ITER-Earthing

Earthing of electrical installations is mainly governed by safety rules. Electromagnetic compatibility also deals with earthing, among other circuit characteristics. Tokamaks are large-scale electrical installations that are known to generate large and low frequency magnetic fields as well as large and high frequency electric fields. Four European Tokamak installations have been investigated, from the earthing point of view, to identify appropriate techniques to earth the electrical equipment and to provide the lowest possible electromagnetic interference with the measurement circuits. But none of these existing installations looks like ITER, not even remotely. The plasma current range, the superconducting coils, the thick and continuous vacuum vessel, the cryostat, the very high voltage of its neutral beam injectors, the available amount of auxiliary heating power, the sensitivity of its magnetic measurements required for long pulses, the size of the site and the powerful supply grid all affect the plant earthing. Based on these investigations and the ITER specificities, a layout of the ITER site electrical supply grid and of the related earthing grid is proposed. Basic rules to reduce the electromagnetic noise at its sources and to improve the measurement immunity are also suggested

Design of the ITER high-frequency magnetic diagnostic coils

This paper is an overview of work carried out on the design of the ITER high-frequency magnetic diagnostic coil (HF sensor). In the first part, the ITER requirements for the HF sensor are presented. In the second part, the ITER reference design of the HF sensor has been assessed and showed some potential weaknesses, which led us to the conclusion that alternative designs could usefully be examined. Several options have been explored, and are presented in the third part: (a) direct laser cutting a metallic tube, (b) stacking of plane windings manufactured from a tungsten plate by electrical discharge machining, (c) coil using the conventional spring manufacture. In the fourth part, sensors using the low temperature co-fired ceramic technology (LTCC) are presented: (d) monolithic 1D magnetic flux sensors based on LTCC technology, and (e) monolithic 3D magnetic flux sensors based on the same LTCC technology. The solution which showed the best results is the monolithic 3D magnetic flux sensor based on LTCC. (C) 2011 Elsevier B.V. All rights reserved

High-power ECH and fully non-inductive operation with ECCD in the TCV tokamak

Experiments with high-power electron cyclotron heating (ECH) and current drive (ECCD) in the TCV tokamak are discussed. Power up to 2.7 MW from six gyrotrons is delivered to the tokamak at the second-harmonic frequency (82.7 GHz) in X-mode. The power is transmitted to the plasma by six independent launchers, each equipped with steerable mirrors that allow a wide variety of injection angles in both the poloidal and toroidal directions. Fully non-inductive operation of the tokamak has been achieved in steady state, for the full 2 s gyrotron pulse duration, by co-ECCD with a highest current to date of 210 kA at full power. The experimentally measured ECCD efficiency agrees well with predictions obtained from linear modelling. We have observed that the highest global efficiency attainable at a given power is limited by stability constraints. While the efficiency is maximum bn the magnetic axis, a disruptive MHD instability occurs when the width of the deposition profile is lower than a minimum value, which increases with total power. Many ECCD discharges display a high level of electron energy confinement, enhanced by up to a factor of two over the Rebut-Lallia-Watkins (RLW) scaling law, which by contrast is well satisfied in ohmic conditions. The longest confinement times (up to four times RLW) are observed with central counter-ECCD. Central electron heat diffusivities comparable to ohmic levels are obtained in these scenarios, with electron temperatures in excess of 10 keV