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Measurements are presented of the time resolved cathode and anode falls of high frequency fluorescent lamps for a range of discharge currents typically encountered in dimming mode. Measurements were performed with the movable anode technique. Supporting spectroscopic emission measurements were made of key transitions (argon 420.1 nm and mercury 435.8 nm), whose onset coincide with cathode fall equalling the value associated with the energy, relative to the ground state, of the upper level of the respective transition. The measurements are in general agreement with the well-known understanding of dimmed lamp operation: peak cathode fall decreases with increasing lamp current and with increasing auxiliary coil heating. However, the time dependence of the measurements offers additional insight.

Investigations of fluorescent lamps (FL) are often focused on the electrodes, since the lifetime of the lamps is typically limited by the electrode lifetime and durability. During steady state operation, the work function lowering emitter material, in particular, barium, is lost. Greater barium losses occur under dimming conditions, in which reduced discharge currents lead to increased cathode falls, the result of the otherwise diminished heating of the electrode by the bombarding plasma ions. In this work the barium density near the electrodes of (FL), operating in high frequency dimming mode is investigated using the high-sensitivity method of laser-induced fluorescence. From these measurements we infer barium loss for a range of discharge currents and auxiliary coil heating currents. We show that the Ba loss can very easily be reduced by moderate auxiliary coil heating.

The high energy ion bombardment during instant start of a fluorescent lamp (FL) leads to intense sputtering of the electrode material including tungsten and emitter. Thus, a cold started FL often suffers from early failures due to coil fracture. The main goal of this paper is to investigate tungsten erosion. We have employed the ultra-sensitive method of laser-induced fluorescence. This technique is particularly well-suited to determining absolute population densities of neutral and singly ionized atoms of liberated electrode material. In addition to FL, our investigations have been performed also on hollow cathode lamps (HCLs). These are useful because they provide a variable source of sputtered tungsten atoms and can serve as tuning tools for precise adjustment of the laser radiation.We will present absolute atomic tungsten population densities in a commercial FL and in an HCL. Furthermore, the results of a theoretical investigation of the argon plasma and the tungsten density in the HCL are represented.

Several experiments were conducted in ASDEX Upgrade to prove the suitability of tungsten as a divertor target material under the conditions of a high density and low temperature divertor. The observed fluxes from a tungsten tile into the plasma are low, in keeping with the extremely low sputtering yields. In addition, the very favourable effect of `prompt redeposition' (redeposition during the first gyration) could be confirmed by the experiments. Cooling of the edge region by neon injection seems permissible, i.e. neon impurity sputtering did not increase the eroded fluxes of tungsten. The transport and accumulation behaviour were investigated by means of the laser blow-off technique. No accumulation effects could be observed in ohmic discharges. In discharges with NBI heating but without ICRH, strong accumulation can occur. High heat flux tests were performed on graphite tiles coated with plasma sprayed tungsten, which withstood a thermal load of 15 MW/m2 lasting 2 s as well as 1000 cycles of 10 MW/m2 for 2 s without disabling damage. Owing to the encouraging results, an experiment using a tungsten divertor is planned in ASDEX Upgrade

The erosion of the graphite divertor plates in the ASDEX Upgrade tokamak is measured spectroscopically. Spatial profiles of the D0 and C+ influxes across the outer target plate are determined from measured absolute line intensities. Plasma parameters (ne, Te) at the target, which are required to determine the appropriate photon emission efficiencies for these lines, are obtained from an in-vessel reciprocating Langmuir probe above the target plate. Yields for the erosion of the graphite by the incident D+ flux are determined from the ratio of the measured C+ to D0 fluxes. Over a range of moderate densities the measured yields of ≤4% are explicable in terms of physical sputtering alone. Chemical sputtering by low energy Franck-Condon neutrals probably contributes, however, to the total erosion. At higher densities detachment of the plasma from the targets occurs owing to formation of a MARFE near the X point. Under these conditions localized physical sputtering of the targets ceases. The impurity level (Zeff) is, however, maintained following detachment, indicating a corresponding maintenance of carbon influx, perhaps due to chemical erosion of the total graphite surface and/or an improvement in particle confinement in the detached state

The completely detached high confinement (CDH) regime established recently in high power ASDEX-Upgrade single null divertor discharges is described. The standard CDH mode scenario with feedback controlled external deuterium and neon puffing is analysed in detail with respect to its divertor detachment and confinement properties. Impurity transport and pumping effects and the density operation windows of the CDH mode are outlined. First results with other impurity radiators (N,Ar) are given. Finally the CDH mode operation space is discussed in terms of main chamber and scrape-off layer plus divertor radiation and possible consequences for future fusion experiments are outlined.

Due to the open field lines, the scrape-off layer and divertor region of tokamak plasmas is a complex, two-dimensional system, involving transport parallel and perpendicular to the magnetic field, as well as interaction of the plasma with surfaces and with the neutral gas. Therefore sophisticated two-dimensional codes are required to model the divertor and edge physics. In this paper, the B2-EIRENE code package is used to simulate the ASDEX-Upgrade scrape-off layer plasma and the neutral gas dynamics in a fully self-consistent way. Specific ASDEX-Upgrade discharges are modelled using the actual magnetic configuration and in-vessel components. Single fluid as well as multifluid calculations including self-consistent target and wall erosion of carbon are described. At given input power and bulk plasma radiation, typical divertor plasma profiles from Langmuir probes are fitted by varying the separatrix density and the transport coefficients. On the basis of such multifluid fits, spectroscopic divertor diagnostics are numerically modelled and compared with measured profiles, and reasonable agreement is found.

The introduction presents a historical review of the role of molecules in tokamak research starting from the first installations at the Kurchatov Institute. Molecular impurities were mostly considered as a transient conditioning problem, but with the use of carbon for wall and limiter elements, it was perpetuated. New results about the elementary processes involved in hydrogenic carbon erosion are reported and the existing data base is briefly discussed. Results from mass spectrometry are presented as well as data from optical spectroscopy including determination of CD 4 and CD fluxes from molecular band intensities. A typical yield of about 5% for hydrogenic chemical erosion is obtained. In combination, all these results show the impact of hydrogenic carbon erosion. They strongly suggest that with boronized walls it remains as the dominating process for the carbon fluxes in the SOL and even dominates the carbon concentration in the central plasma in spite of a high SOL screening action for hydrocarbons.

The two-dimensional Monte Carlo code DIVIMP is used as an interpretative tool for the analysis of spectroscopic measurements in the edge and the divertpr plasma of ASDEX-Upgrade. For a series of standard Ohmic discharges, the spectral lines of C + and C 2+ ions, recorded by two spectrometers viewing perpendicular and tangential to the outer divertor plates, were modelled. The simulations show that carbon production by physical sputtering alone is not sufficient to explain the observed signals. Further sources, possibly caused by chemical erosion processes must be taken into account.

Passive spectroscopy has been used for in situ studies of the erosion of various divertor target materials in ASDEX-Upgrade. Yields measured for the erosion of graphite over a range of moderate densities can be explained by physical sputtering alone, although there may also be small contributions from chemical processes. At high density, detachment of the divertor plasma occurs and sputtering of the target ceases. Under such high-density conditions high-Z materials, e.g. tungsten, offer a promising alternative to graphite. First studies of the erosion of these materials confirm the expected low sputtering rates and the short ionisation lengths of sputtered neutrals. The latter implies efficient prompt redeposition which should suppress production of higher ionisation stages and associated problems with self-sputtering.

In the ASDEX Upgrade, X-point marfe formation and its behaviour up to the density limit is investigated in gas-fuelled ohmically-heated single-null discharges over a wide range of parameters: Ip=0.6-1.2 MA, BTF=1.35-2.4 T, a plasma elongation of 1.6 and Zeff

The erosion and redeposition of silicon and tungsten evaporated onto the divertor plates of ASDEX Upgrade have been investigated. For comparison with the experimental results the computer program, ERO, has been used. The erosion of Si markers is smaller than expected from plasma ion sputtering, but still exceeds the W erosion by more than an order of magnitude. The observed erosion can only be explained by assuming a protective effect of carbon ions coming from the plasma which are deposited on the marker surfaces, thus reducing the marker erosion. A redeposition of the sputtered tungsten atoms has been found close to the original marker spots mainly because of prompt redeposition during the first gyration.

ASDEX Upgrade is a poloidal divertor experiment very similar to ITER with respect to magnetic field properties and especially to the plasma boundary geometry. A large part of the programme on ASDEX Upgrade is therefore dedicated to investigating and optimizing reactor-relevant plasma boundary issues. This contribution is concerned with H-mode studies and edge physics in general. The L/H-power threshold, H-mode confinement, details of ELM dynamic and 'dithering' L/H-transitions will be discussed. The edge physics investigations are concerned with model calculations and validations, the characteristic 'approach' to the density limit (DL), target plate sputtering and the influence of hydrocarbons, asymmetries and drifts depending on the direction of the toroidal magnetic field, and finally first results of high-Z material experiments.

International audience; The transport of barium atoms and ions in the vicinity of the hot spot in fluorescent lamps operating at 25 kHz is investigated by a combined experimental and theoretical approach. By laserinduced fluorescence, the particle densities of barium atoms and ions were measured timeresolved at different distances from the spot center. In addition, the time-dependent cathode fall voltage was measured using an improved band method. The model combines a kinetic part for the electrons with a fluid part for the barium atoms and ions. Both parts are spatially resolved in spherically symmetric geometry. The space-dependent electron Boltzmann equation yields the electron density and the ionization rate coefficient of barium as functions of the cathode fall voltage. These results are used to solve the time-dependent particle balance equations of barium atoms and ions which include the ionization of barium as gain and loss terms, respectively. Good agreement between the measured and calculated particle densities of barium atoms is obtained. A sensitive dependence of the ionization frequency and of the barium particle densities on the cathode fall voltage was found.

The lifetime of fluorescent lamps is mainly limited by the loss of emitter material which is released from the thermionic cathode due to sputtering and evaporation. To predict the lifetime of these lamps it is desirable to understand and quantify the transport of barium in the cathode region. For this purpose, the transport of barium atoms and ions in ground and excited states has been studied by a combination of experimental and theoretical parts. The densities of barium atoms and ions in ground state were measured by time-resolved laser induced fluorescence (LIF) in a short distance from the spot for a T8 lamp driven at 25 kHz. Furthermore, the intensities of transition lines were determined by optical emission spectroscopy. The time-dependent cathode fall voltage was approximately determined using an improved band method. The model comprises the solution of the time-dependent particle balance equations of barium atoms and ions in ground and excited states. The electron density and the rate coefficients of exciting and ionizing collisions of electrons with barium atoms and ions were determined by solving the space-dependent electron Boltzmann equation in spherical geometry using the measured cathode fall voltage and the discharge current as input. As an example the density of Ba atoms in ground state is shown in Fig. 1a and compared with the LIF result (circles) at 1 mm from the spot center. The Good agreement between the measured and calculated density of barium atoms has been obtained. The results demonstrate the sensitive dependence of the Ba density profiles on the ionization which leads to a strong depletion of the Ba density in the cathode phase of the investigated electrode. The model yields the Ba flux from the cathode which limits the lifetime of the lamp.

Summary form only given. The lifetime of fluorescent lamps is typically restricted by the lifetime of their electrodes. During normal operation, the work function lowering emitter material (primarily Ba) is released from the cathode due to evaporation and sputtering. For lifetime prognosis the understanding and quantification of the barium transport in the electrode region is essential. Therefore, the transport of barium atoms and ions has been investigated experimentally and theoretically. In the experimental part the density of 'ground-state' barium atoms and ions was measured time-resolved by laser induced fluorescence (LIF) in a short distance from the hot spot of a clear-ended T8 lamp driven at 25 kHz. Furthermore, corresponding resonance lines were recorded by optical emission spectroscopy. As an example the ground state density of barium atoms measured by LIF at a distance of 0.5 mm from the hot sport during 'normal' operation is shown in Fig. la. The density strongly decays in the cathode phase due to ionization. During fast shorting of the lamp voltage for about 4 ms the atomic barium density escalates and saturates after a few msec, as shown in Fig. lb. This so-called blanking method was first introduced by R. Garner [R.C. Garner, ICOPS 2008] for electron density measurements.In contrast to density measurements on 'normal' operating lamps, the blanking method reduces the influences of the surrounding plasma in the cathode region on barium atoms (excitation and ionization) and stops sputtering. This is used to separate and quantify the effect of barium evaporation.

Feedback-controlled puffing of neon and deuterium has been applied to control the edge-localized-mode behavior and the target plate power deposition during high-power H -mode discharges in ASDEX Upgrade. A regime has been found in which more than 90% of the heating power is lost through radiation and divertor detachment occurs, without deterioration of the energy confinement. The plasma remains in the H mode, exhibiting small-amplitude, high-frequency ELM's, which do not penetrate to the target plates in the strike zone region.

ASDEX Upgrade is equipped with an ICRH system consisting of 4 generators of 2 MW power each and 4 double loop antennas. The generators, tuneable in frequency from 30 to 120 MHz, cover several heating scenarios over a wide range of magnetic fields (1 T

The method of laser induced fluorescence (LIF) is applied to fluorescent lamps (FL) in order to investigate processes of electrode erosion in the vicinity of the electrodes. The life time of FLs which are ignited by instant start is mainly limited by sputtering of the coil electrodes and in final breaking. This sputtering of tungsten mainly occurs during the ignition in the glow discharge phase. Therefore, the density of W atoms is measured in the electrode region during ignition. Temporal and spatial resolved profiles were measured by LIF which has been combined with fast imaging. The life time of FLs which are started with preheated coils is also caused mainly by electrode failures. But the reason differs from the instant start case because here the loss is caused mainly by evaporation. End-of-lamp life is reached if the emitter material which is deposited at the coil to reduce the work function of the coil is lost completely. LIF is used to measure the density of the eroded emitter material, namely Barium atoms. First result of phase resolved absolute Ba atoms densities are presented.

In this paper a method for separate measurement of the extinction of optical thin films is presented. The method combines a laser calorimetric technique and a light-scattering goniophotometer. As an example, the spectral extinction properties of r.f. reactively sputtered TiO2 films were measured. Under certain conditions absorption indices of 10-5 or less can be achieved. Thus light scattering, rather than absorption, is the dominant optical loss mechanism in sputtered TiO2 films.

The method of laser-induced fluorescence was used to study the behavior of the absolute neutral vapor density of a diffuse vacuum arc on FeCu contacts. The local and temporal resolutions were 1 mm/sup 3/ and 10 mu s, respectively. The arc current had a sinusoidal shape of 5.8-ms duration with peak values of 90 and 510 A. It was found that the maximum densities of the iron and copper atoms are 1.2*10/sup 17/ m/sup -3/ and 7.5*10/sup 17/ m/sup -3/, respectively. During the arc the density was correlated with the current. At current zero the measured densities decreased to 10/sup 16/ m/sup -3/. After current zero, an exponential density decay with a time constant of about 100 mu s was observed, indicating the recovery of dielectric strength after current zero. Measurements of the neutron iron vapor density at different spatial positions in the electrode gap reveal a nonisotropic distribution. From the measurements of the population distribution of the iron ground-state multiplet a/sup 5/D, the excitation temperature was derived. This temperature was low compared with the cathode spot temperature 2500-4000 K and decreased from 1600 K at the current maximum to 1000 K at current zero. The results indicate that the generation of neutrals is caused by flying evaporating metal droplets rather than by molten surface areas. >

104 chronically ill patients of an average age of 82.7 years were accommodated on geriatric wards of hospitals totaling 152 times during vacation, stay at a health resort, or illness of their attending relatives. On average, they stayed in hospital for 3 to 4 weeks. Main diagnoses were cerebrovascular circulatory disturbances or condition after insultus, chronic ischaemic heart disease, and tumor diseases. The morbidity rate during that stay was 9.2%, the mortality rate 6.8%. In 8 out of 10 cases the immediate cause of death was directly causally associated with the primary disease. Any severe nosocomial infections did not occur. The authors consider the risk of the temporary hospitalization of people in need of care for the temporary relief of their relatives, with regard to the patient's age and primary diseases, as justifiable.