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First plasma shots for the WEST Gyrotron

First plasma shots for the WEST Gyrotron

The first plasma shots with the new gyrotron took place  on April 8.

The new ECRH heating system for WEST will enable 3 MW of power to be injected at a frequency of 105 GHz in the near future (2026-2027).

The first gyrotron in the series was delivered to the IRFM in September 2024. Its installation enabled the CEA team, in collaboration with THALES, to validate the platform, the control system, and the gyrotron ‘s auxiliary systems, such as the cooling system.

The first free-field pulses (the gyrotron was not connected to the transmission line) were carried out in March 2025, during very short pulses (a few milliseconds), highlighting the shape and alignement of the RF beam pattern on thermal paper.

This step validated several essential elements:

  • Gyrotron ‘s oscillation on the correct mode (105 GHz);
  • Alignment of the “Matching Optics Unit Box,” compatible with the transmission line (beam centered in the transmission line, see figure below);
  • Set operational points: Power as a function of the electron beam acceleration voltage;
  • Validation of the entire platform and technical choices, including the power supply for the gyrotron body and its protection system (crowbar).
RF pattern of the gyrotron
with Vacc = 68 kV, Ibeam = 34A

In order to achieve the goal of a first plasma shot with ECRH power before mid-April, the RF pulses on a calorimeter were not carried out. After free-space pulses, :  the output of the gyrotron’s diamond window was  connected directly to the ECRH antenna, whose transmission lines had been aligned beforehand. These lines were pumped for a week until a vacuum level compatible with the opening of the VAT valves (valves that isolate the transmission line from the ECRH system) was reached to allow the first plasma shots.

The first successful gyrotron shots took place on April 8 and 9, 2025. Carried out with pulses of limited duration (between 10 and 100 milliseconds), they nevertheless made it possible to evaluate the effectiveness of the polarisation of the waves in the plasma and to validate the control system of the ECRH heating system, as well as the exchanges with the plasma control system (PCS).

The next experiments are planned for November 2025.

Figure 3 : first ECRH experiments results with different polarisations (left hand side S1,EC is the signal measured by sniffers has been optimized with the polarisation 11th april, right hand side shot 62220 ECE diagnostic measurements with ECRH injection signature.)

Lena Delpech