As you enter, the computer tells you that all warning lights and sounds have been turned off so as not to agitate the high energy pellet.
As with the previous test chamber, you need to make the high energy pellet go into the containment thing. There is an orange portal below the containment thing, so you just need to create a blue portal where the pellet is hitting the wall, visible by the dark spot.
Once you do that, the unstationary scaffold starts moving, and the computer tells you to use that to reach the chamber lock. You'll need to create a blue portal on the ceiling above the left side of the scaffold path, and then drop through the orange portal when the scaffold is below. If you want to be sure that you position the blue portal correctly, stand below the scaffold when it's under the ceiling part where a portal can be made, then wait for it to move.