RT Amplitude Control Loop: Testing of R&D ICRF Source at High Power

Full text: Full text: Ion cyclotron heating and current drive (ICH&CD) system is one of the important auxiliary heating and current drive systems for the ITER experiment. A total of 20 MW of IC power is required to couple with ITER plasmas using eight independent RF sources (35-65 MHz) having power handling capability of 2.5 MW at VSWR of 2.1 with other stringent specifications. To finalize the source configuration, an R&D activity has been started and diacrode-based amplifier is tested successfully at 1.5 MW for 3600 s, VSWR 2.1 on ITER-India test facility. One of the critical requirements of IC-RF source is to operate the amplifier at constant power for dynamic load condition of VSWR 2:1 and able to match the requested power within 10 ms time scale. To realize this, amplitude control loop is developed using NI make PXI-7841R and LabVIEW-FPGA module. The output power is controlled by changing the drive reference of solid state power amplifier having in-built amplitude control loop. Further to manage the dynamic load condition, online variation of anode biasing is incorporated in this amplitude control loop. In this control loop, other parameters like screen grid current, anode current and anode dissipation are critically monitored and ensure constant output power by adjusting different biasing voltage in real-time. Putting the reliable and safe operation at highest priority, if any of the operating parameter is changing in uncontrolled manner, source will be forced to operate in power down mode forcing internal reference generated by this amplitude control loop itself. Even if the power down mode is also not able to make operating parameter stable, local protection function initiate RF off sequence for reliable and safe operation of RF source. In this paper, characteristics and experimental result of amplitude control loop at high power operation (∼ 1 MW) on ITER-India test bench will be discussed. (author)