We did two 90 degree tests on Monday and the cavity did not move as expected, which means our previous movement was from cable heating. For our first tests, the cavity by chance, moved in the expected direction.
Here are the animated gifs showing the first and last frames for two tests, each at 90 degrees to each other:
Note the slight bend in the coax? In both tests it moved in the same direction, to the top left of the frame. The only thing rotated was the cavity while the coax and camera stayed in the same orientation. If the cavity had worked, there should have been a notable movement first toward the left and then toward the bottom. With at least 10 minutes between each test, the cable had time to cool down.
There was none of the dramatic movement noted during the previous 75 second test.
Please note that we also modified the test setup to straightened the coax and moved the microwave source assembly including the fan, outside the Faraday cage.
The next step is to build a better cavity but we are going to keep the coax. The movement from coax heating is small, we know which direction it moves and as long as the cable has enough time to cool down, we can account for it. We also expect the cavity movement to be readily apparent.