Conceptual study of energy resolved x-ray measurement and electron temperature reconstruction on ITER with low voltage ionization chambers.

In tokamaks with tungsten-based plasma facing components, such as ITER, pollution of the plasma by heavy impurities is a major concern as it can lead to radiative breakdown. The radiation emitted by such impurities is mainly composed of x-rays in the [0.1; 100] keV range. A diagnostic allowing for the reconstruction of the impurity distribution is of high interest. The ITER requirements for the x-ray measurement system make it mandatory for the detector to provide spectral information. Due to the radiation environment during the ITER nuclear phase, advanced detectors exhibiting high resilience to neutrons and gamma rays, such as gas-filled detectors, are required. The use of Low Voltage Ionization Chambers (LVICs) for this purpose is investigated in this paper. Several anodes have been added to the detector in order to allow for spectral deconvolution. This article presents a conceptual study of the use of a multi-anode LVIC for energy resolved x-ray measurement on ITER. It covers the design of the multi-anode LVIC and its modeling, the method for spectral deconvolution, and its application to energy resolved x-ray tomography, as well as the computation of the electron temperature from the reconstructed local x-ray emissivity.

Modeling a low voltage ionization chamber based tomography system on ITER.

Soft x-ray (SXR) tomography is a key diagnostic method for impurity transport study in tokamaks since it allows for local impurity density reconstruction. The International Thermonuclear Experimental Reactor (ITER) radiative environment in deuterium-deuterium and deuterium-tritium phases will limit the choices of SXR detector technologies, and gas detectors are one of the most promising solutions. In this paper, we, thus, investigate the SXR tomography possibilities on ITER using Low Voltage Ionization Chambers (LVICs). The study contains the development of a LVIC synthetic diagnostic and its application to estimate the LVIC tomographic capabilities in an ITER D-T scenario, including the influence of LVIC parameters and noise in the measurements.

Polycapillary lenses for soft x-ray transmission in ITER: Model, comparison with experiments, and potential application.

Measuring Soft X-Ray (SXR) radiation [0.1 keV; 15 keV] in tokamaks is a standard way of extracting valuable information on the particle transport and magnetohydrodynamic activity. Generally, the analysis is performed with detectors positioned close to the plasma for a direct line of sight. A burning plasma, like the ITER deuterium-tritium phase, is too harsh an environment to permit the use of such detectors in close vicinity of the machine. We have thus investigated in this article the possibility of using polycapillary lenses in ITER to transport the SXR information several meters away from the plasma in the complex port-plug geometry.

In situ wavelength calibration of the edge CXS spectrometers on JET.

A method for obtaining an accurate wavelength calibration over the entire focal plane of the JET edge CXS spectrometers is presented that uses a combination of the fringe pattern created with a Fabry-Pérot etalon and a neon lamp for cross calibration. The accuracy achieved is 0.03 Å, which is the same range of uncertainty as when neglecting population effects on the rest wavelength of the CX line. For the edge CXS diagnostic, this corresponds to a flow velocity of 4.5 km/s in the toroidal direction or 1.9 km/s in the poloidal direction.

Bragg x-ray survey spectrometer for ITER.

Several potential impurity ions in the ITER plasmas will lead to loss of confined energy through line and continuum emission. For real time monitoring of impurities, a seven channel Bragg x-ray spectrometer (XRCS survey) is considered. This paper presents design and analysis of the spectrometer, including x-ray tracing by the Shadow-XOP code, sensitivity calculations for reference H-mode plasma and neutronics assessment. The XRCS survey performance analysis shows that the ITER measurement requirements of impurity monitoring in 10 ms integration time at the minimum levels for low-Z to high-Z impurity ions can largely be met.

Development of a spatially resolving x-ray crystal spectrometer for measurement of ion-temperature (T(i)) and rotation-velocity (v) profiles in ITER.

Imaging x-ray crystal spectrometer (XCS) arrays are being developed as a US-ITER activity for Doppler measurement of T(i) and v profiles of impurities (W, Kr, and Fe) with ∼7 cm (a/30) and 10-100 ms resolution in ITER. The imaging XCS, modeled after a prototype instrument on Alcator C-Mod, uses a spherically bent crystal and 2D x-ray detectors to achieve high spectral resolving power (E/dE>6000) horizontally and spatial imaging vertically. Two arrays will measure T(i) and both poloidal and toroidal rotation velocity profiles. The measurement of many spatial chords permits tomographic inversion for the inference of local parameters. The instrument design, predictions of performance, and results from C-Mod are presented.

Modeling the effect of reflection from metallic walls on spectroscopic measurements.

A modification of JET is presently being prepared to bring operational experience with ITER-like first wall (Be) and divertor (W) materials, geometry and plasma parameters. Reflectivity measurements of JET sample tiles have been performed and the data are used within a simplified model of the JET and ITER vessels to predict additional contributions to quantitative spectroscopic measurements. The most general method to characterize reflectivity is the bidirectional reflection distribution function (BRDF). For extended sources however, such as bremsstrahlung and edge emission of fuel and intrinsic impurities, the results obtained in the modeling are almost as accurate if the total reflectivity with ideal Lambertian angular dependence is used. This is in contrast to the experience in other communities, such as optical design, lighting design, or rendering who deal mostly with pointlike light sources. This result is so far based on a very limited set of measurements and will be reassessed when more detailed BRDF measurements of JET tiles have been made. If it is true it offers the possibility of in situ monitoring of the reflectivity of selected parts of the wall during exposure to plasma operation, while remeasurement of the BRDF is performed during interventions. For a closed vessel structure such as ITER, it is important to consider multiple reflections. This makes it more important to represent the whole of the vessel reasonably accurately in the model, which on the other hand is easier to achieve than for the more complex internal structure of JET. In both cases the dominant contribution is from the first reflection, and a detailed model of the areas intersected by lines of sight of diagnostic interest is required.

Collisional-radiative study of lithium plasmas.

The sensitivity of lithium plasma models to the underlying atomic data is investigated. Collisional-radiative modeling is carried out with both the Los Alamos and ADAS suite of codes. The effects of plane-wave Born, distorted-wave, and nonperturbative R -matrix with pseudostates and time-dependent close-coupling electron impact atomic data on derived plasma quantities such as the ionization balance and radiated power are studied. Density and temperature regimes are identified where nonperturbative excitation and ionization rate coefficients must be used. The electron temperature and density ranges investigated were 0.2 eV< or = T(e) < or =90 eV and 10(10) cm(-3) < or = N(e) < or = 10(14) cm(-3).

Elevated plasminogen receptor expression occurs as a degradative phase event in cellular apoptosis.

Plasminogen activation (PA) is involved in a variety of extracellular proteolytic events, such as fibrinolysis, cell migration (e.g. angiogenesis, tumour cell invasion, inflammation, wound healing, bacterial invasion), ovulation, tissue remodelling and the activation of other protease classes and growth factors. These diverse roles are due to the specific localization of components of the PA system to extracellular matrices, basement membranes, fibrin and cell surfaces. We have previously reported that PA is dramatically elevated during cycloheximide (CHX)-induced apoptosis in U937 cells due to a concomitant increase in both plasminogen receptors (PLG-R; i.e. specific PLG binding) and cell-surface urokinase plasminogen activator. We now extend this study by showing that the increase in PLG-R (resulting in an increase in specific PLG binding) is a late apoptotic event coincident with propidium iodide uptake and internucleosomal DNA fragmentation but occurring after elevations in phosphatidylserine exposure. Plasminogen was also observed to dramatically increase the rate of CHX-induced apoptosis. We conclude that PA may play a role in the degradative (i.e. late-stage) events of cellular apoptosis.

Increased plasminogen binding is associated with metastatic breast cancer cells: differential expression of plasminogen binding proteins.

Overexpression of urokinase-type plasminogen activator and its receptor correlates with metastatic capacity in breast cancer. In this study we show that the urokinase/urokinase receptor-overexpressing, metastatic human breast cancer cell line MDA-MB-231 (1) bound significantly more cell-surface plasminogen in a lysine-dependent manner and (2) was capable of generating large amounts of plasmin compared with the non-metastatic cell lines MCF-7 and T-47D. In addition, distinct plasminogen binding proteins were detected in the plasma membranes of the cell lines, suggesting heterogeneity of binding proteins. Plasminogen binding was analysed using a combination of dual-colour fluorescence flow cytometry and ligand histochemistry (for comparative and cellular localization of ligand binding), and fluorimetry (for Scatchard analysis). Apart from revealing the greater plasminogen binding capacity of MDA-MB-231 cells, flow cytometry and histochemistry also revealed that, in all three cell lines, non-viable or permeabilized cells bound significantly more plasminogen in a lysine-dependent manner than viable or non-permeabilized cells. Viable MDA-MB-231 cells bound plasminogen with moderate affinity and high capacity (Kd = 1.8 microM, receptor sites per cell 5.0 x 10(7). Our results indicate that differences in cell surface-specific plasminogen binding capacity between cell lines may not be detectable with binding techniques that cannot distinguish between viable and non-viable cells.

Loss of cell viability dramatically elevates cell surface plasminogen binding and activation.

The plasminogen activation cascade is focused at the cell surface by virtue of the presence of plasminogen and plasminogen activator receptors. We have utilized flow cytometric plasminogen (plg) binding and activation assays to examine both plasminogen binding and activation on the surface of specific subpopulations of U937 cells (viable, apoptotic, and dead cells). A direct relationship was found to exist between cell viability (propidium iodide uptake) and the magnitude of lysine-dependent plasminogen binding, with apoptotic and dead subpopulations of cells binding up to 100-fold more plasminogen than viable cells. Despite the high level of lysine-dependent plasminogen binding on dead cells, plasminogen activation was minimal due to low levels of cell-surface urokinase plasminogen activator. Plasminogen activation readily occurred on the surface of apoptotic cells because of a dramatic increase in both lysine-dependent plasminogen binding and endogenous urokinase plasminogen activator. These results indicate that colocalization of plasminogen and urokinase plasminogen activator are paramount for plasminogen activation to proceed on the cell surface. Our data also strongly implicate the involvement of the plasminogen activation cascade in apoptosis, especially on urokinase plasminogen activator-expressing cell types. The current study clearly supports the important role of flow cytometry in cellular plasminogen binding and activation studies.