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About these proceedings

In order to support the operation of ITER and the planned experimental programme an extensive set of plasma and first wall measurements will be required. The number and type of required measurements will be similar to those made on the present-day large tokamaks while the specification of the measurements—time and spatial resolutions, etc—will in some cases be more stringent. Many of the measurements will be used in the real time control of the plasma driving a requirement for very high reliability in the systems (diagnostics) that provide the measurements. The implementation of diagnostic systems on ITER is a substantial challenge. Because of the harsh environment (high levels of neutron and gamma fluxes, neutron heating, particle bombardment) diagnostic system selection and design has to cope with a range of phenomena not previously encountered in diagnostic design. Extensive design and R&D is needed to prepare the systems. In some cases the environmental difficulties are so severe that new diagnostic techniques are required. a Author to whom any correspondence should be addressed.

https://iopscience.iop.org/article/10.1088/0029-5515/47/6/S07/pdf

Chapter 7: Diagnostics

The area of energetic particle (EP) physics in fusion research has been actively and extensively researched in recent decades. The progress achieved in advancing and understanding EP physics has been substantial since the last comprehensive review on this topic by Heidbrink and Sadler (1994 Nucl. Fusion 34 535). That review coincided with the start of deuterium?tritium (DT) experiments on the Tokamak Fusion Test Reactor (TFTR) and full scale fusion alphas physics studies.Fusion research in recent years has been influenced by EP physics in many ways including the limitations imposed by the ?sea? of Alfv?n eigenmodes (AEs), in particular by the toroidicity-induced AE (TAE) modes and reversed shear AEs (RSAEs). In the present paper we attempt a broad review of the progress that has been made in EP physics in tokamaks and spherical tori since the first DT experiments on TFTR and JET (Joint European Torus), including stellarator/helical devices. Introductory discussions on the basic ingredients of EP physics, i.e., particle orbits in STs, fundamental diagnostic techniques of EPs and instabilities, wave particle resonances and others, are given to help understanding of the advanced topics of EP physics. At the end we cover important and interesting physics issues related to the burning plasma experiments such as ITER (International Thermonuclear Experimental Reactor).

Energetic particle physics in fusion research in preparation for burning plasma experiments

The use of high resolution x-ray crystal spectrometers to diagnose fusion plasmas has been limited by the poor spatial localization associated with chord integrated measurements. Taking advantage of a new x-ray imaging spectrometer concept [M. Bitter et al., Rev. Sci. Instrum. 75, 3660 (2004)], and improvements in x-ray detector technology [Ch. Broennimann et al., J. Synchrotron Radiat. 13, 120 (2006)], a spatially resolving high resolution x-ray spectrometer has been built and installed on the Alcator C-Mod tokamak. This instrument utilizes a spherically bent quartz crystal and a set of two dimensional x-ray detectors arranged in the Johann configuration [H. H. Johann, Z. Phys. 69, 185 (1931)] to image the entire plasma cross section with a spatial resolution of about 1 cm. The spectrometer was designed to measure line emission from H-like and He-like argon in the wavelength range 3.7 and 4.0 A with a resolving power of approximately 10,000 at frame rates up to 200 Hz. Using spectral tomographic techniques [I. Condrea, Phys. Plasmas 11, 2427 (2004)] the line integrated spectra can be inverted to infer profiles of impurity emissivity, velocity, and temperature. From these quantities it is then possible to calculate impurity density and electron temperature profiles. An overview of the instrument, analysis techniques, and example profiles are presented.

Spatially resolved high resolution x-ray spectroscopy for magnetically confined fusion plasmas (invited)

A scintillator based detector for fast-ion losses has been designed and installed on the ASDEX upgrade (AUG) tokamak [A. Herrmann and O. Gruber, Fusion Sci. Technol. 44, 569 (2003)]. The detector resolves in time the energy and pitch angle of fast-ion losses induced by magnetohydrodynamics (MHD) fluctuations. The use of a novel scintillator material with a very short decay time and high quantum efficiency allows to identify the MHD fluctuations responsible for the ion losses through Fourier analysis. A Faraday cup (secondary scintillator plate) has been embedded behind the scintillator plate for an absolute calibration of the detector. The detector is mounted on a manipulator to vary its radial position with respect to the plasma. A thermocouple on the inner side of the graphite protection enables the safety search for the most adequate radial position. To align the scintillator light pattern with the light detectors a system composed by a lens and a vacuum-compatible halogen lamp has been allocated within the detector head. In this paper, the design of the scintillator probe, as well as the new technique used to analyze the data through spectrograms will be described. A last section is devoted to discuss the diagnosis prospects of this method for ITER [M. Shimada et al., Nucl. Fusion 47, S1 (2007)].

Scintillator based detector for fast-ion losses induced by magnetohydrodynamic instabilities in the ASDEX upgrade tokamak.

Being placed in a straight view of burning plasma the First Mirror (FM) is one of most critical elements of ITER diagnostics. The sputtering by charge exchange atoms (CXA) and the deposition of contaminating films and dust on a mirror surface will be the main reasons of FM reflectivity degradation under ITER conditions, and for laser diagnostics the thermomechanical stresses occurring at every laser shot may accelerate the mirror destruction [1]. The materials traditionally used for optical mirrors are not suitable for building-up the ITER diagnostic mirrors. The use of mirror with reflective coating from metals with low sputtering yield and sufficiently high reflectivity (e.g., Rh, Mo, W, Ag) on metallic substrate is one of the possible variant of FM choice for a survival in extreme ITER environments [2]. The production practice of mirrors with Rh and Mo coatings on SS and Mo substrates (Rh/SS and Mo/Mo, correspondingly) by means of sputter deposition of reflective coating on polished substrates is elaborated using a dc planar magnetron [3]. The influence of main damage factors on FM prototypes and experiments on a remote cleaning of mirrors from carbon films by pulsed laser radiation are considered in the paper.

Experimental Study of First Mirror Degradation Under Influence of Iter Relevant Conditions

The development of diagnostic systems for next step Burning Plasma experiments (BPX) such as ITER requires RD (ii) review of the requirements for measurements of the neutron/α source profile and assessment of possible methods of measurement; (iii) determination of the life-time of plasma facing mirrors used in optical systems; (iv) assessment of radiation effects on coils used for measuring the plasma equilibrium and development of new methods to measure steady state magnetic fields accurately in a nuclear environment; and (v) Development of measurement requirements and assessment of techniques for measurement of dust and erosion. This paper presents the recent progress in these areas.

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K. Vukolov

Papers

Experimental Study of First Mirror Degradation Under Influence of Iter Relevant Conditions

Progress with High Priority R&D Topics in Support of ITER/BPX Diagnostic Development

Mirrors for ITER diagnostics: new RD developments, assessment of the mirror lifetime and impact of the mirror failure on ITER performance

Possibilities of Spectral Diagnostics of Impurities and Hydrogen in the Divertor Plasma of the TRT

Role of the Neutron Calculations in the Development of Optical Diagnostics in ITER