Transmission lines

Each of the nine gyrotrons is connected to a Matching Optics Unit (MOU), described below, leading into the transmission line, which conducts the RF-beam into TCV.

sketch transmission lines

Configuration of transmission lines

The transmission lines consist of evacuated 63.5 mm HE11 corrugated waveguides (see sketch below) . The components are supplied by SPINNER GmbH. Each line is ~30 m in length with an average transmission efficiency of ~96%. Included in each line is a switch to allow diverting the beam from the TCV direction to a calorimetric load, and also a power monitor miter bend (90° angles in waveguides with mirrors). The microwave beams are directed into the loads to test the gyrotrons and during TCV-shots, in which not all of the gyrotrons of one cluster need to be used. The lines are insulated at both ends using an in-line DC break.

Transmission line inside the TCV-building

X2 Matching Optics Unit

 

The evacuated Matching Optics Units (MOU) are situated directly at the RF-window of the gyrotrons and are needed to condition the microwave beam for a good coupling into the transmission lines and into the plasma. Due to the different quality of the RF-beam at the gyrotron-output, the MOU’s are designed differently for the X2- and the X3-gyrotrons.

The MOU’s for the GYCOM gyrotrons are made by CRPP and are used for:

  • filtering the input beam : The beam is filtered using TiO2 coated copper plates which absorb ~91 kW of higher order modes coming from the gyrotron.
  • coupling the beam to the waveguide : Optimum coupling to the HE11 waveguide is made by 2 phase correcting (quadratic) mirrors supplied by GYCOM.
  • providing optimum polarization for coupling to the plasma : Included in the MOU are two grating polarizers which can change the beam polarization (linear to circular). The gratings are motorized to allow a change in polarization between discharges.

Scheme of X2 Matching Optics Unit

 

X3 Matching Optics Unit

The Matching Optics Unit is provided with the gyrotron and is designed for the full 210s, 480kW pulse length of the gyrotron. The three internal mirrors and vacuum housing of the MOU are all water cooled. One of the three mirrors is a phase correcting (quadratic) mirror for optimum coupling of the beam to the HE11 waveguide. The other two mirrors are grating polarizers which can change the beam’s polarization to achieve optimum coupling to the plasma. No beam filtering is required since the gyrotron’s output beam is >96% in the TEM00 mode.

X3 Matching Optics Unit