Bibliothek

Notizen: Plasma heating and current drive in future machines for magnetically confined thermonuclear fusion will require neutral beam injectors based upon negative ion sources. Although the technology of filament arc ion sources is considered adequately mature for large scale injectors, such as for ITER, ion source efficiency and reliability need to be improved. The power loading of the source and accelerator are especially problematic. This is particularly important for long pulse (1000 s) operation. Investigations with the Kamaboko source, a small scale model of the ITER arc source, illustrate the importance of the conditions of the plasma grid for reducing electron loading of the accelerator. © 1998 American Institute of Physics.

Notizen: Experimental data on the enhancement of D− (H−) negative ion production due to cesium injection into a large volume multiampere negative ion source (MANTIS) are described. The directed deposition of small cesium amounts (5–100 mg) from a compact, movable oven, placed into the central part of a MANTIS gas-discharge box was used. A calorimetrically measured D− beam with an intensity up to 1.6 A and an extracted current density up to 4.2 mA/cm2 (beam energy 25 kV) was obtained. Exactly 30 mg of cesium provides at least one month of source operation (1000 pulses with a discharge pulse duration of 4 s). The effect of cesium on NI enhancement was immediately displayed after the distributed Cs deposition, but it needed some "conditioning'' of cesium by tens of discharge pulses (or by several hours "pause'') in the case of a localized Cs deposition. No degradation of extraction-acceleration voltage holding on within the tested range of cesium injection was observed. © 1996 American Institute of Physics.

Notizen: Neutral beam injection (NBI) is one of the candidates for plasma heating and current drive in the new generation of large magnetic fusion devices (ITER). In order to produce the required deuterium atom beams with energies of 1 MeV and powers of tens of MW, negative D− ion beams are required. For this purpose, multiampere D− beam production and 1 MeV electrostatic acceleration is being studied at Cadarache. The SINGAP experiment, a 1 MeV 0.1 A D− multisecond beam accelerator facility, has recently started operation. It is equipped with a Pagoda ion source, a multiaperture 60 keV preaccelerator and a 1 MV 120 mA power supply. The particular feature of SINGAP is that the postaccelerator merges the 60 keV beamlets, aiming at accelerating the whole beam to 1 MeV in a single gap. The 1 MV level was obtained in less than 2 weeks, the accumulated voltage on-time of being ∼22 min. A second test bed MANTIS, is devoted to the development of multiampere D− sources. It is capable of driving discharges with current up to 2500 A at arc voltages up to 150 V. A large multicusp source has been tested in pure volume and cesiated operation. With cesium seeding, an accelerated D− beam current density of up to 5.2 mA/cm2 (2 A of D−) was obtained. A modification of the extractor is underway in order to improve this performance. A 3D Monte Carlo code has been developed to simulate the negative ion transport in magnetized plasma sources and optimize magnetic field configuration of the large area D− sources. © 1996 American Institute of Physics.

Notizen: A compact, safe system for directed cesium deposition into large volume sources is described. It consists of a small oven mounted on a feedthrough, which permits one to rotate and move the oven across the discharge chamber length or to remove it from the vacuum box to reload the oven. Special industrial pellets containing the cesium compound (30% of cesium chromate +70% titanium) were used for a pure cesium release. The pellets are insensitive to pollution by air and can provide the cesium release during several cycles of heating and cooling in long-term experiments. There was no "poisoning'' impurities degassing (oxygen, water) during the standard oven operation. The Cs system was reliably operated for cesium deposition in multiampere negative-ion source experiments. © 1996 American Institute of Physics.

Notizen: The role of serotonin (5-HT)1B receptors in the mechanism of action of selective serotonin re-uptake inhibitors (SSRI) was studied by using intracerebral in vivo microdialysis in conscious, freely moving wild-type and 5-HT1B receptor knockout (KO 5-HT1B) mice in order to compare the effects of chronic administration of paroxetine via osmotic minipumps (1 mg per kg per day for 14 days) on extracellular 5-HT levels ([5-HT]ext) in the medial prefrontal cortex and ventral hippocampus. Basal [5-HT]ext values in the medial prefrontal cortex and ventral hippocampus, ≈ 20 h after removing the minipump, were not altered by chronic paroxetine treatment in both genotypes. On day 15, in the ventral hippocampus, an acute paroxetine challenge (1 mg/kg i.p.) induced a larger increase in [5-HT]ext in saline-pretreated mutant than in wild-type mice. This difference between the two genotypes in the effect of the paroxetine challenge persisted following chronic paroxetine treatment. Conversely, in the medial prefrontal cortex, the paroxetine challenge increased [5-HT]ext similarly in saline-pretreated mice of both genotypes. Such a challenge produced a further increase in cortical [5-HT]ext compared with that in saline-pretreated groups of both genotypes, but no differences were found between genotypes following chronic treatment. To avoid the interaction with raphe 5-HT1A autoreceptors, 1 µm paroxetine was perfused locally through the dialysis probe implanted in the ventral hippocampus; similar increases in hippocampal [5-HT]ext were found in acutely or chronically treated wild-type mice. Systemic administration of the mixed 5-HT1B/1D receptor antagonist GR 127935 (4 mg/kg) in chronically treated wild-type mice potentiated the effect of a paroxetine challenge dose on [5-HT]ext in the ventral hippocampus, whereas systemic administration of the selective 5-HT1A receptor antagonist WAY 100635 did not. By using the zero net flux method of quantitative microdialysis in the medial prefrontal cortex and ventral hippocampus of wild-type and KO 5-HT1B mice, we found that basal [5-HT]ext and the extraction fraction of 5-HT were similar in the medial prefrontal cortex and ventral hippocampus of both genotypes, suggesting that no compensatory response to the constitutive deletion of the 5-HT1B receptor involving changes in 5-HT uptake capacity occurred in vivo. As steady-state brain concentrations of paroxetine at day 14 were similar in both genotypes, it is unlikely that differences in the effects of a paroxetine challenge on hippocampal [5-HT]ext are due to alterations of the drug's pharmacokinetic properties in mutants. These data suggest that there are differences between the ventral hippocampus and medial prefrontal cortex in activation of terminal 5-HT1B autoreceptors and their role in regulating dialysate 5-HT levels. These presynaptic receptors retain their capacity to limit 5-HT release mainly in the ventral hippocampus following chronic paroxetine treatment in mice.

Notizen: Abstract: To assess the involvement of the serotonin receptor subtype 5-HT1B as terminal autoreceptor regulating 5-HT release in mice, we compared basal values and potassium-evoked changes of extracellular 5-HT levels obtained by in vivo microdialysis in two serotoninergic terminal projection areas of conscious wild-type mice with those measured in homozygous mutant mice lacking the gene encoding the 5-HT1B receptor. In the frontal cortex and ventral hippocampus, basal and K+-evoked 5-HT release did not differ between the two strains of mice studied. The infusion via reverse microdialysis of the selective 5-HT1B receptor agonist CP-93,129 (500 nM) decreased significantly K+-evoked 5-HT release in the frontal cortex (by −44%) and ventral hippocampus (by −32%) of wild-type mice but had no effect in mutants. In a similar manner, the mixed 5-HT1B-5-HT1D receptor agonist sumatriptan (800 nM) decreased significantly K+-evoked 5-HT release in the frontal cortex (by −46%) of wild-type mice but had no effect in mutants. These results demonstrated that 5-HT1B knockout mice are not as sensitive to full (CP-93,129) and mixed (sumatriptan) 5-HT1B receptor agonists as are wild-type mice. These data provide in vivo evidence that, in mice, 5-HT1B, but not 5-HT1D, autoreceptors inhibit 5-HT release at nerve terminals located in the frontal cortex and ventral hippocampus.

Notizen: Neutral beam injection systems (NBI) are capable of injecting powers greater than 20 MW, with pulse length of 5 s. These systems, based on acceleration and neutralization of positive deuterium ions, provide heating and current drive capability and are highly reliable and available. For possible application to a "next step'' fusion device (ITER or NET), a large extrapolation of neutral deuterium energy is necessary to sustain a noninductively driven toroidal current. For good electrical efficiency of these injectors, the choice of acceleration and neutralization of deuterium negative ions beams is an attractive option. A conceptual European design for ITER/NET is proposed with a pure D− ion source (15 A) biased at a high voltage of −1 MV, a multistage electrostatic accelerator with multihole apertures, a grounded gas neutralizer and an electrostatic deflection beam dump. Special supplies are being studied in order to energize the accelerator (1 MV–15 A) with low stored energy and fast switch off time during a fault in the accelerator. By using nine similar injectors, a neutral power of 75 MW can be installed to drive the ITER current. The expected efficiency is better than 40%. A scalable model (4-A D−, 1 MV) to produce a power of 2-MW D0 can be in operation in 1995. The main areas of uncertainty (D− source, electron trapping, large power accelerator, breakdowns, and power supplies) will be studied with this scalable model. When this first phase has been achieved, the final-size injector will be built.

Notizen: We report the first case of an anaphylactic shock to three different FVIII concentrates, one immuopurified plasma-derived (Monoclate-P®) and two recombinant FVIII products (Recombinate® and Kogenate®). These shocks appeared despite the use of antihistaminic drugs. The use of a highly purified plasma-derived FVIII allowed successful on-demand therapy without any antiallergic drug or desensitization.