We present here our recent results on the development and testing of the first mirrors for the divertor Thomson scattering diagnostics in ITER. The Thomson scattering system is based on several large-scale (tens of centimetres) mirrors that will be located in an area with extremely high (3–10%) concentration of contaminants (mainly hydrocarbons) and our main concern is to prevent deposition-induced loss of mirror reflectivity in the spectral range 1000–1064 nm. The suggested design of the mirrors—a high-reflective metal layer on a Si substrate with an oxide coating—combines highly stable optical characteristics under deposition-dominated conditions with excellent mechanical properties. For the mirror layer materials we consider Ag and Al allowing the possibility of sharing the Thomson scattering mirror collecting system with a laser-induced fluorescence system operating in the visible range. Neutron tests of the mirrors of this design are presented along with numerical simulation of radiation damage and transmutation of mirror materials. To provide active protection of the large-scale mirrors we use a number of deposition-mitigating techniques simultaneously. Two main techniques among them, plasma treatment and blowing-out, are considered in detail. The plasma conditions appropriate for mirror cleaning are determined from experiments using plasma-induced erosion/deposition in a CH4/H2 gas mixture. We also report data on the numerical simulation of plasma parameters of a capacitively-coupled discharge calculated using a commercial CFD-ACE code. A comparison of these data with the results for mirror testing under deuterium ion bombardment illustrates the possibility of using the capacitively-coupled discharge for in situ non-destructive deposition mitigation/cleaning.

Experiments and simulations to achieve high values of plasma parameters at the Globus-M spherical tokamak (ST) at moderate auxiliary heating power (0.2-0.8 MW) are described. Important distinguishing features are the low edge safety factor range, which is unusual for spherical tokamaks, 2.7 < q < 5 and small plasma-outer wall space (3-5 cm). High ion heating efficiency with NB injection was demonstrated. Results of numerical simulation of fast ion trajectories are described and fast ion generation during NB injection and ICR heating is discussed. Also results on their confinement and slowing down processes investigation are presented. Reasons for achievement of high IC heating efficiency are outlined. Reliable H-mode regime achievement is described. Transport ASTRA modeling demonstrated that during NB heated H-mode ion heat diffusivity remains neoclassical and the particle diffusion coefficient inside transport barrier decreases significantly. RGTi divertor tile analysis was performed after irradiation by plasma during big number of shots (10000 shots in average). Mixed layer composition is measured and deuterium retention in different tokamak first wall area is estimated. Plasma jet injection experiments with upgraded plasma jet are described. Jet penetration to the plasma center with immense increase of density and temperature drop is proved and analogy with pellet injection is outlined.

This paper describes the challenges of Thomson Scattering implementation in the ITER divertor and evaluates the capability to satisfy project requirements related to the range of the measured electron temperature and density. A number of aspects of data interpretation are also discussed. Although this assessment and the proposed solutions are considered in terms of ITER compatibility, they may also be of some use in currently operating magnetic confinement devices.

The lifetime of optical components unprotected from reactor grade plasmas may be very short due to contamination with carbon and beryllium-based materials eroded by plasma from beryllium walls and carbon tiles. Deposits result in a significant reduction of optical transmission. In addition, even rather thin and transparent deposits can dramatically change the shape of reflectance spectra owing to interference of reflected beams, especially for mirrors with rather low reflectivity, like W or Mo. Development of optics-cleaning and deposition-mitigating techniques is a key factor in the construction and operation of optical diagnostics in ITER. The most severe problem faces optical elements positioned in the divertor region. The latest achievements in protection of in-vessel optics are presented by example of deposition prevention/cleaning techniques for inmachine components of a Thomson scattering system in divertor. Careful consideration of well-known and novel protection approaches shows that neither of them provides guaranteed survivability of the first in-vessel optics in divertor. Only a set of mutually complementing prevention/cleaning techniques, that include special materials for mirrors and inhibition additives for plasma, is able to manage the challenging task. The essential issue, which needs to be addressed in the nearest future, is an extensive development of introduced techniques under experimental conditions (exposure time and contamination fluxes) similar to those expected in ITER.

Almost all optical diagnostic systems in ITER will require the implementation of mirror recovery and protection systems. Plasma cleaning is considered to be the most promising technique for the removal of metal deposits from optical surfaces. The engineering and physical aspects of RF discharge application for continuous or periodic plasma treatment are discussed with a focus on implementation under ITER conditions. The ion flux parameters obtained in capacitively coupled (CC) RF discharge were measured in the mock-up of a plasma cleaning system. The uniformity of sputtering in CC RF discharge with and without a magnetic field was studied experimentally for the cylindrical discharge reactor geometry and compared with numerical simulations. The sharp increase in the sputtering rate resulting from the non-uniform radial distribution of the ion flux was observed near the electrode edges. The longitudinal magnetic field improves sputtering uniformity. It was demonstrated that Al/Al 2 O 3 deposits can be removed in the Ne and D 2 plasma of CC RF discharge but longterm exposition results in the degradation of the polycrystalline molybdenum mirror surface. The efficiency of Al sputtering in the atmosphere containing O 2 and N 2 fractions was studied in the D 2 /O 2 and D 2 /N 2 plasma of glow discharge. The addition of 2% of oxygen or nitrogen increases the sputtering yield by 3-4 times as compared with that in a nominally pure D 2 discharge. The impact of metal deposits on the performance of diagnostic mirrors is discussed. It was shown that an ultrathin metallic film with a thickness as low as a few nm may cause a significant degradation of diagnostic mirrors with a transparent coating.