Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios.

Ionic Chromatography (IC) has been applied to absolute quantification of ammonia contained in the gas exhaust collected during dedicated experiments executed to study the nitrogen conversion in ammonia. o During the experiments residual RGA and OES diagnostics were both used to monitoring the gas species and radicals resulting from the plasma. o Results indicate that the nitrogen conversion never exceeds 10% and is affected by isotopic and wall material effects

Since the 2016 IAEA Fusion Energy Conference, FTU operations have been mainly devoted to experiments on runaway electrons and investigations into a tin liquid limiter; other experiments have involved studies of elongated plasmas and dust. The tearing mode onset in the high density regime has been studied by means of the linear resistive code MARS, and the highly collisional regimes have been investigated. New diagnostics, such as a runaway electron imaging spectroscopy system for in-flight runaway studies and a triple Cherenkov probe for the measurement of escaping electrons, have been successfully installed and tested, and new capabilities of the collective Thomson scattering and the laser induced breakdown spectroscopy diagnostics have been explored.

The evidence of Parametric Decay Instabilities (PDI) excited by the ECH power injected in O-Mode has been explored in FTU Tokamak, using the Collective Thomson Scattering (CTS) diagnostic. The experiments show evidences to support the hypothesis of low-threshold excitation of waves generated by PDI mechanisms, formerly proposed in the case of 2nd harmonic X-mode injection in TEXTOR and ASDEX-U. Theoretical analysis predicts low-threshold parametric decay also for O-mode pump-wave injection, which can be injected in FTU at frequencies close to the first Harmonic EC resonance. Experiments were made at different magnetic fields, injecting the 140 GHz probe and observing the emission from the second antenna of the EC launcher in poloidally symmetric and asymmetric configurations, in presence of MHD islands. The signal is detected by the CTS radiometers, with a fast digitizer allowing the spectral reconstruction at very fine time and frequency scales. Different types of emissions are studied in detail, comparing them with the magnetic island rotation frequency in different plasma conditions. In order to locate the plasma volume originating the emissions, a new antenna and receiving line has been installed.

During the last years the Collective Thomson Scattering (CTS) system installed on the Frascati Tokamak Upgrade (FTU), operating at 140 GHz, has been exploited to investigate different kinds of phenomena: high-frequency daughter waves by Parametric Decay Instabilities, which, under certain conditions, are recently presumed to be conceivable even under routine ECRH scenarios, and bulk ions thermal emissions stimulated by a 140 GHz gyrotron beam. A new receiving line, giving rise to a second further line of sight from the plasma during the scattering experiments and integrated in the CTS antenna, has been recently completed and installed. Such new line will be useful to recognise signals originating in the volume of beams cross from the ones coupled outside or also to monitor the gyrotron's spectrum in real-time during the shot. The present status of this new installation is shown in the paper.

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Introduction Collective Thomson Scattering (CTS) emission has been studied to investigate the ion dynamics in the plasmas, exploiting the interaction between an injected high power microwave beam and the plasma collective fluctuations that scatter radiation with frequency spectra mainly characterised by ion features. Presently a CTS system is foreseen for ITER, with the main aim of characterizing Fusion born alpha particles [1]. CTS measurements of several bulk ion parameters as temperature, drift velocity and composition have been demonstrated in TEXTOR and in ASDEX [2-4]. The CTS system in FTU can operate in different "non-resonant" regimes, with the Electron Cyclotron resonances outside the plasma, as foreseen for the CTS system in ITER, allowing investigating bulk ions (thermal) features with low disturbance from ECE emission. Up to now, just few non-resonant discharges could be carried out in FTU as part of the experimental programme aimed at studying the effects of Parametric Decay Instabilities (PDIs) on ECH [5]. The scattering set up is described in section 1 and calibrated thermal spectra are compared (in section 2) for the first time with the power spectral densities (PSD) simulated with the Thermal Collective Scattering (TCS) code [6].

A new receiving antenna for collecting signals of the Collective Thomson Scattering (CTS) diagnostics in FTU Tokamak has been recently installed. The squared corrugated section and the precisely defined length make it possible to receive from different directions by remotely steering the receiving mirrors. This type of Remote-Steering (RS) antennas, being studied on FTU for the DEMO Electron Cyclotron Heating (ECH) system launch, is already installed on the W7-X stellarator and will be tested in the next campaign. The transmission of the signal from the antenna in the tokamak hall to the CTS diagnostics hall will be mainly realized by means of oversized circular corrugated waveguides carrying the hybrid HE11 (quasi-gaussian) waveguide mode, with inclusion of a special smooth-waveguide section and a short run of reduced-size square-corrugated waveguide through the tokamak bio-shield. The coupling between different waveguide types is made with ellipsoidal focusing mirrors, using quasi-optical matching formulas between the gaussian-shaped beams in input and output to the waveguides. In this work, after a complete study of feasibility of the overall line, a design for the receiving line will be proposed, in order to realize an executive layout to be used as a guideline for the commissioning phase.

Plasma position reflectometry for ITER requires interfaces between in-vessel and ex-vessel waveguides. An ultra broadband interface (15-75 GHz) was designed between moderately oversized rectangular waveguide (20 x 12 mm), operated in TE01 (i.e., tall waveguide mode), and circular corrugated waveguide, with 88.9-mm internal diameter, propagating HE11. The interface was designed both as a sequence of waveguide components and as a quasi-optical confocal telescope. The design and the simulated performance are described for both concepts. The latter one requires more space but has better performance, and shall be prototyped.

Atmospheric pressure plasmas have achieved great scientific and technological advances for a wide range of applications including the field of antimicrobial treatment. In this paper, a home-made atmospheric pressure plasma jet device was built and the effects of air plasma treatments on the inactivation of pure bacterial culture (Escherichia coli ATCC 8739) deposited onto the surface of agar plates were investigated. Plasmas were generated using high voltage discharge for 30, 60 and 90 s. The number of viable microorganisms was determined using a plate count method. Microbial Log10 reduction depended on the time of exposure and feed gas flow. A significant reduction of about 2.5 Log10 for E. coli was achieved within 60 s of plasma treatment. This result can be related to the presence of reactive species in the plasma volume, in particular, O radicals.

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Iron-tungsten (Fe-W) mixed films were exposed to the low flux deuterium plasma of GyM in order to study the behavior of the sputtering yield with the ion fluence and temperature of the samples. From literature, it is known that an increase of the former lowers the Fe-W layers' sputtering yield as a consequence of the preferential sputtering of Fe leading to an enrichment in W of the outermost layers. An opposite trend was instead found for the latter probably due to the inter-diffusion of Fe and W (effective from 200 degrees C) resulting in the suppression of the W enrichment. Moreover, from 500 degrees C, also W segregation to the surface occurs. What is missing from literature is a systematic investigation of the role of temperature on W enrichment. In this work, dedicated experiments in GyM were carried out to fill this gap. After exposure, W enrichment was evaluated by Rutherford Backscattering Spectrometry (RBS) and inferred from measuring the eroded thickness of the samples using RBS and profilometer. Concerning the Fe-W sputtering yield as a function of fluence, it decreases by a factor of similar to 3 between the lowest (3.0 x 10(22) D+ m(-2)) and the highest fluence (9.0 x 10(23) D+ m(-2)) values considered. The other main result is that, at the lowest fluence, the exposure at room temperature leads to an erosion of the Fe-W samples more pronounced than that associated to the exposure at 500 degrees C. (C) 2017 The Authors. Published by Elsevier Ltd.

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For a burning plasma device (ITER), the removal of radiative power by seed impurities will be inevitable to avoid divertor damage by excessive heat flux [1]. N2 gas is likely to be used to reduce the power load. However, because of re-deposition phenomena, WNx compounds will be produced in the divertor and tritium retention is issue of concern. We report experiments using the GYM linear plasma device that examined D retention in WNx compounds exposed to D plasma at divertor relevant fluence (? 1024 m-2) as a function of sample temperature (Ts) in the range of 300-730 K. In order to determine the D retention, the WNx specimens were examined ex situ by Elastic Recoil Detection Analysis (ERDA). It is shown that WNx compounds have very similar D retention, lower than the case of the tungsten without nitrogen and in any case lower than the acceptable limit for operation in ITER [2]. W-N samples were prepared by reactive plasma sputtering system. The morphological properties and physical structure of the samples were investigated by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Energy Dispersive X-ray (EDX).

In this work results of the first D2/N2 experiments in GyM, a linear device able to produce plasmas of interest for the ITER divertor (ne 5 ? 1010 cm-3, Te 5 eV, ion flux 3-5 ? 1020 m-2s-1) are presented. Plasmas simulating a N-seeding scenario have been performed to evaluate ammonia formation and its effect on exposed W coatings. The presence of ND emission lines in the plasma can be correlated with the formation of ammonia, further directly detected and quantified by chromatography analysis of the exhaust. Four different W specimens were exposed in GyM to a plasma fluence of 8.78 ? 1023 m-2. XPS analysis evidenced the formation of WxNy layers with nitrogen concentration in the range of 1-10% depending on the initial morphology and structure of the W samples. In all analyzed cases, nitrogen was bound and retained within the first 6 nm below the surface and no further diffusion of N into the bulk was observed.

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A new ECRH launcher mainly aimed at experiments on MHD stabilization has been recently installed in FTU and integrated with a Real Time controller. The new plug-in antenna is capable of injecting two beams over wide angular ranges, ±40 in toroidal and ±15 < ? < 44 in poloidal direction with fast mirror speed. The power is delivered to the launcher with two additional transmission lines (TL) connected to the existing ECRH system with remotely controlled switches. After the optical alignment of the TLs, a campaign of tests on the steering antenna was made with the launcher ex- and in-vessel. A procedure to calibrate the absolute mirror angular position was developed and successfully used. First high power pulses were carried out on plasma target delivering 2 × 0.3 MW EC power for 200 ms. © 2013 CNR-IFP Instituto di Fisica Plasma.

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The use of quadrupole mass spectrometers in plasma experiments with magnetic field confinement presents troublesome problems because of the presence of static magnetic fields. In mass spectrometers, the Lorentz force associated with the magnetic field deflects the ion trajectory in the analyzer section with a subsequent loss of instrument sensitivity. In order to reduce the effect of the externally applied magnetic field in the quadrupole, different magnetic materials have been considered as a shielding structure iron Fe-37, soft iron Armco(TM), Amumetal(TM) sheets. The present work describes a solution to shielding quadrupole mass spectrometers against strong magnetic fields giving an introduction to magnetic shield design, by means of finite element calculations, taking into account many factors such as the material used, the length and thickness of the shield, and the effects of openings. To prove the efficiency of the shielding system, the hydrogen signal from the quadrupole instrument has been monitored. The intensity and the direction of the magnetic field with respect to the quadrupole head axes have been varied. Measurements of the magnetic field have been made in order to validate the calculations and an example of application of the shield design guidelines to a magnetic confined plasma device is presented and tested in situ. The principal aim of the present work is to indicate a possible approach to the problem and how to obtain a practical solution with a worthy compromise between costs and performances.