The Thermal Discouragement Beam is a testing element introduced in Portal 2 that is used throughout the Aperture Science Enrichment Center. It is the Portal 2 equivalent of the High Energy Pellets used throughout Portal.
The Thermal Discouragement Beam, a laser created from at least 1998, aims at "discouraging" threats such as Sentry Turrets, thus burning / destroying them with a laser, as well as apparently trigger moving floor plates, allowing access to a specific area. The beam can be redirected using Weighted Pivot Cubes into awaiting receptacles. If the beam is touched, the beam will slowly kill a Test Subject whilst also pushing them away from it. ATLAS and P-body take less damage from this testing element, but can be eventually destroyed by it.
An Aperture Science Weighted Storage Cube or any of its variants can block the beam without being damaged.