PECRH ≤ 600 kW) to the plasma has been possible using two ECRH transmission lines which have different power densities. Both helium and hydrogen fuelled plasmas have been investigated. The article reviews the latest physics results in particle control, configuration effects, and transport and fluctuation studies.

An advanced heavy ion beam probing diagnostic (HIBP) based on simultaneous utilization of two different systems for the secondary ions detection (a multiple cell array detector and 30° Proca-green electrostatic energy analyzer) has been developed for the TJ-II flexible heliac. This innovative design aims at enlarging the HIBP capabilities in order to allow the instantaneous measurements of electron density and plasma potential profiles together with their respective fluctuations. This paper presents the detailed description of the main parts of the HIBP equipment and their characteristics obtained during the first operation on TJ-II. Special attention is employed to the control and data acquisition system built on two VME controllers. The results of the diagnostic beam carrying through the magnetic structure of TJ-II into secondary beam line are presented and compared with the trajectory calculations. The problems of plasma loading of the detection system and HX-ray excitement by the probing beam are considered together with the ways of their solution.

The International Fusion Materials Irradiation Facility (IFMIF) has an essential role to play in the development of fusion power. By characterising the behaviour of candidate power plant materials in relevant neutron irradiation conditions, it will enable the development and selection of materials for DEMO and commercial fusion power stations. On a “fast track” path to fusion, this development is urgent, and delays must be avoided. Thus, when the regulatory approval of IFMIF construction is to be obtained, a rapid positive appraisal of the safety and environmental issues will be essential. With this background, a preliminary compilation has been made of what is currently known about the safety of IFMIF: the potential hazards present, the means to eliminate or mitigate them, and the conceivable consequences for personnel and the public. This is based on safety studies so far performed in the project, which have addressed the key issues but which are not yet fully comprehensive. It is based on a design that is still evolving and for which much detail is yet to be fixed. And it is based on a generic approach to safety requirements, as the regulatory framework in which IFMIF construction will be licensed cannot be anticipated until a site, or at least a host country, is chosen. For these reasons the safety analysis presented here is preliminary and incomplete. Nevertheless it is a starting point from which a full safety analysis can be built, by augmenting it with the outcomes of future studies, by replacing assumptions with design detail as it becomes available, and eventually by providing the information to satisfy the requirements of the regulatory body that will authorise IFMIF construction and operation.

The generation and behaviour of superthermal electrons are studied as a function of magnetic configuration in the TJ-IU torsatron. Characterization of fast electrons is carried out with soft x-ray (SXR) and hard x-ray (HXR) diagnostic systems, covering the range from 0.4 keV to several MeV. The mean energies reached by the superthermal electron populations are found to be consistent with the occurrence of electron cyclotron (EC) off-axis absorption for the different radial magnetic field ripples at the axis. The interpretation of the experimental observations has been based on the influence of trapping factors at the magnetic axis and electron density profiles in the superthermal electron mean energy and density.

In this paper hard x-ray spectra are obtained and compared in hydrogen and deuterium discharges in the TJ-I tokamak and magnetic turbulence characteristics are deduced from these. Significant differences are found in the spectra and, hence, in the magnetic turbulence characteristics of the two types of plasma. In deuterium discharges these changes are interpreted to be due to a reduction of magnetic turbulence amplitude and an enlargement of radial correlation length of the turbulence. The runaway diffusion coefficients for both types of plasma are obtained.

Magnetic turbulence is characterized using anomalous hard x-ray spectra in tokamaks. Two types of spectra are obtained, single slope or normal spectra, and spectra that present roughly two slopes, or anomalous spectra. For normal spectra the amplitude of the turbulence is given by the slope and a lower limit for the radial correlation length of the turbulence is deduced from the maximum detected energy. For anomalous spectra the magnetic turbulence amplitude can be again deduced from the first slope and the radial correlation length can be inferred from the energy at which the slope changes.

In April 1994 first ECRH plasmas (28 GHz, 2nd harmonic) have been produced in the TJ-I U torsatron (R=0.6m, [a]=0.1m, B(0)=0.52 T, E(0)=0.21). In November 1994 a second experimental campaign using a 37.5 GHz gyrotron (B(o)=0.69 T) has started. The main parameters of the device, the basic characteristics of the heating system and some results concerning magnetic surface mapping and first plasma discharges, are reported. 4 refs., 4 figs.

The first experimental campaign of the TJ-II stellarator has been conducted using electron cyclotron resonance heating (f = 53.2 GHz, P-ECRH approximate to 250 kW) with a pulse length of Delta t approximate to (80-200) ms. The flexibility of the device has been used to study five different configurations varying plasma volume and rotational transform. In this paper, the main results of this campaign are presented and, in particular, the influence of plasma-wall interaction phenomena on TJ-II confinement is briefly discussed.

ECR (electron cyclotron resonance) heated plasmas have been studied in the low magnetic shear TJ-II stellarator (R = 1.5 m, a < 0.22 m, B = 1 T, f = 53.2 GHz, P-ECRH = 300 kW, power density = 1-25 W cm(-3)). Recent experiments have explored the flexibility of the TJ-II across a wide range of plasma volumes with different rotational transforms and rational surface densities. In this paper, the main results of this campaign are presented and, in particular, the influence of iota and rational surfaces on plasma profiles is discussed.