Development of the EU gyrotron for ITER: going beyond present-day technology
The first industrial prototype of a 2 MW, coaxial gyrotron at the CRPP EC Test Facility
The measured RF power and efficiency obtained in the recent experiments with the FZK pre-prototype coaxial cavity gyrotron compared to theoretical simulations.
Europe, responsible for one third of the Electron Cyclotron Heating and Current Drive (EC H&CD) power sources for ITER, is developing a 2 MW gyrotron.
The EC H&CD system heats the electrons in the plasma with a high-intensity beam of electromagnetic radiation at a frequency of 170 GHz in ITER, the resonant frequency of electrons. The electrons in turn transfer the absorbed energy to the ions by collision. The radio frequency (RF) power is generated by gyrotrons, vacuum tubes consisting of an electron gun, an acceleration chamber, a resonance chamber (cavity) immersed in a strong magnetic field, and finally of a collector of electrons.
The nominal power of the European so-called “coaxial cavity” gyrotron is about the double compared to the most developed gyrotrons presently installed in fusion facilities.
The development is carried out within a collaboration between the EU Associates (CRPP, KIT, CNR, ENEA, HELLAS, also CEA, FOM, TEKES were involved in previous phases of the programme), whereas the technical design (cooling, vacuum, etc), integration and fabrication of the industrial prototypes is carried out by industrial partners (Thales Electron Devices for the first gyrotron prototype). A dedicated EC test facility was established at the CRPP, in Lausanne for the full power testing of the 2 MW tube in steady-state conditions. The test facility has been equipped by power supplies with excellent dynamic performances, operational flexibility and efficiency, cooling and cryogenics systems control and acquisition system, and other auxiliaries.
The first tests with the industrial gyrotron prototype were done in 2008. The tube is currently being refurbished with some improved internal components. Remarkable experimental results have recently been obtained with the new internal configuration implemented into the pre-prototype tube: 2.2 MW of RF power at the correct operating mode – correct ITER frequency – has been measured in a reproducible way with an efficiency of 30% without collector depression. Moreover, the quality of the RF beam emerging from the gyrotron window is very high – approximately 97% of Gaussian mode content and higher than the ITER specifications. The simulations correspond very well with the obtained measurements.
Tests with the first industrial prototype, aiming at 2 MW during 1 second, are planned for 2010. The extension of the pulse length up to the ITER specifications of 1 hour is the main objective of the second and third industrial prototypes which will follow.
