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Levonorgestrel-only emergency contraception (EC) inhibits ovulation to prevent fertilization. Misconceptions regarding its mechanism of action contribute to low use in some settings. We aimed to review the mechanism of action of Levonorgestrel EC and assess the evidence for a postovulatory effect on viable pregnancy development in the exposed and subsequent cycles.We searched Pubmed, Embase, Web of Science, clinicaltrials.gov, the Cochrane database, and the US FDA Adverse Event Reporting System. We included studies reporting on the effect of Levonorgestrel EC exposure on (1) ovulation, (2) conception, (3) implantation, (4) ectopic pregnancy, (5) pregnancy viability, and (6) fertility in subsequent cycles. Data were extracted and tabulated from included studies by two researchers. The results were analyzed and summarized in narrative form.We included 33 studies. Women exposed to Levonorgestrel EC at or after the LH (luteinizing hormone) surge had similar rates of inhibited ovulation (3 studies) and conception rates (2 studies) as controls. Nine out of ten studies found no difference in endometrial receptivity to implantation after exposure to Levonorgestrel EC compared to controls. The evidence for an association between Levonorgestrel EC and reduced fallopian tube motility or ectopic pregnancy was conflicting. We found no evidence of increased miscarriage or teratogenicity (3 studies) or disrupted menstrual cycle (3 studies) after Levonorgestrel EC exposure compared to controls.This review supports that Levonorgestrel EC taken after ovulation does not affect implantation and results in similar conception rates compared to placebo. There is no evidence that exposure to Levonorgestrel EC affects fetal development, miscarriage, stillbirth, or subsequent menstruations.

During its second operational campaign (OP 1.2a) W7-X operated with an edge island divertor. Much higher densities (1020m−3) than in to the previous, limiter campaign were achieved. In order to asses this improved performance and the nature of transport with regard to the expected higher densities and other parameters such as the electron and ion temperature, the electric field and plasma flow, measurements at the plasma edge were conducted with reciprocating probe, mounted on a Manipulator. The probe contains a set of Langmuir pins, Mach probes, compensation coils and a set of 3D pick up coils for the measurement of the local magnetic field and fluctuations, and an ion sensitive probe. It has been observed, in addition to differences due to the magnetic configurations, that the magnetic topology is sensitive to the plasma conditions, especially to changes due to a evolving toroidal plasma current. Measurements from divertor cameras showed that an increasing toroidal current in the standard configuration broadened the heat flux and shifted the strike line considerably. These down-stream observation can be complemented with the measurements at the mid-plane with the manipulator mounted probes. During the experiments the edge island remnant was identified with the measured edge plasma profiles and compared with the predictions from the field line tracing code. Those electron densities and temperatures have been used as an input for understanding edge transport with the EMC3-EIRENE modeling. The results from EMC3-EIRENE also help improve the caculated density profiles, since the modelling provides a profile of the effective charge Zeff. Keywords: W7-X, Langmuir probes, Magnetic islands, Plasma edge transport

The operational regimes in the first divertor campaign of W7-X were limited by unexpectedly high heat loads on certain baffle tiles. In the high-mirror configuration, a permanent hotspot on the baffle plate was detected by the thermographic system, which was further confirmed during the post-campaign inspections of the plasma-facing components. The maximum heat load on three baffle tiles reached about 4.5 MW m−2, which is almost an order of magnitude above its designed value of 0.5 MW m−2. The paper presents a detailed analysis to understand how the baffle plate, which is originally designed to screen the recycling neutrals and is therefore hidden from the hot plasma, can receive such a high heat load – a level that is expected for target plates. Three main causes have been identified: 1) the three baffle tiles are radially only about 5 mm away from a main heat channel towards a target, which is much shorter than the radial power decay length of several centimeters derived from the thermographic measurements in this region; 2) the three baffle tiles are intersected with field-lines of about 30 m length, which are long enough to collect considerable amount of heat via cross-field transport; 3) the baffle tiles have locally large grazing angles. In addition, the analysis method shown in this paper is of general use to estimate the heat flows in shadow areas of targets and thus to evaluate heat loads on the potentially critical components occurring in these areas, especially required for the design of complex 3D divertors like the one in W7-X.

While the low frequency part of the response of the Rogowski coils mounted in the stellarator Wendelstein 7-X has been calculated, the high frequency part is planned to be calibrated by means of an actively applied current. In a staged approach different conductors have been designed to be mounted inside the plasma vessel and an AC current of 1 kA is foreseen to be driven through them at frequencies up to 1 kHz to simulate the plasma current.

International audience; The Wendelstein 7-X (W7-X) optimized stellarator fusion experiment,which went into operation in 2015, has been operating since 2017 with anun-cooled modular graphite divertor. This allowed first divertor physicsstudies to be performed at pulse energies up to 80 MJ, as opposed to 4MJ in the first operation phase, where five inboard limiters wereinstalled instead of a divertor. This, and a number of other upgrades tothe device capabilities, allowed extension into regimes of higher plasmadensity, heating power, and performance overall, e.g. setting a newstellarator world record triple product. The paper focuses on the firstphysics studies of how the island divertor works. The plasma heat loadsarrive to a very high degree on the divertor plates, with only minorheat loads seen on other components, in particular baffle structuresbuilt in to aid neutral compression. The strike line shapes andlocations change significantly from one magnetic configuration toanother, in very much the same way that codes had predicted they would.Strike-line widths are as large as 10 cm, and the wetted areas alsolarge, up to about 1.5 m2, which bodes well for futureoperation phases. Peak local heat loads onto the divertor were ingeneral benign and project below the 10 MW m?2 limit of thefuture water-cooled divertor when operated with 10 MW of heating power,with the exception of low-density attached operation in the high-iotaconfiguration. The most notable result was the complete (in all 10divertor units) heat-flux detachment obtained at high-density operationin hydrogen.

Plasma filaments have been observed by reciprocating electric probes in the Scrape-Off Layer (SOL) of the Wendelstein 7-X stellarator. Comparison with target probes indicates that a filament observed in the W7-X SOL extends to the sheath. Two-dimensional simulations of seeded filaments exhibit good quantitative agreement with experimental measurements in filament velocity scalings, despite an assumption of constant field line curvature. Both experiment and simulation show a slow radial propagation of filaments, indicating that filaments are essentially bound to their flux surface and do not perform ballistic radial motion. In contrast, the poloidal propagation along flux surfaces is much faster than the radial motion.

The magnetic diagnostics foreseen for the Wendelstein 7-X (W7-X) stellarator are diamagnetic loops to measure the plasma energy, Rogowski coils to measure the toroidal plasma current, saddle coils to measure the Pfirsch–Schluter currents, segmented Rogowski coils (poloidal magnetic field probes) to add information on the distribution of the plasma current density, and Mirnov coils to observe magnetohydrodynamic modes. All these magnetic field sensors were designed as classical pick-up coils, after the time integration of induced signals for 1/2 hour had been successfully demonstrated. The long-pulse operation planned for W7-X causes nevertheless significant challenges to the design of these diagnostics, in particular for the components located inside the plasma vessel, which may be exposed to high levels of microwave (electron cyclotron resonance) stray radiation and thermal radiation. This article focuses on the tests and modelling performed during the development of the magnetic diagnostics and on the design solutions adopted to meet the conflicting requirements. All pick-up coils foreseen for the initial operation phase of W7-X and their signal cable sections inside the plasma vessel and the cryostat are now installed, and their electronics and data acquisition are under preparation.

Wendelstein 7-X (W7-X) is a modular advanced stellarator with a magnetic field optimized for good plasma confinement and stability, which went into operation in December 2015 at the Max-Planck-Institut fur Plasmaphysik in Greifswald, Germany. The magnet system of W7-X consists of 70 superconducting coils with as-built-shapes and positions which deviate from the designed ones due to manufacturing and positioning tolerances as well as due to deformations under different kinds of loads. Step-by-step evaluation of the magnet system geometry during the machine construction included measurements of the winding pack geometry characterizing deviations of each coil filament caused by the fabrication process and the tracking of coil positions during main assembly steps. In addition finite element calculations were performed with help of the 360° ANSYS Global Model (a finite element model, representing the whole W7-X magnet system, including all superconducting coils and their support structure) in order to define possible coil deformations under the dead-weight, cool-down and electromagnetic loads in different operation regimes. This paper shows the comparative analysis of different types of deviations in the coil geometry and discusses their influence on plasma equilibrium properties.

Classical particle drifts are known to have substantial impacts on fluxes of particles and heat through the edge plasmas in both tokamaks and stellarators. Here we present results from the first dedicated investigation of drift effects in the W7-X stellarator. By comparing similar plasma discharges conducted with a forward- and reverse-directed magnetic field, the impacts of drifts could be isolated through the observation of up-down asymmetries in flux profiles on the divertor targets. In low-density plasmas, the radial locations of the strike lines (i.e. peaks in the target heat flux profiles) exhibited discrepancies of up to 3 cm that reversed upon magnetic field reversal. In addition, asymmetric heat loads were observed in regions of the target that are shadowed by other targets from parallel flux from the core plasma. A comparison of these asymmetric features with the footprints of key topological regions of the edge magnetic field on the divertor suggests that the main driver of the asymmetries at low density is poloidal E × B drift due to radial electric fields in the scrape-off layer and private flux region. In higher-density plasmas, upper and lower targets collected non-ambipolar currents with opposite signs that also inverted upon field reversal. Overall, in these experiments, almost all up-down asymmetry could be attributed to the field reversal and, therefore, field-dependent drifts.

Mirnov coils are used to measure fluctuations of the magnetic field which are in particular generated by magnetohydrodynamic (MHD) modes. The underlying plasma currents have a multipolar structure in a poloidal cross-section. Therefore the amplitude of the magnetic fluctuations decays quickly with increasing distance from the plasma edge. It is hence important to place the Mirnov coils as close to the plasma edge as possible where they are exposed to high thermal loads. Two types of Mirnov coils are proposed to be used in Wendelstein 7-X (W7-X). Type 1 (44 Mirnov coils) should be mounted on the plasma side of wall protection panels with a graphite cap to shield them from direct plasma exposure. Type 2 (137 Mirnov coils) will be located behind the tiles of the heat shields. An important issue concerning the design of these Mirnov coils is to verify their suitability for steady state operation from the thermal point of view. Both steady state and transient finite element thermal analyses were performed for the Mirnov coils under different conditions and with different designs. The paper presents detailed thermal analyses of the Mirnov coils.

The main heating system of W7-X will be a 10 MW, 140 GHz ECRH. It is expected that the non-absorbed ECRH power will be up to 1 MW. Multiple reflections of the ECRH beam result in a nearly isotropic radiation background. The non-absorbed ECRH power has to be considered as an additional thermal load of microwave stray radiation for all W7-X in-vessel components. Several in-vessel diagnostics, especially magnetic diagnostics, partly consist of microwave absorbing materials. The microwave stray radiation could damage these components or, by evaporation due to overheating, perturb the operation of W7-X. Usually these diagnostics are protected against direct plasma radiation and are thermally connected to actively cooled structures. Nevertheless, ECRH stray radiation can cause a critical temperature increase. We present examples of ECRH stray radiation protection by metallic housing. The use of such housing may be in conflict with vacuum compatibility and in particular for magnetic diagnostics, with the requirement to avoid eddy currents limiting the time resolution of magnetic measurements. Details are given on the protection against ECRH stray radiation as well as on thermal connection concepts. Acceptance tests are presented on full-scale mockups.

Qian Yang He Ji (QYHJ) is a traditional Chinese medicine composed of Digitalis purpurea, Uncaria gambir, Fructus tribuli terrestris, and Ligustrum lucidum. Here, we explored whether combining an antihypertensive angiotensin II receptor blocker (ARB) therapy with QYHJ can improve the arterial functionality of hypertensive patients. One hundred and eight hypertensive patients were randomized into 2 groups; 1 group (n = 53) was treated with ARB and the other group (n = 55) was treated with ARB combined with QYHJ. Each of the 2 groups included 3 subgroups (pure hypertension, hypertension with diabetes, and hypertension with coronary heart disease) and was further divided into patients with and without complications. The cardioankle vascular index and intima-media thickness and pulse pressure were the outcome evaluation parameter. Combined QYHJ and ARB treatment reduced the values of cardioankle vascular index, systolic blood pressure, diastolic blood pressure, and pulse pressure to significantly lower levels than ARB treatment alone did in hypertension patients after 6 months of treatment. ARB improves hypertension, but a combined QYHJ treatment can additionally ameliorate the arterial functionality not only in solely hypertensive patients but also in hypertensive patients with diabetes and coronary heart disease complications. QYHJ coapplication might be a choice to further improve the arterial functionality during an ARB hypertension treatment.

For W7-X a set of magnetic diagnostic coils is foreseen to assess plasma properties such as toroidal net current and energy content for real-time monitoring and also for equilibrium reconstruction. In addition to the set of full Rogowski-Coils, diamagnetic coils and saddle loops, a set of segmented Rogowski-Coils is envisaged to access profile information. The planned scheme of equilibrium reconstruction is described and the status of the analysis of the magnetic diagnostics is presented and its prospects are discussed. It is found that the plasma energy may be retrieved with good accuracy. However, the recovery of profile information shows limited accuracy based on the statistical analyses and modeling done so far (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Wendelstein 7-X, currently under construction at the Max-Planck-Institut fur Plasmaphysik in Greifswald, Germany, is a modular advanced stellarator, combining the modular coil concept with optimised properties of the plasma. The magnet system of the machine consists of 50 non-planar and 20 planar superconducting coils which are arranged in five identical modules, forming a toroidal five-fold symmetric system. The majority of operational magnetic configurations will have rotational transform ι /2 π = 1 at the boundary. Such configurations are very sensitive to symmetry breaking perturbations, which are the consequence of imprecisely manufactured coils or assembly errors. To date, all 70 coils have been fabricated, and the first two half-modules of the machine have been assembled. The comparative analysis of manufactured winding packs and estimates of the corresponding level of magnetic field perturbation are presented. The dependency of the error fields on the coil assembly sequence is considered, as well as the impact of the first assembly errors. The influence of different construction uncertainties is discussed, and measures to minimise the magnetic field perturbation are suggested.

In 12 sheep 21 total hip endoprosthesis were implanted, using a polyethylene acetabulum, which was provided with a continuous conique thread for implantation without cement. Out of 14 non luxated hips only 2 acetabula were loosened. After an implantation between 1 week and 18 months the remaining 12 sockets were macroscopically stable and were examined radiologically and histologically. After 3 months of increased osteogenesis a layer of collagenous tissue developed between implant and bone. In the loadbearing area this layer is from 50-80 microns thick and often the ridges of the thread are stabilised by a thin layer of fiber-cartilage, expanding around the implant with longer implantation. Bore-holes in the thread are filled with partially lamellous bone after 6 months. Though sometimes a considerable amount of polyethylene wear particles caused by the disadvantageous and small shape of the sheeparthroplasty was observed, none of the examined acetabula showed any signs of loosening.

Motional analysis of the spinal segments with an x-ray amplifyer and studies of mechanical stress in the spine at oarsmen show, that during the phase of driving through with the oars immersed, the direction of the resulting load in the spine is approximately vertical to the next vertebral body. While referring to the vertebral bodies the direction of the resulting load does not change essentially, the size of the load differs conspicuously during active motion. In rowing the quantity of stress in the spine is limited by the torque of the counterforce, the erector trunci. Using an exact and correct rowing technique the quality of stress is compatible with the physiologically axial stresspattern of the vertebral body and the intervertebral disque. The frequency of peakstress in active rowing may possible lead to early and augmented degenerative changes in the vertebral bodies. In 45 Austrian top oarsmen the spine was examined clinically and radiologically, 68% showed signs of a previous Scheuermann's disease, while degenerative changes of vertebral bodies were found in 48%. Comparing spinal damages in different sports used in the training of the examined oarsmen, only in bicycling a similar pathomechanical effect on the spine could be observed.

Firmly attached screw-in polyethylene acetabula which had been implanted for between 16 and 54 months were explanted after autopsies and subjected to macroscopic, radiologic and histologic examination. Metaplasias were seen around the threads and on the floor of the acetabulum. Their tendency to ossify represents an attempt at secondary stabilization. Due to the low stability of the polyethylene this causes increased wear on the floor of the acetabulum. The small defects in the polyethylene found in the threads, resembling damage done by mice, may be a sign of biodegradation. In view of the tissue reactions pointed out, the material stability of the polyethylene needs to be improved or implantation must be restricted to a very limited range of indications.

The fluctuations in the edge plasma of magnetic fusion experiments play an important role in terms of anomalous energy and particle transport. Experiments on Wendelstein 7-AS (Renner H et al 1989 Plasma Phys. Control. Fusion 31 1579) were conducted to investigate the propagation of actively fed signals driven by electrical probes. The perspective of these investigations is an improved understanding of the turbulence and potentially a method to tailor the edge plasma turbulence. Two moveable poloidal probe arrays were used for the experiments, one located on the inboard side of the vessel and the other on the outboard side. A subset of probe tips was used for actively driving the plasma by different control signals, the remaining probes collected fluctuation data in the plasma boundary. With this set-up it was possible to investigate the signal propagation in the poloidal direction and also parallel to the magnetic field. Poloidally, we find a significant cross-correlation between active and passive probes. From analysis of the cross-coherency and phases of the signal with passive probe tips, a dominant influence of the background plasma rotation on the applied signals is observed. In the case of externally driven waves by several phase-locked active probes, the direction of the wave propagation with respect to the plasma rotation (co- or counter-rotating) is essential for an effective coupling to the turbulence. Also, the signal propagation parallel to the magnetic field depends on co- or counter-rotation with respect to the background plasma rotation. The parallel phase velocity was found to be compatible with the electron thermal velocity.

Edge-localized modes (ELMs) have been observed by diagnostic systems with high spatial and temporal resolution in the ASDEX and JET tokamaks. During the ELMs, substructures exist in the scrape-off layer (SOL) with sizes of 2?5?cm and lifetimes of the order of 20?50??s. Their poloidal?temporal evolution is directly observed, and the radial transport due to turbulent E ? B drift in these substructures is estimated. A comparison is made between 'normal' fluctuations between ELMs and these substructures in terms of poloidal size and velocity and related radial transport. The increased radial transport during ELMs is shown to be mainly due to these substructures. The observed fluctuation amplitudes and velocities of the substructures are found to be compatible with the model of radial transport by plasma 'blobs' and plasma potential gradients generated by the sheath boundary conditions. The transport due to turbulent radial E ? B flows is compared during and between ELMs, and the observation of ELM substructures in the main plasma SOL is put into context with the observation of substructures on the target plates.

Emissive electrostatic probes for the use in fusion experiments must be able to sustain significantly higher thermal loads than in low-temperature plasma experiments. Several types of probe design are discussed, the results from the use of such probes in the edge plasma of the Wendelstein 7-AS stellarator are presented and compared with the predictions of emissive and non-emissive probe models. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The magnetic configurations of the Wendelstein 7-X (W7-X) stellarator are sensitive to perturbations of the magnetic field resonant with ι`/2π = 1. Such perturbations can be caused by deviations of the current filament positions of the real coil system from the design due to the accuracy achievable during the manufacture of the coils and assembly of the magnet system. The sensitivity of the magnetic field to the different types of error has been investigated by introducing randomly distributed errors to the coil shapes and positions within the given tolerances. A statistical analysis of these error distributions was performed. This procedure will be used to assess the magnetic configuration of W7-X before the completion of each assembly step.

We present a method of beam emission spectroscopy (BES) using an atomic Li beam that is generated by means of laser blow-off for the investigation of electron density fluctuations in the edge and scrape-off layer plasmas of fusion devices. We discuss the operational limits of this technique and compare them to those of other atomic Li beam diagnostics. Furthermore, we apply this method to different Wendelstein 7-AS discharges and study the influence of the line integrated electron density and the direction of the main magnetic field on the fluctuations inside and outside the last closed flux surface, and especially on their movement. The information we obtain on the influence of the main magnetic field on the fluctuations gives some insight into the possible origin of certain features of their spatial structure.

Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper, measurements of short wavelength density fluctuations in the HDH-mode using collective scattering of infrared light are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode). The autopower spectra of the measurements show a consistent increase of the fluctuation level associated with the transition from NC-?to HDH-mode. Correlation calculations on a 20??s timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC-but not in HDH-mode. Finally, a comparative analysis between the enhanced D? H-mode (EDA H-mode) found in the Alcator C-Mod tokamak and the HDH-mode in W7-AS is carried out.

Stellarators have the intrinsic property of steady state operation. However, on present-day stellarators the pulse length is usually not only limited due to technical reasons, but also by physical problems. Lack of density control and a subsequent radiation collapse terminate the discharges quite often at high densities. To improve the control of the plasma-wall interaction, the island divertor concept was developed for optimized stellarators. To test this divertor concept on W7-AS, all limiters were removed and replaced by ten divertor modules. In subsequent divertor experiments a promising new plasma operational regime has been discovered which is termed 'high density H-mode' (HDH-mode). During the transition into that regime a clear reduction of ELM-like events and turbulent fluctuations is observed. The HDH-mode combines good energy confinement with very low impurity confinement resulting in low core radiation, but high edge-localized radiation. Consequently, stationary discharges at densities of typically 2 x 10 20 m -3 can be performed within the accessible pulse length of about 1 s. At densities above 3 x 10 20 m -3 a controlled transition from attached to partially detached plasmas is observed. The still edge-localized radiation reaches 90% of the heating power so that the power load onto the divertor target plates is further reduced. At a lower toroidal field of 0.9 T average β-values could be raised from earlier 2% to more than 3% in magnetic field configurations with rather smooth flux surfaces at the plasma boundary. The recently obtained results render excellent prospects for W7-X, the larger superconducting successor experiment of W7-AS.

In this paper measurements of short wavelength electron density fluctuations using collective scattering of infrared light are presented. The Wendelstein 7-AS (W7-AS) stellarator (Renner H et al 1989 Plasma Phys. Control. Fusion 31 1579) and the diagnostic are briefly described. A series of plasma discharges with reproducible confinement transitions was created by ramping up the plasma current. Utilizing the fact that the density fluctuation wavenumber κ is anisotropic in the directions parallel and perpendicular to the local magnetic field, the diagnostic can provide a radial profile of the turbulence during both normal and degraded confinement. The found profiles display an increase of core turbulence for the reduced confinement state. The results are discussed and compared to similar tokamak measurements.

At certain values of the edge rotational transform ιa, the confinement quality of plasmas in the Wendelstein 7-AS (W7-AS) stellarator is found to react very sensitively to small modifications of the edge rotational transform ιa. As ιa can be reproducibly changed either by external fields or by a small plasma current, these transitions offer a precise way to systematically analyse differences in plasma turbulence between bad and good confinement cases. This paper presents results of the study of electron density fluctuations associated with confinement changes. Wavenumber and frequency spectra and radial profiles are compared. A slow and reproducible transition is induced by a small plasma current and the sequence of events leading to bad confinement is investigated. The laser scattering core plasma density fluctuation measurements are complemented by edge beam emission spectroscopy results and magnetic fluctuation measurements with Mirnov coils. Clear correspondence between plasma fluctuations and confinement degradation is observed: the weight of larger structures increases, fluctuations increase in the plasma core, the poloidal flow velocity decreases and regions of mode-like activity move radially in the plasma. These changes occur gradually and controllably if the magnetic configuration is steered by a small plasma current.

In this article measurements of small scale electron density fluctuations in dithering high confinement~H!-mode plasmas obtained by collective scattering of infrared light are presented. A scan of the fluctuation wavenumber was made in a series of similar discharges in the Wendelstein 7-AS ~W7-AS! stellarator @H. Renner et al., Plasma Phys. Control. Fusion 31, 1579 ~1989!#. The experimental setup and discharge properties are described. Ha-light observing an inner limiter was used to separate low confinement ~L!- and H-mode phases of the plasma; the separated density fluctuations are characterized. It was found that L- ~H-! mode fluctuations dominate at high ~low! frequencies, respectively, and that they possess well-defined and distinguishable scaling properties. Wavenumber spectra for L- and H-mode measurements are calculated and fitted by power-laws and exponential functions. The separated measurements can be fitted with the same exponents in L- and H-mode. Correlations between the density fluctuations, the H a-signal and magnetic fluctuations as measured by Mirnov coils were analyzed. Correlation calculations using 50 ms time windows ~several dithering periods! with time lag steps of 100 ms showed that all the fluctuating quantities are highly correlated and that the maximum correlation occurs for high frequency density fluctuations. Performing separate L- and H-mode correlations on a 20 ms time scale between magnetic and density fluctuations leads to the result that the minimum correlation time scale in L-mode is of order 100 ms, while no correlation exists for H-mode. © 2002 American Institute of Physics. @DOI: 10.1063/1.1481747#

In the scrape-off layer of the Joint European Torus [P.-H. Rebut, R. J. Bickerton, and B. E. Keen, Nucl. Fusion 25, 1011 (1985)], Langmuir probes were used to measure the correlation of ion saturation current fluctuations parallel to the magnetic-field B. It was possible to realize three different probe tip separations (connection lengths) ∥B under almost identical plasma conditions and magnetic configuration. Among these, a probe tip separation of 66 m ∥B represents the largest value ever realized for this type of experiment. It was found that the correlation is reduced from ⩾80% at 0.75 m probe tip separation ∥B in the divertor to ≈40% at 23 m, but remains at ≈40% even for the 66 m separation. An upper limit for the ratio between the average wave numbers parallel and perpendicular to the magnetic field |k∥/k⊥

An overview of the diagnostics which are essential for the first operational phase of Wendelstein 7-X and the set of diagnostics expected to be ready for operation at this time are presented. The ongoing investigations of how to cope with high levels of stray Electron Cyclotron Resonance Heating (ECRH) radiation in the ultraviolet (UV)/visible/infrared (IR) optical diagnostics are described.

Floating potential and ion saturation current fluctuations in the scrape-off layer of the Wendelstein 7-AS stellarator are investigated by using conditional averaging. If floating potential fluctuations are taken as the reference signal for the conditional averaging procedure, large-scale single-vortex structures are predominately found. If ion saturation current fluctuations are taken as the reference signal, double-vortex structures are detected. The phase shift between the two different structures is π/2. The double-vortices are interpreted as a superposition of counter rotating single-vortex potential structures. Both lead to ion saturation current fluctuations of the same sign due to E×B convection of plasma in parallel to the background plasma pressure gradient. The conditional averaging approach is directly compared to cross-correlation analysis. Both methods lead to similar physical conclusions. Lifetime and extent of structures are systematically overestimated by correlation analysis. It is demonstrated that only fluctuations with amplitudes larger than 0.5σ contribute to the detected large-scale structures.

The plasma turbulence in the boundary of fusion relevant experiments is known to have a quasi two-dimensional nature: the scale lengths perpendicular to the magnetic field are in the order of mm to cm, but parallel to the magnetic field, the correlation lengths are in the order of several meters. Recent parallel correlation studies with Langmuir probes at the JET tokamak over very long connection lengths (23 m and 66 m probe tip separation along the magnetic field) showed a correlation of less than 50 %, in contrast to the finding of 80-90 % correlation in other devices at measurements with smaller probe tip separations. However, it was not clear if this is a genuine physical property of the electrostatic turbulence in the scrape-off layer or whether perturbations in the magnetic configuration had caused an additional decorrelation by a time-dependent misalignment of the two probe tips along the connecting field line. In this contribution we analyze the effect of such perturbations in the magnetic configuration on the parallel correlation measurements in a simple model and compare the results with those of the measurements at JET.

We describe and demonstrate a two-volume collective scattering system for localized measurements of plasma turbulence. The finite crossfield correlation length of plasma turbulence combined with spatial variations in the magnetic field direction are used to obtain spatially localized turbulence measurements at the Wendelstein 7-AS fusion experiment. By comparing with localized measurements obtained using the single wide beam technique [Truc , Rev. Sci. Instrum. 63, 3716 (1992)] we provide a proof-of-principle demonstration of the two-beam method. An optimized configuration with large toroidal separation of the measurement volumes is predicted to be capable of providing spatial resolution better than 5 cm. (C) 2001 American Institute of Physics.

Reciprocating Langmuir probe measurements were obtained in dedicated JET experiments to investigate turbulent transport at the edge and SOL plasmas. The measured turbulent radial particle flux, radial velocity and diffusion coefficient were compared with results from the 2-D plasma edge code B2-EIRENE. Qualitatively, the experimental results and the modelling calculations show a similar behaviour, with the radial particle flux increasing from inside the separatrix to some point in the SOL and then decreasing again. However, there is a quantitative disagreement between code calculations and measurements in X-point plasmas. Two explanations have been proposed to reconcile these observations: first temperature fluctuations, with the appropriate phase could modify the derived particle turbulent flux. Second, code simulations including the effect of drifts at the plasma edge show that large convective cells appear in this region, leading to large parallel flows in the SOL, which have been measured. Such drifts could lead to a net inwards particle pinch which could compensate for the measured large turbulent out flux.

The fluctuations in the edge plasmas of magnetic fusion experiments are thought to play an important role in terms of anomalous energy and particle transport. Experiments on Wendelstein 7-AS were conducted with the primary goal to investigate the performance of influencing and modifying the turbulence in the plasma boundary using electrical probes. Two movable poloidal probe arrays were used for the experiments, one located on the inboard side of the vessel and the other on the outboard side. A subset of probe tips was used for actively driving the plasma by different control signals, the remaining probes collected fluctuation data in the plasma boundary. Poloidally, we find a significant cross-correlation between active and passive probes. From analysis of the coherency and phases of the passive probe tips, it can clearly be seen that the background E×B-rotation of the plasma plays a crucial role for the applied signals. In the case of externally driven waves by several phase-locked active probes, the direction of the wave propagation with respect to the plasma rotation (co- or counter-rotating) is essential for a proper coupling to the turbulence. In toroidal direction we find that the propagation of the signals along the magnetic field lines depends on co- or counter-rotation with respect to the background plasma rotation.

Plasma edge fluctuations show a degree of intermittency similar to fluid turbulence. Using fluctuation measurements obtained with Langmuir probe data from two confinement devices, it is shown that plasma fluctuations have a multifractal character over the fluctuation range of scales with intermittency levels comparable to the levels measured in neutral fluid turbulence. In the mesoscale range, that is, for time scales between 10 times the turbulence decorrelation time and plasma confinement time, plasma fluctuations have a structure closer to a monofractal with very low intermittency.

Electrostatic turbulence has been investigated in the plasma boundary region of the JET tokamak. The normalized fluctuation levels are in the range of 10-20% at the plasma radius where the poloidal velocity of the fluctuation reverses sign. In limiter plasmas, the E × B turbulent transport can account for a significant part of the total particle and energy losses. Three regions in the power spectra of the fluctuations with different frequency dependences have been found. The spectral region with power decay close to 1/f has been identified in the frequency range where the turbulent flux, which comes in bursts, is dominant. This result could be an indication of transport close to instability thresholds.

Frequency spectra of fluctuations for the ion saturation current, floating potential, and turbulent transport measured in the plasma edge of plasma confinement experiments (tokamaks and stellarators) have been analyzed to identify the frequency ranges characterized by a power dependence. Three main regions can be identified. For the intermediate frequency region, the decay of the spectra is close to 1/f, as is expected in self-organized criticality systems. This region is particularly important for the role that it plays in plasma transport and the self-similarity of the fluctuations and fluxes. The effect of plasma rotation on the decay indices has also been studied.

The `anomalous' radial transport in the plasma edge is generally thought to be largely due to correlated fluctuations of plasma density, temperature and potential. Experimental results show that fluctuations of these quantities are highly correlated, in phase and of constant amplitude parallel to the magnetic field. The resulting transport is often described by diffusive terms, using anomalous transport coefficients. The objective of this paper is to show that, in keeping with the high correlation and constant amplitude of the fluctuations along the magnetic field, the transport coefficients should scale as the square of the flux expansion (i.e. the separation between magnetic flux surfaces) along a magnetic flux tube in order to describe the fluctuation-induced transport correctly.

The fluctuation of electron density in the scrape-off layer (SOL) and edge plasma regions of the Wendelstein 7-AS stellarator [H. Renner et al., Plasma Phys Controlled Fusion 31, 1579 (1989)] is investigated by the beam emission spectroscopy technique, observing fluctuations in the Li(2p) line emission intensity of a 50 keV accelerated Li beam. A recently developed numerical technique enables correct reconstruction of correlation functions (and as a consequence, fluctuation amplitudes as well) of the electron density fluctuations from correlations of beam light fluctuations. Depending on the plasma electron density, the radial range of the measurement is either limited to r/a>0.9 (at the highest densities) or can extend to about r/a>0.3 at the lowest densities. As the technique is nonperturbing to the plasma, several hundred shots were analyzed and a catalog of the observed phenomena was established. The results always show a change in the properties of the fluctuations at approximately the last closed flux surface. This observation might indicate differences in the turbulence drive in the SOL and the edge plasma. However, one cannot exclude that the same turbulence phenomenon results in different density fluctuations in the two regions due to the different magnetic topologies. The relevance of the observed phenomena to anomalous transport is discussed.

From the Langmuir probe measurements in low-power Ohmically heated or electron cyclotron heated plasma discharges and for several types of confinement devices, we have concluded that the electrostatic potential and density fluctuations at the plasma edge are self-similar over a broad range of time scales [1,2]. The selfsimilarity range is, in general, for time scales longer than the turbulence decorrelation times up to times of the order of confinement time, the mesoscale range. The upper bound of the self-similarity range is difficult to determine because of the lengths of time records available and the varying plasma conditions on these longer time scales. It was found that for fluctuation measurements within the plasma confinement region the self-similarity parameter [3] varies between H 0.62 and H 0.75, a relatively small range of variation given the diversity of plasma confinement devices considered. To find out whether these properties of the plasma fluctuations have any bearing on the dynamics of plasma transport, we must investigate the properties of their induced fluxes. The relative phase between density and potential fluctuations could be such that the induced particle flux does not share the self-similarity properties. The problem with studying fluxes is the scarcity of experimental measurements. Flux measurements for core plasmas are practically nonexistent. At the plasma edge, the turbulence-induced particle flux can be inferred from the simultaneous measurement of the density and potential fluctuations. By measuring the density fluctuations at one point in the plasma, ˜ n1 ˜

Frequency spectra of fluctuations of the ion saturation current, floating potential, and turbulent transport measured in the plasma edge of different fusion devices (tokamaks and stellarators) have been compared. All of the spectra show the same behavior over the whole frequency range investigated, which supports universality of plasma turbulence or turbulent transport. The results obtained are an indication of edge-plasma turbulence evolving into a critical state, independent of the size and plasma characteristics of the device.

Spatially highly resolved Langmuir probe measurements of ion saturation current and floating potential fluctuations in the scrape-off layer (SOL) and edge of several tokamaks and stellarators have revealed the spatial structure of these fluctuations. The knowledge of the phase angle and coherency between the fluctuations of these quantities is important for a comparison with models and for the calculation of the induced radial transport. The fluctuations occur as individual events, causing burst-like E×B flows which are very localised in poloidal position and in time and interchange plasma of different density and temperature radially. The resulting particle transport can account for the confinement time inferred from particle balance considerations and from the observed gradients in the SOL. The role of fluctuations of the electron temperature and our understanding of the instability mechanism acting in the plasma edge is summarised. A brief account is given on the changes of the fluctuations and the resulting transport when discharge parameters are varied.

At W7-AS, confinement properties are analysed and compared mainly with neoclassical predictions for quite different conditions. Low-density electron cyclotron resonance heating (ECRH) discharges allow access to the very-long-mean-free-path regime for electrons (T e up to 6 keV) whereas pure neutral beam injections (NBI) and combined NBI/ECRH discharges at high density (T i T e ≥ I keV at n e 10 20 m -3 ) lead to high performance (τ E up to 50 ms). Depending on the achieved temperatures, the experimental transport analysis in the plasma core is consistent with the neoclassical predictions. The experimentally observed 'electron root' feature with strong E r > 0 is driven by the convective flux of ripple-trapped suprathermal electrons generated by the ECRH absorption. 'Optimum' confinement is obtained in discharges with narrow density, but broad temperature profiles with steep gradients in the region of low densities and strong E r < 0 close to the plasma edge. The large radial electric fields, both positive and negative, strongly reduce neoclassical transport. The achieved temperatures, however, are limited by the strong temperature dependence of the neoclassical transport.

Analysis of the edge plasma fluctuation in several confinement devices reveals the self-similar character of the fluctuations through the presence of long-range time correlations. These results show that the tail of the autocorrelation function decays as a power law for time lags longer than the decorrelation time and as long as times on the order of the particle diffusion time. The algebraic decay of the longrange time correlations is consistent with plasma transport characterized by self-organized criticality. [S0031-9007(98)06077-3]

This paper presents an overview of the advance in probe design and measurements made at JET during the MkIIa divertor experimental campaign. In addition to the fixed probe system, new probes have been implemented specifically to investigate the effect of plasma resistivity on probe derived electron temperatures and to measure turbulence in the SOL.

To measure fluctuations of plasma density, electron temperature and electric plasma potential in the edge of fusion experiments simultaneously and with high spatial resolution, the best approach is generally agreed to be the fast sweeping of the Langmuir probe characteristic, a technique which has been applied on several experiments in the past few years. “Fast” in this context means that the sweep frequency should be well above typical fluctuation frequencies which are known to range up to a few 100 kHz. A new experimental arrangement for such measurements has been used on the Wendelstein 7-AS stellarator, making use of amplifiers in the reciprocating probe head, only few cm from the probe tips. It is thus possible to sweep the probes in the MHz range and to obtain good quality probe characteristics without having to correct for cable resonances and capacitance. Four poloidally displaced probe tips were swept with 1–4 MHz and the voltage and current signals were recorded with a sampling frequency of 50–200 MHz. Ion saturation current and floating potential fluctuations obtained from the swept signals are compared with static measurements of these two quantities measured simultaneously by further tips on the same probe head. If we use “standard” probe theory to analyse these measurements, the temperature fluctuations contribute significantly when calculating the plasma potential from the floating potential. In standard probe theory some basic assumptions are made, e.g., on the ratio of electron to ion temperature or the secondary electron emission coefficient of the probe tips. The influence of changes in these assumptions on the calculated phase angle between density, electron temperature and electric potential fluctuations and on the resulting radial particle and thermal transport is discussed. The fluctuation-induced radial particle transport is compared with the value obtained from ion saturation current and floating potential neglecting temperature fluctuations.

All major JET systems have been fully commissioned for D-T and the DTE1 series of experiments has started with the D-T fuel mixture and operating conditions foreseen for ITER. In the area of ITER physics, significant results have been produced in both D-D and D-T. In D-D, the LH threshold power database has been extended, the bounds on edge-electron temperature and density in ELMy H-modes have been defined and the advantages of Types I and III ELMy discharges have been compared. In D-T plasmas, the isotope effect on H-mode threshold power and transport has been determined so that a more accurate assessment can be made of the ignition margin and heating requirements for ITER. Trace tritium experiments have provided first particle transport measurements and an assessment of the ITER reference ion-cyclotron resonance-frequency heating scenarios has been started, In the area of fusion performance, record D-D neutron yields have been obtained by controlling the plasma and current profiles in hot ion ELM-free H-modes and optimized shear modes. In D-T, internal transport barriers have been readily established in optimized shear discharges and Alfven eigenmodes have been observed.

The Wendelstein 7-X experiment is a concept test for properties of reactor relevant plasmas in advanced stellarators. Prominent features include a modular superconducting coil assembly, a fivefold toroidal symmetry, and a helical magnetic axis. Due to the optimization process, W7-X is characterized by a vacuum magnetic field configuration with smooth magnetic surfaces, improved equilibrium properties with a weak dependence of rotational transform and shear on the plasma pressure β, good magneto-hydrodynamic stability properties due to magnetic well stabilization, reduced neoclassical transport losses and negligible bootstrap current in the long mean-free-path regime, good collisionless α-particle confinement in an equivalent reactor, and, as a technical aspect, good feasibility of the superconducting modular coils. W7-X will be heated by continuous electron cyclotron resonance heating and pulsed neutral beam injection and ion cyclotron resonance heating. The envisaged parameters are Te⩽10 keV, Ti⩽6 keV ce...