Energy Confinement in Self-Organized Tokamak Plasma (without Transport Barriers)

Plasma Physics Reports - 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...     

Plasma Cooling During Disruptions of Ohmic Discharges at the T-10 Tokamak

Plasma Physics Reports - Experimental data on plasma cooling during slow discharge disruptions at the T-10 tokamak are analyzed. It is shown that, in the initial phase of thermal quench at T-10,...     

Dynamic evaluation of blood flow microcirculation by combined use of the laser Doppler flowmetry and high‐speed videocapillaroscopy methods

The dynamic light scattering methods are widely used in biomedical diagnostics involving evaluation of blood flow. However, there exist some difficulties in quantitative interpretation of backscattered light signals from the viewpoint of diagnostic information. This study considers the application of the high‐speed videocapillaroscopy (VCS) method that provides the direct measurement of the red blood cells (RBCs) velocity into a capillary. The VCS signal presents true oscillation nature of backscattered light caused by moving RBCs. Thus, the VCS signal can be assigned as a reference one with respect to more complicated signals like in laser Doppler flowmetry (LDF). An essential correlation between blood flow velocity oscillations in a separate human capillary and the integral perfusion estimate obtained by the LDF method has been found. The observation of blood flow by the VCS method during upper arm occlusion has shown emergence of the reverse blood flow effect in capillaries that corresponds to the biological zero signal in the LDF. The reverse blood flow effect has to be taken into account in interpretation of LDF signals.      

Investigation of the possibility of exceeding the Greenwald density limit during ECRH in T-10

In T-10 experiments, attempts were made to significantly exceed the Greenwald limit $\bar n_{Gr} $ during high-power (P _ab=750 kW) electron-cyclotron resonance heating (ECRH) and gas puffing. Formally, the density limit $(\bar n_e )_{\lim } $ exceeding the Greenwald limit $({{(\bar n_e )_{\lim } } \mathord{\left/ {\vphantom {{(\bar n_e )_{\lim } } {\bar n_{Gr} }}} \right. \kern-0em} {\bar n_{Gr} }} = 1.8)$ was achieved for q _L=8.2. However, as q _L decreased, the ratio ${{(\bar n_e )_{\lim } } \mathord{\left/ {\vphantom {{(\bar n_e )_{\lim } } {\bar n_{Gr} }}} \right. \kern-0em} {\bar n_{Gr} }}$ also decreased, approaching unity at q _L≈3. It was suggested that the “current radius” (i.e., the radius of the magnetic surface enclosing the bulk of the plasma current I _p), rather than the limiter radius, was the parameter governing the value of $(\bar n_e )_{\lim } $ . In the ECRH experiments, no substantial degradation of plasma confinement was observed up to $\bar n_e \sim 0.9(\bar n_e )_{\lim } $ regardless of the ratio ${{(\bar n_e )_{\lim } } \mathord{\left/ {\vphantom {{(\bar n_e )_{\lim } } {\bar n_{Gr} }}} \right. \kern-0em} {\bar n_{Gr} }}$ . In different scenarios of the density growth up to $(\bar n_e )_{\lim } $ , two types of disruptions related to the density limit were observed.     

Time evolution of the ion temperature in the T-10 tokamak during simultaneous pellet injection and electron-cyclotron resonance heating

Results are presented from studies of the time evolution of the ion temperature in the T-10 tokamak in the course of injection of several (up to five) deuterium pellets into a deuterium plasma the electron component of which is heated at the second harmonic of the electron gyrofrequency. It is shown that, at an electron cyclotron heating power of 900 kW, the injection of five pellets is accompanied by an increase in the ion temperature to 1200 keV, which is a record value for T-10. It is noted that energy exchange between the electron and ion components in these experiments is a purely classical, Coulomb process.     

Formation of electron transport barriers under ECR control of the q(r) profile in the T-10 tokamak

Abstract-the formation of transport barriers under electron cyclotron resonance heating and current drive in the t-10 tokamak is studied. in regimes with off-axis co-eccd and q _L <4 at the limiter, a spontaneous transition to improved confinement accompanied by the formation of two electron transport barriers is observed. the improvement resembles an L-H transition. It manifests itself as density growth, a decrease in the D_α emission intensity, and an increase in the central electron and ion temperatures. Two deep wells on the potential profile (the first one at r/a _L ≈0.6, where a _L is the limiter radius, and the second one near the edge) arise during the transition. the internal barrier is formed when dq/dr～0 with q≈1 in the barrier region.     

Functional Changes in Blood Microcirculation in the Skin of the Foot during Heating Tests in Patients with Diabetes Mellitus

The paper shows the possibility of using the laser Doppler flowmetry method for the assessment of system of blood microcirculation in the lower limbs of patients with diabetes mellitus. A series of experimental studies involving 76 patients with diabetes mellitus and 46 healthy volunteers was carried out. The state of peripheral blood flow was assessed during the local heating tests with different temperature regimes. The wavelet analysis of LDF-grams was used to evaluate the adaptive changes of microcirculation during the temperature tests. The data show that the proposed methodology in the form of heating tests and the use of the wavelet transform in the analysis of LDF-grams allows the evaluation of adaptation processes in the microcirculatory bed during thermal tests and the detection of the preclinical stage of trophic disorders.     

Improvement of plasma energy confinement in tokamak under radiative cooling of the edge plasma

Improvement of plasma energy confinement in the T-10 tokamak by injection of impurity gases was studied experimentally. Injection of Ne and He in the ohmic and ECR heating regimes allows one to separate the dependences of energy confinement on the plasma density and on the edge plasma cooling rate. It is shown that the well-known dependence of the energy confinement time on the plasma density is, in fact, the dependence on the radiative loss power. This phenomenon can be explained by plasma self-organization. The experiments are described by a thermodynamic model for self-organized plasma in which the transport coefficient depends on the difference between the actual and self-consistent pressure profiles. The reduction in the heat flux at the plasma edge due to radiative cooling leads to a decrease in the transport coefficient in this region and, accordingly, improves energy confinement. Results of approximate model calculations for experiments with Ne injection are presented.     

Evaluation of microcirculatory disturbances in patients with rheumatic diseases by the method of diffuse reflectance spectroscopy

Immunoinflammatory reactions affecting the state of the microvasculature play the key role in the genesis of rheumatic diseases. Therefore, it is important to develop new methods for the early detection of microcirculatory disorders. The purpose of this study was to assess the possibilities of diffuse reflectance spectroscopy used to identify microcirculatory disturbances in patients with rheumatic diseases by measuring skin blood supply and oxygenation rate and their relationship with the varying degrees of inflammatory activity. A total of 36 patients with rheumatic diseases and 31 healthy volunteers took part in the study. We analyzed the skin diffuse reflectance spectra recorded on the palmar side of the distal phalange of the right middle finger using a FLAME spectrometer. The erythema index and saturation rate were calculated to quantify the content of hemoglobin and oxygen saturation of tissues in both groups. The differences in the parameters under study between the groups were found to be statistically significant. The average value of erythema index was twofold higher in patients with rheumatic diseases with the second degree of inflammatory activity and about 2.5-fold higher in patients with the third degree of inflammatory activity, compared to the control group. This fact indicates impaired blood circulation with increased blood flow caused by inflammatory processes. Thus, diffuse reflectance spectroscopy can be used as an additional non-invasive diagnostic test for assessing the severity of microcirculatory disturbances and the activity of inflammation in rheumatic diseases.     

Characteristics of discharge disruptions in the T-10 tokamak

The results of experimental studies of discharge disruptions in the T-10 tokamak at the limiting plasma density are presented. On the basis of measurements of the generated soft X-ray emission, for a group of “slow” disruptions, the dynamics of the magnetic configuration of the central part of the plasma column is studied and the possible role of the m/n = 1/1 mode in the excitation of predisruptions or the final stage of disruption is analyzed. It is shown that the characteristics of plasma electron cooling in predisruptions correspond to those of electron cooling upon pellet injection into T-10 and in discharge predisruptions occurring in regimes with the “quiet mode.” It is found that, in the latter case, the reason for predisruptions and fast electron cooling in the plasma core is the instability of the m/n = 2/1 mode, its spontaneous spatial reconstruction, and the generation of a “cooling wave” during this process. Measurements of the electron temperature (determined from the plasma radiation intensity at the second electron cyclotron harmonic) in the zone of the m/n = 2/1 mode have shown that the transformation of the m/n = 2/1 mode leads to the excitation of predisruptions and the final phase of disruption not only in regimes with the “quiet mode,” but also in disruptions of ordinary ohmic discharges. The experimental results obtained in this work make it possible to determine the scenario of the development of “slow” discharge disruptions in the T-10 tokamak at the limiting plasma density.