Status Status of the final design of the EC UPP launcher

Four EC H&CD (Electron Cyclotron Heating and Current Drive) launchers will be installed into the upper ports #12, #13, #15 and #16 in ITER. Beside plasma heating their main purpose is to counteract plasma instabilities by injecting up to 20 MW of microwave power at a frequency of 170 GHz at dedicated positions into the plasma. The microwave power is generated in 24 Gyrotrons outside the Tokamak and transmitted into the dedicated ports by 8 waveguide lines per launcher. After passing a CVD (Chemical Vapor Deposition) diamond window and another section of circular waveguides, the microwaves are quasi-optically guided into the plasma by an adjusted set of mirrors. These mirrors and also the foremost segments of the waveguides are mounted into the Upper Port Plug, which is a massive steel structure capable to dissipate up to 800 kW heat and to withstand heavy mechanical loads induced mainly from plasma disruptions. This paper presents the most recent status of the design of the EC H&CD Upper Port Plug (UPP), featuring the construction of the supporting structure and the BSM (Blanket Shield Module) with its plasma facing First Wall, the PHTS (Primary Heat Transfer System) water cooling layout, the shielding components engineering, the microwave system integration and comprehensive manufacturing strategies. Also correlated computational analyses to prove the final design of the launchers structural system are given.

An alternative ECRH front steering launcher for the ITER upper port

René Chavan, Francisco Sanchez

Presently, a remote steering (RS) antenna [C.P. Moeller, A method of remotely steering a microwave beam launched from a highly overmoded corrugated waveguide, in: Proceedings of the 23rd International Conference on IRMMW, Colchester, UK, 1998] is envisioned for launching the electron cyclotron current drive (ECCD) from the ITER upper port. The RS launcher has a strong engineering advantage in that the steering mechanism is placed outside of the ITER blanket, however, at the cost of reduced performance. In particular, the launcher has a limited steering range and a wide deposition width that results in submarginal performance for neoclassical tearing mode (NTM) stabilization. An alternative front steering (FS) launcher is proposed [M.A. Henderson, R. Chavan, F Sanchez, Front Steering ECCD Launcher Study for the ITER upper port, CRPP LRP 791/04], which has a wider steering range and a narrower deposition width offering above marginal performance for all plasma equilibria investigated. A two-mirror system (one focusing and one flat steerable) is used to project the RF beam waist far into the plasma. The steering mechanism avoids frictional surfaces that risk to block during operation and uses a gaseous He pneumatic system as a control actuator. D 2005 Published by Elsevier B.V.

2005

Plasma production and transport in a simple magnetised toroidal plasma

Mario Podesta

This Thesis addresses questions related to transport phenomena and the plasma production mechanisms by injection of microwaves in the electron-cyclotron frequency range in the simple magnetised toroidal plasma TORPEX. The second subject is investigated in detail in Part II. The mechanisms of the interaction between the injected microwaves and the plasma are identified. The experimental results highlight the different roles played by the electron-cyclotron and upper-hybrid plasma resonances in the absoprtion of the microwave power by the plasma. The effects of the plasma-wave interaction on the electron distribution function are investigated, confirming that the high-energy electrons that are able to ionise the neutral gas mainly come from interactions at the upper-hybrid resonance. Based on the experimental results, an expression is derived for the particle source term, which can be used in numerical codes simulating the plasma dynamics on TORPEX. The plasma production mechanisms are then related to the properties of the time-averaged plasma profiles. A set of control parameters, including the injected microwave power and the vertical magnetic field, are identified. These allow one to vary in a systematic way the plasma profiles, as needed for a detailed study of plasma instabilities and related transport. The study of particle and heat transport is undertaken in Part III. A number of experimental and analysis techniques, including a method based on the combination of "conditional-average sampling" and "boxcar-averaging", are applied to identify and quantify specific contributions to the total fluxes. The two-dimensional temporal behaviour of density, electron temperature and plasma potential is simultaneously reconstructed, thus contributing significantly to the characterisation of transport mechanisms at play in TORPEX plasmas. Two clearly distinct mechanisms are mainly responsible for the transport across the magnetic field. They are respectively associated to unstable low-frequency electrostatic modes, identified as drift waves and interchange modes, and to intermittent high-density plasma structures (or blobs). It is shown that the blobs originate from the intermittent radial expansion of the unstable modes in a region of strongly sheared E × B flow.

EPFL2007

Conceptual design of the EU DEMO EC-system: main developments and R&D achievements

Stefano Alberti, Konstantinos Avramidis, Falk Hans Braunmüller, Ioannis Pagonakis, Emanuele Poli, Minh Quang Tran

For the development of a DEMOnstration Fusion Power Plant the design of auxiliary heating systems is a key activity in order to achieve controlled burning plasma. The present heating mix considers electron cyclotron resonance heating (ECRH), neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH) with a target power to the plasma of about 50 MW for each system. The main tasks assigned to the EC system are plasma breakdown and assisted start-up, heating to L-H transition and plasma current ramp up to burn, MHD stability control and assistance in plasma current ramp down. The consequent requirements are used for the conceptual design of the EC system, from the RF source to the launcher, with an extensive R&D program focused on relevant technologies to be developed. Gyrotron: the R&D and Advanced Developments on EC RF sources are targeting for gyrotrons operating at 240 GHz, considered as optimum EC Current Drive frequency in case of higher magnetic field than for the 2015 EU DEMO1 baseline. Multi-purpose (multi-frequency) and frequency step-tunable gyrotrons are under investigation to increase the flexibility of the system. As main targets an output power of significantly above 1 MW (target: 2 MW) and a total efficiency higher than 60% are set. The principle feasibility at limits of a 236 GHz, conventional-cavity and, alternatively, of a 238 GHz coaxial-cavity gyrotron are under investigation together with the development of a synthetic diamond Brewster-angle window technology. Advanced developments are on-going in the field of multi-stage depressed collector technologies. Transmission line (TL): different TL options are under investigation and a preliminary study of an evacuated quasi-optical multiple-beam TL, considered for a hybrid solution, is presented and discussed in terms of layout, dimensions and theoretical losses. Launcher: remote steering antennas have been considered as a possible launcher solution especially under the constraints to avoid movable mirrors close to the plasma. With dedicated beam tracing calculations, the deposition locations coverage and the wave absorption efficiency have been investigated, considering a selection of frequencies, injection angles and launching points. An option for the EC system structure is proposed in clusters, in order to allow the necessary redundancy and flexibility to guarantee the required EC power in the different phases of the plasma pulse. Number and composition of the clusters are analysed to have high availability and therefore maximum reliability with a minimum number of components.