Alan Costley

Toroidal interferometer/polarimeter density measurement system on ITER

In order to measure the line integrated electron density on the International Thermonuclear Experimental Reactor (ITER), a vibration-compensated five-channel CO2 laser interferometer/polarimeter system is being developed. The design of the interferometer/polarimeter has been improved from the previous design, which used a CO2 laser (wavelength, λ=10.6 μm) and a CO laser (λ=5.3 μm), on the basis of experience gained with a dual CO2 system (λ=10.6 and 9.27 μm) on JT−60U. The JT−60U system gives good reliability for both interferometry and polarimetry operation. The performance of the dual CO2 laser is expected to meet the requirements for measurements on ITER (accuracy; 1%, time resolution; 1 ms).

Overview of the ITER Diagnostic System

The individual diagnostics which constitute the ITER Diagnostic System are outlined and the present state of development of the designs is summarised. The results of an assessment of the overall performance of the System are presented and the areas where the probable performance falls below the target specifications are identified. The design and RsD plans which are in place to address the shortcomings are outlined.

Irradiation Tests on ITER Diagnostic Components

Radiation effects on key components of diagnostic systems expected to be subjected to high neutron and gamma fluxes and fluences are being examined in irradiation tests to evaluate and establish an ITER-relevant database to support the design. A comprehensive irradiation database has been accumulated and permits conclusions to be drawn on the application of these components in ITER. The design studies on prototypical assemblies of diagnostic components are continuing based on the irradiation data bases, neutronics calculations for evaluating irradiation environment of diagnostic components and required specification of diagnostic systems. These studies will aid the recognition of detailed requirements of diagnostic systems leading to more specific irradiation tests on diagnostic components.

ITER diagnostics: Integration and engineering aspects

ITER diagnostic equipment is integrated in six equatorial and 12 upper ports, five lower ports, and the 16 divertor cassettes directly in front of them, and at many locations in the vacuum vessel. The integration has to satisfy multiple requirements and constraints and at the same time must deliver the required diagnostic performance. Design work has been carried out in problematical and interfacing areas for most diagnostics. The main diagnostic support components, the port plugs and divertor port racks, comprise common structural elements with dedicated modules from several diagnostics. The scope of the engineering task is summarized and an overview of the integration of the diagnostic equipment is given. The engineering work to date represents the input to the port engineering tasks of the construction phase with common or repeated elements being assessed for feasibility, resolving issues, and identifying show stoppers. It has been dominated by allocation and spatial integration in the tokamak. The work that follows will be more oriented towards the acceptability for operation, suitability for function, and conformity for licensing.

Role and Requirements for Plasma Measurements on ITER

Measurement of plasma and key first wall parameters will have three main roles on ITER. Some of the measurements will be used in real time to prevent the on-set of conditions which could potentially damage the first wall and other in-vessel components (machine protection); others will be used in real-time feedback control loops to control the value of key parameters at values required for specific plasma performance (plasma control); while others will be used to evaluate the plasma performance and to provide information on key phenomena which may limit ITER performance (physics studies). The measurements of some parameters may contribute to all three roles although the requirements on the measurements (accuracies, resolutions etc.) may be different depending on the role.

INTEGRATION OF VACUUM COUPLED DIAGNOSTICS

A special class of ITER diagnostics consists of those which extend the primary or tokamak vacuum outside the cryostat wall. This diagnostic set consists of the x-ray crystal spectrometers (XCS) [1], the vacuum ultra-violet spectrometers (VUV) [2], the neutral particle analysers (NPA) [3] and the low-field-side microwave reflectometers [4]. Two XCS systems are included, a high resolution five radial channel array system (XCS-A) designed to view specific spectral lines for temperature and rotation velocity profiles and a survey instrument package (XCS-S) to monitor a broad spectrum for identifying impurity concentrations. The vacuum vessel rough-out line is also located at this port.

An overview of ITER diagnostics (invited)

The requirements for plasma measurements for operating and controlling the ITER device have now been determined. Initial criteria for the measurement quality have been set, and the diagnostics that might be expected to achieve these criteria have been chosen. The design of the first set of diagnostics to achieve these goals is now well under way. The design effort is concentrating on the components that interact most strongly with the other ITER systems, particularly the vacuum vessel, blankets, divertor modules, cryostat, and shield wall. The relevant details of the ITER device and facility design and specific examples of diagnostic design to provide the necessary measurements are described. These designs have to take account of the issues associated with very high 14 MeV neutron fluxes and fluences, nuclear heating, high heat loads, and high mechanical forces that can arise during disruptions. The design work is supported by an extensive research and development program, which to date has concentrated o...

Diagnostic Requirements for the ITER Divertor

The requirements for the divertor diagnostics have originally been determined by the examination of the diagnostic experience on present large divertor tokamaks. In the past years the design of most diagnostic systems inclusive of those for the divertor has progressed beyond the conceptual stage so that their expected performance can now be predicted using this design information and the results of 2D modelling of the divertor plasma in a regime close to the desired operating point. The profiles of plasma parameters and the line integrals of spectral emission, which would be measured along the chords of the planned diagnostics, have been calculated for 3 cases for which the 2D model predicts sustainable heat loads on the divertor target. The results are assessed according to their capability to fulfil the requirements for protection, plasma control and physics understanding.

The US Role in ITER Diagnostics

There are ~40 specialized diagnostics planned to measure the many plasma parameters needed for research on ITER. The US played a key role in this planning effort and is gearing up to play a major role in providing these systems. This paper gives a brief status of diagnostic planning for ITER and summarizes the challenges posed by the ITER environment. It then describes the 16% of the ITER diagnostic hardware provisionally allocated for development in the US, and explains key elements of that development