F. Gandini

THE EC H&CD TRANSMISSION LINE FOR ITER

Abstract The transmission line (TL) subsystem associated with the ITER electron cyclotron heating and current drive system has reached the conceptual design maturity. At this stage the responsibility of finalizing the design has been transferred from the ITER Organization to the U.S. Domestic Agency. The purpose of the TL is to transmit the microwaves generated by the 170-GHz gyrotrons installed in the radio-frequency building to the launchers located in one equatorial and four upper tokamak ports. Each TL consists of evacuated HE11 waveguides, direct-current breaks, power monitors, mitre bends, polarizers, switches, loads, and pumping sections and will have a typical length that ranges from 100 to 160 m. Overall transmission efficiency could be as high as 92% depending on the specific path between a given gyrotron and launcher. All components are required to be 2-MW compatible, and their layout and organization have been optimized for simplifying the maintenance accessibility and monitoring the primary tritium barrier integrity. Two different TL layouts are at the moment under study, to accommodate the two alternative options for the European sources: four 2-MW units or eight 1-MW units. In this paper the actual design is presented and the technical requirements are discussed.

The targeted heating and current drive applications for the ITER electron cyclotron system

A 24 MW Electron Cyclotron (EC) system operating at 170 GHz and 3600 s pulse length is to be installed on ITER. The EC plant shall deliver 20 MW of this power to the plasma for Heating and Current Drive (H&CD) applications. The EC system is designed for plasma initiation, central heating, current drive, current profile tailoring, and Magneto-hydrodynamic control (in particular, sawteeth and Neo-classical Tearing Mode) in the flat-top phase of the plasma. A preliminary design review was performed in 2012, which identified a need for extended application of the EC system to the plasma ramp-up, flattop, and ramp down phases of ITER plasma pulse. The various functionalities are prioritized based on those applications, which can be uniquely addressed with the EC system in contrast to other H&CD systems. An initial attempt has been developed at prioritizing the allocated H&CD applications for the three scenarios envisioned: ELMy H-mode (15 MA), Hybrid (∼12 MA), and Advanced (∼9 MA) scenarios. This leads to the ...

High-Power Millimeter-Wave Calorimetric Beam Absorbers

Abstract Beam absorbers play an important role both in electron cyclotron heating systems at high power and in millimeter-wave diagnostics that need a low level of stray or reflected power. In the first case short- and long-pulse loads are used, whose back-reflection can be kept within a few percent with proper techniques. In the second case, absorbers or scramblers are envisaged, to be put in hostile environments. At Istituto di Fisica del Plasma in Milan, a number of calorimetric loads have been developed, adopting several techniques for overall reflectivity reduction, which are suitable for beam sinking with calorimetric capability. They achieve a low overall reflectivity and high-power capability by a properly chosen power distribution in the absorbing wall provided by a dispersing mirror, by a smooth geometrical shape, by heat-resistant absorbing coatings of optimized thickness, and by accurate trapping of most of the escaping radiation with preload structures. Fundamental, when it becomes impossible to diffuse the incoming beam by the mirror alone, mostly because of side lobes at large angles, is the use of a newly developed phase-scrambling surface presented in this paper. It provides the necessary spreading, complementing all the other techniques into a set that can be helpful in designing millimeter-wave systems and diagnostics, in order to reduce spurious or unwanted signals.

ECH/ECCD applications for MHD studies and automatic control in FTU tokamak

Abstract The paper describes experimental studies performed on the FTU tokamak on magnetohydrodynamic (MHD) instabilities and their active control by electron cyclotron (EC) heating and EC current drive (ECH/ECCD). It deals in particular with implementing of an automatic system that detects both the onset and localization of tearing modes and the localization of the EC power deposition and that is capable of actuating the stabilizing reaction with ECH/ECCD. The system is composed of a digital signal processor–based control unit to analyze electron temperature fluctuations (mostly from EC emission) and Mirnov coil data and to control gyrotron power supplies. The action is provided by an arrangement of four Gaussian beams at 140 GHz, coupling up to 1.6 MW power in total. The detection/reaction system, successfully tested in the experiments described, is very fast since no mirror motion is foreseen. In fact, the Gaussian beams are preliminarily oriented in an array covering the whole region where the mode is expected, and only the one closest to the mode is switched on at its appearance. The measurement of the deposition layer σdep is performed by analyzing the transient response to modulated EC power. Different modulation waveforms are used, both periodic and pseudorandom, in order to select the most sensitive and fastest technique.

Directional Couplers-Polarimeters for High-Power Corrugated Waveguide Transmission Lines

Abstract Compact directional couplers-polarimeters were developed for the circular corrugated waveguide transmission lines of the joint IFP-ENEA Electron Cyclotron Resonance Heating experiment at 140 GHz, 2 MW on the Frascati Tokamak Upgrade in Frascati. A linear array of cutoff holes was drilled in the mirrors of the quasi-optical miter bends. The radiated pattern preserves the symmetry and polarization of the waveguide mode in the plane of the array. The direction of propagation is preserved too. Two pairs of standard gain horns with detectors are placed in the plane of the array along the propagation axes of incident and reflected radiation to detect both linear components. The whole assembly is enclosed in a shielded anechoic box of suitable geometry.

A Low-Sidelobe, High Frequency Corrugated Feed Horn for CMB Observations

We have produced a prototype broadband, low-sidelobe conical corrugated feed horn suitable for measurements of the Cosmic Microwave Blackground (CMB) radiation in the frequency band 120–150 GHz. The antenna is a first prototype for the Low Frequency Instrument array in ESAs PLANCK mission, a space project dedicated to CMB anisotropy mesurements in the 30–900 GHz range. We describe the fabrication method, based on silver electro-formation, and present the two-dimensional antenna beam pattern measured at 140 GHz with a milimeter-wave automated scalar test range. The beam has good symmetry in the E and H planes with a far sidelobe level approaching –60 dB at angles ∼ 80°. An upper limit to the return loss was measured to be –21 dB.

MHD Structure Analysis by Singular Value Decomposition as a Tool for ECRH RT‐Control of Instabilities on FTU

In this work we present the results obtained applying Singular Value Decomposition (SVD) on a Mirnov coil array in FTU discharges where experiments on MHD stabilization or disruption avoidance via ECRH were performed. In these shots the mode analysis has been consolidated off line by means of FFT and SXR‐tomography. Although the Mirnov setting was not necessarily optimised, results show that the algorithm based on SVD is able to detect the mode with a precision equal or better than the FFT, while acting on a smaller time interval. The short execution time required, even in the present preliminary form, suggests that this analysis can be a suitable tool to be implemented in a real time control chain.

Evaluation of EC stray radiation in ITER and its implication for diagnostics

Antoine Sirinelli∗a, Franco Gandini, Mark Henderson, Johan W. Oosterbeekb and George Vayakis ITER Organization Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France. aFircroft Engineering Lingley House, 120 Birchwood Point, Birchwood Boulevard, Warrington, WA3 7QH, UK. bEindhoven University of Technology P.O. Box 513, 5600 AZ, Eindhoven, The Netherlands. E-mail: Antoine.Sirinelli@iter.org

The Engineering Analysis in Support of the ITER Electron Cyclotron Heating and Current Drive Transmission Lines

Abstract An engineering study has been performed on the ITER electron cyclotron transmission lines with the aim of optimizing its conceptual design. The support types and optimum spacing, cooling, vacuum, seismic, and gravitational effects were reviewed. For the vacuum system it was shown that two pumps per line, with a capacity of 50 l/s, are sufficient. It was explained that the temperature variation inside the building is the predominant factor that influences the thermal expansion of the lines. The support strategy is one of minimizing the number of constraints. Variation in support interspacing reduces the degree of harmonic disturbances. The section of transmission line inside the ITER port cell was identified as critical with regards to occurrence of deformation and stresses. Potential solutions are described. The use of seismic breaks is discussed in light of the differences in foundation and structure of the ITER tokamak building and assembly hall. It is proposed that this interface be studied in more detail, after more data is available on the behavior of these buildings. The geometry of individual supports should be simple, with the fewest possible adjustments. The supports are designed to allow small movements of the waveguide to compensate for the thermal expansion or contraction. The transmission line system can be made for optimum alignment during nominal operating temperatures by prestressing during installation.

Status and functional capabilities of ITER EC H&CD system

Summary form only given. A 24MW CW Electron Cyclotron Heating and Current Drive (EC HC present day systems are operating in relatively short pulses (≤10s) and installed power levels of ≤4.5MW.