D. Roux

The ECRH/ECCD system on Tore Supra, a major step towards continuous operation

The 118 GHz electron cyclotron heating and current drive (ECRH/ECCD) system under development in Cadarache, France, for use on the Tore Supra tokamak (Pain M. et al 1994 Proc. 18th SOFT (Karlsruhe) pp 481–4: Darbos C. et al 2000 Proc. 21st SOFT (Madrid) pp 605–9), is designed to launch 2.4 MW of power for up to 10 min into the plasma. At present two out of six gyrotrons are installed and available for injection of up to 800 kW. This paper concentrates on the generation and transmission of the ECRH/ECCD power for very long pulse operation. The power is injected into the plasma as Gaussian beams by an antenna which, using actively cooled mirrors inside the Tore Supra vacuum vessel, allows extensive control of both the poloidal and toroidal injection angles. The toroidal field on Tore Supra is normally in the range of 3.8–4 T, which for 118 GHz gives almost central deposition at the fundamental electron cyclotron resonance. A pair of actively cooled corrugated mirrors is installed in each matching optics unit at the output of each gyrotron allowing complete control of the polarization of the wave transmitted to the antenna, with the result that pure O-mode—or pure X-mode—power injection can be achieved for all injection angles. In tokamak experiments, a world record energy of 17.8 MJ has been injected into the plasma. New upgraded gyrotrons specified to produce 400 kW for up to 10 min will be introduced over the next 3–4 years.

Very long pulse testing of the TH 1506 B 118 GHz Gyrotron

Note: Proc. 14th Topical Conference on Radio Frequency Power in Plasmas, Oxnard, 7-9 May 2001, 477-481 (2001) Reference CRPP-CONF-2001-041 Record created on 2008-05-13, modified on 2017-05-12

The Tore Supra Front Steering Long Pulse ECRH Antenna. Past Experience - Present Evolution - Future Experiments

The long pulse capability of Tore Supra and its ECRH system makes it an ideal machine to prove steady state feedback control as required in ITER. Although Neoclassical Tearing Modes (NTMs) have not yet been observed on Tore Supra, the control of other MHD modes represents a very similar task from a control point of view and the stabilisation of such modes for long periods using ECRH will provide essential experience for the implementation of such control schemes on ITER. For this work to progress on Tore Supra, it must be possible to vary the injection angles in real time under feedback control from measured plasma parameters. At Tore Supra the front mirror position - and hence the injection angles - is adjusted using stepper motors controlled through a serial link. The use of a serial link limiting the sampling time for the control system to 50-100 ms and the dynamic response of the stepper motors results in a system frequency response <5 Hz. For following the evolution of the current profile this seems fully acceptable though it could prove somewhat slow for reacting to fast beta changes. In any case the time constants typically associated with growth rate of NTMs on ITER would not require a significantly faster system. Initial commissioning of such real time control was performed in 2004. Unfortunately, following a limited number of cycles and prior to using the system for plasma experiments, one water bellows in the antenna ruptured indicating a major weakness in the design of the water-cooling system for the antenna. As a consequence the water-cooling of the mobile mirror has been redesigned. Careful calculations and subsequent tests have been used to optimise the trajectories of the flexible water connections and a more robust layout is being implemented, ready for operation in the summer 2005.

Status of the ECRH system of Tore Supra

Summary form only given. A system working at the electron cyclotron resonance frequency is under construction at CEA Cadarache for heating and current drive experiments in the thermonuclear controlled fusion field of research. This system will be able to couple 3 MW with a 5 s pulse length or 2.4 MW for up to 600 s into the plasma of the Tore Supra Tokamak at the resonant electron cyclotron frequency of 118 GHZ.

Development and application of European high power CW gyrotrons for ECRH experiments

In the frame of a collaboration between Association Euratom-CEA, Association Euratom-Confederation Suisse and Thomson Tubes Electroniques, a high power quasi-CW gyrotron number TH 1506 working at the frequency of 118 GHz has been developed for plasma heating and current drive by Electron Cyclotron Resonance (ECR) interaction. The RF output of the gyrotron TH 1506 is under a Gaussian TEM/sub 0,0/ mode through a sapphire window cooled at liquid nitrogen temperature, characterized by a global efficiency of 30% after conversion to the HE11 mode. This mode allows a low losses transmission. Three of these tubes, rated at 500 kW 2 s, will be used for the Tokamak TCV and six tubes, 500 kW 5 s or 400 kW 210 s, for the Tokamak Tore Supra. One prototype and three series tubes have already been manufactured and accepted.

ECRH power injection in TORE SUPRA

The ECRH experiment on TORE SUPRA is designed to inject up to 3 MW of power at 118 GHz, using an antenna consisting of six fixed spherical mirrors and three mobile steering minors. The position of the mobile mirrors can be varied in real time using two stepper motors for each mobile mirror. In addition to controlling the injection angle, the position of the mobile mirrors also affects the polarisation of the injected wave. Accurate formulae to computer in real time, the stepper motor positions required to obtain the desired beam injection angles have been derived. Formulae to determine the effect on the wave polarisation, of the actual mobile mirror positions have also been determined. These formulae have been verified by precise laser measurements and by comparison of power deposition calculations and experimental results. Experiments with different values of polarisation and injection angles have been carried out in the 2001 campaign.

LOW POWER RADIATION FIELD PATTERN MEASUREMENTS OF MAIN COMPONENTS OF THE TORE SUPRA ECRH TRANSMISSION LINE

Publisher Summary The mechanical defects produce spurious modes when millimeter waves propagate in oversized waveguides. Classical techniques of measurement in transmission with a network analyzer cannot measure and separate ohmic losses and conversion losses into spurious modes. A right method is to feed the device to be tested with HE11 pure mode and to measure and analyse the radiated beam. The measured field pattern depends on the modal composition at the guide output. Theoretical calculations and computer programs are used in order to obtain the mode power content and the modal composition. This chapter presents the details of the equipment and the work method used. The TS system is composed of 5 parts — network analyzers, robot of movement, manual remote control console, master computer driver, and mechanical stands of the devices to be tested. A manual remote control console allows to set parameters of 6 axis numerical controls of the motors and to implement simple movements.

Improvement of the gyrotron TH 1506B for Tore Supra [Tokamak application]

For heating and current drive experiments by electron cyclotron resonance interaction on the Tore Supra Tokamak, an ECRH system with a generator power of 2.4 MW (3 MW) for a pulse duration of 210 s (5 s) at a frequency of 118 GHz is presently under construction at CEA Cadarache. The generator is made of six TH 1506B gyrotrons. The main design parameters of the gyrotron are given in this paper. Prototype and first series gyrotrons are already installed on Tore Supra.