The Electron Cyclotron (EC) system for the ITER tokamak is designed to inject >= 20 MW RF power into the plasma for Heating and Current Drive (H&CD) applications. The EC system consists of up to 26 gyrotrons (between 1 and 2 MW each), the associated power supplies, 24 transmission lines and 5 launchers. The EC system has a diverse range of applications including central heating and current drive, current profile tailoring and control of plasma magneto-hydrodynamic (MUD) instabilities such as the sawtooth and neoclassical tearing modes (NTMs). This diverse range of applications requires the launchers to be capable of depositing the EC power across nearly the entire plasma cross section. This is achieved by two types of antennas: an equatorial port launcher (capable of injecting up to 20 MW from the plasma axis to mid-radius) and four upper port launchers providing access from inside of mid radius to near the plasma edge. The equatorial launcher design is optimized for central heating, current drive and profile tailoring, while the upper launcher should provide a very focused and peaked current density profile to control the plasma instabilities.The overall EC system has been modified during the past 3 years taking into account the issues identified in the ITER design review from 2007 and 2008 as well as integrating new technologies. This paper will review the principal objectives of the EC system, modifications made during the past 2 years and how the design is compliant with the principal objectives. (C) 2011 ITER Organization. Published by Elsevier B.V. All rights reserved.

A 24MW CW Electron Cyclotron Heating and Current Drive (EC H&CD) system operating at 170GHz is to be installed for the ITER tokamak. The EC system will represent a large step forward in the use of microwave systems for plasma heating for fusion applications; present day systems are operating in relatively short pulses (<= 10s) and installed power levels of <= 4.5MW. The magnitude of the ITER system necessitates a worldwide collaboration. This is also reflected in the EC system that is comprised of the power supplies, sources, transmission line and launchers. A partnership between Europe, India, Japan, Russia, United States and the ITER organization is formed to collaborate on design and R&D activities leading to the procurement, installation, commissioning and operation of this system.

The ITER ECRH upper launcher (UL) uses a steering mechanism assembly (SMA) to steer the beams in the appropriate location for controlling magnetohydrodynamic (MILD) activity in the plasma (NTMs and sawtooth oscillations).Switching and modulation rotation cycles with an accuracy of 0.1 degrees are requirements for Neoclassical Tearing Modes (NTMs) stabilisation in ITER.Two SMA prototypes have been manufactured. A test stand that reproduces the expected pneumatic configuration of the UL has been built to perform control tests on both SMA prototypes. The first SMA prototype has been tested, and tests on the second prototype are foreseen on the second half of the present year.An "off-the-shelf" commercial servo-valve with a HD controller has been used to control the pressure with good results for the switching cycle. These tests have shown that a more sophisticated control strategy will be needed to attain the desired accuracy for the modulation cycles, since the present controller presents a permanent tracking error for ramp commands.

A full quasi-optical setup for the internal optics of the Front Steering Electron Cyclotron Resonance Heating (ECRH) Upper Launcher for ITER was designed, proving to be feasible and favorable in terms of additional flexibility and cost reduction with respect to the former design [1]. This full quasi-optical solution foresees the replacement of the mitre-bends in the final section of the launcher with dedicated free-space mirrors to realize the last changes of directions in the launcher. A description of the launcher is given and its advantages presented. The parameters of the expected output beams as well as preliminary evaluations of truncation effects with the physical optics GRASP code are shown. Moreover, a study of mitre-bends replacement with single mirrors for multiple beams is described. In principle it could allow the beams to be larger at the mirror locations (with a further decrease of the peak power density due to partial overlapping) and has the additional advantage to get a larger opening with compressed beams to avoid conflicts with side-walls port. Constraints on the setup, arising both from the resulting beam characteristics in the space of free parameters and from mechanical requirements are taken into account in the analysis.

The purpose of the ITER electron cyclotron resonance heating (ECRH) upper launcher (UL), or antennae will be to provide localised current drive by accurately directing mm-wave beams up to 2MW, out of the four allocated upper port plugs, at chosen rational magnetic flux surfaces in order to stabilise neoclassical tearing modes (NTMs). This paper will present an overview of the UL, with emphasis on the mm-wave components. The mm-wave layout includes corrugated waveguide sections and a quasi-optical path with both focusing mirrors and plane steering mirrors. One of the essential components of the UL is the Steering Mechanism Assembly (SMA), providing variable poloidal injection angles fulfilling high deposition accuracy requirements at the plasma location. The Actuator principle and rotor bearings are frictionless and backlash free, avoiding tribological difficulties such as stickslip and seizure. The underlying working principle is the use of mechanically compliant structures. Validation and proof testing of the steering principle is achieved with an uncooled first prototype demonstrator. A second prototype is currently being manufactured, comprising the functionalities needed for the ITER compatible system such as water cooling and high power mm-wave compatibility. In order to perform the fatigue tests of the actuator bellows, a test facility has been built, under ITER-like vacuum and temperature working conditions. Results of the cyclic fatigue tests are compared to the various manufacturer standards and codes, combining stress and strain controlled material fatigue properties.

The aim of the ITER electron cyclotron heating and current drive upper launcher (UL) is to control magnetohydrodynamic activity in the plasma, in particular neoclassical tearing modes, requiring a narrow and peaked deposition of the radio-frequency (rf) power.The millimeter-wave (mm-wave) system of the UL is optimized to ensure that the eight rf beams are all focused to a small beam width at the resonance location. The present design uses two mitre bends per beam and a focusing mirror for each set of four beams, orientating each set onto a single steering mirror (SM) to inject it into the plasma. The SM is rotated using a frictionless and backlash free pneumo-mechanical system. A first prototype of the SM has been constructed to demonstrate the manufacturability and the actuation principle and to develop an adequate control strategy.A test program has been developed to ensure the integrity of the launcher from the pre-build-to-print design phase (research and development) up to the tests after maintenance.This paper presents a general overview of the system, a description of the progress in the mm-wave optical layout, low-power tests, alignment specifications of the mm-wave components, and SM capabilities to meet the ITER requirements.

Four of the 16 ITER upper port plugs will be devoted to electron cyclotron resonance heating (ECRH) in order to control the magneto-hydrodynamic (MHD) instabilities.In order to achieve the stabilisation of the neoclassical tearing modes (NTM) and sawtooth oscillation, a deposition of a very localized, narrow and peaked current density profile over a broad poloidal steering range at the ITER rational surfaces q=1 to q=3/2 and q=2 is required [1]. The quasi-optical configuration consists of eight mm-wave beams entering each of the four upper launchers (UL) through waveguides into the vacuum vessel. Each beam is then directed to the plasma using a serial arrangement of four mirrors, the first set of 2 (mirrors M1 and M2) zigzag the beam line to avoid stray radiation, while the beam-waist locations and beam-shaping properties in the vacuum vessel are defined by the last two mirrors, a static focusing mirror (M3) and a flat poloidally-steerable mirror (M4). These last mirrors (M3 and M4) reflect a group of four beams coming of four individual M1/M2. The plane mirror M4 is steered using a backlash and friction free mechanism that is pneumatically actuated using helium gas. A first prototype of this has been manufactured as a proof of principle and tested for controller design purposes. A second prototype, ITER compatible in terms of the materials used and cooling circuits, will be subject to similar tests throughout the last half of 2009 period.The UL mirrors (static and steerable) absorb heat generated essentially by three sources: the ohmic loss of the RF beam reflected at the mirror surfaces (which is mirror-temperature dependant) and by nuclear (volumetric heating) and thermal radiation (surface heating) coming from the plasma. While the average heat load is calculated to be 2MW beam compatible with reasonable engineering limits, three more important constraints conditioned the actual mirror design, the peak ohmic heat load (the electromagnetic forces generated in ver- tical disruption events (VDE), and the ITER cooling water requirements. This paper provides an overview of the different upper port-plug mirror designs and stresses several different prototype manufacturing methods for the steering mirror, outlining lessons learned.

Reference EPFL-CONF-148659 URL: http://www.iter-india.res.in/ecrhannouncement.php URL: http://crpplocal.epfl.ch/pinboard/papers/091201203.pdf Record created on 2010-05-04, modified on 2017-05-12

The main objective of the ITER ECRH Upper Launcher (UL) is to control magnetohydrodynamic (MHD) activity: sawtooth oscillations and neoclassical tearing modes. 170GHz RF beams are oriented and focused to obtain a maximum overlapping of the waists of all the beams throughout the deposition location range in the plasma. The steering of the beams is done using 8 independent steering mirrors (SM) placed in the front par t of each one of the four dedicated por t plugs. Accurate and rapid control of the SMs for directing the beams at the required location is crucial in order to achieve an efficient MHD control. An assessment of the SM first prototype capabilities to meet the ITER requirements has been carried out giving promising results for this application.

The ITER electron cyclotron (EC) upper port antenna (or launcher) is nearing completion of the detailed design stage and the final build-to-print design stage will soon start. The main objective of this launcher is to drive current locally to stabilize the neoclassical tearing modes (NTMs) (depositing ECCD inside of the island that forms on either the q = 3/2 or 2 rational magnetic flux surfaces) and control the sawtooth instability (deposit ECCD near the q = 1 surface). The launcher should be capable of steering the focused beam deposition location to the resonant flux surface over the range in which the q = 1, 3/2 and 2 surfaces are expected to be found for various plasma equilibria susceptible to the onset of NTMs and sawteeth. The aim of this paper is to provide the design status of the principal components that make up the launcher: port plug, mm-wave system and shield block components. The port plug represents the chamber that provides a rigid support structure that houses the mm-wave and shield blocks. The mm-wave system comprises the components used to guide the RF beams through the port plug structure and refocus the beams far into the plasma. The shield block components are used to attenuate the nuclear radiation from the burning plasma, protecting the fragile in-port components and reducing the neutron streaming through the port assembly. The design of these three subsystems is described; in addition, the relevant thermo-mechanical and electro-magnetic analyses are reviewed for critical design issues.

The purpose of the ITER ECRH upper port antenna (or launcher) will be to drive current locally to stabilise the NTMs (depositing ECCD inside of the island that forms on either the q=3/2 or 2 rational magnetic flux surfaces) and control the sawtooth instability (deposit ECCD near the q=1 surface). The launcher should be capable of steering the focused beam deposition location to the resonant flux surface over the range in which the q=1, 3/2 and 2 surfaces are expected to be found, for the various plasma equilibria susceptible to the onset of NTMs and sawteeth. ITER’s present reference design uses a front steering (FS) concept, with the moveable mirror close to the plasma. Two separate mirrors are used to decouple the focussing and steering aspects resulting in an optimised optical configuration providing a well focused beam over a large steering range. The launcher is capable of steering eight 2MW beams in all of the four allocated upper port plugs. Details of the FS launcher design relating to physics performance, mm-wave optical design and steering mechanism design are discussed in this paper. Introduction ITER is planned to have 24MW of installed EC power, which will be launched into the plasma via either the equatorial (EL) or upper (UL) launchers [1,2]. A remote controllable switch deviates the power to either launcher depending on the physics requirements as defined in the ITER Project Integration Document [3]. Initially, the four ports of the UL were dedicated to the single application of stabilising the neoclassical tearing modes [4] that could occur on either the q=3/2 or 2 flux surfaces in the relevant scenarios 2, 3a and 5. This translates into a steering range accessing 0.52 ≤ ρtor ≤ 0.85, where ρtor being the square root of the normalized toroidal flux. This steering range provided an adequate coverage to accommodate the uncertainties of the flux surfaces that will one day be realised in ITER. The single port of the EL was dedicated to all other physics applications (sawtooth control, central heating and current drive) as illustrated in figure 1a. This partitioning of applications had several shortcomings, mainly because the single port EL was given the majority of the physics applications, while the four port UL was dedicated to the single task of NTM stabilistation. The EL required a relatively large steering range accessing from on axis to ρtor ~ 0.55. Due to geometrical limitations the EL could not deposit the full power over the entire steering range and resulted in less than 100% full pass absorption in the outer 20% of its steering range [5] (see red band regions of figure 1a) FIGURE 1. (a) The capabilities of the EC system based on the PID (<2007) and (b) that offered with the launcher synergy. Note that the vertical axis corresponds to ρpol (square root of the poloidal flux) and not ρtor. A revision of the physics objectives was proposed in Ref. [6] that partitioned the applications of each launcher based on the need for either a narrow current deposition (control of sawtooth [7] and NTMs) as provided by the UL or bulk current drive and central heating as provided by the EL. To achieve this, the UL had to have an increased steering range to access the q=1 surfaces, or into ρtor ~ 0.3. This alleviates the EL of the required large steering range required (to access the q=1) and permits the launcher to be modified for better central coverage and the potential for counter ECCD and pure heating capabilities as outlined in Ref. [6] and illustrated in figure 1b. Note that the counter ECCD is useful for control of the q-profile in advanced (scenario 3a) and reverse shear (scenario 4) scenarios [8] as well as combining with co-ECCD to provide pure heating with no net current drive as has been demonstrated on ASDEX-Upgrade [9]. Note that the EC system is the only heating and current drive source on ITER that can provide either co-ECCD, counter-ECCD or pure heating, simultaneously with the capability to vary the deposition location and all via external actuators. These functions provide minor modifications to the EL, while increasing the flexibility of the EC systems to be applicable to a greater number of plasma scenarios. The key issue in achieving the full capabilities of the EC system 8Ass illustrated in figure 1b) is to increase the steering range of the UL, which has been achieved in the enhanced performance launcher (EPL) design [2]. The two steering mirrors of the UL are directed to two overlapping regions in the plasma cross section, 0.3 ≤ ρtor ≤ 0.8 for the upper steering mirror (USM) and 0.55 ≤ ρtor ≤ 0.85 for the lower steering mirror (LSM) as illustrated in figure 2. The overall steering range of each mechanism is actually decreased to reduce the induced stresses and prolong the steering mechanism longevity prior to the onset of cyclic fatigue. Note this design was prompted by ITER-IT request that the front steering launcher design use four upper ports (even though only three ports are required for steering the 24 beams) with the fourth port used to increase the launchers functionality and reduce the engineering constraints, both of which have been achieved at the cost of an additional fourth port to the European parties procurement package. The enhanced performance offered by the revision of the UL has now been incorporated in the revised PID [10]. FIGURE 2. The EPL has the range of the two steering mirrors (USM and LSM) scanning two different regions such that a larger region in the plasma is accessible. Each steering mirror can inject up to 13.3MW, the full 20MW can be deposited in the overlap region. Enhanced Performance UL design A simplified view of the current FS launcher design is shown in Figure 3. Eight circular HE11 waveguides (φWG=63.5mm, similar to the waveguide used in the transmission line) enter the port plug entrance on the right (note that there are four waveguides superimposed in this poloidal cut). Prior to the closure plate a diamond window and an in-line isolation valve is placed to provide the primary tritium barrier. The waveguide continue after the closure plate to a set of miter bends in a ‘dog-leg’ configuration used to angle the 8 beams (both in toroidal and poloidal directions) to two focusing mirrors with the incident beams partially overlapping in both toroidal and poloidal directions. The reflected beams are then directed downward to two flat steering mirrors, which redirect the beams into the plasma with a toroidal injection angle of β≈20o. FIGURE 3. The layout of the principle mm-wave components of the upper launcher. The deposition region of the two UL steering mirrors are displaced so that the upper steering mirror (USM) access further inward providing access to the inner NTMs and q=1 surfaces covering a range of ~0.3≤ρtor≤~0.8, while the lower steering mirror (LSM) access the outer NTMs covering a range of ~0.55≤ ρtor ≤0.85. An additional switching system is used prior to the port entrance that can deviate the beams coming from the 24 gyrotrons to either the 16 entrances associated with the USM or the 16 entrances with the LSM depending on the physics requirements. The optical design is optimized [11] so that the beam from the USM projects a slightly larger beam waist (29mm) further into the plasma to compensate for the longer path length as compared to the LSM with a waist of 21mm. This process was performed with dedicated beam tracing scans system [5,12] to insure a narrow and peaked jCD profile over the entire steering range. Note that four beams are incident on a single focusing and steering mirror, the overlapping of the beams permit the largest beam for a finite focusing mirror size within the confined space of the blanket shield module (BSM). The space in the BSM is shared between the mm-wave components and shield blocks to protect the components and port plug from the neutron flux. Nuclear analysis of the EPL has demonstrated that there is adequate shielding to protect both the critical components of the launcher and neighboring components [13]. Alternative configurations are under investigation to either improve the physics performance of the launcher, reduce complexity and/or to enhance maintenance access. For example, relocating the valves and windows located several meters from the closure plate alleviates the congestion at the port plug entrance and enhances the maintenance access to these components. Also replacing the mitre bends with free space mirrors improves the focusing of the beams for improved NTM stabilization efficiencies, while reducing the overall cost and complexity of the optical systems. These design modifications are under consideration for the next optical design of the launcher, which is expected for the end of 2007. Steering Mechanism design

The ITER ECRH upper port antenna (or launcher) will be used to drive current locally for stabilising the neoclassical tearing mode (NTM) by depositing ram-wave power inside of the island which forms on the q=3/2 or 2 rational magnetic flux surfaces and control the sawtooth instability by driving current near the q=l surface. This requires the launcher to be capable of steering the focused beam deposition location across the resonant flux surface over the range where the q=l, 3/2 and 2 surfaces are expected to be found (roughly the outer half of the plasma). ITER'S present reference design uses a front steering (FS) concept, which uses a moveable mirror close to the plasma. Two separate mirrors are used to decouple the focusing and steering aspects resulting in an optimized optical configuration providing a well focused beam over a large steering range. The steering mechanism providing the mirror rotation uses a frictionless and backlash free mechanical system based on the elastically compliant deformation of structural components to avoid the in vessel tribological difficulties. Traditional designs are based on push-pull rods acting on a mirror which rotates with ball bearings, they present the risk of gripping or result in stick-slip movements. The ball bearings are replaced with a set of flexure pivots while the classic actuation through a push-pull rod scheme is replaced by a directly acting pneumatic system consisting on a fast feed line, bellows and springs, in which the pressure acting on the bellows pushes the mirror against the compressive springs. The rotation of the mirror is thus produced by the counteraction between the forces exerced by the springs and the bellows, themselves piloted by the pressure of the system. A servovalve placed outside of the port plug and connected to the bellows by a small tube will control this pressure. The system also includes flexible water cooling pipes which allow the removal of heat generated by the ohmic surface losses of the reflected mm-wave beams and the nuclear and radiation volumic heating of the rotating mirror components. This paper will give an overview of the engineering and design issues and their solutions, and provide the development status of the different components of the mechanism. Special attention will be given to the engineering analysis performed to ensure compliance of the steering mechanism with the various ITER requirements.

Reference CRPP-CONF-2007-039 URL: http://sofe22.sandia.gov/ Record created on 2008-05-13, modified on 2017-05-12