High-Power Helicon System Upgrades at DIII-D*

  Helicon current drive is a promising new technology for plasma heating and current drive-in fusion reactors. The DIII-D tokamak has one such system, which operates at 476 MHz and can deliver up to 1.2 megawatts (MW) of power. However, the system has had problems reaching high power in the past.

  This year, the DIII-D team made several upgrades to the Helicon system, which allowed it to reach at the klystron output up to 0.7 MW for 2-second pulses and up to 850kW for 0.5s pulses. One of the upgrades was to pressurize the coaxial lines with dry air to 15 PSI. Another upgrade was to install a gas break at the output of the circulator to prevent any pressure from reaching the klystron window. The team also implemented an automatic voltage ramp up for the klystron filament.

  In the coming maintenance period, the DIII-D team plans to make additional upgrades and repairs to the Helicon system. They will replace a damaged bellows on the 150-degree side of the system. Additionally, they are working on a feedback loop controller to smooth out any power fluctuations from the klystron.

  These upgrades are expected to further improve the performance of the DIII-D Helicon system and make it a more reliable and versatile tool for plasma research.