Critical interface issues associated with the ITER EC system

Abstract

The ITER ECH system is an in-kind procurement consisting of four different types of gyrotrons (from EU, IN, JA and RF), transmission lines (from US) and two types of launchers (from EU and JA). Each subsystem must interface not only with the other but also with the auxiliary systems control and data acquisition computer and with the plasma (in the case of the launchers). The definition and management of interfaces is therefore essential for the system to guarantee performance, availability and reliability. The proper description of each interface boundary is essential for assembly and operation of the entire system as a single unit. In addition, progress has been made in the development of high power, long pulse systems and associated components that have not been integrated into the ITER EC design since the present ITER EC system was essentially specified prior to 2000. The ultimate physics performance and operational reliability in some situations is limited by this old design, which has not taken advantage of the knowledge and experience gained in operating the multi-megawatt ECH systems on present tokamaks and stellarators. The objective of this paper is to review the present ITER ECH system, which includes the power supplies, gyrotrons, transmission lines and launchers. Modifications are proposed which are performance driven and are engineered for reliability and maintainability, whilst reducing complexity and cost. Potential operating scenarios are discussed which require an intelligent and automatic decision making process, for example, directing the EC power to either of the two EC launchers, based on the immediate physics requirements. The interfaces between the subsystems are described and when possible improvements to each interface are proposed.

Overview of the ITER EC H&CD system and its capabilities

“…The in-kind procurement strategy taken to build the ITER EC system requires careful management by the IO of the interfaces between each sub-system and with interfacing services such as coolants, vacuum, buildings and so on [3] . The EC subsystems are to come as a complete package including cabling, control systems, water manifolds, etc., such that all packages fit together without the IO procuring any components.…”

Feedback control of ECRH polarization on LHD

“…Also, changes in the density may alter the degree of power coupling between O and X-modes in the sheared field configuration in a heliotron such as LHD, requiring adjustment of the polarization to maintain optimal coupling. Finally, changes in the ray path while changing the launcher injection of the ITER upper and equatorial ECRH Launchers [10] [11] will require corresponding changes to the polarizer settings.…”

“…As pulse lengths of several minutes are achieved with this system, optimizing the degree of first-pass absorption is of great importance since the total energy deposited on in-vessel components may become significant in the case of nonnegligible shine-through or multiple reflections of the injected ECRH power. This will also be of great importance in future long-pulse devices such as W7-X [8], [9] and ITER [10], [11] and is a topic of research on LHD.…”

Assessment of the ITER EC Upper Launcher Performance

“…The ITER Electron Cyclotron (EC) Heating and Current Drive (H & CD) system, operating at 170 GHz, will deliver up to 20 MW to the plasma through one Equatorial (EL) and four Upper Launchers (UL) [1]. The capabilities foreseen for the system include central heating and bulk current drive, the control of Magneto-Hydrodynamic (MHD) activity such as Neoclassical Tearing Modes (NTMs) at the q = 3/2 and q = 2 surfaces and sawtooth instabilities at the q = 1 surface, the assist to break-down and L-to H-mode transition phases of the plasma discharge.…”