Concussion Burst is a 13th level psion At-Will, augmentable attack that was introduced in Player's Handbook 3.
Concussion Burst
Psion Attack 13
The air ripples as you knock your foes down with a wave of pummeling force.
Area burst 1 within 10 squares
Target: Each creature in burst
Attack: Intelligence vs Reflex
Hit: Intelligence modifier force damage, and the target falls prone.
Augment 1
Hit: As above, and if the target is hit by an attack against Fortitude before the start of your next turn, the target falls prone.
Augment 4
Hit: 3d6 + Intelligence modifier force damage, and the target falls prone.