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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.

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.

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. © 2018 ENEA. Published by IOP Publishing Ltd on behalf of Sissa Medialab.

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.

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 < θ < 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.

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.

An increased power handling of rf-beam loads is required by the development of high power gyrotrons for fusion research, as well as the achievement of full capability to work under vacuum conditions, which is imposed by the use of evacuated transmission lines. New techniques were developed at IFP/CNR, leading to two prototypes. One is capable of 1 MW CW operation, while the second one is designed for precise measurements at short-pulses (0.1 s) at higher peak power (2 MW). Preliminary tests at 140 GHz, high power and long pulse (500 kW, 10 s) were performed. (c) 2005 Published by Elsevier B.V.

In this work results of the first D 2 /N 2 experiments in GyM, a linear device able to produce plasmas of interest for the ITER divertor ( n e 5 ⋅ 10 10 cm −3 , Te 5 eV, ion flux 3–5 ⋅ 10 20 m −2 s −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 ⋅ 10 23 m −2 . XPS analysis evidenced the formation of W x N y 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.

The non-axisymmetric magnetic field, naturally present in every tokamak, constraints the machine operational space. A set of dedicated ‘Error Field Correction Coils’ (EFCC) is proposed for JET, which will replace the unreliable existing ‘saddle coils’. The new coils are specified to compensate the main harmonic contribution to error field induced modes. The EFCC structural design comprises a cable coil wound in a metallic casing supported on the JET iron magnetic circuit. Existing power supplies will drive the coils. The EFCC are expected to be installed in 2001 JET shutdown.

For the electron cyclotron resonance heating (ECRH) system on the frascati tokamak upgrade (FTU), composed of four 0.5 MW gyrotrons pulsed for 0.5 s, two different calorimetric loads were designed to measure the mm-wave power at 140 GHz propagating either as a gaussian beam or as an HE(11) mode carried by an oversized corrugated waveguide. The first one, designed for low reflectivity and I MW power handling capability, is now routinely used for gyrotron testing, conditioning and optimization on the generator side of the transmission line at 500 kW, 0.5 s. The basic design of the load, with a substantial upgrading of the cooling system for adequate heat removal, has full CW operation capability. The other one, whose cylindrical shape allows positioning as a waveguide replacement, is occasionally used when tests on the transmitted power along the 40 m of waveguide are needed. The loads are described together with low power measurements of reflected radiation. (C) 2001 Elsevier Science BN. All rights reserved.

Barrier windows are critical components in electron cyclotron plasma heating/current drive (ECRH/ECCD) systems for fusion plasma experiments in which high frequency and high power microwave beams are used as additional heating or plasma profiles control. Even though material characteristics and thickness are chosen in order to reduce the absorbed power to a minimum, the window temperature is of major concern in high power, long pulse or CW operation. An infrared diagnostic device has been implemented on one of the boron nitride windows of the 140 GHz, 0.5 s, 0.5 MW per line ECRH system of the FTU tokamak. The evolution of the temperature of the barrier window can be monitored by acquisition of several IR emission profiles during the gyrotron pulse. Moreover, information on the beam pattern quality can be inferred. (C) 2001 Elsevier Science BN. All rights reserved.