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The problem of power exhaust is one of the grand challenges of nuclear fusion research today. In order to understand the physics phenomena occurring in the scrape-off layer and the divertor regions of tokamaks, it is essential to correctly determine the divertor plasma parameters, which are often measured by swept Langmuir probes (LPs). While the construction and operation of this diagnostic can be straightforward, the data analysis using three- or four-parameter fits presents a challenge and can potentially lead to erroneous values of electron temperature and ion saturation current. In this work, we present modelling and experiments aimed at determination of conditions for proper analysis of swept LPs using these two fitting models. Particle-in-cell modelling was employed to evaluate the sheath-expansion effects for particular probe geometry and plasma conditions, yielding a semi-empirical rule capable of predicting its magnitude. Experiments with unusually wide range of swept voltage in the divertor of the COMPASS tokamak explored the magnitude of voltage range required for successful analysis with either three or four-parameter fitting. With the use of our new semi-empirical rule, it is possible to improve the four-parameter fit reliability in situations where the available voltage range is limited. In addition, we introduce the tangent method—an independent and fast method of electron temperature estimation, which allows to reliably determine the available voltage range and as such assist more complex methods of probe analysis.

The characterisation of plasma current quench and understanding of its underlying physical processes play a crucial role when designing large fusion devices such as ITER. For the first time, an extensive analysis of the COMPASS tokamak disruption database is presented. A unique set of magnetic diagnostics allows the investigation of local toroidal and poloidal vessel currents, including currents flowing along the open magnetic field lines from the plasma to the vacuum vessel (VV) (i.e., halo currents). Area-normalised current quench times are in agreement with the ITPA 1.67 ms m−2 lower limit. Extremely fast I p quench rates of up to 0.6 MA ms−1 are observed during runaway electron campaigns at COMPASS, which are under the ITPA lower limit. Vertical movement of the plasma column is accelerated by the I p quench during major disruptions. Toroidal vessel currents of around 2% – 4% of the predisruptive plasma current I p d i s r are observed during I p quench. Net poloidal eddy currents are obtained by Mirnov coils and diamagnetic loop, reaching 3% of I p d i s r . Using the Mirnov coils it is shown that the halo current magnitude grows and its poloidal profile broadens with increasing plasma current I p . Geometric features of the VV structure and in-vessel component positions on the poloidal vessel current measurements are discussed.

This article introduces a concept based on flush-mounted probes embedded in the limiters of the COMPASS-Upgrade tokamak. Main issues related to flush probe geometry are taken into account and discussed. Calculations of heat fluxes and the incident angle of the field lines on the different limiters using the PFCflux code are performed to support in probe arrangement optimization. Model current-voltage characteristics for a flush probe are simulated using the SPICE2 code and their dependence on the angle of incidence is studied. The results are used to predict the current to be collected by the flush probes for different magnetic fields and to examine the reliability of the proposed diagnostics. A discussion is included on the capability of the electronic system considered for the measurements.

Introduction The accepted treatment of pilonidal disease still consists of surgical excision with primary wound closure. This treatment has complications such as excessive pain, delayed wound healing, and recurrence. We introduced this technique using a radial laser probe (SiLaCTM, Biolitec, Germany). Previous studies have shown encouraging results with respect to safety, patient satisfaction, and minimal recurrence rates. Method The pilot project was planned with the objectives to assess postoperative complications and reoperation rates. All operations were performed as day case procedures under general anaesthesia. We studied the data of our first 25patients operated with this technique between January 2019 and December 2019 using a prospective database and outpatient clinic follow up. Results The median follow up duration was 13 months. The initial success rate was 64%(16/25), reoperation was required in 32%(8/25) and one patient was lost to follow up. one patient returned with abscess formation in the postoperative period. Conclusions SiLaC is a safe and minimally invasive technique for the destruction of the pilonidal cyst and sinus. The success rate is modest, making this new therapy a minimally invasive option for the majority of the patients with pilonidal disease but it should be offered with caution.

COMPASS-U, a high magnetic field tokamak with hot walls, will be designed and built at IPP Prague. Unique features of this new device bring noticeable constraints and requirements on plasma diagnostics, which make their development highly demanding. In this paper, the main expected constraints influencing the conceptual design of diagnostic tools for COMPASS-U (high temperature of the vacuum vessel, high plasma density, high heat flux density, strong auxiliary plasma heating, spatial constraints, liquid metals in the divertor) are reviewed and possible solutions are indicated.

The presented experimental study realized in the COMPASS tokamak demonstrates, for the first time, that the current density that flows from the plasma into the vacuum vessel during disruptions is limited by the ion particle flux. Such a limitation shows that, at least in COMPASS, the sheath that forms between the plasma and the first wall dominates the halo current flow. This observation is achieved by measuring simultaneously the ion saturation current with negatively biased Langmuir probes and the halo current with grounded probes to the vacuum vessel. These comparative measurements, which were never performed during disruptions in other machines, directly confirm that the halo current density remains below the ion particle flux in COMPASS. The study also shows, using Mirnov coils measurement, that the total electric current entering the wall grows with the plasma current while the current density obtained by Langmuir probes remains unaffected. This, together with the current density limitation, leads to a novel finding that the halo current width increases with the pre-disruptive plasma current, which limits the local forces. The new findings reported here could also provide potential constraints on the modeling of disruption-induced loads on future reactor scale tokamaks and motivation for further experiments on existing devices.

Substantial power dissipation in the edge plasma is required for the safe operation of ITER and next-step fusion reactors, otherwise unmitigated heat fluxes at the divertor plasma-facing components (PFCs) would easily exceed their material limits. Traditionally, such heat flux mitigation is linked to the regime of detachment, which is characterised by a significant pressure gradient between upstream and downstream scrape-off layer (SOL). However, the physics phenomena responsible for power dissipation and pressure loss are distinctly different, especially when the power dissipation is achieved by impurity seeding. In principle, it is possible to achieve substantial mitigation of the heat fluxes while maintaining conservation of the pressure along the open field lines in the SOL. This regime can be accessed by injection of medium- or high-Z impurities, which mostly radiate inside the last closed flux surface. The critical question related to such an approach is the effect on confinement and perspective fusion power generation in future thermonuclear reactors. In this work, we report on experiments at COMPASS tokamak, where neon and argon impurities were injected in ohmic or NBI-heated low confinement plasmas. With appropriate seeding waveform, stable scenarios were achieved, avoiding the radiative collapse of plasmas. Significant reduction of heat fluxes at the outer target was observed, with heat flux pattern similar to the one previously achieved by nitrogen seeding. The reduction of downstream pressure was, however, accompanied by an equal reduction of upstream pressure, indicating that the power dissipation occurred inside the separatrix. Indeed, the impurity cooling is causing a significant drop of edge temperature; however, the effect in the plasma centre is much less pronounced.

COMPASS Upgrade is a new medium size, high magnetic field tokamak (R = 0.9 m, Bt = 5 T, Ip = 2 MA) currently under design in the Czech Republic. It will provide unique capabilities for addressing some of the key challenges in plasma exhaust physics, advanced confinement modes and advanced plasma configurations as well as testing new plasma facing materials and liquid metal divertor concepts. This paper contains an overview of the preliminary engineering design of the main systems of the COMPASS Upgrade tokamak (vacuum vessel, central solenoid and poloidal field coils, toroidal field coils, support structure, cryostat, cryogenic system, power supply system and machine monitoring and protection system). The description of foreseen auxiliary plasma heating systems and plasma diagnostics is also provided as well as a summary of expected plasma performance and available plasma configurations.

This paper presents measurements of the plasma turbulence with an emphasis on the ion temperature fluctuations in comparison to the electron temperature and the ion saturation current fluctuations in the edge of the COMPASS tokamak. The ion temperature values are obtained by using a fast swept ball-pen probe, with temporal resolution up to 10 µs, accompanied by independent 1 µs measurements of the electron temperature and ion saturation current. The experimental results obtained for a wide range of line-averaged densities show that statistical properties of the fluctuations are in good agreement with a form of beta or gamma distribution function. In addition, the dependence of the averaged ion and electron temperatures on the line-averaged density is studied in the near and main scrape off layer region.

Three new in-vessel manipulators are designed and built for the new COMPASS Upgrade tokamak with uniquely high vessel temperature (250–500 °C) and heat flux density (perpendicular to divertor surface q ⊥ ∼ 80 MW/m2 and q ∥ ∼ GW/m2 at separatrix), which challenges the edge plasma diagnostics. Here we show their detailed engineering designs supported by heat conduction and mechanical models. Deep reciprocation of electrostatic probes near the separatrix should be possible by optimizing older concepts in (a) the head and probe geometry, (b) strongly increasing the deceleration up to 100× gravity by springs and strengthening the manipulator mechanical structure. One reciprocates close to the region of edge plasma influx (the outer midplane), the other at the plasma sink (between the outer divertor strike point and X-point), for studying the plasma divertor (impurity-seeded) detachment and liquid metal vapor transport. Both probe heads are equipped with a set of ball-pen and Langmuir probes, measuring reliably and extremely fast (10−6 s) local (1 mm resolution) plasma potential, density, electron temperature and heat flux and even ion temperature with 10−5 s resolution. The divertor manipulator (without reciprocation) will place various material test targets at the outer divertor. Unique will be its capability to increase 15× the surface heat flux with respect to the surrounding tungsten tiles just by controllable surface inclination of the test targets. We plan to test liquid metal targets where such inclined surface was found critical to achieve the desired mode with lithium vapor shielding. Even in the conservative expected performance of COMPASS Upgrade, we predict to reach and survive the EU DEMO relevant heat fluxes.

The COMPASS tokamak (R = 0.56 m, a = 0.2 m, BT = 1.3 T, Ip ~ 300 kA, pulse duration 0.4 s) operates in ITER-like plasma shape in H-mode with Type-I ELMs. In 2019, we plan to install into the divertor a test target based on capillary porous system filled with liquid lithium/tin. This single target will be inclined toroidally in order to be exposed to ITER-relevant surface heat flux (20 MW/m2). Based on precisely measured actual heat fluxes, our simulations predict (for 45° inclination, without accounting for the lithium vapor shielding) the surface temperature rises up to 700°C within 120 ms of the standard ELMy H-mode heat flux with ELM filaments reaching hundreds MW/m2. Significant lithium vaporization is expected. The target surface will be observed by spectroscopy, fast visible and infrared cameras. The scientific program will be focused on operational issues (redeposition of the evaporated metal, ejection of droplets, if any) as well as on the effect on the plasma physics (improvement of plasma confinement, L–H power threshold, Zeff, etc.). After 2024, a closed liquid divertor may be installed into the planned COMPASS Upgrade tokamak (R = 0.84 m, a = 0.3 m, BT = 5 T, Ip = 2 MA, Pin = 8 MW, pulse duration ~2 s) with ITER-relevant heat fluxes loading the entire toroidal divertor.

The paper describes the conceptual design of the COMPASS Upgrade (COMPASS-U) tokamak which represents a compact, medium-size, high-magnetic-field and high-density device with a flexible set of poloidal field coils for generation of single, double null and snowflake configurations. In addition, COMPASS-U will be equipped with a closed divertor, which will be operated at high plasma and neutral density and with high optical opacity similar to future reactors. COMPASS-U is capable of addressing some of the key challenges in the field of the plasma exhaust physics, reactor-relevant edge plasma physics, advanced confinement regimes, advanced magnetic configurations and materials for next-step devices. The conceptual design of the individual COMPASS-U systems is presented with emphasis on magnets, support structure and power supply system enhancement.

Magnetic field sensors are fundamental for control and physics exploitation of fusion devices. Their inductive nature implies high dynamic ranges and a broad bandwidth, thus a precise characterization and calibration of these probes is paramount. COMPASS-U will have a completely new set of magnetic diagnostics, from sensors to data acquisition. Sensors installed in-vessel will operate at 300–500 ◦C and should survive transients of even higher temperatures and thus materials used should be high-temperature compatible. These design limitations will have an impact on the dynamic range and bandwidth of the sensors, which needs to be reliably quantified, optimally with the same test bench for all sensor types. The first part of this work presents a test bench and the process of how to calibrate the effective area using a large solenoidal coil and frequency response of the magnetic sensor prototypes with a Helmholtz coil. In the second part, test results of the sensor prototypes are presented and discussed in detail. The low-bandwidth sensors made of mineral insulated cable (MIC), intended for plasma control and machine protection, show negligible attenuation up to 10 kHz, sufficient for their role. For fast coils consisting of bare wire wound on ceramic mandrel and Thick Printed Copper (TPC) sensors the negligible attenuation measured below 1 MHz is again sufficient for their intended purpose of detecting fast coherent plasma fluctuations. Resonances introduced by the capacitance of long cables from the vacuum vessel feedthroughs to the data acquisition systems are measured, to model their influence on the signal.

The reduction of the incident heat flux onto the divertor will be a necessity for the future thermonuclear reactors. Impurity seeding is recognized as an efficient way to achieve the partial detachment regime, which allows to dissipate a large fraction of power flux by radiation. This paper presents a heat flux real-time feedback system (RTFS) based on impurity seeding controlled by a combined ball-pen and Langmuir probe divertor array in the COMPASS tokamak. A number of features of the system have been studied, such as the type of impurity, seeding location, constants used in the real-time controller and the diagnostic selections. A detailed description of the designed RTFS and the results of the implementation are presented. The findings confirm the applicability of the RTFS for reduction and control of the divertor heat fluxes. Another important implication of this research is the ability of installing such systems in next-step devices.

International audience; Following the lead of [Nguyen van Yen Nucl. Fus. 52 (2012) 013005 (11pp)], this article tackles the problem of tomographic inversion with one camera assuming a constant emissivity of light along the magnetic field lines. In this way, the 3D problem reduces to 2D by helical symmetry, allowing for the reconstruction of any poloidal plane in the field of view of the camera. It is shown in this article that the complexity of using a wavelet basis for the reconstruction, as presented by Nguyen van Yen, is not necessary. The method is also validated by confronting it to 3D numerical data coming from the TOKAM3X code, for which the emissivity is slowly varying along the field lines (up to 20 %), showing the robustness of the reconstruction. The technique is then applied to real camera data recorded during a D-shaped ohmic plasma shot realized in the COMPASS tokamak. The method is experimentally validated by comparing reconstructed data from camera and ion saturation currents measured by Langmuir probes in the divertor region. Finally, it is shown that automatic detection and tracking of structures visible in the reconstructed poloidal plane enables unique investigations of edge plasma physics and opens wide perspectives for this method.

Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened. Peer Reviewed Article escrit per 365 autors/autores: Labit, B.; Eich, T.; Harrer, G. F.; Wolfrum, E.; Bernert, M.; Dunne, M. G.; Frassinetti, L.; Hennequin, P.; Maurizio, R.; Merle, A.; Meyer, H.; Saarelma, S.; Sheikh, U.; Adamek, J.; Agostini, M.; Aguiam, D.; Akers, R.; Albanese, R.; Albert, C.; Alessi, E.; Ambrosino, R.; Andr be, Y.; Angioni, C.; Apruzzese, G.; Aradi, M.; Arnichand, H.; Auriemma, F.; Avdeeva, G.; Ayllon-Guerola, J. M.; Bagnato, F.; Bandaru, V. K.; Barnes, M.; Barrera-Orte, L.; Bettini, P.; Bilato, R.; Biletskyi, O.; Bilkova, P.; Bin, W.; Blanchard, P.; Blanken, T.; Bobkov, V.; Bock, A.; Boeyaert, D.; Bogar, K.; Bogar, O.; Bohm, P.; Bolzonella, T.; Bombarda, F.; Boncagni, L.; Bouquey, F.; Bowman, C.; Brezinsek, S.; Brida, D.; Brunetti, D.; Bucalossi, J.; Buchanan, J.; Buermans, J.; Bufferand, H.; Buller, S.; Buratti, P.; Burckhart, A.; Calabr, G.; Calacci, L.; Camenen, Y.; Cannas, B.; Cano Megías, P.; Carnevale, D.; Carpanese, F.; Carr, M.; Carralero, D.; Carraro, L.; Casolari, A.; Cathey, A.; Causa, F.; Cavedon, M.; Cecconello, M.; Ceccuzzi, S.; Cerovsky, J.; Chapman, S.; Chmielewski, P.; Choi, D.; Cianfarani, C.; Ciraolo, G.; Coda, S.; Coelho, R.; Colas, L.; Colette, D.; Cordaro, L.; Cordella, F.; Costea, S.; Coster, D.; Cruz Zabala, D. J.; Cseh, G.; Czarnecka, A.; Cziegler, I.; D’Arcangelo, O.; Dal Molin, A.; David, P.; De Carolis, G.; De Oliveira, H.; Decker, J.; Dejarnac, R.; Delogu, R.; Den Harder, N.; Dimitrova, M.; Dolizy, F.; Domínguez-Palacios Durán, J. J.; Douai, D.; Drenik, A.; Dreval, M.; Dudson, B.; Dunai, D.; Duval, B. P.; Dux, R.; Elmore, S.; Embréus, O.; Erds, B.; Fable, E.; Faitsch, M.; Fanni, A.; Farnik, M.; Faust, I.; Faustin, J.; Fedorczak, N.; Felici, F.; Feng, S.; Feng, X.; Ferreira, J.; Ferr, G.; Février, O.; Ficker, O.; Figini, L.; Figueiredo, A.; Fil, A.; Fontana, M.; Francesco, M.; Fuchs, C.; Futatani, S.; Gabellieri, L.; Gadariya, D.; Gahle, D.; Galassi, D.; Gałązka, K.; Galdon-Quiroga, J.; Galeani, S.; Gallart, D.; Gallo, A.; Galperti, C.; Garavaglia, S.; Garcia, J.; Garcia-Lopez, J.; Garcia-Mu oz, M.; Garzotti, L.; Gath, J.; Geiger, B.; Giacomelli, L.; Giannone, L.; Gibson, S.; Gil, L.; Giovannozzi, E.; Giruzzi, G.; Gobbin, M.; Gonzalez-Martin, J.; Goodman, T. P.; Gorini, G.; Gospodarczyk, M.; Granucci, G.; Grekov, D. 1; Grenfell, G.; Griener, M.; Groth, M.; Grover, O.; Gruca, M.; Gude, A.; Guimarais, L.; Gyergyek, T.; Hacek, P.; Hakola, A.; Ham, C.; Happel, T.; Harrison, J.; Havranek, A.; Hawke, J.; Henderson, S.; Hesslow, L.; Hitzler, F.; Hnat, B.; Hobirk, J.; Hoelzl, M.; Hogeweij, D.; Hopf, C.; Hoppe, M.; Horacek, J.; Hron, M.; Huang, Z.; Iantchenko, A.; Iglesias, D.; Igochine, V.; Innocente, P.; Ionita-Schrittwieser, C.; Isliker, H.; Ivanova-Stanik, I.; Jacobsen, A.; Jakubowski, M.; Janky, F.; Jardin, A.; Jaulmes, F.; Jensen, T.; Jonsson, T.; Kallenbach, A.; Kappatou, A.; Karpushov, A.; Kasilov, S.; Kazakov, Y.; Kazantzidis, P. 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T.; Walkden, N.; Wauters, T.; Weiland, M.; Weinzettl, V.; Wensing, M.; Wiesen, S.; Wiesenberger, M.; Wilkie, G.; Willensdorfer, M.; Wischmeier, M.; Wu, K.; Xiang, L.; Zagorski, R.; Zaloga, D.; Zanca, P.; Zaplotnik, R.; Zebrowski, J.; Zhang, W.; Zisis, A.; Zoletnik, S.; Zuin, M.

In this work we report on results of full size kinetic modelling of the COMPASS tokamak SOL. Presented simulations indicate, that i. kinetic effects are significant in the inner divertor (ID) plasma; ii. normalized power loads to the ID are above the classical values and are caused by non-Maxwellian super-thermal electrons; iii. different divertor current regimes do not influence overall SOL parameters, except those of the divertor sheath; iv. ions at the divertors plasma are colder than the electrons; v. parallel heat transport is strongly non-local. Modelling results are in a reasonable agreement with the experimental measurements.

We present a uniquely fast (10 μs) ion temperature measurements in the tokamak edge plasma. Our approach is based on the sweeping of a ball-pen probe, where the ion temperature is obtained by fitting the electron branch of the corresponding I–V characteristic. We have performed measurements on the COMPASS tokamak during L-mode discharge. The temperature histograms reveal a non-Gaussian shape with a high-temperature tail peaking at low values. The fitted values of fast I–V measurements can be used to reconstruct (emulate) the slow swept I–V characteristic of a retarding field analyzer. The resulting ion temperature profile is nearly flat and provides a ratio of ion to electron temperature close to 1–2 in the vicinity of the last closed flux surface during L-mode discharges, as observed on other tokamaks.

Power handling experiments with a special liquid metal divertor module based on the capillary porous system technology were performed in the tokamak COMPASS. The performance of two metals (Li and LiSn alloy) were tested for the first time in a divertor under ELMy H-mode conditions. No damage of the capillary mesh and a good exhaust capability were observed for both metals in two separate experiments with up to 12 MW/m(2) of deposited perpendicular, inter-ELM steady-state heat flux and with ELMs of relative energy similar to 3% and a local peak energy fluence at the module similar to 15 kJ.m(-2). No droplets were directly ejected from the mesh top surface and for the LiSn experiment, no contamination of the core and SOL plasmas by Sn was observed. The elemental depth profile analysis of 14 stainless-steel samples located around the vacuum vessel for each experiment provides information about the migration of evaporated/redeposited liquid elements.

Bei der Descemet-Membran-Endothel-Keratoplastik (DMEK) ist ein hyperoper Shift, d. h. eine Verschiebung der Refraktion in Richtung Pluswerte, beschrieben. Dies ist besonders bei der Kombination mit einer Kataraktoperation (Triple-DMEK) wegen der erforderlichen Auswahl einer Intraokularlinse relevant. In der vorliegenden Arbeit wurden die durch Triple-DMEK induzierten refraktiven Veranderungen ausgewertet. Es erfolgte eine Aufschlusselung der zugrunde liegenden Mechanismen anhand gemessener topographischer Daten. Retrospektive Auswertung bei 29 Augen von 26 Patienten mit einer Triple-DMEK. Die pra- und postoperative Refraktion wurde mit der ursprunglich angestrebten Zielrefraktion verglichen. Anhand hornhauttopographischer Daten erfolgten Berechnungen zur Brechkraft mittels der Gullstrand-Formel. Im Mittel kam es zu einem hyperopen Shift. Die Operation fuhrte zu einer Aufsteilung der Hornhautruckflache und Abflachung der Hornhautvorderflache. Beides bedingte jeweils eine Abnahme der kornealen Brechkraft, wobei die Veranderungen der Ruckflache als der wichtigste Faktor identifiziert wurden. Diejenigen Patienten, die mit beiden Augen in der Studie reprasentiert waren, erreichten unabhangig von den praoperativen Werten sehr ahnliche postoperative Topographien beider Augen. Bei dem beobachteten hyperopen Shift handelte sich um einen Mittelwert. Eine Vorhersage der Refraktion im konkreten Einzelfall war anhand der gemessenen Parameter nicht moglich. Generell ist die Auswahl einer IOL mit einer starker myopen Zielrefraktion als bei einer standardmasigen Kataraktoperation zu empfehlen.

Microsecond probe measurements of the electron temperature during the tokamak edge localised mode (ELM) instability show that the peak values significantly exceed those obtained by conventional techniques. The temperatures measured at the plasma facing component (divertor) are around 80% of the initial value (at the pedestal). This challenges the current understanding, where only several percent of the pedestal value are measured at the divertor. Our results imply a negligible energy transfer from the electrons to the ions during the ELM instability, and therefore no associated increase of the ion power loads on the divertor. This observation is supported by the simple analytic free-streaming model, as well as by full kinetic simulations. The energetic ELM ion loads are expected to be one of the main divertor damaging factors; therefore, the obtained results give an optimistic prediction for next generation fusion devices.

Uncertainties and errors in magnetic equilibrium reconstructions are a wide-spread problem in interpreting experimental data measured in the tokamak edge. This study demonstrates errors in EFIT++ reconstructions performed on the COMPASS tokamak by comparing the outer midplane separatrix position to the Velocity Shear Layer (VSL) position. The VSL is detected as the plasma potential peak measured by a reciprocating ball-pen probe. A subsequent statistical analysis of nearly 400 discharges shows a strong systematic trend in the reconstructed separatrix position relative to the VSL, where the primary factors are plasma triangularity and the magnetic axis radial position. This dependency is significantly reduced after the measuring coils positions as recorded in EFIT input are optimised to provide a closer match between the "synthetic" coil signal calculated by the Biot-Savart law in a vacuum discharge and the actual coil signal. In conclusion, we suggest that applying this optimisation may lead to more accurate and reliable reconstructions of the COMPASS equilibrium, which would have a positive impact on the accuracy of measurement analysis performed in the edge plasma., Comment: Published in the Journal of Instrumentation, 2019

This paper describes a new filamentary probe recently introduced on the COMPASS tokamak. It allows the measurement of electrostatic and magnetic properties of the filaments and their changes in dependence on distance from the separatrix in the region between a divertor and midplane. The probe head is mounted on a manipulator moving the probe radially on a shot-to-shot basis. This configuration is suitable for the long term statistical measurement of the plasma filaments and the measurement of their evolution during their propagation from the separatrix to the wall. The basics of the filamentary probe construction, the evolution of the plasma parameters, and first conditional averages of the plasma filaments in the scrape-off layer of the COMPASS tokamak during the L-mode regime are presented.

We report the latest results on fast measurements of the electron temperature and parallel heat flux in the COMPASS tokamak scrape-off layer (SOL) and divertor region during ELMy H-mode plasmas. The system of ball-pen and Langmuir probes installed on the divertor target, the horizontal reciprocating manipulator and the fast data-acquisition system with sampling frequency rate f = 5 MSa s−1 allow us to measure the electron temperature and parallel heat flux during inter-ELM and ELM periods with high temporal resolution. The filamentary structure of the electron temperature and parallel heat flux was observed during ELMs in the SOL as well as in the divertor region. The position of the filaments within ELMs is not regular and therefore the resulting conditionally averaged ELM neglects the peak values of the electron temperature and parallel heat flux. We have found a substantial difference between the value of the radial power decay length in the inter-ELM period λ q,inter = 2.5 mm and the decay length of the peak ELM heat flux λ q,ELM = 13.1 mm. The decay length of the ELM energy density was found to be λ E,ELM = 5.4 mm.

Experimental investigations of the plasma potential by means of a ball-pen probe and self-emitting Langmuir probe technique were performed on the tokamaks COMPASS and ASDEX Upgrade. A spontaneous transition between the cold and self-emitting Langmuir probe has been observed during the deep reciprocation in the vicinity or even inside the last closed flux surface (LCFS) of both tokamaks. These measurements of the plasma potential allow us to compare two independent probe techniques based on heating and non-heating processes. The observed different conditions of the spontaneous transition can be ascribed to different physical mechanisms. Nevertheless, the comparison of the power spectra of ball-pen probe and self-emitting Langmuir probe indicates very good agreement in all measurements and therefore these two probe techniques are interchangeable. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New results from MAST are presented that focus on validating models in order to extrapolate to future devices. Measurements during start-up experiments have shown how the bulk ion temperature rise scales with the square of the reconnecting field. During the current ramp up models are not able to correctly predict the current diffusion. Experiments have been performed looking at edge and core turbulence. At the edge detailed studies have revealed how filament characteristic are responsible for determining the near and far SOL density profiles. In the core the intrinsic rotation and electron scale turbulence have been measured. The role that the fast ion gradient has on redistributing fast ions through fishbone modes has led to a redesign of the neutral beam injector on MAST Upgrade. In H-mode the turbulence at the pedestal top has been shown to be consistent with being due to electron temperature gradient modes. A reconnection process appears to occur during ELMs and the number of filaments released determines the power profile at the divertor. Resonant magnetic perturbations can mitigate ELMs provided the edge peeling response is maximised and the core kink response minimised. The mitigation of intrinsic error fields with toroidal mode number n>1 has been shown to be important for plasma performance., 34 pages, 10 figures. This is an author-created, un-copyedited version of an article submitted for publication in Nuclear Fusion. IoP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it

Currents flowing in the scrape-off layer (SOL) are routinely observed in a number of tokamaks. They are usually closed through the divertor plates, either between the inner and outer target or between different poloidal sections of each target. The most common driving mechanisms of SOL currents are the thermoelectric effect (due to electron temperature difference between the two targets) and Pfirsch-Schlüter flows caused by radial pressure gradient. The SOL currents are commonly used for diagnostic purposes-e.g. as ELM monitors or for real-time estimation the divertor electron temperature. In this paper, we report on attempts to extract the SOL currents and related electrical power from the tokamak COMPASS using a dedicated insulated divertor tile and electronics setup, which allows for fast switching between grounded and floating state. It is observed that plasma acts as an ideal power source and that the magnitude of SOL currents scales with upstream separatrix temperature T e,sep.

A hyperopic shift, i.e. a shift of refraction in the direction of plus values, in Descemet membrane endothelial keratoplasty (DMEK) is a well-known phenomenon. Because of the need to select an appropriate intraocular lens power this becomes particularly relevant in triple DMEK, which is a combination of DMEK and cataract surgery.In this study the refractive changes induced by triple DMEK were evaluated. The underlying mechanisms were classified based on corneal topographical data.The study involved a retrospective evaluation of 29 eyes from 26 patients who underwent triple DMEK. The preoperative and postoperative refractions were compared with the initially desired target refraction. Calculations concerning refractive power were performed using corneal topographical data and the Gullstrand formula.On average a hyperopic shift was observed. The operation led to steepening of the posterior corneal surface and flattening of the anterior corneal surface. Both resulted in a reduction of corneal refractive power but changes of the posterior corneal surface were identified as the most important factor. Those patients in whom both eyes had been operated on, showed very similar postoperative topography for both eyes, irrespective of the preoperative values.The observed hyperopic shift was a mean value. A prediction of refraction in the individual cases by means of the available parameters was not possible. In general, the selection of an intraocular lens with a stronger myopic target refraction than that for standard cataract surgery is recommended.

The ball-pen probe (BPP) technique is used successfully to make profile measurements of the electron temperature on the ASDEX Upgrade (Axially Symmetric Divertor Experiment), COMPASS (COMPact ASSembly), and ISTTOK (Instituto Superior Tecnico TOKamak) tokamak. The electron temperature is provided by a combination of the BPP potential (ΦBPP) and the floating potential (Vfl) of the Langmuir probe (LP), which is compared with the Thomson scattering diagnostic on ASDEX Upgrade and COMPASS. Excellent agreement between the two diagnostics is obtained for circular and diverted plasmas and different heating mechanisms (Ohmic, NBI, ECRH) in deuterium discharges with the same formula Te = (ΦBPP - Vfl)/2.2. The comparative measurements of the electron temperature using BPP/LP and triple probe (TP) techniques on the ISTTOK tokamak show good agreement of averaged values only inside the separatrix. It was also found that the TP provides the electron temperature with significantly higher standard deviation than BPP/LP. However, the resulting values of both techniques are well in the phase with the maximum of cross-correlation function being 0.8.