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Conventional Langmuir probes used in tokamak devices get damaged easily and even melt when exposed to divertor plasma with high thermal and particle loads. Recently, the Institute of Plasma Physics, Chinese Academy of Science, aimed to overcome this issue by designing and manufacturing an uncompensated tungsten/oxygen-free copper (OFC)/CuCrZr-alloy structure-based actively water-cooled Langmuir probe, which showed excellent heat removal capability in finite element analyses (FEA). The heat resistance and antiheat fatigue property of the proposed probe were verified by conducting electron beam high heat flux (HHF) tests. Results show that the maximum temperatures of the probe's tungsten surface were approximately 445 °C and 875 °C under heat loads of 10 and 20 MW/m2, respectively. The probe successfully passed 600 cycles of 10 and 20 MW/m2 thermal fatigue HHF tests. Moreover, no obvious damages were found on the tungsten surface and W/OFC/CuCrZr joints. FEA and HHF test results proved the reliability of the newly designed uncompensated probe. In view of this progress, it is promising to apply this actively water-cooled probe in tokamak devices for plasma diagnostics. [ABSTRACT FROM AUTHOR]

The ITER Heating Neutral Beam (HNB) injector is required to deliver 16.7 MW power into the plasma from a neutralised beam of H−/D− negative ions, produced by an RF source and accelerated up to 1 MeV. To enhance the H−/D− production, the surface of the acceleration system grid facing the source (the plasma grid) will be coated with Cs because of its low work function. Cs will be routinely evaporated in the source by means of specific ovens. Monitoring the evaporation rate and the distribution of Cs inside the source is fundamental to get the desired performances on the ITER HNB. In order to proper design the source of the ITER HNB and to identify the best operation practices for it, the prototype RF negative ion source SPIDER has been developed and built in the Neutral Beam Test Facility at Consorzio RFX. A Laser Absorption Spectroscopy diagnostic will be installed in SPIDER for a quantitative estimation of Cs density. By using a wavelength tunable laser, the diagnostic will measure the absorption spectrum of the 852 nm line along 4 lines of sight, parallel to the plasma grid surface and close to it. From the absorption spectra the line-integrated density of Cs at ground state will be measured. The design of this diagnostic for SPIDER is presented, with details of the layout and of the key components. A preliminary installation of the diagnostic on the test stand for Cs ovens is also described, together with its first experimental results; the effect of ground state depopulation on collected measurements is discussed and partially corrected. [ABSTRACT FROM AUTHOR]

A first conceptual design of the Balance of Plant for a HELIAS power plant equipped with a Helium Cooled Pebble Bed (HCPB) Breeder Blanket (BB) is presented in this work. 5 inboard and 10 outboard cooling loops extract the heat from the blanket. Heat exchangers are used to transfer the thermal power from the helium to solar salt, which transports the heat out of the stellarator building and into an industrial 2-tank thermal energy storage system (IHTS/ESS). For electricity generation, the heat from the solar salt is transferred to the feedwater, which is boiled and superheated in the steam generator and then used in the turbine. In absence of a detailed design for the HCPB BB in stellarator geometry and the ex-vessel piping, a sensitivity study was carried out for the pressure drop of the cooling loops which showed that even small changes in the pressure drop have significant impact on the required pumping power. Finally, an exemplary runtime scenario is presented demonstrating the capability of a stellarator fusion power plant equipped with an IHTS/ESS to operate very flexibly (±20%) in an envisaged dynamic future energy system. Considering demand forecasts and the ESS, a stellarator fusion power plant (FPP) seems well equipped to cope with fluctuating grid demands within its technical limitations. If the conceptual idea for the HELIAS BoP as presented in this paper can be confirmed by more detailed technical studies, then a stellarator FPP could potentially contribute to grid stabilization in a future energy system while replacing fossil fuel power plants as a sustainable energy source. [ABSTRACT FROM AUTHOR]

• HVD1 and HVBA are unique devices for size, electrostatic and mechanical features. • HVD1 and HVBA are installed inside a large HV hall. • The main design choices leading to the final hall layout are presented. • The manufacturing design and the factory type tests are reported. • The on-site installation, commissioning and testing activities are described. MITICA is the full scale prototype of the ITER Heating Neutral Beam (HNB) currently under construction at the Neutral Beam Test Facility in Padova (Italy). In the ITER HNB, negative ions (H−/D−) are produced in the Ion Source (IS) polarized to ground at −1012 kV, then extracted and accelerated to ground at 1 MeV energy and finally neutralized. The complex power supply system feeding the IS includes two non-standard equipment, beyond the current industrial standard for insulation voltage level (-1 MVdc) and dimensions: 1) the High Voltage Deck1 (HVD1), a large air insulated Faraday cage (12.5 m (L) x 8.4 m (W) x 9.6 m (H)) hosting the IS power supplies and diagnostics; 2) the High Voltage Bushing Assembly (HVBA), a -1 MVdc air to SF6 Bushing which interfaces the HVD1 with the SF 6 insulated Transmission Line (TL) connecting the Acceleration Grid Power Supply system with the IS, carrying inside its High Voltage electrode all IS power and diagnostics conductors. The HVD1 and HVBA are installed inside a large HV hall. The main design choices leading to the final hall layout, integrating the HV experimental equipment and the conventional building plants assuring the necessary clearance required by such very high electric insulation level, are presented. Moreover, the paper reports on the manufacturing design developed by the supplier, the factory type tests to validate the design of the HVD1, the factory tests carried out on the HVBA and the on-site installation, commissioning and testing activities. [ABSTRACT FROM AUTHOR]

This paper describes the manufacturing study of ITER Lower Cryostat Thermal Shield (LCTS) cylinder components, which are to be delivered to ITER site. All LCTS cylinder 20 ° sectors will be assembled at the ITER site by the flange joints, which are welded to the shells. Reliability of cooling pipe welding was checked by two inspection methods: endoscopy and vacuum leak test. Pre-assembly of three 20 ° sectors is one of the important step to ensure dimensional tolerance and its process is described in details. Dimensions of the pre-assembled 60 ° sector was measured by a laser tracker. The qualification of silver coating facility was carried out using a simple well-defined plate mock-up. After the facility qualification, silver coating of LCTS cylinder 20 ° sectors had been conducted. Technical efforts to improve the coated surface quality are presented in this paper. [ABSTRACT FROM AUTHOR]

A multi-purpose overview video system, based on EDICAM cameras, was set up at Wendelstein 7-X stellarator, in order to fulfill both machine protection and scientific observation purposes. Places of strong plasma-wall interaction, which can easily evolve to hot-spots, were detected by the EDICAM operators during plasma operation, based on intense local light emission. The EDICAM system was successfully used to avoid hot-spot formation during the commissioning of magnetic configurations with plasma operation. Featuring non-destructive readout capability, smaller areas of the torus interior could be monitored ca. two orders of magnitude faster, in parallel to the normal full frame overview. These fast measurements could be used to show the presence of plasma turbulence (filaments), also detected by other diagnostic systems. [ABSTRACT FROM AUTHOR]

• Bootstrap current was measured in all reference magnetic configurations of OP1.2a. • Experimental profiles can be reliably mapped with vacuum pre-calculated equilibria. • VMEC calculations show good agreement with Minerva and V3FIT reconstruction. Wendelstein 7-X (W7-X) is a modular advanced stellarator, which successfully went into operation in December 2015 at the Max-Planck-Institut für Plasmaphysik in Greifswald, Germany, and continued to thrive at the experimental campaign with the first divertor phase in August-December 2017. The nested magnetic surfaces in W7-X are created by a system of 3-D toroidally discrete coils, providing both toroidal and poloidal field components, and designed with the aim to create optimum equilibrium properties. The optimization criteria included the high quality of vacuum magnetic surfaces, good finite beta equilibrium and MHD-stability properties as well as a substantial reduction of the neoclassical transport and bootstrap current in comparison to classical stellarators. Equilibrium calculations, devoted to the analysis of the experiment programs dedicated to measure the bootstrap current, were performed with help of the Variational Moments Equilibrium Code, available as Wendelstein 7-X web service. Pressure profiles based on experimental data served as an input for calculations. The mapping of measurements using pre-calculated equilibria for different beta values has been analyzed. A comparison with reconstruction results obtained by means of the Minerva Framework, considering only experimental data of magnetics measurements, and the V3FIT code is presented. [ABSTRACT FROM AUTHOR]

The ITER Radial Neutron Camera (RNC) is a multichannel detection system hosted in the Equatorial Port Plug 1 (EPP 1). It is designed to measure the uncollided neutron flux from the plasma, providing information on the neutron emissivity profile and total strength. The RNC structure consists of two sub-systems based on fan-shaped arrays of cylindrical collimators: the ex-port system, covering the plasma core with 2 sets of lines of sight lying on different toroidal planes, and the in-port system, enclosed in a dedicated cassette within the EPP1 diagnostic shielding module, for the measurement of neutrons generated in the plasma edge. Due to the harsh environment in which it has to operate, the design of the in-port RNC system is particularly critical both from the measurements point of view (low signal to noise ratio induced by the high level of scattered neutrons at the detector positions) and from the structural point of view. The paper presents the results of the neutronic analyses performed with the MCNP Monte Carlo code with the aim of optimizing the in-port RNC design in order to enhance the diagnostic measurement performance and evaluating the nuclear loads that have to be withstand by its structural elements, detectors and associated components. [ABSTRACT FROM AUTHOR]

• application of DevOps practices to operation phase of a fusion machine. • guaranteeing high quality, reliability and efficiency. • achievement of short developement (component configuration change) cycles. The stellarator Wendelstein 7-X (W7-X) is a fusion device designed for steady state operation. It is a complex technical system. To cope with the complexity a modular, component-based control and data acquisition system has been developed. During operation phases of W7-X components steadily evolve. For instance, measurement devices for diagnostics are improved, technical processes are optimized, experienced limits of the machine have to be taken into account or simple "bug fixing" is done. This requires continuous further development of the components while operating them at W7-X – a typical use case for DevOps practices. DevOps is a software engineering practice. The term is a compound of development and operations. It aims at shorter development cycles, while the quality of the changed system must stay at a high level. This is achieved by using a highly automated tool chain. [ABSTRACT FROM AUTHOR]

The stellarator Wendelstein 7-X is being prepared for long pulse operation. This includes diagnostics for investigation of plasma wall interaction processes. A versatile optical observation system has been developed for local characterization of the divertor plasma and the divertor target surface. The optical systems consist of two endoscopes each with perpendicular fields of view and the opportunity of tomographic reconstruction. Mirror based optics has been chosen in order to assure good optical properties independent of the wavelength. A narrow field of view allows for high spatial resolution while rotation of the first mirror covers the full poloidal divertor sections. An integrated shutter mechanism and a vacuum window far back minimize coating of optical components. For assessment of change of light transmission, a relative calibration function is implemented. The output light is split into wavelength ranges. Both, cameras equipped with narrow band filters as well as spectrometers are connected. The first endoscope was mounted at W7-X after successfully passing mechanical, optical and functional tests. [ABSTRACT FROM AUTHOR]

The "C/O Monitor" system for the Wendelstein 7-X (W7-X) stellarator is a dedicated spectrometer with high throughput and high time resolution (order of 1 ms) for fast monitoring of content of low-Z impurities in the plasma. The observed spectral lines are fixed to Lyman-α lines of H-like atoms of carbon (3.4 nm), oxygen (1.9 nm), nitrogen (2.5 nm), and boron (4.9 nm). The quality of the wall condition will be monitored by the measurements of oxygen being released from the walls during the experiments. The strong presence of carbon is an indication for enhanced plasma-wall interaction or overload of plasma facing components. The presence of nitrogen (together with oxygen) may indicate a possible leakage in the vacuum system, whereas the intensity of the spectral emission of boron indicates the status of the boron layer evaporated onto the wall in order to reduce the influx of heavier steel ingredients or oxygen. The spectrometer will be fixed in a nearly horizontal position and is divided into two vacuum chambers, each containing two spectral channels assigned to two impurity species. Each channel will consist of a separate dispersive element and detector. The line-of-sight of both subspectrometers will cross at the main magnetic axis. This paper presents the conceptual design of the "C/O Monitor" for W7-X which has already entered the executive stage. [ABSTRACT FROM AUTHOR]

The Active spectroscopy plasma diagnostics (CXRS, charge eXchange recombination spectroscopy) and plans for its use in the ITER tokamak are described. A technique for the wavelength calibration of a multichannel polychromator spectrometer using a Fabry–Perot etalon is presented. This idea of the wavelength calibration of the spectrometer was originally used for the CXRS diagnostics in the JET tokamak. Using this technique, a high-resolution tri-band polychromator spectrometer, which was created for the CXRS diagnostics at the ITER facility, was calibrated. This polychromator spectrometer allows simultaneous measurements in three spectral ranges: 469–477, 529–538, and 650–661 nm. The obtained error of the calibration for various wavelengths was evaluated, which was on average 0.003 nm. The resulting calibration accuracy for different wavelengths is enough to meet the requirements for the CXRS diagnostics in the ITER tokamak with a margin. [ABSTRACT FROM AUTHOR]

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay that has been able to reach the 1-ton scale. The detector consists of an array of 988 TeO 2 crystals arranged in a cylindrical compact structure of 19 towers. The construction of the experiment and, in particular, the installation of all towers in the cryostat was completed in August 2016 and data taking started in spring 2017. In this contribution the achievement of the commissioning phase and the performance of the detector and the cryostat during the first physics run will be presented. • Improvement in the reduction of the noise induced by the mechanic vibration of the Pulse Tubes system. • Improvement of the energy resolution between two data taking periods as a result of a dedicated detector optimization campaign. • Plans on how to lower the trigger threshold to identify very low energy signals and enhance detector sensitivity to Dark Matter. [ABSTRACT FROM AUTHOR]

XGC (X-point Gyrokinetic Code) is a whole-volume, total-f gyrokinetic particle-in-cell code developed for modeling tokamaks. In recent work, XGC has been extended to model more general 3D toroidal magnetic configurations, such as stellarators. These improvements have resulted in the XGC-S version. In this paper, XGC-S is benchmarked in the reduced delta-f limit for linear electrostatic ion temperature gradient-driven microinstabilities, which can underlie turbulent transport in stellarators. An initial benchmark of XGC-S in tokamak geometry shows good agreement with the XGC1, ORB5, and global GENE codes. A benchmark between XGC-S and the EUTERPE global gyrokinetic code for stellarators has also been performed, this time in the geometry of the optimized stellarator Wendelstein 7-X. Good agreement has been found for the mode number spectrum, mode structure, and growth rate. [ABSTRACT FROM AUTHOR]

We investigated the dynamic fragmentation of laser shock-loaded tin to gain insights on the underlying mechanism of this process. In the experiments, tin samples were shock-loaded by nanosecond laser over sequential pressures ranging from 7 GPa to 43 GPa. Integrated diagnostic techniques, including four-frame optical transverse shadowgraph imaging system, soft recovery, and photonic Doppler velocimetry (PDV), were employed. They provide the shape of the ejecta in the dynamic fragmentation process, the recovered ejecta, as well as the loading parameters. These experimental results were compared with those obtained using one-dimensional Lagrangian hydrodynamics simulation. The crossed results over sequential pressures allowed us to gain better insights on the different dynamic fragmentation processes of spall fracture and micro-spalling, which can help develop reliable models for dynamic fragmentation of triangular-wave shocking metals. [ABSTRACT FROM AUTHOR]

The superconducting stellarator Wendelstein 7-X (W7-X) started plasma operation in December 2015 after the commissioning phase of the machine. The main technical and diagnostic systems have been finished successfully. The timing system is an important part of the control, data acquisition, and communication systems of W7-X. The first version of the trigger-time-event (TTE) system is in routine operation at the W7-X experiment. Since 2004, it has been used for the commissioning of the control and data acquisition components and also for the stellarator WEGA. The commission of the second version of the TTE-system is still on-going and planned to be finished at the end of 2016. Starting with an introduction of the TTE-system of W7-X, this contribution describes the main features of the TTE-system. The actual state of the TTE-system and the network topology will be presented. Finally, the first experiences of W7-X operational phase OP1.1 related to the TTE-system are discussed. [ABSTRACT FROM AUTHOR]

A detailed description of a prototype setup for real-time (RT) Thomson scattering (TS) analysis is presented and implemented in the multi-point Thomson scattering (MPTS) diagnostic system at the National Spherical Torus Experiment Upgrade (NSTX-U). The data acquisition hardware was upgraded with RT capable electronics (RT-analog digital converters and a RT server) that allow for fast digitization of the laser pulse signal of eight radial MPTS channels. In addition, a new TS spectrum analysis software for a rapid calculation of electron temperature (Te) and electron density (ne) was developed. Testing of the RT hardware and data analysis software was successfully completed and benchmarked against the standard, post-shot evaluation. Timing tests were performed showing that the end-to-end processing time was reproducibly below 17 ms for the duration of at least 5 s, meeting a 60 Hz deadline by the laser pulse repetition rate over the length of a NSTX-U discharge. The presented RT framework is designed to be scalable in system size, i.e., incorporation of additional radial channels by solely adding additional RT capable hardware. Furthermore, it is scalable in its operation duration and was continuously running for up to 30 min, making it an attractive solution for machines with long discharges such as advanced, non-inductive tokamaks or stellarators. [ABSTRACT FROM AUTHOR]

Ion flow velocity measurement in the edge and scraper-off layer region is beneficial to understand the confinement related phenomenon in fusion devices such as impurity transport and plays an important role in impurity control. During the Wendelstein 7-X (W7-X) operation phase 1.2a, a multi-channel (MC) Mach probe mounted on the multi-purpose manipulator has been used to measure radial profiles of edge ion flow velocity. This MC-Mach probe consists of two polar and two radial arrays of directional Langmuir pins (28 pins in total) serving for different aims, of which the polar arrays could obtain a polar distribution of ion saturation current, while the radial arrays can be used to study the dynamic process of a radially propagated event. In this paper, we report the observation of the radially outward propagation of a low frequency mode with a speed of around 200 m/s. The first measurement of the radial ion flow velocity profile using the MC-Mach probe in the boundary plasma of the W7-X with an island divertor will also be presented. [ABSTRACT FROM AUTHOR]

Tokamak-like sawtooth oscillations are observed in the Compact Toroidal Hybrid (CTH), a current-carrying stellarator. CTH has the unique ability to change the amount of the applied vacuum rotational transform from external stellarator coils relative to the rotational transform generated by the internal plasma current to investigate the effects of strong three-dimensional magnetic shaping on sawtooth behavior. The observed sawteeth in CTH, for plasmas with monotonically decreasing rotational transform profiles dominated by the plasma current, have characteristics of those observed on tokamaks including (1) a central emissivity rise and then a sudden crash with a well-defined inversion radius, (2) the presence of an m = 1 emissivity fluctuation, and (3) the normalized inversion surface radius scales with the total edge rotational transform. We explore the properties of an ensemble of discharges in CTH in which the fractional rotational transform, defined as the vacuum rotational transform divided by the total rotational transform, is systematically varied from 0.04 to 0.42 to observe changes in sawtooth oscillation dynamics. Over this range of the fractional rotational transform, the measured sawtooth period decreased by a factor of two. At a high fractional rotational transform, the sawtooth amplitude is observed to consist of only low-amplitude oscillations while the measured crash time of the sawtooth oscillation does not appear to have a strong dependence on the amount of the fractional transform applied. Experimental results indicate that the low-amplitude sawteeth are accompanied by a decrease in the sawtooth period and predominantly correlated with the mean elongation (due to the increasing fractional rotational transform) of the non-axisymmetric plasmas within CTH rather than other global equilibrium parameters. [ABSTRACT FROM AUTHOR]

Whole volume simulations of stellarators are necessary to address a number of important physics and engineering issues, including turbulent transport prediction and optimising divertor operation. In this work, advances in the development of a whole volume stellarator capability for the global gyrokinetic particle-in-cell code XGC are detailed. A 3D interpolation of the equilibrium magnetic field to the last close flux surface, calculated using the VMEC ideal magnetohydrodynamic equilibrium code, has been implemented. Orbit tracing with the XGC code is verified for the Wendelstein 7-X stellarator by comparison with the BEAMS3D and EUTERPE codes. The XGC stellarator version has then been used to consider collisionless alpha particle confinement in representative quasi-isodynamic and quasi-axisymmetric designs. It has been shown that, at least without further optimisation for energetic particle confinement, the Wendelstein 7-X-like quasi-isodynamic reactor design exhibits better alpha particle confinement. [ABSTRACT FROM AUTHOR]

Turbulent dynamos that exponentially amplify initially small, seed magnetic fields are crucial in magnetizing the Galaxy and beyond. Until now, the ideal environment for turbulent dynamos to grow has been difficult to recreate. In a new approach, we leverage the long pulse capability of the OMEGA-EP laser to recreate the highly conductive and inviscid ( Re m ∼ 5500 , Pr m ≳ 1) growth environment of the turbulent dynamo within the magnetized plasma jet ablated from a simple cone target of CH plastic. In 3-D FLASH simulations of our scheme, we find that the ideal dynamo environment is a typically ∼1 mm3, ≳ 1.5 keV hot spot where the laser beams intersect to produce maximum direct heating of the jet plasma. The dynamo environment is maintained from the onset of steady flows through the ∼10 ns length of the laser pulse. For a plasma vorticity of 0.3–3.0 ns–1 and a dynamo active over ∼5 ns, the magnetic energy increases on an exponential trajectory by more than a decade. Fourier analysis reveals that the dynamo progressively saturates up to E B / E K ∼ 20 % from small scales k ≳ 30 cm−1 to large in the time it is sustained. We find robust agreement between the evolution of magnetic energy spectra extracted from the FLASH physics simulation and that derived from synthetic sheath-accelerated proton deflectometry images, thereby demonstrating that the dynamo activity can be quantified in a real experiment. [ABSTRACT FROM AUTHOR]

In this paper, we present a method for numerical computation of collective Thomson scattering (CTS). We developed a forward model, eCTS, in the electrostatic approximation and benchmarked it against a full electromagnetic model. Differences between the electrostatic and the electromagnetic models are discussed. The sensitivity of the results to the ion temperature and the plasma composition is demonstrated. We integrated the model into the Bayesian data analysis framework Minerva and used it for the analysis of noisy synthetic data sets produced by a full electromagnetic model. It is shown that eCTS can be used for the inference of the bulk ion temperature. The model has been used to infer the bulk ion temperature from the first CTS measurements on Wendelstein 7-X. [ABSTRACT FROM AUTHOR]

Quasisymmetric stellarators are appealing intellectually and as fusion reactor candidates since the guiding-centre particle trajectories and neoclassical transport are isomorphic to those in a tokamak, implying good confinement. Previously, quasisymmetric magnetic fields have been identified by applying black-box optimization algorithms to minimize symmetry-breaking Fourier modes of the field strength $B$. Here, instead, we directly construct magnetic fields in cylindrical coordinates that are quasisymmetric to leading order in the distance from the magnetic axis, without using optimization. The method involves solution of a one-dimensional nonlinear ordinary differential equation, originally derived by Garren & Boozer (Phys. Fluids B, vol. 3, 1991, p. 2805). We demonstrate the usefulness and accuracy of this optimization-free approach by providing the results of this construction as input to the codes VMEC and BOOZ_XFORM, confirming the purity and scaling of the magnetic spectrum. The space of magnetic fields that are quasisymmetric to this order is parameterized by the magnetic axis shape along with three other real numbers, one of which reflects the on-axis toroidal current density, and another one of which is zero for stellarator symmetry. The method here could be used to generate good initial conditions for conventional optimization, and its speed enables exhaustive searches of parameter space. [ABSTRACT FROM AUTHOR]

The large flexibility of the proposed QUASAR facility [Gates et al., Nucl. Fusion 57, 126064 (2017)] is leveraged in order to explore the effect of magnetic shear on adiabatic Ion Temperature Gradient (ITG) turbulence. The QUASAR facility is a reimagining of the National Compact Stellarator Experiment utilizing and expanding upon the already constructed coil set. Recent work using fixed boundary optimization of the LI383 equilibrium (upon which QUASAR is based) has suggested possible improvements to ITG turbulence [Mynick et al., Plasma Phys. Controlled Fusion 56, 094001 (2014)]. In this work, a different approach is taken, wherein a series of self-consistent free boundary VMEC equilibria are developed for QUASAR. These equilibria assume temperature and density profiles consistent with 2% beta and ohmic current drive. In each configuration, the toroidal field coils are energized to different values and the STELLOPT code is used to vary the modular coil current and net toroidal current. The edge value of rotational transform is targeted in the optimization, producing a magnetic shear scan. All these configurations share similar neoclassical transport levels, while nonlinear GENE flux tube simulations show up to a factor of four change in adiabatic ITG turbulence at various radii. Comparisons of proxy functions and linear flux tube runs are also made. This work highlights the capability of the QUASAR experiment as a tool to explore transport in 3D magnetic fields and the possibility of the further improvements to stellarators through optimization. [ABSTRACT FROM AUTHOR]

Abstract The method and device have been developed and used for operative estimation of impurity level, outgassing rate and molecular layers number on high vacuum chamber surfaces of magnetic confinement fusion devices in situ. The method is based on the thermal desorption of gases into a vacuum vessel from the surface of a special metal probe during its heating up to temperature of 300 °C. To investigate and use this method, the probe was designed, manufactured and installed into the vacuum vessel of the Uragan-2 M stellarator. The technique was tested after applying VHF/RF cleaning discharges in different scenarios. A decrease of the released gas amount from the surface by more than one order of magnitude was recorded. The mass-spectrometer registered the atomic masses 18 u (H 2 O), 28 u (CO + N 2) and 44 u (CO 2), as the main gases desorbed from the probe surface during its heating. Heavy hydrocarbon masses (mainly 58 u) were also registered. The method had also been tested in the regime of hydrogen gas retained in the wall. [ABSTRACT FROM AUTHOR]

Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors. [ABSTRACT FROM AUTHOR]

The relativistic generalization of the linearized drift kinetic equation solver NEO-2 is presented which is used for computation of neoclassical transport coefficients and the generalized Spitzer function in 3D toroidal fusion devices (tokamaks and stellarators). This upgrade allows computations of the Spitzer function playing the role of current drive efficiency in the whole experimentally relevant temperature range, from mild temperatures where finite plasma collisionality effects are important to high temperatures where relativistic effects should be taken into account. Within the Galerkin method used for problem discretization over energy, relativistic effects are included into a set of matrices constant on a flux surface. Those matrices determine coefficients of a coupled set of integro-differential equations with a reduced dimension which is of the same form as in the non-relativistic case. For energy discretization of the linearized relativistic Coulomb collision operator, it is presented in spherical momentum space variables in the symmetric integral form derived directly from Beliaev-Budker expressions. The cancellation problem pertinent to the fully analytical representation of Braams and Karney [Phys. Fluids B 1, 1355 (1989)] does not appear in this form. Examples of evaluation of relativistic transport coefficients and the Spitzer function are presented. [ABSTRACT FROM AUTHOR]

Presents a study that investigated the control of emittance growth due to mismatches in accelerators that use stellarator transport. Numerical modeling of the spiral line induction accelerator (SLIA); Emittance growth control in the SLIA; Comparison between simulation and experiment.

Presents a study that developed two focusing field configurations that provide high midplane accessibility stellarator windings for toroidal accelerators. Methodology; Benefits of the focusing field configuration; Analysis of the bandwidth of the configurations.

Considered is thermal performance for the squealer blade tip of four film cooling configurations, B1, B2, B3 and B4, with hole exits for each arrangement positioned along a different portion of the upper pressure side of a transonic turbine blade. Each upper pressure side configuration includes five film cooling holes, such that each hole has a compound angle of 45 ° with respect to the circumferential/axial plane, also with an angle orientation of 40 ° relative to the plane tangent to the exit cross sectional area of each hole. Results are given for blowing ratios ranging from 0.42 to 3.20 in the form of spatially-resolved and spatially-averaged surface distributions of heat transfer coefficients and heat transfer coefficient ratios. In regard to tip surface variations, surface heat transfer coefficient ratios distributions are a consequence of the manner in which the film coolant collects in a substantial manner along the pressure side rim and then advects above and across the squealer recess with little to no coolant collecting within the cavity, or along the recess surface, to then collect in a substantial manner further downstream along the suction side rim. Such flow characteristics affect heat transfer coefficient ratio variations for all four film cooling configurations, but are especially influential for the B3 arrangement. Considering local heat transfer coefficient ratio distributions along the upper pressure side surface, the most significant local variations in the vicinity of a film cooling hole exit locations. Here, heat transfer coefficient ratio distributions for the B1 and the B4 configurations, in particular, show evidence of a horseshoe-shaped vortex which forms around each emerging coolant concentration. The two downstream legs of each vortex are associated with a pair of locally augmented heat transfer coefficient streaks, often with a streak of locally-lower coefficient ratios positioned between. Local and line-averaged heat transfer coefficient ratios along the upper pressure side also vary significantly with blowing ratio, with additional periodic variations as the normalized circumferential/axial coordinate varies. Within the resulting distributions, local heat transfer coefficient ratio increases are associated with locally augmented mixing and turbulent transport, which are especially present near the exits of different film cooling hole locations. [ABSTRACT FROM AUTHOR]