Interpretation of D_alpha Imaging Diagnostics Data on the ASDEX Upgrade Tokamak

The Tokamak configuration is a promising concept for magnetic confinement fusion. Cross-field transport in the plasma core leads to a plasma flux across the separatrix into the scrape-off layer, where it is guided along field lines towards the divertor targets. A return flux of neutral particles after plasma-wall interaction is directed towards the plasma chamber. Each discharge scenario is accompanied by a characteristic recycling pattern. The dominant mechanisms of neutralplasma interaction are ionisation and atom-ion charge exchange. The impact of neutrals on the particle-, momentum- and energy-balance of the plasma is relevant for the understanding of the properties of the edge plasma and the state of the divertor plasma. Neutrals may cause energyand momentum-detachment, a state of reduced power and particle fluxes, at the targets, which is a prerequisite for acceptable wall loads under reactor conditions. The distribution of neutral particles in the plasma chamber can be determined by the analysis of line emission. Parameters of neutrals have been available so far only from localised measurements and it is therefore desired to extend the observation area. At the ASDEX Upgrade Tokamak, two cameras are installed to record the Deuterium Balmer-alpha (D_alpha) emission with high spatial resolution and dynamic range in the divertor and midplane regions. Two methods for data deconvolution are presented. A simple profile-fit is used to resolve the radial profile of emission at the low and high field sides for low and medium density discharges. This emission profile is translated to neutral parameters by comparison to the results obtained from kinetic modelling of neutral penetration (KN1D). An algorithm for tomographic reconstruction is applied to image data of the divertor region. In general, radiance data recorded is blurred due to the impact of diffuse reflection from surfaces of the plasma facing components in the all-Tungsten machine. Therefore, the tomographic algorithm has been extended by a model for reflection based on a solid angle resolved measurement. The sensitivity of the procedures is proven by the accurate analysis of different edge plasma configurations. Poloidally resolved neutral flux densities at the plasma edge and corresponding core fuelling rates are presented for the high field side. Underlying estimates of plasma parameters indicate a drop of static plasma pressure along the magnetic field towards the inner target. Changes of the poloidal flux density profile during a radial shift of the plasma column, indicate a correlation of plasma-wall gap and scrape-off layer parameters at the high field side. From the deconvolution of divertor view data separate emission patterns have been resolved. Besides the character of emission at the strike zones which can give a hint on the level of detachment, the occurrence of radiation above the inner target indicates that the distribution of plasma parameters is probably more complex than expected from simple radial decay lengths. The experimental emission profiles and inferred neutral parameters display an important boundary condition for complex 2D edge modelling codes like SOLPS. The comparison of experimental and code results question the applicability of the standard recipe (concerning code settings) for arbitrary plasma scenarios. An interface to theory is required to reasonably exploit the experimental data on neutral penetration. The essential result of this thesis is a reference frame for the quantitative analysis of video diagnostics data recorded on a Tokamak plasma, including the impact of reflecting plasma facing components

Verified modeling of a low pressure hydrogen plasma generated by electron cyclotron resonance

A self-consistent fluid model has been successfully developed and employed to model an electron cyclotron resonance driven hydrogen plasma at low pressure. This model has enabled key insights to be made on the mutual interaction of microwave propagation, power density, plasma generation, and species transport at conditions where the critical plasma density is exceeded. The model has been verified by two experimental methods. Good agreement with the ion current density and floating potential—as measured by a retarding energy field analyzer—and excellent agreement with the atomic hydrogen density—as measured by two-photon absorption laser induced fluorescence—enables a high level of confidence in the validity of the simulation

Membrane attack complex inhibitor CD59a protects against focal cerebral ischemia in mice

<p>Abstract</p> <p>Background</p> <p>The complement system is a crucial mediator of inflammation and cell lysis after cerebral ischemia. However, there is little information about the exact contribution of the membrane attack complex (MAC) and its inhibitor-protein CD59.</p> <p>Methods</p> <p>Transient focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in young male and female CD59a knockout and wild-type mice. Two models of MCAO were applied: 60 min MCAO and 48 h reperfusion, as well as 30 min MCAO and 72 h reperfusion. CD59a knockout animals were compared to wild-type animals in terms of infarct size, edema, neurological deficit, and cell death.</p> <p>Results and Discussion</p> <p>CD59a-deficiency in male mice caused significantly increased infarct volumes and brain swelling when compared to wild-type mice at 72 h after 30 min-occlusion time, whereas no significant difference was observed after 1 h-MCAO. Moreover, CD59a-deficient mice had impaired neurological function when compared to wild-type mice after 30 min MCAO.</p> <p>Conclusion</p> <p>We conclude that CD59a protects against ischemic brain damage, but depending on the gender and the stroke model used.</p

Inhibition of the alternative complement activation pathway in traumatic brain injury by a monoclonal anti-factor B antibody: a randomized placebo-controlled study in mice

BACKGROUND: The posttraumatic response to traumatic brain injury (TBI) is characterized, in part, by activation of the innate immune response, including the complement system. We have recently shown that mice devoid of a functional alternative pathway of complement activation (factor B-/- mice) are protected from complement-mediated neuroinflammation and neuropathology after TBI. In the present study, we extrapolated this knowledge from studies in genetically engineered mice to a pharmacological approach using a monoclonal anti-factor B antibody. This neutralizing antibody represents a specific and potent inhibitor of the alternative complement pathway in mice. METHODS: A focal trauma was applied to the left hemisphere of C57BL/6 mice (n = 89) using a standardized electric weight-drop model. Animals were randomly assigned to two treatment groups: (1) Systemic injection of 1 mg monoclonal anti-factor B antibody (mAb 1379) in 400 μl phosphate-buffered saline (PBS) at 1 hour and 24 hours after trauma; (2) Systemic injection of vehicle only (400 μl PBS), as placebo control, at identical time-points after trauma. Sham-operated and untreated mice served as additional negative controls. Evaluation of neurological scores and analysis of brain tissue specimens and serum samples was performed at defined time-points for up to 1 week. Complement activation in serum was assessed by zymosan assay and by murine C5a ELISA. Brain samples were analyzed by immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) histochemistry, and real-time RT-PCR. RESULTS: The mAb 1379 leads to a significant inhibition of alternative pathway complement activity and to significantly attenuated C5a levels in serum, as compared to head-injured placebo-treated control mice. TBI induced histomorphological signs of neuroinflammation and neuronal apoptosis in the injured brain hemisphere of placebo-treated control mice for up to 7 days. In contrast, the systemic administration of an inhibitory anti-factor B antibody led to a substantial attenuation of cerebral tissue damage and neuronal cell death. In addition, the posttraumatic administration of the mAb 1379 induced a neuroprotective pattern of intracerebral gene expression. CONCLUSION: Inhibition of the alternative complement pathway by posttraumatic administration of a neutralizing anti-factor B antibody appears to represent a new promising avenue for pharmacological attenuation of the complement-mediated neuroinflammatory response after head injury

Simulating Divertor Detachment of Ohmic Discharges in ASDEX Upgrade Using SOLPS: the Role of Carbon

With divertor detachment being a prerequisite for burning plasma operation in ITER, numerical codes such as SOLPS [1] have been developed for predicting and interpreting the divertor performance at all operational regimes in current tokamaks and ITER. In ITER complete detachment from the outer divertor target is not permitted as this might result in an X-point MARFE, imposing an upper limit for the upstream separatrix density, n{sub e}{sup sep}. Despite the knowledge of the basic mechanisms required for achieving detachment, such as radiative power exhaust, volumetric momentum and charge removal [1], a quantitative evaluation of experimentally observed detached regimes proves to be particularly difficult for several tokamaks. In particular the strong asymmetry of the ion flux density between the inner, {Lambda}{sub it}, and the outer target {Lambda}{sub ot} with increasing line averaged density, {bar n}{sub e}, and in particular ''vanishing'' of the ion flux, defined as full/complete detachment, at the inner target cannot be reproduced. It is unclear how this is related to divertor target plates or other plasma facing components containing carbon. As part of a combined effort at various experimental devices this paper contributes to the validation of the SOLPS code against experimental data from ASDEX Upgrade, AUG, at the onset of divertor detachment. In the framework established under the International Tokamak Physics Activity (ITPA) Divertor and SOL working group a series of ohmic discharges have been performed in AUG, which had as similar as possible plasma parameters as companion discharges undertaken in DIII-D [2]. The effect of activating drift terms, the influence of the chemical sputtering yield at the inner target and in addition to [3] the role of impurity influx from the inner heat shield are analyzed