Search

The phenomenon of improved energy confinement during radiative cooling at the plasma edge was studied experimentally in the T-10 tokamak. It was shown that the effect is independent on the kind of radiating gas. No substantial differences were observed using Ne, which radiates at two-thirds of the plasma radius, or He, which radiates at the very edge. This phenomenon is explained in frames of nonequilibrium thermodynamics. In a self-organized plasma, the energy balance is described by a Smoluchowski-type equation, where the plasma thermal conductivity and its functional dependence on the intensity of the heat flux, perturbing the pressure profile, is determined from experiment.

The tungsten limiters were tested in the T-10 tokamak during the 2015–2017 experimental campaign. The limiters were made from the ITER-grade WMP “POLEMA” tungsten. Inspection of the tungsten limiters after experimental campaign has revealed their strong destruction due to the combination of the high heat and particle fluxes from the edge plasma toward the limiters surface. The influence of the edge tokamak plasma on tungsten limiters leads to significant cracking of the tungsten. Heat load up to 2 MW m−2 leads to micro-cracks at the grain boundaries. Heat loads exceeding 5 MW m−2 lead to macro-cracks formation. In the areas of highest heat loads, tungsten plates are melted and close to full destruction. In these zones, intensive sparking and arcing were observed. Arc craters have been scattered across the surface, and along the cracks. It is supposed that the nonambipolar flow due to the arcs and sparks can explain the observed overheating and melting of the tungsten surface. Disruptions and runaway electrons beams have driven extreme heat loads of more than 1 GW/m2 causing strong melting of the tungsten on the outer board of the ring limiter.

The results of numerical modeling of impurity concentration profiles of tungsten ions for discharges with ohmic heating (OH) on the T-10 tokamak with W limiter (for Zeff ≈ 1) are described. It is shown that in OH discharges the maximum values of relative concentrations for each tungsten ion state are located on their radii of coronal equilibrium. Fulfillment of coronal equilibrium on the T-10 tokamak makes it possible to determine the full radiation intensity from the total concentration of tungsten ions. The results show that modeling of the Prad(r) profile for tungsten using currently accepted scaling of anomalous transport coefficients of light and moderate impurities for T-10 plasma does not make it possible to obtain complete alignment with the experimental data. The dependences of tungsten radiation intensity profiles on different published data on excitation, ionization, recombination rates, and anomalous transport coefficients are shown in the paper. A conclusion about the value of the anomalous diffusion coefficient and its radial distribution for heavy impurity (tungsten) in OH discharges at the T-10 tokamak is made.

The investigations of tungsten transport in T-10 plasma are presented in the current paper. The process of tungsten accumulation in OH discharges and its dependence on parameters ne, Ip, and Zeff are discussed. Peaked tungsten density profiles nW(r) are observed in plasmas with Zeff ≈ 1–1.5. In plasmas with Zeff ≈ 3–4, W accumulation is mainly integral with no profile peaking with regard to electron density ne(r). Lower densities of W are observed in discharges with a lithized T-10 vacuum vessel in comparison with plasma contaminated with light impurities. The disposal of W accumulation is produced by auxiliary ECRH input. During the central ECRH, the tungsten density profile flattens with the central density drop off by ~10 times together with W source increase up to 4 times.

An investigation of lithium influx to plasma, radiation, transport, and its influence on plasma parameters is carried out using spectroscopy and transport modeling methods. Lithium source in discharge of the T-10 tokamak is a moving Li-limiter based on tungsten capillary-pore system (CPS). A strong dependence of Li influx to plasma on a distance between the Li-limiter and plasma current boundary in Scrape-Off Layer (SOL) region is found. It is shown that if the Li-limiter is located on the radius of the chamber wall (≈40 cm), lithium influx to plasma is at a low level with value ~21018 s-1 and Li nuclei concentration in plasma does not exceed ~0.5 % of electron density ne with effective charge value Zeff ≈ 1.2. If the Li-limiter is moved to the current radius (aL =30 cm), lithium influx to plasma reaches ~31020 s-1, that leads to a formation of lithium plasma with the density limit of ≈ 0.5ne Gw (Greenwald density limit) with Zeff value of ≈2.9 and ≈10 % of remaining deuteron density. In this case, lithium radiation losses power estimated in Li-plasma is extremely low and does not exceed ≈15 % of ohmic power. All obtained results are interpreted using transport models. Changing the lithization level of the chamber walls can significantly reduce the level of impurities C, O, and W and greatly affect the Zeff values. Dependencies of energy confinement times in the electron and ion components on the value of averaged electron density are investigated in regimes with significantly varying Zeff values. The paper presents the computational analysis of the lithium radiation power at the plasma periphery and in SOL as a function of boundary conditions, transport characteristics, and confinement times of lithium ions.

Cрывы разряда в крупных токамаках и будущих реакторах являются серьёзной проблемой, ограничивающей срок их службы. Представлены результаты исследований влияния напуска благородных газов на динамику развития срыва разряда в токамаке Т-10. Срывы разряда вызывались разными способами: наращиванием плотности плазмы до предельной и/или инжекцией дейтериевой или примесной (углеродной) макрочастицы. Инжекция благородных газов (гелия, аргона или ксенона) проводилась как в стационарной стадии для инициации срыва разряда, так и во время спада тока. Обнаружено, что спад тока при срыве разряда в Т-10 происходит в две фазы (медленную и быструю), отличающиеся существенно разным характерным временем. Инжекция дейтериевых макрочастиц при параметрах имеющегося инжектора не влияет на динамику спада тока, а массивный напуск благородных газов при выcоком давлении приводит к переходу спада тока из медленной фазы в быструю и инициации вторичных МГД-возмущений во время не слишком быстрого спада тока, а также к подавлению пучка ускоренных электронов.

The COMPASS tokamak, a divertor device with clear H-mode and ITER-relevant geometry, has been re-installed in IPP Prague after its transport from CCFE in UK. The first plasma was achieved in December 2008. Many new diagnostic tools with both high temporal and spatial resolutions have been developed to address the scientific programme of COMPASS focused on H-mode physics and pedestal investigations. In the paper, an overview of existing and in near future planned diagnostics (magnetic, spectroscopy, microwave, probe and beam/particle) on COMPASS is given including their basic technical specifications and achievements.