Design of the shattered pellet injection system for ASDEX Upgrade.

A new shattered pellet injection system was designed and built to perform disruption mitigation experiments on ASDEX Upgrade. The system can inject pellets with diameters of 1, 2, 4, or 8 mm with variable lengths over a range of L/D ratios of ∼0.5-1.5. By using helium or deuterium as propellant gas, the pellets can be accelerated to speeds between 60 and 750 m/s. The velocity range slightly depends on the pellet mass. The injection system is capable of preparing three pellets in separate barrels at the same time. Once accelerated by the propellant gas pulse, the pellets travel through one of three parallel flight tubes. Each flight tube is separated into three sections with increasing diameters of 12, 14, and 16 mm. Two gaps between the sections allow for removal of the propellant gas by expansion into two separate expansions tanks (0.3 and 0.035 m3), pellet observation in the first gap and the torus gate valve in the second. Each flight tube end is equipped with an exchangeable shatter head with different shatter angles, square or circular cross-section, and different lengths. The gas preparation and control systems allow highly automated pellet generation for precision of the pellet composition and an excellent reproducibility of shattered pellet experiments.

Experimental observation of a magnetic-turbulence threshold for runaway-electron generation in the TEXTOR tokamak.

Magnetic turbulence is observed at the beginning of the current quench in intended TEXTOR disruptions. Runaway electron (RE) suppression has been experimentally found at magnetic turbulence larger than a certain threshold. Below this threshold, the generated RE current is inversely proportional to the level of magnetic turbulence. The magnetic turbulence originates from the background plasma and the amplitude depends strongly on the toroidal magnetic field and plasma electron density. These results explain the previously found toroidal field threshold for RE generation and have to be considered in predictions for RE generation in ITER.

First results from the modular multi-channel dispersion interferometer at the TEXTOR tokamak.

At the TEXTOR tokamak in Jülich, Germany, a modular dispersion interferometer was installed and operated for the first time. Equipped with four lines of sight, the line-integrated density could be measured in parallel at different major radii with a resolution of better than 3 × 10(17) m(-2). This paper will describe the setup and show the first measurement results. Among others, it was possible to detect the evolution of a disruption with a time resolution of 4 µs. The movement of the runaway beam following the disruption could be resolved spatially and temporarily.

Resonant pedestal pressure reduction induced by a thermal transport enhancement due to stochastic magnetic boundary layers in high temperature plasmas.

Good alignment of the magnetic field line pitch angle with the mode structure of an external resonant magnetic perturbation (RMP) field is shown to induce modulation of the pedestal electron pressure p(e) in high confinement high rotation plasmas at the DIII-D tokamak with a shape similar to ITER, the next step tokamak experiment. This is caused by an edge safety factor q95 resonant enhancement of the thermal transport, while in contrast, the RMP induced particle pump out does not show a significant resonance. The measured p(e) reduction correlates to an increase in the modeled stochastic layer width during pitch angle variations matching results from resistive low rotation plasmas at the TEXTOR tokamak. These findings suggest a field line pitch angle resonant formation of a stochastic magnetic edge layer as an explanation for the q95 resonant character of type-I edge localized mode suppression by RMPs.

Spectral measurements of runaway electrons by a scanning probe in the TEXTOR tokamak.

Energy spectral measurements of runaway electrons were performed by a scanning probe with high spatial and temporal resolution in the TEXTOR tokamak. The probe consists of ten YSO (Y(2)SiO(5):Ce) crystals, which are shielded by tungsten filters. The probe can resolve electrons with different energies between 4 and 30 MeV. An insertion of the probe to the plasma boundary several times during the discharge allowed spectral measurements of runaway electrons at different minor radial positions at the plasma edge as well as the study of runaway production in time. The high temporal resolution of the probe, 0.05 ms, enabled measurements of runaway electrons not only during low density discharges, but also during plasma disruptions.

Suppression of runaway electrons by resonant magnetic perturbations in TEXTOR disruptions.

The generation of runaway electrons in the international fusion experiment ITER disruptions can lead to severe damage at plasma facing components. Massive gas injection might inhibit the generation process, but the amount of gas needed can affect, e.g., vacuum systems. Alternatively, magnetic perturbations can suppress runaway generation by increasing the loss rate. In TEXTOR disruptions runaway losses were enhanced by the application of resonant magnetic perturbations with toroidal mode number n=1 and n=2. The disruptions are initiated by fast injection of about 3x10{21} argon atoms, which leads to a reliable generation of runaway electrons. At sufficiently high perturbation levels a reduction of the runaway current, a shortening of the current plateau, and the suppression of high energetic runaways are observed. These findings indicate the suppression of the runaway avalanche during disruptions.

Main characteristics of the fast disruption mitigation valve.

The article presents a detailed investigation of the fast disruption mitigation valve developed at FZJ Juelich. The essence of this study is the novel direct observation of the piston motion by means of a fast framing camera. The piston stroke and the injection duration are shown to strongly depend on the operational pressure and the used gas. The same is true for the valve throughput. The analysis revealing the leading contribution of the injection duration in this modification is given. The knowledge of the injection duration is also used to reconstruct the characteristic pressure decay rates and the gas outflow rates. The means to increase the gas outflow are discussed. The main found valve characteristics are: (1) valve reaction time, i.e., the delay between the application of the trigger signal and the achievement of reliably observable opening 0.5 mm, is about 0.3 ms; (2) the maximum achieved throughput is 7.5 bar l for argon and 9.5 bar l for helium; (3) the maximum delivery rates are 500 bar l s(-1) for Ar and 1500 bar l s(-1) for He.

Improved confinement due to open ergodic field lines imposed by the dynamic ergodic divertor in TEXTOR.

The ergodization of the magnetic field lines imposed by the dynamic ergodic diverter (DED) in TEXTOR can lead both to confinement improvement and to confinement deterioration. The cases of substantial improvement are in resonant ways related to particular conditions in which magnetic flux tubes starting at the X points of induced islands are connected with the wall. This opening process is connected with a characteristic modification of the heat deposition pattern at the divertor target plate and leads to a substantial increase and steepening of the core plasma density and pressure. The improvement is tentatively attributed to a modification of the electric potential in the plasma carried by the open field lines. The confinement improvement bases on a spontaneous density built up due to the application of the DED and is primarily a particle confinement improvement.

Forced magnetic reconnection and field penetration of an externally applied rotating helical magnetic field in the TEXTOR tokamak.

The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization.

Change of the magnetic-field topology by an ergodic divertor and the effect on the plasma structure and transport.

The magnetic-field perturbation produced by the dynamic ergodic divertor in TEXTOR changes the topology of the magnetic field in the plasma edge, creating an open chaotic system. The perturbation spectrum contains only a few dominant harmonics and therefore it can be described by an analytical model. The modeling is performed in the vacuum approximation without assuming a backreaction of the plasma and does not rely on any experimentally obtained parameters. It is shown that this vacuum approximation predicts in many details the experimentally observed plasma structure. Several experiments have been performed to prove that the plasma edge behavior is defined mostly by the magnetic topology of the perturbed volume. The change in the transport can be explained with the knowledge of only the magnetic structures; i.e., the ergodic pattern dominates the plasma properties.

[Successful therapy of a rheumatoid leg ulcer with intravenous immunoglobulins]. / Erfolgreiche Therapie eines Ulcus cruris rheumaticum mit systemischen Immunglobulinen.

Rheumatoid arthritis (RA) is a chronic, systemic inflammatory disease. Leg ulcers in rheumatoid arthritis may be caused by vasculitis and are an interdisciplinary therapeutic challenge. A 69 year old women with rheumatoid arthritis and many other medical problems presented with widespread vasculitis-induced therapy-resistant ulceration on her right lower leg. Since previous therapeutic efforts had a negative effect on wound healing, we administered intravenous immunoglobulins which led to complete healing of the ulcer was achieved. Both the serological and rheumatologic features of her rheumatoid arthritis also improved. Intravenous immunoglobulins represented an effective therapeutic option with fewer side effects in the therapy of vasculitis-induced leg ulceration in this patient with rheumatoid arthritis.

[Contact allergies in patients with chronic wounds: results of a study from 1999 to 2004]. / Kontaktsensibilisierungen von Patienten mit chronischen Wunden: Resultate einer Untersuchung im Zeitraum von 1999-2004.

Patients with chronic wounds frequently acquire clinically relevant contact sensitization. We examined the results of the skin patch tests in patients with chronic wounds, who were treated between 1999-2004 in the Department of Dermatology, University School of Medicine, Essen, Germany. Altogether 105 patients with chronic wounds underwent patch testing. In 68 individuals, contact sensitization to at least one substance was detected. The most frequent contact allergens were to balsam of Peru, Amerchol L-101, fragrance mix, wool wax alcohols and rosins. Contact sensitization to wound dressing materials was also identified in 4 patients. Our results demonstrate the current spectrum of contact sensitization of patients with chronic wounds. Our results show the importance of paying attention to the ingredients in wound dressings and performing patch testing if there is any clinical suggestion of allergic contact dermatitis.

Influence of the dynamic ergodic divertor on the density limit in TEXTOR.

A significant influence of the dynamic ergodic divertor (DED) on the density limit in TEXTOR has been found. In Ohmic discharges, where without DED detachment normally arises at the density limit, a MARFE (multifaceted asymmetric radiation from the edge) develops when the DED is operated in a static regime. The threshold of the MARFE onset in the neutral beam heated plasmas is increased by applying 1 kHz ac DED at the high-field side. The theoretical predictions based on the parallel energy balance taking poloidal asymmetries into account agree well with the experimental observation.

[Comparison of the minimal erythema dose for narrowband UV-B and broad spectrum UV-B using a new UV hand-held device]. / Vergleich der minimalen Erythemdosis von Schmalspektrum-UV-B- und Breitspektrum-UV-B-Strahlern mit einem neuen UV-Handgerät.

BACKGROUND: Phototherapy requires an individually adapted therapeutic regime that is based upon the minimal erythema dose for each patient. Whereas this is well established for UV-B broadband, so far no standardized equipment existed that allowed for determination of the MED for UV-B 311 nm narrowband irradiation. Thus, the starting dose for UV-B 311 nm is usually adjusted to the clinical skin type or the MED for broad-spectrum UV-B irradiation. PATIENTS AND METHODS: We determined the MED for UV-B 311 nm in a cohort of 110 healthy test persons with a newly constructed hand-held UV-light source and compared it to UV-B broadband MED. RESULTS: For UV-B broadband, the MEDs ranged from 46.2 to 210.9 mJ/cm(2) with an average value of 108.45 mJ/cm(2). For the MED of narrowband UV-B 311 nm, the values ranged from 300.9 to 1.386.0 mJ/cm(2) with an average value of 838.88 mJ/cm(2). Concerning the factor of the MED UV-B broad-spectrum related to MED UV-B 311 nm narrowband, values from 4.01 to 13.68 with a average value of 7.91 resulted. No significant differences could be detected for the MED of UV-B broad-spectrum and narrowband in correlation to age, sex or clinical skin type. CONCLUSION: Our data emphasize the presence of extensive inter-individual differences in the MED of both UV-B-spectra and point to the necessity to test patients before the first irradiation.

Increased activity of factor VIII coagulant associated with venous ulcer in a patient with Klinefelter's syndrome.

Klinefelter's syndrome is the most frequent major abnormality of sexual differentiation in men with two or more X chromosomes. Recurrent venous ulcers as a result of a post-thrombotic syndrome are a well known symptom in patients with Klinefelter's syndrome. Until now the underlying pathomechanisms are not completely understood. Platelet hyperaggregability, factor V Leiden mutation and abnormalities in fibrinolysis were implicated as possible contributing factors. Here we describe the detection of an increased activity of factor VIII coagulant (factor VIII:C). This is the first case report on increased factor VIII:C activity associated with venous ulcers in a patient with Klinefelter's syndrome. Elevated factor VIII plasma levels are gradually accepted to be associated with an increased risk for venous thromboembolism. Therefore, we discuss that the examination of factor VIII:C may help in clarifying individual thromboembolic risks, especially in patients with Klinefelter's syndrome.

Toroidal plasma rotation induced by the dynamic ergodic divertor in the TEXTOR tokamak.

The first results of the Dynamic Ergodic Divertor in TEXTOR, when operating in the m/n=3/1 mode configuration, are presented. The deeply penetrating external magnetic field perturbation of this configuration increases the toroidal plasma rotation. Staying below the excitation threshold for the m/n=2/1 tearing mode, this toroidal rotation is always in the direction of the plasma current, even if the toroidal projection of the rotating magnetic field perturbation is in the opposite direction. The observed toroidal rotation direction is consistent with a radial electric field, generated by an enhanced electron transport in the ergodic layers near the resonances of the perturbation. This is an effect different from theoretical predictions, which assume a direct coupling between rotating perturbation and plasma to be the dominant effect of momentum transfer.