The Gyrotron commissioned and integrated (Extreme left pic) at IPR

The Institute for Plasma Research (IPR) in Gujarat has successfully commissioned and integrated an advanced 82.6 GHz Gyrotron with the SST‑1 Tokamak (State Superconducting Tokamak-1), marking a major milestone in India’s fusion energy program.

This system enables plasma heating at both fundamental and second harmonics, significantly enhancing experimental capabilities for long‑pulse fusion operations.

The Electron Cyclotron Resonance Heating system (ECRH) is a crucial component for Tokamaks and fusion reactors. Its applications include low‑loop voltage plasma Start‑Up, heating, current drive, and control of instabilities. A standard ECRH system comprises a high‑power microwave source, corrugated waveguide transmission line, and quasi‑optical launcher.

On SST‑1 and Aditya‑U Tokamaks, two ECRH systems are deployed: a 42 GHz 500 kW unit and the newly commissioned 82.6 GHz 400 kW unit. The 82.6 GHz Gyrotron is capable of delivering 400 kW of RF power for 500 milliseconds. It was mounted on the cryomagnet with precision, while the mirrors of the matching optic unit were replaced and aligned to couple power effectively into the transmission line. The Gunn coil was installed, and all cooling and electrical connections were completed following standard procedures.

Cold high‑voltage tests validated the voltage withstand capability and tube integrity. Initial low‑power, short‑pulse operations ensured precise mirror alignment, with burn‑patterns confirming correct beam propagation. The Gyrotron achieved stable operation at rated parameters on a water‑cooled dummy load, with beam voltage at −45 kV, beam current around 20 A, and anode voltage at +20 kV.

Following dummy load commissioning, the system was integrated with SST‑1 using a 20‑metre transmission line. Launcher mirrors inside the Tokamak were realigned to deliver EC power to the desired plasma location, validated through burn‑pattern observations. This integration enabled plasma heating experiments at both fundamental and second harmonics.

During the recent SST‑1 campaign, the 82.6 GHz system was successfully used for plasma pre‑ionisation and heating. For the first time, SST‑1 operated at a toroidal magnetic field of approximately 2.8 T with the 82.6 GHz system applied for plasma breakdown and heating. Power levels varied between 150 kW and 300 kW, with durations ranging from 75 ms to 200 ms.

The system was also employed for second‑harmonic pre‑ionisation at 1.5 T with different polarisation settings, achieving effective breakdown in synergy with the Klystron‑based LHCD system.

This achievement represents a significant advancement in India’s fusion research. SST‑1, India’s first superconducting Tokamak, was designed for long‑pulse steady‑state plasma operations.

The integration of the 82.6 GHz Gyrotron strengthens India’s capability to conduct advanced plasma heating experiments, contributing to global efforts in developing practical fusion energy. The system’s commissioning also demonstrates India’s growing expertise in high‑power microwave technology, superconducting magnet integration, and fusion plasma control.

IDN (With Agency Inputs)