Color filamentation in ultrarelativistic heavy-ion collisions

We study color fluctuations in the quark-gluon plasma produced at the early stage of nucleus-nucleus collision at RHIC or LHC. The fluctuating color current, which flows along the beam, can be very {\it large} due to the strong anisotropy of the parton momentum distribution. A specific fluctuation, which splits the parton system into the current filaments parallel to the beam direction, is argued to grow exponentially. The physical mechanism responsible for the phenomenon, which is known as a filamentation instability, is discussed.