Design of the electron cyclotron heating system expansion on EAST

The electron cyclotron resonance heating (ECRH) system on the EAST tokamak is undergoing a significant expansion to enhance its plasma heating capability. This upgrade introduces two new gyrotron systems (#5 and #6), increasing the total output power at 140 GHz to 4.5 MW for pulses of up to 1000 s. To accommodate EAST’s full toroidal magnetic field range, the systems are designed to operate primarily at 140 GHz while retaining the flexibility to switch to a secondary frequency of 105 GHz for low-toroidal-field operations. The expansion includes dual-frequency transmission lines, quasi-optical antennas, and an independent control system tailored for robust long-pulse operation. The transmission lines feature corrugated circular waveguides with a radius of 31.75 mm, optimized for low-loss propagation of high-power millimeter waves. Each line incorporates functional miter bends, such as polarizers and power monitors, and is supported by three vacuum pumping stations. The antenna system, integrated into EAST’s Port B, employs quasi-optical components—including ellipsoidal focusing mirrors and steerable mirrors—to direct the beam precisely into the plasma. Multiphysics simulations confirm the thermal and structural reliability of these components under high-power loads. A key innovation lies in the control system, which introduces a central timing controller with three operational modes: self-check, test, and EAST experiment mode. The system supports automatic restart functionality to swiftly recover from transient faults, minimizing disruption to plasma experiments. Additionally, a real-time power control subsystem interfaces with EAST’s Plasma Control System to dynamically adjust gyrotron output power, while an RF protection mechanism safeguards against reflected power and mode competition. This expansion not only augments EAST’s heating capacity but also strengthens its capability to explore advanced plasma scenarios, including turbulence suppression and edge-localized mode control. By enabling sustained, high-power operations, the upgraded ECRH system aligns with EAST’s objective of achieving steady-state fusion conditions.