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The International Fusion Materials Irradiation Facility (IFMIF) is a project aiming to investigate candidate materials to be used in the most exposed zones of future fusion reactors. The linear IFMIF prototype accelerator (LIPAc), presently under commissioning in Rokkasho, Japan, is a prototype of the frontend section of one of the IFMIF accelerators. Eight quadrupole magnets, six pairs of corrector magnets and one dipole are responsible for generating the magnetic fields needed for a proper beam handling along the 10 m long LIPAc high energy beam transport line, which connects the end of the superconducting radio frequency Linac with the beam dump. A novel design of combined magnets with the correctors integrated in the quadrupole poles is chosen for compactness reasons. The different stages of the production of the combined magnets, from the magnetic and mechanical design to their manufacturing and testing, including exhaustive characterization of the magnetic performance are described in this work. The results from the tests revealed the quality of the magnetic field produced. The materials selection was done carefully, to withstand the high levels of ionizing radiation expected at the magnet locations. This paper focuses on the activities performed in Europe, before sending the magnets to Japan for their installation and commissioning at the Rokkasho site.

Along 2017 ALBA magnetic measurements facility has measured LIPAc HEBT quadrupoles and dipole designed by CIEMAT and built by ELYTT company. ALBA magnetic measurements laboratory has been improved through an upgrade program of its measurement benches to complete their measurements. One of the main aims of the upgrade has been to standardize both the hardware and software and therefore ensure an easy maintenance. Especially relevant has been the upgrade of the flipping coil bench, in which the DC motors and the obsolete controller have been replaced by step-motors and ICEPAP controller. Also, software has been migrated to Tango package. Hardware and software of Hall probe bench has been upgraded as well, using the last DeltaTau motion controller. Tango has been upgraded too, using Devian 8 as operative system. Next step will be the upgrade of the rotating coil hardware and software using also step-motor and ICEPAP controller. In parallel, new shafts have been build and tested, with specific designs to improve the sensitivity and minimize the noise to signal ratio. In this contribution we detail the upgrades and the results of performance tests., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The DAC file (Demande d’Autorisation de Creation) is the principal document supporting the application for the licensing of ITER. It includes the Preliminary Safety Report (RPrS - Rapport Prelimina...

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.

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 edge parameters of electron cyclotron resonance heated plasmas in the TJ-II stellarator are reported. Data from atomic beam diagnostics and electrical probes have been used for edge and scrape-off layer characterization. Scans in heating power and plasma density for H and He plasmas have been performed, for a given magnetic configuration. A linear increase of the diffusion coefficient at the last-closed magnetic surface with the ratio of injected power to plasma density and a similar value of that parameter for the two atomic species investigated were obtained. Global particle confinement times between 3 and 15 ms have been deduced, and transition to an enhanced confinement mode in H plasmas has been observed under some conditions. The role of high-energy particle losses, due to trapping into the relatively high magnetic ripple, in the global energy balance of TJ-II plasmas is addressed.

TJ-II is a medium size (major radius R= 1.5 m, average minor plasma radius a < 0.2 m, on axis magnetic field B= I T) helical axis stellarator operating in its first phase with up to 600 kW of ECH power. Two mobile poloidal limiters can control the last closed magnetic surface (LCMS) and diagnose the plasma boundary with a set of Langmuir probes and with CCD-cameras equipped with interference filters. In the described experiments, plasmas with different minor radii interact either with the toroidal limiter or with the mobile poloidal limiters. The electron density and temperature profiles are characterised in the plasma centre, boundary and scape-off layer (SOL) for the different configurations. The global energy for the different configurations is compared and the ratio of the energy confinement time to that obtained by the LHD-scaling-law, seem to be improved when inserting the poloidal limiters. Finally, it is discussed whether the large connection lengths obtained in certain poloidal limiter SOL regions effectively reduce the plasma size, making the definition of the plasma minor radius ambiguous.

He and Li beams have been installed and set into operation at the TJ-II stellarator with the aim of measuring electron temperature and density profiles in the edge and scrape-off layer regions of the plasma. The effusive thermal Li beam penetrates up to a normalized effective radius of ρ=0.6–0.7 in typical electron cyclotron heated plasmas. Density profiles deduced from the Li beam are wider than those obtained from extrapolation of the profile measured by Thomson scattering. The He beam is a pulsed supersonic one. Simultaneous detection of three emission lines (667.2, 706.5, and 728.1 nm) is made with a set of three photomultipliers. First He beam measurements of ne and Te in TJ-II are presented and the agreement among results of different plasma edge diagnostics is discussed.

ELM-like activity has been recently observed in TJ-II, in plasmas with stored energy above 1 kJ. The plasma is observed to develop bursts of magnetic activity (seen in Mirnov coil signals) which are followed by a large and distinct spike in the Hα signal. An increase in electrostatic and magnetic fluctuations at the plasma edge and a cold pulse towards the plasma centre are also characteristics of these events. In addition, the electron temperature profile locally flattens at the plasma radius where the temperature is in the range 100-200 eV. This flattening can be explained in terms of enhanced electron heat conductivity. Between ELM-like events the electromagnetic turbulence at the edge decreases and the Te profiles recover their former shapes. This activity is probably triggered by a resonant m = 2, n = 3 mode.

We show that the modulational instability growth rate of zonal flows is determined directly from the quasilinear wave kinetic equation. We also demonstrate the relation between zonal-flow growth and the cross bispectrum of the high-frequency drift-wave-driven Reynolds stress and the low-frequency plasma potential by explicit calculation. Experimental measurements of the spatiotemporal evolution of the spectrum integrated bicoherence at the L → H transition near the edge shear layer indicate a modification in the nonlinear phase coupling, which might be linked to the generation of sheared E × B flows © 2000 The American Physical Society.

In this article we present experimental results obtained with a heterodyne/amplitude modulated (AM) reflectometer at W7-AS and simulations [two-dimensional (2D) (WKB)] of reflection on a rotating cutoff layer corrugated by turbulence for the W7-AS conditions. When the turbulence has a large amplitude and a small size relative to the illuminated spot, the calculations show the existence of a phase runaway and reproduce the typical behavior of the measured phase and amplitude signals. It is not possible to deduce the plasma rotation from the phase runaway value at “close to normal” incidence, as this value depends on the turbulence characteristics. When the illuminated cutoff surface is smooth, no runaway occurs, amplitude and phase signals are coherent and in certain poloidal wavelength ranges (∼1 to 2 cm for W7-AS conditions) their relative phase is π/2, conditions that have been observed experimentally during H mode. The phase runaway can affect the ne(r) measurements. However, the comparison between the...

Amplitude modulation (AM) reflectometry is a technique for density profile measurements in magnetic fusion plasmas based on the measurement of the phase delay of the modulation in the amplitude of a microwave beam launched and reflected at the plasma. Results from AM experiments in the PBX-M tokamak and the W7-AS stellarator are presented. A general analysis of the capabilities of the technique is performed, particularly centered in the effects of spatial turbulence. Simulations of the effects of two-dimensional turbulence have been performed for medium size (W7-AS) and large devices (LHD stellarator, ITER), showing the capability of the AM technique to operate in turbulent plasmas. Finally, possible solutions to the problem of parasitic reflections in AM systems are presented as development options.

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.

Experimental evidence of the nonlinear nature of the broadband edge fluctuations has been obtained in edge turbulence in the Advanced Toroidal Facility torsatron. Whereas little nonlinear wave interaction is found in the scrape-off layer region, three-wave coupling is enhanced in the plasma edge region (r

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.

A microwave reflectometer has been used in the TJ‐I tomakak (R=0.30 m, a=0.10 m, IpIp< 50 kA, Bt < 1.5 T) to monitor density fluctuations in the plasma bulk. Experiments were made in the range 33–50 GHz, x mode. The system uses a single antenna for launching and receiving the microwave beam. Since broadband operation usually requires homodyne detection, different techniques were used to overcome the limitations due to this detection scheme. Radial profiles of the density turbulence were taken and the behavior of the spectra analyzed. A slow frequency sweeping has been performed to provide a method to normalize the signals reflected from different radial positions. In addition this technique can be used to obtain information on the absolute value of the phase oscillation amplitude. Spectra of the edge density fluctuations obtained by reflectometry and by Langmuir probes are compared. By the use of two reflectometers in the same antenna, radial correlation experiments can be performed. Some discussions on t...

One of the limiting factors in reflectometers when trying to measure the density profile in fusion plasmas is the existence of a fraction of experiments where the measurement becomes impossible: very noisy signals leading to nonsense density profiles. Those so called “bad shots” are usually linked with strongly turbulent plasmas and the remaining problem is to be able to assess “a priori” if the data coming from a given experiment will correspond to a normal profile or if they will be meaningless.

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.

Recent experiments in the Advanced Toroidal Facility (ATF) torsatron [Plasma Physics and Controlled Nuclear Fusion Research 1990 (IAEA, Vienna, in press)] have emphasized the role of magnetic configuration control in transport studies. Long‐pulse plasma operation up to 20 sec has been achieved with electron cyclotron heating (ECH). With neutral beam injection (NBI) power of ≥1 MW, global energy confinement times of 30 msec have been obtained with line‐average densities up to 1.3×1020 m−3. The energy confinement and the operational space in ATF are roughly the same as those in tokamaks of similar size and field. The empirical scaling observed is similar to gyro‐reduced Bohm scaling with favorable dependences on density and field offsetting an unfavorable power dependence. The toroidal current measured during ECH is identified as the bootstrap current. The observed currents agree well with predictions of neoclassical theory in magnitude and in parametric dependence. Variations of the magnetic configuration ...

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.