1. Purpose of the ex-p: commission the LH coupler
Purpose of the ex-p: commission the LH coupler. Check the phase system and and the amplitude of the forward and reflected waves
S. Bernabei, J. Hosea, J, R. Wilson
probes
The first operation that has to be done after installation is to make sure that the phase across the 24-waveguide array is correct. Several tests can be performed to this end.
The coupler is built to have complete control of the launched spectrum: the phase of each vertical stack of 4 waveguides is independently controlled.
low power
phase shifter
directional
couplers
high power
phase shifter

2. Phase scans
Low power phase scans should follow a certain pattern, if not the precise value of the reflection coefficient.
In vacuum (air), the reflection coefficient should be like an inverse gaussian centered around zero degrees.
The reflection coeff. approximately reverses as soon as there is plasma in front of the coupler.
As an example, to the right is the response of the total reflection vs. phase as the coupler-plasma distance is varied.

3. Reflection pattern along the array
The reflection in each single waveguide follows a specific pattern for a specific phase like in the example where the incremental phase is 90°.
Reversing the incremental phase, the pattern should reverse too.