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

In this chapter, we consider generic issues affecting the implementation of diagnostics in a burning plasma experiment (BPX). These are, directly or indirectly, caused by the radiation environment....

Chapter 12: Generic Diagnostic Issues for a Burning Plasma Experiment

In this chapter we discuss the various diagnostic techniques in which active spectroscopy plays a role. The use of an injected neutral beam - either a dedicated diagnostic beam or the main heating beams - to localize and enhance the spectroscopic measurements described in Chap. 5 has been exploited for a number of key physics measurements, in particular detailed profile information on ion parameters, the radial electric field, plasma current density, and turbulent transport. The ability to make these detailed measurements has been a key element in the development of improved plasma performance. The neutral beam techniques have been extended by the use of such beam analogs as laser beams, gas puffs, and pellet injection for specific measurements. In each case we describe the general principle behind the measurement and include several successful examples of their implementation, briefly touching on some of the more important physics results. We conclude with a few remarks about the relevance and re...

Chapter 6: Active Spectroscopy

Problems related to the development of diagnostics for steady state fusion plasma experiments are discussed. The paper concentrates on those necessities already appearing in current non-burning plasma fusion experiments when extending pulse lengths beyond 10 s, i.e. thermal load, erosion, deposition and long-time signal integration in magnetic diagnostics. Problems arising from high power ECRH under conditions of incomplete absorption are outlined. Individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation. Burning plasma experiments characterized by intense n- and γ-radiation are briefly reviewed for reasons of completeness, dealing with radiation induced processes in windows, fibres, cables and mirrors. Methods of data handling, real time monitoring and plasma control are outlined.

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Diagnostics for steady state plasmas

Particle deposition and erosion can affect mirrors used in plasma diagnostics and this is a major concern for future fusion reactors. This subject is analysed for the first and second mirrors of the proposed motional Stark effect edge plasma current diagnostic for ITER. Particle fluxes to the diagnostic module aperture are given by edge plasma/impurity-transport solutions for convective plasma flow for full-power fusion conditions. The MC-Mirror code with input of TRIM-SP results is used to compute in-module direct, reflected and sputtered particle transport. Particles analysed are D–T and He atoms/ions from the plasma, and Fe, Be and W from first wall sputtering and/or in-module sputtering. Many of the results are encouraging for optical diagnostic use in ITER and possibly for post-ITER high duty-factor reactors. The LLNL-4B module design analysed works well in minimizing particle flux to the mirrors, with a factor of ~200–400 reduction in aperture-to-first-mirror flux. Sputtering erosion/degradation of Mo or Rh coated mirrors by incident D, T and He is negligible. IMD optical effects code analysis shows probably tolerable changes in light reflection and polarization due to mirror beryllium deposition. Tungsten flux to the mirrors is very low. Based on available but limited data, however, there is major concern about the effect of the predicted helium flux on mirror optical properties.

/pdf/particle-deposition-and-optical-response-of-iter-motional-9vhg1kf6e3.pdf

Particle deposition and optical response of ITER Motional Stark Effect diagnostic first mirrors

An overview is given of the present design of the active beam spectroscopy diagnostics for the ITER. Present spatial resolution and signal-to-noise indicate that, in principle, all proposed measurements are possible covering the entire plasma minor radius. Calculations show that the mirror based periscopes and the impurity coating of the first mirror affect the signal strength and the polarization characteristics of the measured spectra having an impact in the measurement accuracy. On-line calibration techniques and methods to access the first mirror status are addressed.

A Gorshkov

Papers

Active beam spectroscopy diagnostics for ITER: Present status (invited)