The Mid-Infrared Instrument for the James Webb Space Telescope, III: MIRIM, The MIRI Imager

In this article, we describe the MIRI Imager module (MIRIM), which provides broad-band imaging in the 5 - 27 microns wavelength range for the James Webb Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed view of 74"x113". The remainder of its nominal 113"x113" field is occupied by the coronagraphs and the low resolution spectrometer. We present the instrument optical and mechanical design. We show that the test data, as measured during the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton Laboratory, and at the NASA Goddard Space Flight Center, indicate that the instrument complies with its design requirements and goals. We also discuss the operational requirements (multiple dithers and exposures) needed for optimal scientific utilization of the MIRIM.Comment: 29 pages, 9 figure

Achievements on Engineering and Manufacturing of ITER First-Mirror Mock-ups

Most of ITER optical diagnostics will be equipped with in-vessel metallic mirrors as plasma viewing components. These mirrors will be exposed to severe plasma environment and must withstand these conditions without change of their optical properties. This implies important research and developments on the design and manufacturing of such components. Therefore, investigations on engineering and manufacturing have been carried out on diagnostic mirrors toward the development of full-scale stainless steel and TZM (Mo-based alloy) ITER mirrors. Several-micrometer coatings of rhodium and molybdenum have been deposited on the components to ensure long-lasting of the mirrors exposed to an environment which could be dominated by charge-exchange neutral flux. Three major issues have been addressed and reported in this paper: First, investigations have been performed on the design and manufacturing of the integrated cooling system to limit the mirror optical surface deformation due to radiations from the plasma and nuclear heating. For the thermomechanical design of the mock-ups, a plasma radiation flux of 0.5 MW/m 2 and a neutron head load of 7 MW/m 3 have been considered. Second, the polishing capability of full-scale (109 mm in diameter) metallic mirrors has been demonstrated: The mock-up surface front error is lower than 0.1 μm root mean square, and the mirrors exhibit low roughness ( Ra <; 2 nm) and low surface defects (scratch width lower than 0.02 mm) after polishing. Third, the manufacturing feasibility of thick molybdenum and rhodium coating layers deposited by magnetron sputtering has been evaluated. The objective of depositing layers up to 3-5 μm thick has been achieved on the mock-ups, with spectral reflectance reaching the theoretical values and showing high reflectivity over a large spectral range (from 400 nm to 11 μm). Finally, the test campaign of the manufactured mirrors, which is being prepared in several European facilities to expose the mirrors to deuterium plasma, ELMs, neutrons, erosion, and deposition conditions, is reported

Achievements on Engineering and Manufacturing of ITER First Mirrors Mock-Ups

Most of ITER optical diagnostics will be equipped with in-vessel metallic mirrors as plasma viewing components. These mirrors will be exposed to severe plasma environment which implies important research and developments on their design and manufacturing. Therefore investigations on engineering and manufacturing have been carried out on diagnostic mirrors towards the development of full-scale stainless steel and TZM (Mo-based alloy) ITER mirrors. Several micrometers in thickness of rhodium and molybdenum reflective coating layers have been deposited on the components to insure long-lasting of the mirrors exposed to an environment that could be dominated by neutral flux (charge-exchange). Three major issues have been addressed and reported in this paper: First, investigations have been performed on the design and manufacturing of the mirror integrated cooling system, so that the optical surface deformation due to radiations from the plasma and nuclear heating is limited. For the thermo mechanical design of the mock-ups, plasma radiation flux of 0,5 MW/m2 and neutron head load of 7 MW/m3 have been considered. Secondly, the polishing capability of full-scale (109 mm in diameter) metallic mirrors has been demonstrated: the mock ups Surface Front Error is lower than 0,1 μm Root Mean Square, and the mirrors exhibit low roughness (Ra <; 2 nm) and low surface defects (scratch width lower than 0,02 mm) after polishing. Thirdly, the manufacturing feasibility of molybdenum and rhodium thick coating layers deposited by magnetron sputtering has been evaluated. The objective of depositing layers up to 3 μm to 5 μm thick has been achieved on the mock-ups, with spectral performances reaching the theoretical values and showing high reflectivity over a large spectral range (from 400 nm to 11 μm). Finally the test campaign of the manufactured mirrors, which is being prepared in several European facilities to expose the mirrors to deuterium plasma, ELMs, neutrons, erosion and deposition conditions, is reported

Engineering and manufacturing of ITER first mirror mock-ups

Most of the ITER optical diagnostics aiming at viewing and monitoring plasma facing components will use in-vessel metallic mirrors. These mirrors will be exposed to a severe plasma environment and lead to an important tradeoff on their design and manufacturing. As a consequence, investigations are carried out on diagnostic mirrors toward the development of optimal and reliable solutions. The goals are to assess the manufacturing feasibility of the mirror coatings, evaluate the manufacturing capability and associated performances for the mirrors cooling and polishing, and finally determine the costs and delivery time of the first prototypes with a diameter of 200 and 500 mm. Three kinds of ITER candidate mock-ups are being designed and manufactured: rhodium films on stainless steel substrate, molybdenum on TZM substrate, and silver films on stainless steel substrate. The status of the project is presented in this paper

Thermo-Mechanical Analysis of ITER First Mirrors and Its Use for the ITER Equatorial Visible/Infrared Wide Angle Viewing System Optical Design

ITER first mirrors (FMs), as the first components of most ITER optical diagnostics, will be exposed to high plasma radiation flux and neutron load. To reduce the FMs heating and optical surface deformation induced during ITER operation, the use of relevant materials and cooling system are foreseen. The calculations led on different materials and FMs designs and geometries (100 mm and 200 mm) show that the use of CuCrZr and TZM, and a complex integrated cooling system can limit efficiently the FMs heating and reduce their optical surface deformation under plasma radiation flux and neutron load. These investigations were used to evaluate, for the ITER equatorial port visible/infrared wide angle viewing system, the impact of the FMs properties change during operation on the instrument main optical performances. The results obtained are presented and discussed

The ITER VIS/IR Wide Angle Viewing System: Challenges and on-Going R&D

The ITER tokamak is the next generation fusion device which will allow studying burning plasma obtained by a Deuterium-Tritium (D-T) fusion reaction during hundreds of seconds. ITER vacuum vessel real-time protection will be mandatory during plasma operation to avoid water leaks and critical plasma facing components degradation. The protection system will be based on a wide angle viewing system (WAVS) composed with 18 visible (VIS) and 18 infrared (IR) cameras covering 80 % of the vacuum vessel which will be one of the major imaging systems of ITER. Compared to protection systems routinely used on current tokamaks and based on imaging (VIS and/or IR), new constraints must be taken into account because of their influence on the system performance: the harsh environment (high neutron flux) and the metallic plasma facing components (both first wall and divertor). In this new demanding context, we have achieved three mandatory R&D studies starting from the understanding of the source of signals by using realistic photonic simulation up to real-time processing strategy taken into account first order optical design constraints to define what type of performance could be reached for ITER vacuum vessel protection

Optical design for the 5-28mum NGST infrared imager MIRI

International audienc

Optical design for the 5-28mum NGST infrared imager MIRI

International audienc

Optical design for the 5-28mum NGST infrared imager MIRI

International audienc