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We demonstrate the successful preparation of ordered C60 films on Co/Au(111) by scanning tunneling microscopy (STM). In particular, we show that the C60 molecules arrange in a close-packed hexagonal pattern after postdeposition annealing at T = 350 °C. From STM measurements with intramolecular resolution we find domains with different orientational ordering, that is ultimately a result of the lateral arrangement of the C60 molecules on the Co surface. The local ordering of the various domains is also clearly reflected in the measured differential conductance spectra. In particular, we find an energetic shift of the LUMO + 1 due to the reconstruction of the cobalt substrate. Our study opens the way for the introduction of ordered “spinterfaces” in molecular spintronics.

Recently, research has revealed that molecules can be used to steer the local spin properties of ferromagnetic surfaces. One possibility to manipulate ferromagnetic-metal–molecule interfaces in a controlled way is to synthesize specific, non-magnetic molecules to obtain a desired interaction with the ferromagnetic substrate. Here, we have synthesized derivatives of the well-known semiconductor Alq3 (with q = 8-hydroxyquinolinate), in which the 8-hydroxyquinolinate ligands are partially or completely replaced by similar ligands bearing O- or N-donor sets. The goal of this study was to investigate how the presence of (i) different donor atom sets and (ii) aromaticity in different conjugated π-systems influences the spin properties of the metal–molecule interface formed with a Co(100) surface. The spin-dependent metal–molecule-interface properties have been measured by spin-resolved photoemission spectroscopy, backed up by DFT calculations. Overall, our results show that, in the case of the Co–molecule interface, chemical synthesis of organic ligands leads to specific electronic properties of the interface, such as exciton formation or highly spin-polarized interface states. We find that these properties are even additive, i.e. they can be engineered into one single molecular system that incorporates all the relevant ligands.

We present a rational design approach to customize the spin texture of surface states of a topological insulator. This approach relies on the extreme multifunctionality of organic molecules that are used to functionalize the surface of the prototypical topological insulator (TI) Bi2Se3. For the rational design we use theoretical calculations to guide the choice and chemical synthesis of appropriate molecules that customize the spin texture of Bi2Se3. The theoretical predictions are then verified in angular-resolved photoemission experiments. We show that, by tuning the strength of molecule-TI interaction, the surface of the TI can be passivated, the Dirac point can energetically be shifted at will, and Rashba-split quantum-well interface states can be created. These tailored interface properties-passivation, spin-texture tuning, and creation of hybrid interface states-lay a solid foundation for interface-assisted molecular spintronics in spin-textured materials.

The first hundred attoseconds of the electron dynamics during strong field tunneling ionization are investigated. We quantify theoretically how the electron's classical trajectories in the continuum emerge from the tunneling process and test the results with those achieved in parallel from attoclock measurements. An especially high sensitivity on the tunneling barrier is accomplished here by comparing the momentum distributions of two atomic species of slightly deviating atomic potentials (argon and krypton) being ionized under absolutely identical conditions with near-infrared laser pulses (1300 nm). The agreement between experiment and theory provides clear evidence for a nonzero tunneling time delay and a nonvanishing longitudinal momentum of the electron at the ``tunnel exit.''

Channel-selective electron emission from strong-field photoionization of ${\mathrm{H}}_{2}$ molecules is experimentally investigated by using ultrashort laser pulses and a reaction microscope. The electron momenta and energy spectra in coincidence with bound and dissociative ionization channels are compared. Surprisingly, we observed an enhancement of the photoelectron yield in the low-energy region for the bound ionization channel. By further investigation of asymmetrical electron emission using two-color laser pulses, this enhancement is understood as the population of the autoionizing states of ${\mathrm{H}}_{2}$ molecules in which vibrational energy is transferred to electronic energy. This general mechanism provides access to the vibrational-state distribution of molecular ions produced in a strong-field interaction.

In the Wendelstein 7-X stellarator with its twisted magnetic geometry the investigation of plasma wall interaction processes in 3D plasma configurations is an important research subject. For the upcoming operation phase i.e. OP1.2, three different types of material probes have been installed within the plasma vessel for the erosion/deposition investigations in selected areas with largely different expected heat load levels, namely, ≤10 MW m−2 at the test divertor units (TDU), ≤500 kW m−2 at the baffles, heat shields and toroidal closures and ≤100 kW m−2 at the stainless steel wall panels. These include 18 exchangeable target elements at TDU, about 30 000 screw heads at graphite tiles and 44 wafer probes on wall panels, coated with marker layers. The layer thicknesses, surface morphologies and the impurity contents were pre-characterized by different techniques and subjected to various qualification tests. The positions of these probes were fixed based on the strike line locations on the divertor predicted by field line diffusion and EMC3/EIRENE modeling calculations for the OP1.2 plasma configurations and availability of locations on panels in direct view of the plasma. After the first half of the operation phase i.e. OP1.2a the probes will be removed to determine the erosion/deposition pattern by post-mortem analysis and replaced by a new set for the second half of the operation phase, OP1.2b.

Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase {\phi} of the time-dependent dipole-response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also prove the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism amplifies resonantly interacting extreme-ultraviolet light by quantum-phase control. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with scientific applications in many branches of spectroscopy., Comment: 11 pages, 4 figures

Understanding the origin of spin filtering in metal/organic interfaces is important for the control of spin injection in organic semiconductors. A time-resolved photoemission experiment shows that spin filtering can be explained by the trapping of electrons in spin-dependent potentials at the interface.

Channel-selective electron emission from strong-field photoionization of H_{2} molecules is experimentally investigated by using ultrashort laser pulses and a reaction microscope. The electron momenta and energy spectra in coincidence with bound and dissociative ionization channels are compared. Surprisingly, we observed an enhancement of the photoelectron yield in the low-energy region for the bound ionization channel. By further investigation of asymmetrical electron emission using two-color laser pulses, this enhancement is understood as the population of the autoionizing states of H_{2} molecules in which vibrational energy is transferred to electronic energy. This general mechanism provides access to the vibrational-state distribution of molecular ions produced in a strong-field interaction.

Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron., 31 pages, 15 figures including appendix

Recently, research has revealed that molecules can be used to steer the local spin properties of ferromagnetic surfaces. One possibility to manipulate ferromagnetic-metal-molecule interfaces in a controlled way is to synthesize specific, non-magnetic molecules to obtain a desired interaction with the ferromagnetic substrate. Here, we have synthesized derivatives of the well-known semiconductor Alq

Wendelstein 7-X, a superconducting optimized stellarator built in Greifswald/Germany, started its first plasmas with the last closed flux surface (LCFS) defined by 5 uncooled graphite limiters in December 2015. At the end of the 10 weeks long experimental campaign (OP1.1) more than 20 independent diagnostic systems were in operation, allowing detailed studies of many interesting plasma phenomena. For example, fast neutral gas manometers supported by video cameras (including one fast-frame camera with frame rates of tens of kHz) as well as visible cameras with different interference filters, with field of views covering all ten half-modules of the stellarator, discovered a MARFE-like radiation zone on the inboard side of machine module 4. This structure is presumably triggered by an inadvertent plasma-wall interaction in module 4 resulting in a high impurity influx that terminates some discharges by radiation cooling. The main plasma parameters achieved in OP1.1 exceeded predicted values in discharges of a length reaching 6 s. Although OP1.1 is characterized by short pulses, many of the diagnostics are already designed for quasi-steady state operation of 30 min discharges heated at 10 MW of ECRH. An overview of diagnostic performance for OP1.1 is given, including some highlights from the physics campaigns.

We introduce and demonstrate an in situ method for characterizing intense few-cycle laser pulses with transient absorption spectroscopy. Thereby, we obtain crucial pulse properties precisely where the physics of ultrafast quantum dynamics experiments takes place.

In-vessel inspections of AUG reveal arc tracks at different locations. This paper presents investigation of arcing at the inner transition and retention module where arc tracks were found around the whole toroidal circumference. A representative tile was investigated with profilometry, SEM, EDX, RBS, and colourimetry. Type 2 arc tracks with an area fraction of 12% were found in a 10 mm wide region near to the leading edge. Here the tungsten coating (3–4 μm) is removed and a small amount of carbon (max. 1–2 μm) is eroded. Droplets are detected at the surface. The region of the inner divertor where the arcs are observed shows a local enhancement of plasma density, n e ≈ 10 20 m −3 , and neutral pressure, 0.1 mbar, favouring the arc ignition. A high sheath potential at the beginning of an ELM might trigger the arc. The arc pattern and the target load as measured with a fast IR-camera coincide. 2 g of tungsten are eroded in the inner divertor. If 10% of the material is eroded as droplets, 10 8 droplets (5 μm diameter) are ejected.

The filamentary structure in the SOL of ASDEX Upgrade during type-I ELMs was investigated by combined measurements of reciprocating Mach probe, filament probe – a combination of Langmuir probes and magnetic sensor for the radial component of the magnetic field, and IR-thermography of the reciprocating probe head. A correlation along field lines between the Langmuir probes was found, confirming the field aligned structure of the observed filaments. The ELM radial e-folding lengths of particle and heat flux are comparable (about 2 cm). This may be explained by an approximately constant ion temperature well above the electron temperature in the far SOL. The ion temperature estimated from the comparison of heat and particle flux is about 30–60 eV.

Wendelstein 7-X (W7-X) is a large optimized stellarator (B=2.5T, V=30m3) aiming at demonstrating the reactor relevance of the optimized stellarators. In 2015 W7-X will begin its first operation phase (OP1.1) with five inertially cooled inboard limiters made of graphite. Assuming the heat loads can be spread out evenly between the limiters, 1 second discharges at 2 MW of ECRH heating power could be run in OP1.1. The expected plasma parameters will be sufficient to demonstrate the readiness of the installed diagnostics and even to run a first physics program. The diagnostics available for this first operation phase, including some special limiter diagnostics, and their capabilities are being presented. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

The Fano phase formalism enables measurement and control of phase and amplitude of an emitting dipole. Here, we use this formalism to measure and understand the dynamics of bound states in strong laser fields.

Significant progress has been made on ASDEX Upgrade during the last two years in the basic understanding of transport, in the extension of the improved H-mode in parameter space and towards an integrated operating scenario and in the development of control methods for major performance limiting instabilities. The important features were the understanding of particle transport and the control of impurity accumulation based on it, the satisfactory operation with predominantly tungsten-clad walls, the improved H-mode operation over density ranges and for temperature ratios covering (non-simultaneously) the ITER requirements on ν*, n/nGW and Te/Ti, the ELM frequency control by pellet injection and the optimization of NTM suppression by DC-ECCD through variation of the launching angle. From these experiments an integrated scenario has emerged which extrapolates to a 50% improvement in n T τ or a 30% reduction of the required current when compared with the ITER base-line assumptions, with moderately peaked electron and controllable high-Z density profiles.

Large molybdenum mirrors have been exposed in the SOL of TEXTOR in order to simulate conditions relevant for ITER optical components. Distortions of the reflectivity - increase as well as decrease - are found in the erosion and deposition dominated areas, respectively. The changes are most pronounced in the near UV and level off in the IR and can partly be attributed to observed surface changes. A novel periscope system was installed and mirrors exposed in a pilot experiment to simulate the transmission of light to distant sensors in ITER.

Numerous traces of arcs have been found on W-covered graphite tiles of ASDEX Upgrade after exposure. The distributions of number density, lengths and orientation are calculated and compared to pure graphite tiles at comparable locations. It was established that arcs perforate a 1 μm tungsten layer down to the carbon substrate. The amount of removal should rise with arc current, but a surface fraction of about 8% is eroded at 10 A already. At tiles of the divertor baffle the layer is continuously removed along the entire track pointing to higher currents. The carbon of the stripped parts is subject to subsequent erosion processes. The distribution of materials in and around arc tracks was investigated by sputter depth profiling (SIMS and AES) and the characteristic geometry was studied using an electron microscope. Observations are interpreted using results from laboratory vacuum arcs on the same material.

Plasma sprayed B4C-layers considered as wall coatings for the W7X stellarator have been studied during and after exposure to TEXTOR and after arcing experiments in vacuum. Arcing through the B4C layer occurred favoured by high power fluxes and not restricted to less stable phases. But this arcing implies an especially noisy scrape-off layer (SOL). Instead of moving retrograde in the external magnetic field, the arc spot on the B4C-layer sticks to the same location for its whole lifetime. Consequently, the arc erodes the entire B4C layer, finally burning down to the Cu substrate. In the neighbourhood of craters the surface contains Cu originating from those craters. This material, hauled to the surface by the arc, is subject to subsequent erosion, transport, and redeposition by the SOL-plasma. The behaviour of arcs on B4C is most probably caused by the peculiar temperature dependences of the electrical and heat conductivity of B4C. 2003 Elsevier Science B.V. All rights reserved.

Analysis of Type I ELMs from present experiments shows that ELM energy losses decrease with increasing pedestal plasma collisionality ( ν ∗ ped ) and/or increasing τ Front ∥ , where ( τ ∥ Front =2π Rq 95 / c s ,ped ) is the typical ion transport time from the pedestal to the divertor target. ν ∗ ped and τ Front ∥ are not the only parameters that affect the ELMs, also the edge magnetic shear influences the plasma volume affected by the ELMs. ELM particle losses are influenced by this ELM affected volume and are weakly dependent on other pedestal plasma parameters. ‘Minimum’ Type I ELMs, with energy losses acceptable for ITER, where there is no change in the plasma temperature profile during the ELM, are observed for some conditions in JET and DIII-D. The duration of the divertor ELM power pulse is well correlated with τ Front ∥ and not with the duration of the ELM-associated MHD activity. Similarly, the time scale of ELM particle fluxes is also determined by τ Front ∥ . The extrapolation of present experimental results to ITER is summarised.

The concerted motion of two or more bound electrons governs atomic1 and molecular2,3 non-equilibrium processes including chemical reactions, and hence there is much interest in developing a detailed understanding of such electron dynamics in the quantum regime. However, there is no exact solution for the quantumthree-body problem, and as a result even the minimal system of two active electrons and a nucleus is analytically intractable4. This makes experimental measurements of the dynamics of two bound and correlated electrons, as found in the helium atom, an attractive prospect.However, although the motion of single active electrons and holes has been observed with attosecond time resolution5-7, comparable experiments on two-electron motion have so far remained out of reach. Here we showthat a correlated two-electron wave packet can be reconstructed froma 1.2-femtosecondquantumbeatamong low-lying doubly excited states in helium.The beat appears in attosecond transient-absorption spectra5,7-9 measured with unprecedentedly high spectral resolution and in the presence of an intensity-tunable visible laser field.Wetune the coupling10-12 between the two low-lying quantum states by adjusting the visible laser intensity, and use the Fano resonance as a phase-sensitive quantum interferometer13 to achieve coherent control of the two correlated electrons. Given the excellent agreement with large-scalequantum-mechanical calculations for thehelium atom, we anticipate thatmultidimensional spectroscopy experiments of the type we report here will provide benchmark data for testing fundamental few-body quantumdynamics theory in more complex systems. Theymight also provide a route to the site-specificmeasurement and control of metastable electronic transition states that are at the heart of fundamental chemical reactions, We thank E. Lindroth for calculating the dipole moment (2p2|r|sp2,3+), and also A. Voitkiv, Z.-H. Loh, and R. Moshammer for helpful discussions. We acknowledge financial support by the Max-Planck Research Group Program of the Max-Planck Gesellschaft (MPG) and the European COST Action CM1204 XLIC. L. A. and F. M. acknowledge computer time from the CCC-UAM and Mare Nostrum supercomputer centers and financial support by the European Research Council under the ERC Advanced Grant no. 290853 XCHEM, the Ministerio de Economía y Competitividad projects FIS2010-15127, FIS2013-42002-R and ERA-Chemistry PIM2010EEC-00751, and the European grant MC-ITN CORINF

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.

Fano line shapes observed in absorption spectra encode information on the amplitude and phase of the optical dipole response. A change in the Fano line shape, e.g., by interaction with short-pulsed laser fields, allows us to extract dynamical modifications of the amplitude and phase of the coupled excited quantum states. We introduce and apply this physical mechanism to near-resonantly coupled doubly excited states in helium. This general approach provides a physical understanding of the laser-induced spectral shift of absorption-line maxima on a sub-laser-cycle time scale as they are ubiquitously observed in attosecond transient-absorption measurements.

One of the key unresolved issues in the design of a future fusion reactor is the power handling capability of the divertor target plates. Earlier we reported on the existence of narrow power deposition profiles in JET, obtained mainly from Langmuir probe measurements. We repeated these measurements in the MkI, MkII and MkIIGB divertor configurations with an upgraded probe system, which allowed us to study the profile shape in more detail. The main results of this study are: In NB heated discharges the electron temperature and power flux at the outer target show a distinct peak of ∼5 mm half-width near the separatrix strike point. The corresponding profiles on the inner target do not show a similar feature. The height of the narrow peak increases with NB heating power and decreases with deuterium and impurity gas puffing. Ion orbit losses are suggested as a possible explanation of the observed profile shape.

We found a complete extinction of the CD molecule emission in the inboard divertor of ASDEX Upgrade at high density with the transition to a recombining divertor plasma. The electron temperature in the recombining divertor plasma ranges from 1.2 down to 0.3 eV. Two effects may explain the extinction at such low temperatures, (1) a steep decay of the yield for chemical sputtering as theoretically predicted and (2) a suppression of the optical emission while the methane molecules dissociate unchanged via charge exchange.

Sound waves have been detected from an electrode acting as the cathode in a vacuum discharge. Results from arcing on carbon fibre reinforced carbon (CFC) and stainless steel (SST) an reported. Distinct frequencies could be reproducibly detected in the power spectrum belonging to different groups. Most of the modes show a strong damping demonstrating that the nonlinear disturbance associated with the breakdown excites a wide spectrum. Very few frequencies are present during the arc but no obvious dependence of their power on the arc current was found. To identify eigen-oscillations of the plate some experiments have been repeated using an electrode with reduced thickness. For comparison with a different material additional experiments on stainless steel have been carried out.

Relaxation oscillations found in the divertor of the ASDEX Upgrade tokamak by means of spectroscopy and probe diagnostics are reported. They are observed in both electron density and temperature with frequencies in the range from 45 to 80 Hz. In the line emission they are detected in C III, but not in Dalpha light. Interpretation of the experimental data indicates that the relaxation oscillations are associated with periodic movements of the thermal front and the power loss zone against each other

In this paper we describe impurity line emission measurements in the divertor of ASDEX Upgrade during high power neutral beam heated discharges. We focus on detached conditions where the dominating part of the radiation comes from the X-point region. Spatially resolved line emission in the VUV and visible spectral region of the intrinsic carbon and additionally puffed impurities (neon and nitrogen) is presented. A simple interpretation of the line emission profiles is given and they are also compared to the results of bolometry.

In this paper we present first measurements of the plasma potential close to the separatrix in ASDEX Upgrade using a self emitting tip. The probe was inserted into the edge plasma of AUG using the midplane manipulator. Assuming Maxwellian plasmas, the observations agree with the predicted voltage drop in the plasma sheath, V pl ps − V fl = 2.5 T e , where V pl ps is the plasma potential at the presheath boundary and V fl the floating potential. Applying this technique a rapid change of the plasma potential was observed close to the separatrix during Ohmic discharges. From the gradient we derive a radial electric field E r of about −5 kV / m close to separatrix. Further out the field strength changes sign and we find up to +7 kV / m in the SOL.

We experimentally and numerically control high-harmonic generation (HHG) by time delaying variable segments of a few-cycle driving laser spectrum. In this configuration combs of fractional high harmonics can be produced by interference of two temporally spaced attosecond pulse trains. We explain the observed beating of the high-harmonic intensity with the time delay and study the influence of the spectral segmentation on the high harmonics. By the implementation of additional carrier-envelope phase (CEP) control, we extend the control configuration and demonstrate independent multi-parameter controllability of HHG purely enabled by the CEP and the time delay between two spectral segments. We present how specific properties of the fractional harmonics can be optimized. Analyzing the measured fractional harmonic combs by a spectral interferometry method, we find that the relative phase between the two contributing attosecond pulse trains can be freely set by the CEP of the driving laser field. We also discuss how, in the future, this method can be applied to simultaneously measure transient dispersion and absorption in the extreme ultraviolet spectral region.

A two-electron wave packet among the lowest-lying doubly-excited states in helium is experimentally observed. It creates a 1-femtosecond modulation in the transient-absorption signal modified by a time-delayed coupling laser.

Few-cycle laser fields enable pulse-shaping control of high-order harmonic generation by time delaying variable broadband spectral sections. We report the experimental generation of fractional (noninteger) high-harmonic combs by the controlled interference of two attosecond pulse trains. Additionally the energy of the high harmonics is strongly tuned with the relative time delay. We quantify the tuning to directly result from the controlled variation of the instantaneous laser frequency at the shaped driver pulse intensity maximum.

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.

We experimentally control high-order harmonic generation by applying a versatile few-cycle pulse-shape control method: splitting up a single broadband continuous laser spectrum into two sections and applying sub-femtosecond relative time delays. For certain time delays, fractional high-harmonic combs (noninteger harmonics) are generated which we find to result from the controlled interference of two attosecond pulse trains. We also observe time-delay-dependent energy-tunability of the high-order harmonics for an asymmetrically split spectrum consisting of a strong and a weak component. The tuning mechanism is quantitatively understood by the controlled modulation of the instantaneous driver frequency at the peak of the shaped laser pulse.

The critical issues in the development of diagnostics, which need to work robust and reliable under quasi-steady state conditions for the discharge durations of 30 min and which cannot be maintained throughout the one week duration of each operation phase of the Wendelstein 7-X stellarator, are being discussed.

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.

This addendum applies to papers authored by contributors from the Axially Symmetric Divertor Experiment (ASDEX) Upgrade Team published in Review of Scientific Instruments. This addendum provides the full list of ASDEX Upgrade Team contributors and their affiliations.

The stellarator Wendelstein 7-X will allow for quasicontinuous operation with the duration only being limited to two 30 min discharges per day, at a continuous heating power of 10 MW electron cyclotron resonance heating (ECRH) at 140 GHz, by the capacity of the cooling water reservoir. This will result in high thermal loads on all plasma facing components of 50-100 kW/m(2) from radiation alone and of up to about 500 kW/m(2) on components additionally exposed to convective loads. In high density scenarios toroidally varying ECRH stray radiation levels of 50-200 kW/m(2) need to be coped with, requiring careful material selection and different shielding and hardening techniques. Furthermore, a gradual buildup of coatings on plasma facing optical components, which without any measures being taken, would lead to high transmission losses already within a few days of long pulse operation (equivalent to about 1 year of operation in pulsed devices like JET or ASDEX-upgrade) and therefore needs to be prevented as much as possible. In addition in situ cleaning as well as absolute calibration techniques need to be developed for all plasma facing optical systems. Here we report about some of our efforts to find, for various types of diagnostics, ways to cope with these adverse effects. Moreover, we give a few examples for individual diagnostic specific issues with respect to quasicontinuous operation, such as the development of a special integrator for the magnetic diagnostics as well as special interferometer types which can cope with unavoidable vibrations and slow path length changes due to, e.g., thermal expansion of the plasma vessel.

ASDEX Upgrade has recently finished its transition towards an all-W divertor tokamak, by the exchange of the last remaining graphite tiles to W-coated ones. The plasma start-up was performed without prior boronization. It was found that the large He content in the plasma, resulting from DC glow discharges for conditioning, leads to a confinement reduction. After the change to D glow for inter-shot conditioning, the He content quickly dropped and, in parallel, the usual H-Mode confinement with H factors close to one was achieved. After the initial conditioning phase, oxygen concentrations similar to that in previous campaigns with boronizations could be achieved. Despite the removal of all macroscopic carbon sources, no strong change in C influxes and C content could be observed so far. The W concentrations are similar to the ones measured previously in discharges with old boronization and only partial coverage of the surfaces with W. Concomitantly it is found that although the W erosion flux in the divertor is larger than the W sources in the main chamber in most of the scenarios, it plays only a minor role for the W content in the main plasma. For large antenna distances and strong gas puffing, ICRH power coupling could be optimized to reduce the W influxes. This allowed a similar increase of stored energy as yielded with comparable beam power. However, a strong increase of radiated power and a loss of H-Mode was observed for conditions with high temperature edge plasma close to the antennas. The use of ECRH allowed keeping the central peaking of the W concentration low and even phases of improved H-modes have already been achieved.

We experimentally investigated the asymmetry of photo-ion and photoelectron momentum spectra of argon and nitrogen by ionizing an argon-nitrogen gas mixture in a strong two-color (400 nm + 800 nm) laser field. By changing the time delay between the 400 nm laser pulse and the 800 nm pulse, the fan-like stripes in low-energy electron momentum shift from negative momentum to positive for both argon and nitrogen. A clear difference of asymmetric electron emission between Ar and N2 is observed.

Dedicated experiments have been carried out in vacuum to study breakdown and arc burning on graphite cathodes covered by a thick (lμm) tungsten layer. The motivation originates from the usage of similar layers as first wall material in fusion devices where a large number of arcs appeared during plasma operation. Besides the standard measurements of current and voltage optical observations of the developing cathode spot and the retrograde motion in a transverse magnetic field on a short time scale have been carried out to determine the arc velocity reliably. Special attention was payed to non-reversible modifications of the layer by arcing. Electron microscopy (SEM) has been applied to specify the geometric structure of the tracks together with the distribution of elements. Main result is the observation that a lμm tungsten layer is permanently perforated by passing of an arc exposing carbon from the underlying graphite to all subsequent erosion processes. The effect depends nonlinearly on the arc current and is used to estimate qualitatively arc currents from remnant tracks found on plasma lacing components. The erosion rate is about one order of magnitude higher than for arcing on bulk W.

The traces of strong erosion found on solid components covered with thick (0.17 mm) B/sub 4/C-layers facing the edge of a fusion plasma are identified as relicts of arcing. Spots of light observed on the surface seem to exist during the whole lifetime of the fusion plasma (4...5s) and stay motionless despite the strong external magnetic field (B=2.3 T). The related big craters are single cylindrical holes reaching through the B/sub 4/C-layer down to the Cu-substrate. In subsequent discharges the re-ignition of a new arc at the location of an old crater was found to be very probable. The interesting peculiarities of ignition and burning of arcs on B/sub 4/C-layers have been confirmed in laboratory experiments (B=0.4 T) revealing that the arc current has remarkably low noise. Theoretical investigations show that a thermal runaway does not exist because of the rise of the conductivity of the semiconducting B/sub 4/C with temperature. Long living arcs influence strongly the stability of the imbedding fusion plasma and the final erosion of the substrate material at the bottom of the crater holes reduces the suitability of B/sub 4/C as coverage material.

We laser-dress several doubly-excited states in helium. Tuning the coupling-laser intensity from perturbative to the strong-coupling regime, we are able to measure phases imprinted on the two-electron wavefunctions, and observe a new continuum coupling mechanism.

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.

We describe the growth of high quality tetrathiofulvalene tetracyanoquinodimethane (TTF-TCNQ) organic charge-transfer thin films which show a clear non-Fermi liquid behavior. Temperature dependent angle resolved photoemission spectroscopy and electronic structure calculations show that the growth of TTF-TCNQ films is accompanied by the unfavorable presence of neutral TTF and TCNQ molecules. The quality of the films can be controlled by tuning the evaporation temperature of the precursor in physical vapor deposition method.