A diagnostic system for Thomson scattering of the central, edge and divertor plasma regions of a tokamak with reactor technologies is discussed. The rationale and choice of technical solutions are given, the composition of the Thomson scattering diagnostic complex is discussed, as well as an estimate of the accuracy of measuring the electron temperature and plasma density in the central edge and divertor regions of the TRT tokamak. Particular attention is paid to ensuring the functionality of the proposed diagnostics in the reactor mode of the tokamak operation and the results of testing diagnostic equipment in experiments on the Globus-M2 tokamak.

Thomson scattering of the core edge and divertor plasma regions of a tokamak with reactor technologies is discussed. The rationale and choice of technical solutions are given, the composition of the Thomson scattering diagnostic complex is discussed, as well as an estimate of the accuracy of measuring both electron temperature and density. Particular attention is paid to ensuring the functionality of the proposed diagnostics in the reactor mode of the tokamak operation and the results of testing diagnostic equipment in the experiments on Globus-M2 tokamak.

Migration of plasma erosion products in plasma facilities is studied experimentally and numerically within the framework of modeling transport of plasma-facing materials in the diagnostic ducts of fusion devices. Material transport simulation is discussed for two cases of low and high background neutral gas pressures. Monte Carlo software KITe was used to simulate transport at a neutral gas background pressure 0.1–0.5 Pa—typical during steady-state tokamak operation and during pressure pulses caused by edge localized modes (ELMs). The simulation approach was implemented to describe experiments at the MAGNUM-PSI facility. Fluid dynamic code FLUENT is used to simulate transport during pressure surges as high as 1000 Pa, which can occur in the case of severe disruptions in tokamak plasma discharges, such as vertical displacement events (VDE) or accidental events. The hydrodynamic approach was verified in simulation of target sputtering in the QSPA plasma gun facility.

As a part of ITER diagnostics design and development, ultrasonic and stick-slip piezoelectric motors and several types of piezoelectric ceramics were tested under severe neutron and gamma ray irradiation (-10(19) per cm(2) at E > 0.1 MeV) in a pool-type fission reactor. The fission neutron and gamma ray spectra were corrected to comply with conditions expected under ITER divertor cassettes. Taking into account possible neutron-induced amorphization of crystal structure, four types of piezoelectric ceramics were pre-selected. To restore the electronic structure of piezoelectric ceramic damaged by gamma rays, recovery polarization (i.e. heating while applying reverse bias) was suggested. The motors and piezoceramic samples were assessed for performance before and after irradiation as well as after recovery polarization. Recovery polarization was performed at 330 degrees C as it is expected close to the divertor cassettes during baking. Two most promising types of piezoelectric ceramics survived multiple cycles of depolarization/polarization at both 330 degrees C and 200 degrees C as appropriate for baking ITER divertor and vacuum vessel, respectively. All the experiments and procedures are described in detail.

Studies of contaminants obtained by spraying ITER-grade Be on a quasi-stationary plasma gun facility QSPA-Be are presented. Contaminating films, consisting mainly of Be and O in approximately equal proportions, were deposited on substrates of quartz, sapphire, single crystalline silicon (SC-Si) and NaCl crystal. Characterization of the deposits was performed using SEM, XPS, EBS, AFM, SE, TEM&SAED and micro-interferometry showing polycrystalline BeO films similar as found in JET-ILW. Films on SC-Si and NaCl were used to characterize their composition and morphology. The cleaning rates in the 81.36 MHz RF discharges in He or D2 at 2 Pa were measured on the SC-Si target. The measured etching rate of the deposited films was several times higher than the rate calculated from the theoretical value of beryllium oxide sputtering yield. Test cleaning of these contaminants was carried out in a capacitively coupled RF discharge (CCRF) from the surface of sapphire and quartz plates, which were considered as a mock-ups of the protective window of the first mirror unit (FMU) designed for ITER divertor Thomson scattering diagnostic system (DTS).

Combined Thomson scattering (TS) and laser-induced fluorescence (LIF) diagnostics are being developed. The Thomson scattering and laser-induced fluorescence are laser diagnostics, with joint both probing and c-ollecting optical systems, which are the most complex and expensive parts of the diagnostic systems of large tokamaks, can be combined. Thomson scattering by free electrons is the use-proven diagnostic method for measuring profiles of important parameters of the plasma electron component (electron tempera-ture T e and electron density n e ), which requires a minimum of model assumptions. Almost all existing tokamaks are equipped with one or more TS systems, and by now, considerable experience has been accumulated in practical methods for implementation of these systems. The use of laser-induced fluorescence for measuring parameters of ion and neutral plasma components is less common, also because it requires knowledge of electron parameters to calculate populations of excited levels. The joint diagnostics of the Thomson scattering and laser-induced fluorescence in divertor plasma will be used to simultaneously measure the plasma parameters necessary for fundamental understanding physics of plasma detachment from divertor plates. These parameters are: the local parameters of plasma electrons ( T e , n e ), ion temperature ( T i ) measured from the data on emission of helium ions (HeII), as well as densities of helium atoms ( n a (He)) and hydrogen isotopes ( n a (H,D,T)). The measured parameters make it possible to calculate the following characteristics: (i) the ionization and recombination rates (using the data on T e , n e , T i , and n a (H, D, T)); (ii) the friction force of the plasma flow due to collisions with neutral particles (using the data on T i , n i (assuming n i = n e ), and n a (H, D, T)); and (iii) the pressure of the oncoming plasma flow (using the data on T e , n e , T i , and n i ). The article discusses advantages of combining laser diagnostics and ways of further development of the joint diagnostcs, based on the experience of creating similar diagnostics for domestic tokamaks and the similar diagnostics developed for ITER.

Transport and redeposition of plasma-facing materials in future fusion devices may have a critical influence on performance of in-vessel components. Evaluation of the impurity migration in diagnostic ports is important to predict degradation of in-vessel optics during the main plasma discharges as well as for development of in-situ cleaning maintenance. The Monte-Carlo code KITe was developed for modeling transport of neutral particles in weakly ionized plasma. The code employs advanced neutral particle collision model. The first KITe simulation and experimental validation of sputtered atom transport demonstrate performance of the proposed approach.

Divertor Thomson scattering (DTS) and laser-induced fluorescence (LIF) are both laser aided diagnostics well suited to combination with common probing and collecting optics that are the most sophisticated and expensive part of any ITER optical diagnostic system. The combination of DTS and LIF are used for simultaneous measurement of local electron (Te, ne), ion (Ti, nHeII) and atom (nHeI, nH(D,T)) parameters and provide basic information on rates of electron and ion processes to allow basic understanding of the physics of divertor plasma detachment. The measured parameters permit the calculation of rates of ionization and recombination using Te, ne, Ti, ni, nHeI and nH(D,T); emission intensity—Te, ne, ni, nHeI and nH(D,T); frictional force of the plasma flow due to collisions with neutrals—Ti, ni, T0, nHeI and nH(D,T) and pressure of the incoming plasma flow—Te, ne, Ti and ni. The paper discusses the benefits of DTS and LIF integration, suggests new approaches to the estimation of DTS capability, LIF implementation and possibilities for further diagnostic development.

Scientific and technological program of ITER requires measurement of plasma parameters using variety of diagnostics, ~ 20 of which are the optical ones [1]. The plasma emitted light and/or laser beams will travel by in-vessel optical labyrinths between torus and analyzing equipment. The closest to plasma optical elements, so-called first mirrors (FMs) and windows (FWs), will operate in harsh environmental conditions such as high temperature, particle fluxes and deposition of eroded first wall materials (Be, W etc.) [3]. During periods of Mirror Conditioning States (MCS), the optical performance of FMs and FWs has to be restored by an appropriate cleaning system. The system based on the radio frequency capacitively coupled (RFCC) discharge with a mirror or window used as a RF electrode is currently considered as the main approach [4]. However, most research of the plasma cleaning were performed using Be proxy materials (Al, Au etc.) due to its high toxicity. The study of sputtering Be deposits are of high importance to prove the plasma cleaning efficiency. The report presents results of pilot experiments on deposition and in-situ sputtering of Be deposits in the QSPA-Be facility located in Bochvar institute. QSPA-Be facility was designed to simulate plasma heat loads related to ITER ELMs / disruptions [5]. The pure Be target evaporation by one pulse of QSPA-Be provided deposition of ~7 nm contaminant layer with ~70% of beryllium. The beryllium films were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The in-situ plasma cleaning was realized by exposing in 81 MHz helium discharge at pressure of 2 Pa. The cleaning process was controlled observing beryllium emission line in plasma column spectrum. The FW mock-up characterization was performed after 2 hours of the plasma exposure. Cyclic removal of Be-depositions in QSPA facility is planned to be done in 2020.

Physical and engineering aspects of RF plasma cleaning developed for actively cooled first mirror serving as grounded DC-coupled electrode are under consideration. Feasibility of the water-cooling lines implemented as the coaxial notch filter for ITER in-vessel diagnostic mirrors was demonstrated for Capacitively Coupled Radio Frequency (CCRF) discharge in neon at 1-10 Pa. The impinging ions energy as a function of absorbed RF power was measured for both the DC-coupled and -decoupled schemes. Sputtering yield variation over rectangular surface of stainless steel mirror was studied experimentally. The measured sputtering yield profiles were found to be in qualitative agreement with the RF plasma numerical simulations. It was demonstrated that Al/Al2O3 used as Be/BeO proxy can be removed from the water cooled mirror surface by 100 eV neon ions with the use of the notch filter. The 14 h plasma exposure didn't affect the mirror reflectivity.