G. T. Razdobarin

Measurements of atomic hydrogen density in the plasma of FT-1 Tokamak by the resonance fluorescence method

The laser-induced fluorescence at Halpha line was used to study the neutral hydrogen behaviour in the FT-1 Tokamak. Absolute measurements of the hydrogen density profiles were carried out, and the influence of recycling and gas puffing on the particle balance was studied.

Perspectives of Use of Diagnostic Mirrors with Transparent Protection Layer in Burning Plasma Experiments

We evaluate using of metal mirrors over‐coated with transparent protection layer for the in‐vessel diagnostic systems in reactor‐grade fusion devices. Ideally, these should satisfy the contradictory demands of high reflectivity and small rate degradation when being bombarded by CX atoms. The serious threat to the performance of diagnostic mirrors is surface contamination with carbon‐based material eroded from carbon tiles. Via coupling the protective layer to a bulk mirror we can mitigate the deposit infiuence on the reflectance spectra. The regards are given to survivability in plasma environment of protected coated metallic mirrors.

Measurement of neutral density profile in a tokamak plasma using the principle of laser induced ionization

An application is discussed of a new method based on laser induced ionization that is an alternative to the laser induced fluorescence diagnostics. Here ionization of the hydrogen upper atomic states gives the local hydrogen densities in a plasma. On the basis of a rate equation analysis for a diffusion dominated plasma a probe saturation flux density of a few MW/cm2 was introduced and appropriate values were used for the plasma diagnostics. A multipulse neodymium laser was designed for plasma probing on the FT-I tokamak to measure the neutral density profiles along the plasma diameter. Local neutral densities as low as 1*108 cm-3, which is close to the sensitivity limit of the employed device, have been detected in a single tokamak discharge. The experimental results obtained on the FT-1 tokamak are presented and discussed

Research on mirror cleaning in inductively and capacitively driven radio-frequency discharges

Bench tests are used to compare cleaning performance of inductively and capacitively driven radio-frequency (RF) discharges as a potential tool for in-situ maintenance of in-vessel diagnostic mirrors in fusion devices. The effect of erosion of hydrogenated carbon coating is studied in different processing conditions. Stainless steel (SS) mirrors have been exposed to CH4‒Ar and H2‒Ar plasmas in an RF discharge at a pressure of 10−2 Torr with an input power of 0.5 kW at 13.6 MHz. The samples, which exhibit a slow rate of chemical erosion, become essentially erosive in both inductively and capacitively driven RF discharges. The cleaning ability of a capacitively driven RF discharge is studied in dedicated experiments with SS samples retrieved from the tokamaks T-10 and Globus-M after long-term exposure to the working and wall conditioning discharges.

New features of the energy confinement from TUMAN-3 ohmic H-mode experiments

New features of the energy confinement were observed in the Ohmic regime with reduced transport - Ohmic H-mode. Parametric dependencies as well as absolute values of the energy confinement time are in agreement with scaling proposed for description of the ELM-free H mode in bigger devices with powerful auxiliary heating (DIII/JET H-mode scaling). In particular, strong dependencies of tau E on plasma current and input power and weak dependencies on density were found. Energy confinement time is enhanced by a factor of 15 compared to predictions of the usual ohmic scalings (Neo-Alcator, Merezhkin-Mukhovatov). In the small tokamak TUMAN-3 30ms energy confinement time was achieved.

Thomson scattering diagnostics in the Globus-M tokamak

Specific features of the Thomson scattering diagnostics, its main characteristics and capabilities, and the results of its experimental testing in the Globus-M tokamak are described. A powerful multipulse neodymium-glass laser is designed for investigating both fast and slow processes in the tokamak plasma. The laser is capable of generating up to 20 pulses uniformly distributed in time during one tokamak discharge. In order to investigate fast transient processes, the laser repetition rate can be increased within a specified time interval. The possibility of varying the time interval between laser pulses from 0.5 ms to 1.0 s makes this diagnostics highly informative. The optical scheme developed in the course of these studies allowed one to simplify the power supply system and create a comparatively inexpensive laser system. The use of avalanche photodiodes and filtering polychromators with a high optical transparency provides high sensitivity of the diagnostics. A special software was designed that allows automatic processing of several hundred signals during one shot and provides data on the electron density and temperature immediately in the course of measurements. The diagnostics allows one to trace the time behavior of the spatial profiles of the electron temperature and density in both ohmic discharges and discharges with auxiliary heating, as well as in experiments with particle injection with a plasma gun.

Interfaces for Thomson Scattering Diagnostics in the Divertor and Sol Near the X-Point Plasmas of Iter-Feat

ITER design has highlighted the fundamental need to monitor and deepen understanding of divertor operations. The designed Thomson scattering (TS) for the divertor leg and SOL near the X-point, has gained a lot from present State-of-the-Art in the diagnostics. However, hostile environment, very restricted access, and required spatial resolution, all impose severe constraints on the diagnostic design for ITER. Signal transmission from diagnostics introduces the further considerations of relative movements of the machine components. Despite the constraints it is feasible using of crossed probe and viewing beams to make measurements of the electron temperature and density profiles in outer divertor leg at the extent from the strike-point to X-point vicinity, and the LIDAR TS technique to make the electron temperature and density scan along the major radial line-of-sight at ∼0.5 m above the X-point. The interfaces for each of the subsystems are presented and discussed in the sections below.

Laser Induced Breakdown Spectroscopy Technique For In-Situ Dust Detecting In A Next-Step Tokamak

A technique based on laser-induced breakdown spectroscopy (LIBS) is proposed for detecting in-situ dust on the plasma-exposed surfaces and in the grooves of plasmafacing components in the next-generation of fusion devices (e.g., ITER-FEAT). It is based on laser-induced ablation of wall material and spectral analysis of the laser spark flash-light collected by imaging optics and transmitted to the detection system. This could give space- and time-resolved information on the presence of dust, or loosely bound films, their characteristic deposition patterns, elemental composition, and possibly their hydrogen content, without the necessity of breaking the machine vacuum. We have performed some simple proof-of-principle experiments to demonstrate the suitability of this technique, which might provide an effective non-intrusive in-situ surface analysis method for surveying in-vessel dust accumulation in future fusion devices.

The globus-m diagnostics design

Abstract Diagnostics which is currently installed or under active development for a newly commissioned spherical tokamak (ST) Globus-M is described. Among the commonly implemented plasma diagnostics the priority is given to those of the enhanced locality and repetition rate response. Technical summaries of each diagnostics are given with special emphasis on innovative approaches.

The Concept of ITER Divertor Plasma Diagnostics by Means of LIDAR Technique

The general considerations of Thomson and Rayleigh scattering diagnostic methods using a time-of-flight (LIDAR) principle in ITER divertor are discussed regarding the dynamic gas target divertor operation. Compatibility with specific plasma conditions and divertor operation scenario is examined to define the guidelines of a design. In order to validate the concept a lot of experimental activity and technological developments is to be fulfilled. Some of them that have recently been carried out are demonstrated and discussed.