In an ECRH system, a launcher is used to define the angle and location at which a microwave beam will be launched into the plasma.
There are 6 X2 launchers at TCV (one for each X2 gyrotron). They direct the microwave beams from the tokamak side (low field side): 2 are at an equatorial level while 4 are at an upper level.
Each launcher has 4 mirrors in a frame that can be rotated between plasma discharges providing toroidal coverage (φL=-180° to +180°). The last mirror (i.e., the closest to the plasma) directs the beam in an angle that provides poloidal coverage (θL=7° to 55°). This mirror can do a full sweep within 250ms during a discharge (multiple sweeps are also possible).
These launchers allow scientists to: do on- or off-axis heating, provide co- or counter-current drive to the ohmic current, optimize the spot size of the power deposition region.
There’s a unique X3 launcher which is located on the top of TCV. It has a single mirror that reflects down all X3 gyrotron microwave beams vertically into the plasma. This way, the path length through the plasma is increased, improving the total absorbed power into the plasma.
The mirror can be vertically rotated (from 40o to 50o) during a plasma discharge, providing poloidal coverage. It can also be displaced radially between shots (0.83 to 0.96m), providing radial coverage (required for optimal absorption).
This launcher allows bulk heating mainly for high density plasmas (X2 launchers have a lower ‘density limit’ at which the microwave beams can’t progate through the plasma and are reflected back).