T. Bonicelli

From Series Production of Gyrotrons for W7-X Toward EU-1 MW Gyrotrons for ITER

Europe is devoting significant joint efforts to develop and to manufacture MW-level gyrotrons for electron cyclotron heating and current drive of future plasma experiments. The two most important ones are the stellarator Wendelstein W7-X at Greifswald and the Tokamak ITER at Cadarache. While the series production of the 140 GHz, 1 MW, CW gyrotrons for the 10-MW electron cyclotron resonance heating system of stellarator W7-X is proceeding, the European GYrotron Consortium is presently developing the EU-1 MW, 170 GHz, CW gyrotron for ITER. The initial design had already been initiated in 2007, as a risk mitigation measure during the development of the advanced ITER EU-2-MW coaxial-cavity gyrotron. The target of the ITER EU-1-MW conventional-cavity design is to benefit as much as possible from the experiences made during the development and series production of the W7-X gyrotron and of the experiences gained from the earlier EU-2-MW coaxial-cavity gyrotron design. Hence, the similarity of the construction will be made visible in this paper. During 2012, the scientific design of the ITER EU-1-MW gyrotron components has been finalized. In collaboration with the industrial partner Thales electron devices, Vélizy, France, the industrial design of the technological parts of the gyrotron is being completed. A short-pulse prototype is under development to support the design of the CW prototype tube. The technological path toward the EU ITER-1 MW gyrotron and the final design will be presented.

First experimental results from the EU 2 MW coaxial cavity ITER gyrotron prototype

The EU is working towards providing 2 MW, coaxial-cavity, CW, 170 GHz gyrotrons for ITER. Their design is based on results from an experimental pre-prototype tube in operation at FZK for several years, having a pulse length of several milliseconds. The first industrial prototype tube is designed for CW operation, but, in a first phase, will be tested out to Is at the European Gyrotron Test Facility in Lausanne, Switzerland as part of a phased testing/development program (1s, 60 s, CW). It is known that RF beam profile shaping, stray radiation handling, and collector cooling at these high power levels are three issues for the gyrotron. The gyrotron, magnet and body power supply have been delivered and successfully installed at the test stand, hosted by the CRPP. The main high voltage power supply delivery is delayed, so one of the power supplies dedicated to 3 of 9 gyrotrons in the TCV EC system is being used as a backup power source (all 3 TCV power sources can be interfaced with the test stand). Cathode conditioning began in November 2007 followed by collector conditioning in December. Parasitic low frequency oscillations have not hindered operation, and the tests have progressed to conditioning out to 0.14 s pulses by March 2008. During this period, the performance concerning microwave generation has been characterised and the RF beam profile has been measured at several planes to allow reconstruction of the phase and amplitude profile at the gyrotron window and to provide the necessary information permitting proper alignment of the compact RF loads prior to pulse extension. The power will be measured, according to the pulse length, using either a very-short pulse (<0.01 s) load on loan from FZK, or short-pulse (<0.2 s) or long-pulse (CW), spherical, calorimetric loads developped as part of this program by CNR. This paper presents the preliminary results of these operations.

Design of the EU-1MW gyrotron for ITER

EU is developing a 1 MW cylindrical cavity gyrotron. In the last year the design of the components of the new gyrotron has been finalized while the technological design of the new tube has been defined. In the present paper, the main characteristics of the new EU gyrotron for ITER are presented.

Vacuum Breaker for High DC Current: Experimental Performances and Operational Limits

This paper presents a new method to assess the performances of vacuum circuit breakers (VCBs) for high DC based on the measurement of the energy dissipated in the contacts before the opening of the breaker. This energy is given by the product of the closed-contact resistance times the specific energy (I 2 t) flowing through the breaker. The results of an extensive experimental campaign on VCB prototypes, customized for special applications in the field of thermonuclear fusion, are reported in this paper, showing that, whenever the energy dissipated before the opening exceeds a threshold, the probability of VCB restrike increases. It is also demonstrated that vacuum tubes need initial training at low current prior to the operation at full performance.

Parameterization technique for the preliminary gun design of the EU 170GHz 1MW conventional cavity gyrotron for ITER

A preliminary gun design for the EU 170 GHz, 1 MW conventional cavity gyrotron, for the TE32,09 mode [1], will be presented. The ASG magnet of the EU 170 GHz, 2 MW coaxial cavity gyrotron for ITER is used for the required magnetic field. A parameterization of the diode gun has been defined. Using the Ariadne++ code [2] the geometry has been optimized with respect to several criteria, such as the small velocity spreads, the acceptable width of the beam radius at the cavity, etc. The neutralization effect has been taken into account using a simple model.

The European 2MW, 170GHz coaxial cavity gyrotron for ITER

In the reference ECH design, ITER requires a total of 20 MW/CW power at 170 GHz using gyrotrons with a unit power of 1 MW. A higher power per unit (2 MW/gyrotron) would result in a strong reduction of the cost of the whole ECRH system, and would also relax the room constraints on the launcher antenna design. The high power capability of coaxial cavity gyrotrons has been demonstrated with short pulse experiments at FZK. A collaborative effort between European research associations CRPP-EPFL, FZK and Thales Electron Devices (TED) has been launched by the European Fusion Development Agreement (EFDA) in 2003, aiming at the development of an industrial 170 GHz/2 MW/CW coaxial cavity gyrotron. The first prototype, although designed to be CW compatible is expected to reach 2 MW/ls and has been delivered by end of 2006. It will be tested in Lausanne, where a specially dedicated test facility has been built. The test facility has been designed to be flexible enough, allowing the possible commissioning of tubes with different characteristics, as well the tests of the launcher antenna at full performances. Initial experiments are planned for the end of the third quarter 2007.

Heating neutral beams for ITER: Present status

The heating neutral beam (HNB) systems at ITER are designed to inject a total of 33 MW of either 1 MeV D0 or 870 keV H0 beams into the ITER plasma using two injectors with a possible addition of a third injector later to increase the injected power to ~50 MW. The injectors become radioactive due to the neutron flux from ITER and, in order to avoid the resulting complex remote maintenance, the design, choice of materials and the manufacturing process of each component of the injector is, wherever possible, such that they survive the life time of ITER. To ensure a smooth operational phase of neutral beams at ITER a neutral beam test facility (NBTF) is under construction at Consorzio RFX, Padova, (hereinafter referred to as RFX), which consists of 2 test beds, the 100 kV “SPIDER”, and a 1 MV “MITICA” facilities, which will be used to optimize the source operation for H and D beams. MITICA is essentially a full scale ITER prototype injector for the ITER beam parameters. The manufacturing and operation of the facility will allow validation of the operational space of the injectors and provide valuable information about the manufacturing processes applicable to HNB components. Operation of the two facilities is expected to begin in 2016 and 2019 respectively. Currently experiments on the ELISE facility with a half ITER sized RF beam source are underway. ITER relevant parameters for the H beams have almost been achieved. Efforts are underway to optimise the same with D beams. The experimental database from ELISE will be an important input for establishing the ITER relevant parameter space on the SPIDER source. This paper discusses the present status of the design and development of the injectors for ITER and the progress on the test facilities.

Heating Neutral Beams for ITER: Present Status

The heating neutral beam (HNB) systems at ITER are designed to inject a total of 33 MW of either 1 MeV D0 or 870 keV H0 beams into the ITER plasma using two injectors with a possible addition of a third injector later to increase the injected power to ~50 MW. The injectors operate in a radioactive environment and should survive the life time of ITER, placing thereby stringent requirements on material and manufacturing choices. To ensure a smooth operational phase of neutral beams at ITER, a neutral beam test facility is under construction at Consorzio RFX, Padova, (hereinafter referred to as RFX), and consists of two test beds. The 100-kV SPIDER test bed will be used to optimize the source operation for H and D beams. The 1-MV MITICA test bed is essentially a full scale ITER prototype injector. The manufacturing and operational experiences at MITICA will not only establish the manufacturing processes of ITER HNB components but will also allow validation of the operational space of the injectors for ITER HNB. Operation of the two facilities is expected to begin in 2016 and 2019, respectively. Currently, the experiments on the ELISE facility, IPP Garching, with a half ITER sized RF beam source are underway. The ITER relevant parameters for the H beams have been achieved. Efforts are underway to optimize the same with D beams. The experimental database from ELISE will be an important input for establishing the SPIDER operation. This paper discusses the present status of the design and development of the injectors for ITER and the progress on the test facilities.

From W7-X towards ITER and beyond: Status and progress in EU fusion gyrotron developments

In Europe, significant progress in gyrotron research, development and manufacturing has been made in 2014, starting from the successful continuation of the 1 MW, 140 GHz gyrotron production for the stellarator Wendelstein 7-X (W7-X) at Greifswald, Germany and the accelerated development of the EU 1 MW, 170 GHz conventional cavity gyrotron for the ITER tokamak at Cadarache, France. Based on that, a physical design activity was started which shall lead to a dual frequency gyrotron for TCV, Lausanne, Switzerland. Within the European fusion development consortium (EUROfusion), advanced gyrotron research and development has started towards a future gyrotron design which shall fulfil the needs of DEMO, the nuclear fusion demonstration power plant that will follow ITER. Within that research and development, the development of advanced design tools, components, and proper test environment is progressing as well. A comprehensive view over the status and prospects of the different development lines shall be presented.

Gyrotron body power supply, validation of design with test results

A 170 GHz, 2 MW, steady state gyrotron is being developed in a collaboration between European research associations and industries to be used for the electron cyclotron resonance heating (ECRH) system of ITER, the next step in nuclear fusion research. The gyrotron is presently in the prototype state. For the test facility dedicated to the testing of this gyrotron, new power supplies need to be procured. A feasibility study was performed aimed at using new designs based on present day techniques and at performing and constructing a prototype for further testing and evaluation. The prototype BPS (body power supply) which is connected to the body of the gyrotron is now in an advanced stage of construction and the first test results are in close agreement with the design objectives of the feasibility study