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New diagnostic measurements have driven important steps forward in the JET experimental program in areas related to H-mode, advanced tokamak physics, and divertor erosion-redeposition phenomena. As a consequence, a program of diagnostics developments has been started. The first part of the article describes recent diagnostic measurements, with special emphasis on the motional stark effect observation of the currentless core, the poloidal velocity measurements by charge exchange recombination spectroscopy, the edge profile measurements with light detecting and ranging Thomson scattering and Li-beam emission, the real-time control of the q profile, and the first results from the quartz microbalance on divertor carbon deposition. The second part describes the program of diagnostics developments on JET that is being prepared for commissioning in 2004. Special emphasis will be devoted to the new high-resolution Thomson scattering, the Li-beam polarimetry system (still under assessment), ITER-relevant activity, like the mirror test program (as a support activity for the ITER diagnostics), and the effort on fusion products diagnostics: neutron spectroscopy and lost alpha collectors.

The advanced tokamak research program at DIII‐D relies critically on the measurement of the current density profile. This was made possible by the development of a Motional Stark Effect (MSE) polarimeter that was first installed in 1992. Three major upgrades have since occurred, and improvements in our understanding of critical performance issues and calibration techniques are ongoing. In parallel with these improvements, we have drawn on our DIII‐D experience to begin studies and design work for MSE on burning plasmas and ITER. This paper first reviews how Motional Stark Effect polarimetry (MSE) is used to determine the tokamak current profile. It uses the DIII‐D MSE system as an example, and shows results from the latest upgrade that incorporates an array of channels from a new counter‐Ip injected neutral beam. The various calibration techniques presently used are reviewed. High‐leverage or unresolved issues affecting MSE performance and reliability in ITER are discussed. Next, we show a four‐mirror collection optics design for the two ITER MSE views. Finally, we discuss measurements of the polarization properties of a few candidate mirrors for the ITER MSE. Work supported by the U.S. Department of Energy under W‐7405‐ENG‐48.

Electron cyclotron resonance heating (ECRH) and current drive (ECCD), disruptive instability events and sawtooth activity have been demonstrated to produce suprathermal electrons in fusion devices. The importance of these phenomena for fusion reactors renders suprathermal electron generation and dynamics a key topic in the physics of burning plasmas. Here some significant results from the TCV tokamak are briefly reviewed and a preliminary design of a novel tomographic hard X-ray spectrometer proposed for TCV is discussed. The design is aided by simulations of tomographic reconstruction.

The code SPECE has been developed for the analysis of electron cyclotron emission (ECE) in a general tokamak equilibrium. The code solves the radiation transport equation along the ray trajectories in a tokamak plasma, in which magnetic equilibrium and plasma profiles are given either analytically or numerically, for a Maxwellian plasma or a non thermal plasma characterized by a distribution function that is the sum of drifting Maxwellian distributions. Ray trajectories are computed making use of the cold dispersion relation, while the absorption and emission coefficients are obtained solving the relevant fully relativistic dispersion relation valid at high electron temperature. The actual antenna pattern is simulated by means of a multi‐rays calculation, and the spatial resolution of the ECE measurements is computed by means of an algorithm that takes properly into account the emission along each ray of the beam. Wall effects are introduced in the code by means of a heuristic model. Results of ECE simulations in a standard ITER scenario are presented.

This tutorial gives a brief introduction into passive spectroscopy and describes the working principles of bolometers, a high‐resolution grating spectrometer, and a novel X‐ray imaging crystal spectrometer, which is also of particular interest for profile measurements of the ion temperature and plasma rotation velocity on ITER and future burning plasma experiments.

Laser‐aided plasma diagnostics, aiming for establishment of reliable density measurement in next step magnetically confined fusion devices, are under development at the National Institute for Fusion Science. A new type of two color laser (57.2/47.6‐μm CH3OD) interferometer has been developed and its original function, vibration subtraction, was confirmed in a test stand. The line integrated density measurements by the polarimeter were demonstrated at Compact Helical System by the Cotton‐Mouton polarimeter and at the LHD by the Faraday rotation polarimater.

The present status of investigations on the first mirror (FM) problem is discussed on the basis of the last experimental results obtained in modern tokamaks and laboratory devices. Engineering solutions that are necessary for protection of Fms for CXRS and H‐alpha diagnostics are considered. Future plans for R&D that has yet to be done are presented. Results of neutron irradiation and heating tests of multilayered dielectric mirrors are given briefly.

For continuous operation expected in DEMO, all the plasma current must be non‐inductively driven, with self‐generated neoclassical bootstrap current being maximized. The control of such steady state high performance tokamak plasma (so‐called ‘Advanced Tokamak Plasma’) is a challenge because of the strong coupling between the current density, the pressure profile and MHD stability. In considering diagnostic needs for the advanced tokamak research, diagnostics for MHD are the most fundamental, since discharges which violate the MHD stability criteria either disrupt or have significantly reduced confinement. This report deals with the development in diagnostic application to control advanced tokamak plasma, with emphasized on recent progress in active feedback control of the current profile and the pressure profile under DEMO‐relevant high bootstrap‐current fraction. In addition, issues in application of the present‐day actuators and diagnostics for the advanced control to DEMO will be briefly addressed, where port space for the advanced control may be limited so as to keep sufficient tritium breeding ratio (TBR).

A second‐harmonic interferometer based on a CW Nd:YAG laser is presented. The device is extremely compact and versatile and is developed for line‐integrated electron density measurements in large plasma machines. A sensitivity in measuring line‐integrated electron density of 4×1013 cm−2 with time resolution of 8 μs, and 1013 cm−2 with time resolution of 50 μs, is demonstrated.

During ITER lifetime, dusts and flakes will be produced due to the interaction of plasmas with the in‐vessel materials or due to maintenance. They will be made of carbon, beryllium and tungsten and will be activated, tritiated and chemically reactive and toxic. Safety limits have been set in order to reduce dust hazards. Thus dust diagnostics and removal methods need to be developed for ITER within the constraints linked to magnetic field, radiation, vacuum and temperature. This paper reviews potential diagnostics to monitor the dust content using techniques already used for erosion or deposition monitoring or techniques specially developed for measuring dust in suspension.

Charge eXchange Recombination Spectroscopy (CXRS) will play a crucial role in the diagnosing of burning plasmas: items like helium ash, transport barriers, impurity content or fuel ratio can all be assessed with CXRS. In fact this is the only direct method to obtain information about the light impurity ions, such as temperature, concentrations and rotation, in the core of the plasma. Two of such systems are foreseen at ITER, one in the upper port plug and one on the equatorial level, both viewing the 100 keV diagnostic H-beam. Challenges for this diagnostic development project are: constructing a mirror close to the plasma able to keep its reflectivity under the extreme bombardment by neutrons, erosion by fast neutrals and deposition of sputtered material, design of an optical labyrinth with well enough neutron shielding, developing spectrometers with a throughput about a factor 100 larger than on present day devices, with a similar or better dispersion, calibration and alignment techniques and last but not least, finding ways to obtain the physics relevant information from the measured complicated spectra in real time. With all these issues in mind, an ITER-CXRS pilot experiment has been developed and became operational on the TEXTOR tokamak, to address some of the above aspects. The results of this show the feasibility and the sensitivity of the ITER system: the simulation code for ITER signal levels could be verified, the sensitivity to the current profile has been tested, the beam emission has been compared to beam attenuation calculations and used to obtain absolute impurity concentrations and a high throughput spectrometer became operational.

The ASDEX Pressure Gauge is, at present, the main candidate for in‐vessel neutral pressure measurement in ITER. Although the APG output is found to saturate at around 15 Pa, below the ITER requirement of 20 Pa. We show, here, that with small modifications of the gauge geometry and potentials settings we can achieve satisfactory behaviour up to 30 Pa at 6 T.

An advanced X‐ray imaging crystal spectrometer is currently under development using a segmented position sensitive detector and time‐to‐digital converter (TDC) based delay‐line readout electronics for burning plasma diagnostics. The proposed advanced XICS utilizes an eight‐segmented position sensitive multi‐wire proportional counter and supporting electronics to increase the spectrometer performance includes the photon count‐rate capability and spatial resolution.

The ITER Tokamak will require many diagnostics both for safe and reliable operation of the machine and for understanding of the physics underlying the performance. The design of these diagnostics raises many challenging technical issues not faced on smaller machines. These arise partly from the increase demands on established diagnostics arising from the increased size, higher magnetic field, large heating power, and in particular the dramatically longer pulse duration of ITER, which make issue such as power loading on first wall components more challenging. The demands on reliability and availability of the machine in order to achieve the objectives within the agreed time schedule also place severe additional demands on the design, quality assurance and maintainability of diagnostics. ITER will produce many orders of magnitude more neutrons than previous Tokamaks and will be a licensed nuclear facility. This has important implications for the traceability, quality assurance and availability of safety critical diagnostics, and for the control of the design and procurement of all diagnostics. The high neutron flux/fluence also constrains the design of diagnostics, which must offer shielding consistent with the allowable dose rates on critical components of the Tokamak, and themselves be tolerant of the radiation level at the diagnostic. This paper presents an overview of the more critical issues for ITER diagnostics.

In low temperature plasmas, tokamaks and other experimental fusion devices, the electron temperature and densities in the plasma can be measured with high accuracy by detecting the effect of Thomson scattering of light from a high‐intensity laser fired through the device. It has been established as a robust technique to measure these parameters and in particular it can be used to provide detailed profiles right through the plasma.

In the course of the development of a concept for a spectrally resolving infrared thermography diagnostic for the ITER divertor we have tested 3 types of infrared (IR) fibres in Co60 irradiation facilities under γ irradiation. The fibres were ZrF4 (and HfF4) fibres from different manufacturers, hollow fibres (silica capillaries with internal Ag/AgJ coating) and a sapphire fibre. For the IR range, only the latter fibre type encourages to go further for neutron tests in a reactor. If one restricted the interest onto the near infrared range, high purity core silica fibres could be used. This study might be seen as a typical example of the relation between diagnostic development for a nuclear environment and irradiation experiments.

The operating conditions of a neutron diagnostic systems which are responsible for measuring of the total neutron yield in the ITER tokamak reactor are analyzed. Based on results of neutronic calculations and analysis of suitable methods for measuring the neutron yield, a concept of a system for neutron flux measurement in the divertor is proposed. The design for the neutron flux monitor located in the divertor cassette of the tokamak is selected in view of the requirements specified for the neutron diagnostic system of the ITER and its operating conditions. Several fission chambers with different sensitivities and radiator materials will be used for measurements. System is capable of neutron fluxes measuring over the entire dynamic range of the ITER neutron yield with an error of {delta}

The ignition experiment Ignitor will produce high performance plasma regimes with neutron fluxes at the first wall comparable to those expected in power generating reactors (1015n/cm2/s at the first wall). An appreciable degradation of the inorganic insulators surrounding the conductors is expected and the measurement of basic plasma parameters, such as plasma current and position, by electromagnetic diagnostics can become problematic. Thus an R&D program, aimed at the development of effective and affordable devices for electromagnetic diagnostics with higher damage threshold, is being carried out. Prototype diagnostic coils of different shapes have been manufactured, in collaboration with SALENTEC and Università di Lecce. At the same time, an alternative plasma position control method is being explored, based on the diffraction and detection of the soft X-ray radiation emitted, mostly by Molybdenum impurities, near the top or bottom of the plasma column, where the distance of the plasma last closed magnetic surface from the wall is only few millimeters. The underlying principles and general layout of the new system is essentially an adaptation of a 2-dimensional curved crystal spectrometer. © 2008 American Institute of Physics.

A key component for the ITER core LIDAR Thomson Scattering (TS) diagnostic would be a detector with good sensitivity in the 850-1060 nm near infrared (NIR) spectral region. Covering this spectral region becomes necessary if a Nd:YAG laser system operating at ? = 1.06 ?m is used as the laser source, which is a very attractive choice in terms of available energy, repetition rate, reliability and cost. In this paper we review the state of the art of two types of detectors available for the above spectral range: the transferred electron (TE) InGaAs/InP hybrid photodiode and the InxGa1-xAs microchannel plate (MCP) image intensifier and we describe the advancements necessary for a possible application in the ITER LIDAR TS. In addition we describe the preliminary characterization of new GaAsP fast MCP photomultipliers (PMTs) suitable for the detection of the visible part of the LIDAR TS spectrum in JET and ITER.

International audience; This paper deals with the numerical reconstruction of the plasma current density in a Tokamak and of its equilibrium. The problem consists in the identification of a non-linear source in the 2D Grad-Shafranov equation, which governs the axisymmetric equilibrium of a plasma in a Tokamak. The experimental measurements that enable this identification are the magnetics on the vacuum vessel, but also polarimetric and interferometric measures on several chords, as well as motional Stark effect or pressure measurements. The reconstruction can be obtained in real-time using a finite element method, a non-linear fixed-point algorithm and a least-square optimization procedure.