Identification of the plasma boundary shape and position in the Damavand tokamak

A series of experiments and numerical calculations have been done on the Damavand tokamak for accurate determination of equilibrium parameters, such as the plasma boundary position and shape. For this work, the pickup coils of the Damavand tokamak were recalibrated and after that a plasma boundary shape identification code was developed for analyzing the experimental data, such as magnetic probes and coils currents data. The plasma boundary position, shape and other parameters are determined by the plasma shape identification code. A free-boundary equilibrium code was also generated for comparison with the plasma boundary shape identification results and determination of required fields to obtain elongated plasma in the Damavand tokamak.     

Determination of the resonant harmonics of the error field from dynamic magnetic measurements in a tokamak

The possibility is discussed of determining the amplitude and phase of a static resonant error field in a tokamak by means of dynamic magnetic measurements. The method proposed assumes measuring the plasma response to a varying external helical magnetic field with a small (a few gauss) amplitude. The case is considered in which the plasma is probed by square pulses with a duration much longer than the time of the transition process. The plasma response is assumed to be linear, with a proportionality coefficient being dependent on the plasma state. The analysis is carried out in a standard cylindrical approximation. The model is based on Maxwell’s equations and Ohm’s law and is thus capable of accounting for the interaction of large-scale modes with the conducting wall of the vacuum chamber. The method can be applied to existing tokamaks.     

Time-of-flight measurements of the plasma density in the T-11M tokamak

The average plasma density in the T-11M tokamak is determined by means of an O-mode time-of-flight refractometer measuring the propagation time τ of microwave pulses through the plasma. Since the front duration τ_fr of these pulses is shorter than 2 ns, filtering the measured signal cannot reduce the signal-to-noise ratio below a certain level. This circumstance impedes the use of this diagnostics in larger devices, where the signals may be substantially attenuated because of the larger chamber size and larger waveguide losses. There are several ways to overcome these difficulties: to raise the microwave power, to increase the sensitivity of the receivers, etc. In this paper, a technique is described that is based on the differential method for determining the propagation time of a microwave signal through the plasma. In this method, the plasma is probed by two continuous microwaves with close frequencies and the phase difference between them Δφ₁₂ is measured. As long as the condition Δφ₁₂ < 2π is satisfied, the measurements are unambiguous, because there are no phase jumps by a value multiple of 2π, as is usually the case in conventional interferometers at an increased level of MHD activity, in regimes with a rapid density growth, etc. This method allows the signal to be filtered, thereby ensuring an appreciable improvement in the signal-to-noise ratio in comparison with the pulsed methods. The first measurements of the average density along the +3-cm chord were performed with the help of this new differential time-of-flight refractometer in the T-11M tokamak. The refractometry data agree well with the interferometric data and are used to recover the plasma-density profile.     

Real-time estimation of plasma insulin concentration from continuous glucose monitor measurements

Continuous glucose monitors can measure interstitial glucose concentration in real time for closed-loop glucose control systems, known as artificial pancreas. These control systems use an insulin feedback to maintain plasma glucose concentration within a narrow and safe range, and thus to avoid health complications. As it is not possible to measure plasma insulin concentration in real time, insulin models have been used in literature to estimate them. Nevertheless, the significant inter- and intra-patient variability of insulin absorption jeopardizes the accuracy of these estimations. In order to reduce these limitations, our objective is to perform a real-time estimation of plasma insulin concentration from continuous glucose monitoring (CGM). Hovorka’s glucose–insulin model has been incorporated in an extended Kalman filter in which different selected time-variant model parameters have been considered as extended states. The observability of the original Hovorka’s model and of several extended models has been evaluated by their Lie derivatives. We have evaluated this methodology with an in-silico study with 100 patients with Type 1 diabetes during 25 h. Furthermore, it has been also validated using clinical data from 12 insulin pump patients with Type 1 diabetes who underwent four mixed meal studies. Real-time insulin estimations have been compared to plasma insulin measurements to assess performance showing the validity of the methodology here used in comparison with that formerly used for insulin models. Hence, real-time estimations for plasma insulin concentration based on subcutaneous glucose monitoring can be beneficial for increasing the efficiency of control algorithms for the artificial pancreas.     

First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50–100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution α and correctly determine the linear density 〈Nl〉, regardless of the density profile (assuming a smooth density profile of the form of N(ρ) = N(0)(1 − ρ²)^α, where N(0) is the central plasma density and ρ = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of ∼6 × 10¹⁹ m⁻³ was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.     

Analysis of quasistatic MHD perturbations and stray magnetic fields in a tokamak plasma

Mechanisms for the development of quasistatic MHD perturbations in a viscous rotating tokamak plasma are considered. The influence of stray magnetic fields on the stability of MHD modes in the plasma of the TFTR tokamak is analyzed.     

On the boundary of an equilibrium plasma near the magnetic separatrix in a tokamak

It is shown that plasma rotation near the tokamak the wall can result in a shift of the isobaric separatrix with respect to the magnetic one. This shift is calculated analytically, and this effect is exemplified by simple plasma equilibrium states. The plasma rotation that causes the shift of the separatrices can be driven either by a nonzero radial electric field at the plasma edge or by the Hall effect, which may take place even in the absence of the electric field.     

Cell shape and plasma membrane alterations after static magnetic fields exposure

The biological effects of static magnetic fields (MFs) with intensity of 6 mT were investigated in lymphocytes and U937 cells in the presence or absence of apoptosis-inducing drugs by transmission (TEM) and scanning (SEM) electron microscopy. Lectin cytochemistry of ConA-FITC conjugates was used to analyze plasma membrane structural modifications. Static MFs modified cell shape, plasma membrane and increased the level of intracellular [Ca++] which plays an antiapoptotic role in both cell types. Modifications induced by the exposure to static MFs were irrespective of the presence or absence of apoptotic drugs or the cell type. Abundant lamellar-shaped microvilli were observed upon 24 hrs of continuous exposure to static MFs in contrast to the normally rough surface of U937 cells having numerous short microvilli. Conversely, lymphocytes lost their round shape and became irregularly elongated; lamellar shaped microvilli were found when cells were simultaneously exposed to static MFs and apoptosis-inducing drugs. In our experiments, static MFs reduced the smoothness of the cell surface and partially impeded changes in distribution of cell surface glycans, both features being typical of apoptotic cells. Cell shape and plasma membrane structure modifications upon static MFs exposure were time-dependent. Lamellar microvilli were clearly observed before the distortion of cell shape, which was found at long times of exposure. MFs exposure promoted the rearrangement of F-actin filaments which, in turn, could be responsible for the cell surface modifications. Here we report data that support biological effects of static MFs on U937 cells and human lymphocytes. However, the involvement of these modifications in the onset of diseases needs to be further elucidated.     

Fordisc and the determination of ancestry from cranial measurements

Determining the ancestry of unidentified human remains is a major task for bioarchaeologists and forensic anthropologists. Here, we report an assessment of the computer program that has become the main tool for accomplishing this task. Called Fordisc, the program determines ancestry through discriminant function analysis of cranial measurements. We evaluated the utility of Fordisc with 200 specimens of known ancestry. We ran the analyses with and without the test specimen''s source population included in the program''s reference sample, and with and without specifying the sex of the test specimen. We also controlled for the possibility that the number of variables employed affects the program''s ability to attribute ancestry. The results of the analyses suggest that Fordisc''s utility in research and medico-legal contexts is limited. Fordisc will only return a correct ancestry attribution when an unidentified specimen is more or less complete, and belongs to one of the populations represented in the program''s reference samples. Even then Fordisc can be expected to classify no more than 1 per cent of specimens with confidence.     

Thermodynamic properties of strongly coupled plasma in the presence of an external magnetic field

Thermodynamic properties of a Yukawa system consisting of dust particles in plasma are studied in the presence of an external magnetic field. It is assumed that dust particles interact with each other by a modified potential in the presence of a magnetic field. A molecular dynamics code is developed to calculate this internal energy for the entire system. Based on the values of the internal energy given by the code, the Helmholtz free energy and pressure are calculated for the system.     

Liquid chromatographic determination of the enantiomers of ibuprofen in plasma using a chiral AGP column

A reversed-phase high-performance liquid chromatographic method has been developed for the determination of the R- and S-enantiomers of ibuprofen. The enantiomers and the internal standard 4-pentylphenylacetic acid are extracted from plasma, separated and quantified on a Chiral-AGP column using ultraviolet detection. The simplicity, sensitivity and precision of the method makes it convenient for use in pharmacokinetic studies.     

Determination of the plasma velocity in an imploding wire array from magnetic field measurements by a gradient probe

A method for measuring the gradient of the magnetic field in the plasma of an imploding wire array is described. Results from measurements of the magnitude and gradient of the magnetic field in a tungsten wire array on the Angara-5-1 facility at currents of ∼3 MA are presented. A novel method for calculating the velocity of the current-carrying plasma in the framework of MHD equations from data on the magnitude and gradient of the magnetic field at a certain point inside the array is proposed. It is demonstrated that a gradient magnetic probe can be used to investigate the plasma current sheath in plasma focus facilities.     

Electrostatic electron vortex structure in a plasma in an external magnetic field

A previously developed method for describing vortex structures is used to construct electrostatic vortices in a plasma in an external magnetic field. An equation for the radial electric field that gives rise to azimuthal electron drift in crossed electric (E _r ) and magnetic (B _z ) fields is derived without allowance for the magnetic field of the electron currents. Two types of the resulting electrostatic vortex structures with a positive and a negative electric potential at the axis are analyzed. The results obtained are compared with experimental data on vortex structures.     

Reduced kinetic models of neutral transport in the tokamak plasma

A method for constructing reduced models of neutrals transport for problems with a reduced dimension has been proposed on the basis of the kinetic equation. The case of a cylindrically symmetric plasma column, which is a good approximation for the tokamak geometry, has been thoroughly analyzed. For this geometry, the kinetic model of neutrals in the isotropic approximation is implemented using an algorithm based on energy grouping of neutrals; this algorithm for atomic hydrogen isotopes is integrated in the ASTRA code.     

Evaluation of the ion temperature profile from measurements of the DD fusion products in the T-10 tokamak

Results are presented from measurements of the energy spectra and fluxes of the escaping charged fusion products and fluxes of fusion neutrons in ohmic regimes of the T-10 tokamak. The central temperature of the plasma ions is determined from the broadening of the energy spectra of thermonuclear protons and tritons. The ion temperature profile is evaluated from the dependence of the fluxes of charged fusion products on the radial plasma shift. It is proposed to use a single spectrometric detector with several collimators and slowing-down foils to measure the distribution of charged fusion products over pitch angles, which permits the determination of the ion temperature profile in a single shot. The feasibility of the method proposed is proved experimentally.     

High-performance liquid chromatographic determination of diclofenac in human plasma using automated column switching

A validated high-performance liquid chromatographic procedure employing ultraviolet detection for the analysis of diclofenac in human plasma is reported. The method is rapid and, coupled with column switching, leads to a sensitive, accurate and reproducible assay. The retention times of diclofenac and the internal standard (4′-methoxydiclofenac, CGP-4287) are 6.4 and 7.6 min, respectively. The peak height versus plasma concentration is linear over the range 5.0–2000 ng/ml with a detection limit below 2.5 ng/ml. The mean absolute recovery of diclofenac using the described assay is 96.5% (n = 24). The inter- and intra-day accuracy and precision are within 8.3% of the actual values for all concentrations investigated. Furthermore, this procedure is applied to assess the pharmacokinetics of a single 75-mg oral dose of diclofenac sodium.     

Accurate measurements of coupling constants from two-dimensional nuclear magnetic resonance spectra of proteins and determination of phi-angles

A new and simple method to measure 3JHNH alpha coupling constants of proteins by adding and subtracting traces from corresponding two-dimensional nuclear Overhauser enhanced spectroscopy and two-dimensional correlated spectroscopy cross peaks after scaling is proposed. The optimal scaling for the addition and the subtraction of the two traces is obtained by minimizing an error function. The method was proven to give accurate and precise measurements of coupling constants when tested with a series of simulated spectra. The accuracy of the method was better than 0.1 Hz for all test cases including the limiting case of J = 2.0 Hz and line-width = 11.0 Hz. The accuracy of the method was better than 0.1 Hz for all test cases including The 3JHNH alpha coupling constants were measured in two-dimensional nuclear magnetic resonance spectra of the two proteins barley serine proteinase inhibitor (CI-2) and the bacterial ribonuclease (barnase) of Bacillus amyloliquefaciens. The experimentally measured coupling constants were used to calculate the constants in a Karplus equation to be: 3JHNH alpha = 6.7 cos2(phi-60) -1.3 cos(phi-60) +1.5. These constants are in good accordance with those obtained for basic pancreatic trypsin inhibitor (BPTI). In addition, special emphasis is given to the measurements of positive phi-angles, and to the contribution of molecular dynamics on the apparent coupling constants.     

Simulation of plasma density evolution in the T-10 tokamak

Analysis of the experimental profiles of the plasma density and pressure in the T-10 tokamak shows that in the plasma core they are close to the corresponding canonical profiles. This allows one to construct an expression for the particle flux in terms of the canonical profile model. T-10 experiments performed with ohmic discharges have revealed transitions from improved to low particle confinement, similar to the effect of the density pump-out from the central part of the plasma upon switching-on of the electron cyclotron resonance heating (ECRH). It is shown that such a change in the particle confinement is associated with the deviation of the radial pressure profile from the canonical one. A nonlinear model of particle transport in discharges with density variations that allows for the transition effects is proposed. The plasma density evolution is numerically simulated for a number of ohmic and ECRH T-10 discharges.