Optimizing the Microwave Performance of the ITER ECH Transmission Line System

The Electron Cyclotron Heating and Current Drive (ECH) system performs a variety of functions for ITER including plasma startup, instability suppression, current drive, and heating. The system consists of gyrotrons to produce the microwave power, launchers to inject it into the plasma, and transmission lines with their various components to transmit that power from the gyrotron to the launcher.

To analyze the microwave performance consequences of ECH Transmission Line (TL) design decisions, we require a model of the system from the microwave point-of-view. It should account for the effects that each component has on microwave propagation, including manufacturing tolerances and installation alignment. It should also account for external loadings (thermal, gravitational, etc.) that can affect microwave propagation.

The tolerances and precision to which the TL components can be fabricated, installed, and aligned gives a practical limit to which the uncertainty of the microwave performance of the system can be calculated. Monte Carlo methods are a natural fit and employed to calculate the probability distribution that a given line can deliver its required power and mode purity. These techniques allow us to optimize the performance requirements relative to the fabrication costs.