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A new magnetic diagnostics system has been designed for the 2005 JET experimental campaigns onward. The system, which is integrated into the existing magnetic diagnostics, consists of in-vessel and ex-vessel sensors, and is intended to provide an improvement in the accuracy and reliability of the present equilibrium reconstruction and iron modelling capabilities [V. Coccorese, et al., Design of new magnetic sensors for JET, in: Proceedings of the 15th Topical Conference High-Temperature Plasma Diagnostics, April 19–22, 2004, San Diego, CA, USA, in press]. In this paper, the ex-vessel system is described, which consists of an array of pick-up coils, Hall probes and flux loops probes to be installed in the proximity of the upper horizontal iron limbs and inside the iron collar. The sensors are designed to produce an absolute measurement of the magnetic field configuration in the vicinity of the magnetic structure of the machine, which is considered valuable information for the tuning of the axisymmetric models used for plasma equilibrium reconstruction. On the basis of recent results obtained with Hall probe prototypes on JET, the choice of type and location of probes, together with other design and manufacturing issues of the ex-vessel magnetic diagnostics are presented and discussed.

Halo currents (HCs), flowing through the plasma and the vacuum vessel during plasma disruptive events, induce severe mechanical stresses in the plasma facing components and in the vessel, and are a major concern for present and future fusion experiments like ITER. The new system of halo current sensors (HCS) designed for JET-EP (enhanced performance, EP) should help to evaluate HC density distribution, localization and rotation as well as toroidal and poloidal current asymmetries. The HCS system will include four identical mechanical structures each including eight Rogowski coils and two toroidal pick-up coils. The Rogowski coils will measure directly the current flowing through some of the tiles of the upper dump plate. The toroidal field pick-up coils will estimate the total poloidal HC. The coil assemblies are installed at the top of the vessel close to secondary X-point in four octants equally spaced along the toroidal coordinate. In the paper, the design and the manufacturing of the HCS system are presented in detail.

Two new main-vessel bolometric cameras (KB5) with horizontal and vertical views of the plasma cross-section have been installed on JET, providing a substantial upgrade in capabilities: more viewing chords (24 chords for each camera), higher energy range (up to 8 keV), higher sensitivity (∼6.2 V/W), lower noise and therefore, lower detectable signals (∼2 μW/cm 2 at a bandwidth of 200 Hz), higher temporal resolution (∼2 ms). In addition, three new dedicated divertor bolometer cameras (KB3) with 12 lines-of-sight in total, optimised views and technical improvements have replaced the old ones. The combination of KB3 and KB5 systems provides measurements with significantly improved spatial resolution, allowing the divertor and main chamber radiation fractions to be clearly resolved. The sensitivity measured with an in situ electrical method matches very well with that obtained using a light source calibration. The deviation between the two methods is less than 7% and is in the range of the measurement accuracy. The experimentally measured geometric functions closely match those computed using the design values of geometry. Tomographic reconstructions of high density divertor plasmas with ITER-like configuration are presented which clearly demonstrate the capability of the new diagnostic.

To improve the quality of radiation measurements, two new bolometric cameras with horizontal and vertical views of the plasma cross-section have been installed on JET. These cameras provide measurements with significantly improved spatial resolution, allowing the divertor and main chamber radiation fractions to be clearly resolved. Analysis of radiation profiles under attached and detached divertor conditions as well during the formation of an X-point MARFE (XPM) close to an ohmic density limit are presented. The radiation power fraction y = P rad /P heat increases from 0.5 to 0.8 just before XPM onset. A large fraction of this radiation is located in the divertor (P div rad /P tot rad = 0.56 at low density and about 0.67 at XPM onset). In addition, spatial distributions of radiation in recent ITER-like configuration discharges are presented.

The JET tokamak is currently using about 7000 transient recorder channels for data acquisition, mainly sampling at 5 kHz but including a few at 1 MHz or higher. Nearly half of the channels are provided by module designs with front ends that are galvanically isolated to over 1000 V. Performing analogue-to-digital conversion before isolation provides many benefits. This paper reviews three such designs that have been commissioned or developed by control and data acquisition systems (CODAS) personnel over the past 10 years and examines the trends.

This paper presents the status of the halo current sensors (HCS) diagnostic enhancement project for JET. The HCS system includes four sets of probes located in four octants equally spaced along the toroidal coordinate, with a total of 24 Rogowski coils and 5 toroidal field pick-up coils. These sensors are meant to provide a measurement of the current flowing through each single tile of the upper dump plate and an estimate of the total poloidal halo current flowing through the first wall structures. The HCS system was installed in the JET vacuum vessel in March 2005 during the 2004/2005 shutdown and the acquisition of signals started during the restart phase of the machine in autumn 2005. This paper firstly summarises the critical aspects encountered during the final phase of the procurement of the system and the in-vessel installation, which was accomplished using the remote handling system. The paper then focuses on the analysis and interpretation of the data collected during the functional commissioning of the new system, carried out during the restart phase of the machine preceding the experimental campaigns.

The JET neutral beam injection system has proved to be both effective and reliable as a plasma heating device. The ion heating and plasma fuelling characteristics of the system are ideally suited to the production of high fusion performance plasmas while the flexibility in the choice of beam species (H, D, T, 3 He or 4 He) and the ability to inject into almost any JET plasma configuration allows a wide variety of related physics experiments to be carried out. The capability to inject (for the first time) tritium beams was essential to the successful execution of the first tritium experiments in which 1.7 MW of power from DT fusion reactions was generated.

Impact research in the United Kingdom has embraced a wide range of topics during the last fifteen years and advice has been provided in the form of guidelines for use in safety assessments and design studies. It is now the intention to produce a comprehensive Impact Assessment Procedure encompassing the definition of loading, whipping pipe effects and the response of steel and concrete targets. This paper is restricted to introducing the methods used for characterising missiles from pressurised vessels and for determining the impact damage produced in concrete targets. Considerable reliance has been placed on the interpretation of experimental data and guidance is therefore limited by the availability of such data. This paper indicates the extent to which advice can be given and the issues which still need further attention. An example is given of the use of the methods for characterising missiles from a cylindrical pressure vessel.

After five years of construction JET started its operation in June 1983. In December plasmas with peak currents of 3 MA were produced. Flat top times of a few seconds were obtained for currents of 2.4 MA. The plasmas were slightly elongated ( ~ 20%) with a minor radius of about 1 m. Line densities (peak values) reached 7 × 10 19 m −2 , electron temperatures on the axis 1.5–2 keV and energy confinement times 0.3 s. The paper describes the state of the machine, the methods employed for impurity control and summarises the experimental results obtained during 1983.

It has been recognised in the UK, that where designers or safety assessors have to consider the effects of dropped loads on various targets, there is uncertainty associated with the fact that these are low velocity impacts. This uncertainty arises for a variety of load/target combinations, but in this paper we concern ourselves with loads which are massive and with reinforced concrete floor targets. The major uncertainty for dropped load assessments, lies in the fact that the designer does not have access, in general, to relevant data. Instead, it is usual, for design purposes, to make use of empirical formulae which are intended for high velocity missiles. The design process involves using the empirical formulae not only for the local damage which they are intended to address, but also to define a load-time history or impulse for the purposes of determining slab response. This paper indicates the range of events that need to be considered, the manner in which the designer approaches the task of making his assessment of the target and the limits of applicability of the available empirical methods. The programme now in progress in the UK is outlined and some of the results emerging are presented.