Gyrotron technology to accelerate Tokamak Energy fusion dream

Built by Japanese firm Kyoto Fusioneering the new gyroton, which will be installed in the ST40 later this year, will generate high-power electromagnetic waves for controlling and heating a hydrogen plasma many times hotter than the centre of the sun. It will also be used to start up and drive plasma current.

Using a gyrotron a beam of electrons travels through a strong magnetic field which accelerates them to the point where they emit microwave radiation. This is directed through a waveguide to the plasma of fusion fuels – isotopes of hydrogen.

The frequency of the microwaves is tuned to match the cyclotron resonance frequency of the electrons in the plasma (104GHz or 137GHz in the case of ST40). When the microwaves interact with the plasma, they transfer energy to the electrons, which heats and drives the plasma.

A gyrotron, which uses Electron Cyclotron Resonance Heating (ECRH), solves one of the key challenges for a spherical tokamak – limited space for a central solenoid, which would otherwise be required to induce the plasma current. A gyrotron means the central solenoid can be reduced in size. A big advantage over the current neutral beam heating approach is that gyrotrons can be positioned away from the device itself, whereas neutral beam heating needs to be very close.